The Potential Impacts of Water
Erosion and Assimilation Processes on
Phosphate Budget in Water Bodies
Case Study: Ellen Brook Catchment
Ellena Widjajanto
10217573
Applied Ocean Science Engineering
Supervisor: Associate Professor Keith Smettem
Dissertation submitted in partial fulfilment of the requirements for Bachelor of
Engineering (Applied Ocean Science), University of Western Australia
School of Environmental
Systems Engineering
The University of Western
Australia
ABSTRACT ii
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
ABSTRACT
A number of studies have recognised erosion as a process which increase nutrient input to
water bodies. However, the potential of the eroded sediment to act as a sink for nutrient
has not been explored. This dissertation attempts to determine the possibility of eroded
sediment to act as a sink for nutrient rather than as a source of nutrient. It also attempts to
investigate the effectiveness of soil amendment method in increasing nutrient adsorption
capacity of the eroded sediment. The nutrient being tested in this study is phosphate, the
main form of phosphorus that exists in soils. Ellen Brook catchment was chosen as the
study site due to its significant contribution of phosphorus to the Swan-Canning River.
Soil samples from seven different locations in Ellen Brook catchment were taken and
analysed. These samples were analysed for (1) their likelihood to experience erosion, (2)
their ability to retain water, (3) their natural phosphate adsorption capacity and (4) their
phosphate adsorption capacity after soil amendment.
This study found that all of the investigated bank soils of Ellen Brook catchment are likely
to experience erosion and almost all of the eroded sediments have the potential to act as a
sink for phosphate. It was also found that soil amendment has uniformly increased the
phosphate adsorption capacity for all of the tested soils. Further studies are needed to
confirm these findings. Precautions need to be taken before implementing soil amendment
method to increase phosphate adsorption capacity of various bank soils.
ACKNOWLEDGEMENTS iii
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
ACKNOWLEDGEMENTS
There are a number of people that I would like to express my gratitude to. First of all, I
would like to thank Associate Professor Keith Smettem, my supervisor, for his valuable
input and support throughout this project.
I would like to thank David Weaver and Rob Summers from the Department of
Agriculture Western Australia for their assistance on my inquiries on nutrient and soil
interaction. I greatly appreciate the help I received from people at the Department of
Environment library, the staffs from the Faculty of Natural and Agricultural Science and
the staffs from the School of Environmental Systems Engineering.
Thank you to Dianne Krikke, Water Quality Laboratory Technician, who suggested and
provided me the equipments used in my experiments. To my fellow lab users, Rita
Geoffry, thank you for the good times we had discussing methods and other miscellaneous
topics.
Finally, special thank you for my family, friends and my fellow final year students for
their continual support and encouragement throughout this project. .
Table of Contents iv
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
TABLE OF CONTENTS
ABSTRACT........................................................................................................................ ii
ACKNOWLEDGEMENTS ...............................................................................................iii
TABLE OF CONTENTS................................................................................................... iv
LIST OF FIGURES ........................................................................................................... vi
LIST OF TABLES ............................................................................................................vii
GLOSSARY.....................................................................................................................viii
1. INTRODUCTION ...................................................................................................... 1
1.1. Ellen Brook Catchment ....................................................................................... 2
1.2. Research Objectives ............................................................................................ 2
1.3. Synopsis .............................................................................................................. 3
2. LITERATURE REVIEW............................................................................................ 4
2.1. Water Erosion...................................................................................................... 4
2.2. Known Impacts of Water Erosion....................................................................... 6
2.3. The Impacts of Water Erosion in Australia......................................................... 6
2.4. Interactions Between Nutrient and Soil ............................................................. 7
2.4.1. Nitrogen (N) ................................................................................................ 8
2.4.2. Potassium (K).............................................................................................. 9
2.4.3. Phosphorus (P) .......................................................................................... 10
2.5. Erosion and Nutrient Budget............................................................................. 11
2.6. Phosphorus and its Importance ......................................................................... 14
2.7. Remediation Effort to Reduce Phosphorus....................................................... 16
2.8. Site of Study Background ................................................................................. 18
2.8.1. Swan – Canning River .............................................................................. 18
2.8.2. Ellen Brook Catchment............................................................................. 19
Table of Contents v
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
3. METHODS ............................................................................................................... 22
3.1. Sites and Samples Description .......................................................................... 22
3.2. Soil Erodibility Potential................................................................................... 25
3.3. Hydraulic Conductivity..................................................................................... 28
3.4. Phosphate Adsorption Capacity of the Soil Samples........................................ 30
3.5.1. Phosphate Adsorption Test with Varying Concentration ......................... 33
3.5.2. Phosphate Adsorption Test with Constant Concentration ........................ 34
3.5.3. Phosphate Adsorption under Simulated Site Conditions .......................... 35
3.5.4. Phosphate Adsorption Capacity of Amended Soils .................................. 36
3.5. Measuring Phosphate Concentration ................................................................ 37
4. RESULTS ................................................................................................................. 38
4.1. Soil Composition and its Erodibility Potential ................................................. 38
4.2. Hydraulic Conductivity Test ............................................................................. 44
4.3. Phosphate Adsorption Tests.............................................................................. 46
4.3.1. Phosphate Adsorption Test with Varying Concentration ......................... 46
4.3.2. Phosphate Adsorption Test with Constant Concentration ........................ 51
4.3.3. Phosphate Adsorption Under Simulated Site Conditions ......................... 52
5. DISCUSSION ........................................................................................................... 54
6. CONCLUSION......................................................................................................... 58
7. RECOMMENDATIONS FOR FUTURE WORK ................................................... 59
REFERENCES.................................................................................................................. 60
APPENDICES .................................................................................................................. 63
A. The Investigated Sites and its Respective Soil Samples ................................... 63
B. Soil Composition of Each Sample Taken ......................................................... 67
C. Phosphate Adsorption for each Sample ............................................................ 70
LIST OF FIGURES vi
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
LIST OF FIGURES
Figure 1: The three major types of erosion (Brady and Weil 1996). ....................................4
Figure 2: Ellen Brook catchment map with the location of the investigate sites................23
Figure 3: Current velocities for erosion, sedimentation and transport chart (Hezen and
Hollister, 1964) ...................................................................................................................26
Figure 4: Sieves stack used to separate soil samples to different size fractions .................27
Figure 5: Sample preparation to conduct hydraulic conductivity test ................................28
Figure 6: Equipments used for hydraulic conductivity test ................................................29
Figure 7: Maintaining water level at six cm for hydraulic conductivity test ......................29
Figure 8: The automated adjustable pipette and stock solution ..........................................32
Figure 9: Soil samples immersed in different phosphate concentration .............................34
Figure 10: Glass pipette used to extract solution from the soil-phosphate test...................34
Figure 11: Different soil size fractions are tested for its adsorption...................................35
Figure 12: Soil column experiment simulating wetting and drainage event.......................36
Figure 13: Extracted solutions undergoes centrifugation process.......................................37
Figure 14: Soil composition of Site 1 sample .....................................................................38
Figure 15: Soil composition of Site 2 sample .....................................................................39
Figure 16: Soil composition of Site 3 sample .....................................................................39
Figure 17: Soil composition of Site 4 sample .....................................................................40
Figure 18: Soil compositon of Site 5 sample ......................................................................40
Figure 19: Soil composition of Site 6 sample .....................................................................41
Figure 20: Soil composition of Site 7 sample .....................................................................41
Figure 21: The soil composition of all the sites ..................................................................42
Figure 22: The bankfull - baseflow velocities and D50 values for Ellen Brook samples...43
Figure 23: Phosphate adsorption curve of Site 1 sample ....................................................46
Figure 24: Phosphate adsorption curve of Site 2 sample ....................................................47
Figure 25: Phosphate adsorption curve of Site 3 sample ....................................................47
Figure 26: Phosphate adsorption curve of Site 4 sample ....................................................48
Figure 27: Phosphate adsorption curve of Site 5 sample ....................................................48
Figure 28: Phosphate adsorption curve of Site 6 sample ....................................................49
Figure 29: Phosphate adsorption curve of Site 7 sample ....................................................50
Figure 30: Phosphate adsorption test on sample from Site 2..............................................55
LIST OF TABLES vii
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
LIST OF TABLES
Table 1: Bankfull and baseflow current velocities of each site (Smettem, 2006)...............27
Table 2: The volumes and concentrations to make different phosphate concentration
solution................................................................................................................................33
Table 3: The main size fractions for each soil sample ........................................................42
Table 4: Hydraulic conductivity of each sample.................................................................44
Table 5: Phosphate adsorption of 50 mg/L initial phosphate concentration.......................51
Table 6: Phosphate adsorption capacity of the original and amended soil .........................52
Table 7: Soil composition of the soil samples taken from Ellen Brook catchment ............67
Table 8: Phosphate adsorption capacity of five different phosphate concentrations..........70
GLOSSARY viii
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
GLOSSARY
Anions: negative ions.
Bankfull: the current flow of a water body that has reached or almost reached its full
capacity after a precipitation event.
Baseflow: the current flow of a water body which water is derived from groundwater or
which water exists in the catchment prior to a precipitation event.
Bioassays: measurement of concentration or the potential of a substance by its effects on
living cells or tissues.
Bioavailable: the amount of nutrients available that can be directly assimilated by
organisms.
Bassendean sand: a type of sand which has very low phosphorus binding capacity and has
been identified as major phosphorus leaching source in Peel-Harvey estuary.
Bioturbation: the disturbance of sedimentary deposits by living organisms.
Cations: positive ions.
Cations Exchange Capacity (CEC): the number of sites in soil where cations can attach
itself (Agricultural Bureau of South Australia, 2006).
Colloidal particles: particles larger than individual molecules but small enough to remain
microscopic. These particles would remain suspension in a dispersed state when mixed
with water. This phenomenon is caused by their enormous surface area to volume ratio or
“specific surface area” and electrostatic properties (Ashman and Puri, 2002).
Denitrification: the removal of nitrates or nitrites by chemical reduction.
GLOSSARY ix
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
Dissolved Reactive Phosphorus (DRP): phosphorus existing in a form which size is less
than 45µm.
Eutrophication: a condition where a water body is rich with nutrients.
Exchangeable cations: the positively charged ions (cations) which are loosely attached to
the edge of clay particles or organic matter in the soil. These include Calcium,
Magnesium, Potassium, Sodium, Hydrogen and Aluminium (Agricultural Bureau of South
Australia, 2006).
Gypsum: a soft white or grey mineral consisting of hydrated calcium sulphate, used in
building industry.
Ligand: an ion or molecule that binds to another.
Liming: treating soils with any salt or alkali containing calcium in order to increase the
pH.
Macro-nutrients: nutrients found at concentration in excess of 1000mg/kg.
Macrophyte: aquatic plants which sizes are large enough to be seen by the naked eye.
Nitrification: conversion of ammonium ions to nitrite and nitrate.
Nonpoint source: non-direct source of chemicals, often covering large areas or is a
composite of numerous point sources. For example: pesticide and fertilisers carried over to
other areas by wind or surface runoff, pollutants transported by groundwater flow and
pollution of urban runoff caused by automobile emission.
Nutrients: any substance used by an organism as food.
Oxides/ hydroxides: chemical compound of oxygen or oxygen and hydrogen with other
chemical elements.
GLOSSARY x
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
Particulate form: any substances or particles which size is bigger than 45µm.
Point source: discrete, localised and often readily measurable discharges of chemicals. For
example: industrial outfall pipes, untreated storm water discharge pipes and treated
sewage outfalls.
R2 value: in statistics, this value is used as a quantitative measure of the relationship
between two or more variables. The closer the value is to one, the stronger is the
relationship between the tested variables. The closer the value is to zero, the relationship
between the tested variables is weak or there is no relationship between the variables.
Redfield ratio: molecular ratio of carbon (C), nitrogen (N) and phosphorus (P) in
phytoplankton. Named after its founder, this ratio describes the molar element ratio of
C:N:P in most phytoplankton, which is 106:16:1 when nutrients are not limiting.
Sesquioxides/ hydroxides: An oxide containing three atoms of oxygen with two atoms of
some other substance. For example, alumina is a sesquioxide.
Soil horizons: layers of soil, approximately parallel to soil surface, which differ in
properties and characteristics from adjacent layers below or above it.
INTRODUCTION 1
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
1. INTRODUCTION
Phosphorus is one of the major limiting nutrients for aquatic organisms, especially in fresh
water environment. Excess of phosphorus in an aquatic system could cause unpredictable
changes in the distribution and biomass of aquatic plants. Environmental surveys
conducted at Peel-Harvey estuary system have confirmed that phosphorus took a
significant role in the proliferation of algal bloom in that area. Algal blooms could cause
the deteriorisation of other aquatic plants, reduce the oxygen level and intoxicate the
surrounding environment. These adverse impacts have been observed in Swan-Canning
River estuary system for some time (Summers et al., 1999, Daniel et al., 1998, PPK
Environment and Infrastructure, 2000).
Phosphorus and other nutrients may be transported to water bodies by erosion. Eroded
sediment often carries a greater concentration of adsorbed nutrients than the original soil.
It was thought that this came about due to the tendency of erosion events to transport
smaller soil particles, which are relatively rich in nutrients. This statement is supported by
a number of studies that found smaller soil particles contain more nutrients compared to
the bigger particles from the same area (Kronvang, 1992, McDowell and Sharpley, 2003).
Even though soil particles have the ability to transport nutrients, it also has the ability to
adsorb nutrients and other chemical compounds. Previous studies found that soil has
strong preference of phosphate ions. This was stronger in soils containing clay and
sesqui-oxides/ hydroxides minerals. This finding was utilised to increase phosphorus
retention of sandy soil in Peel-Harvey estuary. In this study, red mud (fine fraction of
bauxite residue containing mainly silica, iron and aluminium oxide) was applied to certain
sites and its phosphorus retention capacity was compared to other untreated sites. This five
year study showed that the treated sites experienced significant reduction in phosphorus
loss and leaching compared to the untreated sites (Brady and Weil, 1996, Bolt, 1976,
Summers et al., 1992).
INTRODUCTION 2
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
1.1. Ellen Brook Catchment
Ellen Brook is the largest contributor of phosphorus to the Swan-Canning estuary. This
catchment contributes 26 tonnes of phosphorus annually and this represents 36% to 39%
of total phosphorus load to the Swan-Canning estuary. This total load could be
underestimated as it does not include nutrient load during storm event (PPK Environment
and Infrastructure, 2000, Deeley et al., 1993, Banfield, 2001).
The central portion of the catchment has been cleared extensively to accommodate its
main land usages. The clearance of this catchment leaves about 35% of its natural
vegetation. The land clearance led to the increase of land degradation potential, which
includes erosion, flooding and nutrient export to waterways (PPK Environment and
Infrastructure, 2000, Viney and Sivapalan, 2001).
A study conducted in Ellen Brook catchment in 1993 indicated the possibility of
suspended particles to adsorb phosphorus from the surrounding water bodies. It was found
that one of the investigated sites has low phosphorus concentration and high sediment
load. This suggest that suspended particles might have adsorbed phosphorus from the
surrounding water (Deeley et al., 1993).
1.2. Research Objectives
Erosion process is more widely recognised to be a source of nutrients and the possibility of
this process to act as a sink has not been explored. This concept has enthuse the author to
engage a project, which main objective is to further investigate the possibility of eroded
bank sediment to act as a sink instead of source for nutrients. This project will also attempt
to find out whether soil amendment is a worthwhile investment in order to increase the
adsorption capacity of the soil particles. Whilst investigating the behaviour of eroded
sediment, this project is also interested on the capacity of the existing bank soils to retain
and/or adsorb nutrients.
The adsorption of nutrient from the water bodies will decrease total nutrient load and
hence reduce environmental issues caused by eutrophication. Ellen Brook catchment was
INTRODUCTION 3
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
chosen as the case study due to its large phosphorus contribution to the Swan-Canning
River. The reduction of phosphorus load from this catchment could significantly reduce
eutrophication problems of the Swan-Canning system.
This project is using phosphate in its experiment as this is the main form of phosphorus
existing in soils. The experiments were designed to determine the following:
i. The likelihood of Ellen Brook soils to erode under its present bankfull and
baseflow current velocities;
ii. The ability of the bank soil to retain water and hence determine its chances to
adsorb phosphate;
iii. The maximum phosphate adsorption capacity of the bank soils;
iv. The phosphate adsorption capacity of the different soil size fractions of each
sample to find out whether or not adsorption capacity is affected by soil particle
size;
v. The phosphate adsorption of the original soils under simulated site condition of
Ellen Brook catchment; and
vi. The phosphate adsorption of the amended soils under simulated site condition of
Ellen Brook catchment.
1.3. Synopsis
The next chapter, Literature Review, explains further erosion processes and its impacts.
It also looks into nutrient bonding by soil particles, how erosion affects nutrients being
transported to water bodies and the importance of phosphorus load from Ellen Brook
catchment. Experimental designs and equipments used in this project are detailed in
Methods, chapter 3. The findings will be presented in Results followed by Discussion
and Conclusion. There are some limitations of the current work and ways to improve it is
discussed in Recommendations for Future Work.
LITERATURE REVIEW 4
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
2. LITERATURE REVIEW
2.1. Water Erosion
Water erosion is a complex process that depends on various, often interrelated, factors.
This process generally begins with energy being applied to soil by rainfall and runoff.
Some of the energy will be absorbed by plants and/or other structures, and the remaining
energy will impact the soil surface directly. This impact disrupts soil aggregates, breaks it
into constituent particles and transports it away from the eroded landscapes (Starr et al.,
2000, Brady and Weil, 1996, Charman and Murphy, 1991).
There are three main types of water erosion: sheet, rill and gully. In sheet erosion, soil is
removed almost uniformly from every part of the slope. When sheet erosion occurs
accompanied by tiny dispersed channels, it is called rill erosion. It is known as gully
erosion when the volume of runoff water is further concentrated and it forms larger
channels or gullies (Brady and Weil, 1996).
Figure 1: The three major types of erosion (Brady and Weil 1996).
Sheet erosion
Rill erosion
Gully erosion
LITERATURE REVIEW 5
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
There are few main factors that influence water erosion. These are: rainfall and runoff, soil
characteristics, topography, vegetation cover and land management. Each of these factors
affected the potential of erosion to occur in different ways. Some of them will be
discussed further.
There are many soil characteristics that need to be considered in relation to water erosion.
However, the two most significant ones are infiltration capacity and structural stability.
These characteristics are affected by soil properties such as organic matter content, soil
texture and the type and amount of swelling clays. A national land survey in Australia
revealed that heavy clay soils and chemically dispersible sodic soils were highly erodible,
whilst rocky and weakly developed soils were least erodible. It was also revealed that soils
with high organic content are less erodible than ones with low organic content (Brady and
Weil, 1996, National Land and Water Resources Audit, 2001).
In assessing how rainfall and runoff affect erosion, there are several different factors that
need to be taken into account. For example, it is necessary to take into account total
rainfall, rainfall intensity and seasonal distribution of the rainfall. Frequent low intensity
rains may cause little erosion whilst few high intensity rains may result severe erosion.
The quantity and size of material that can be transported by runoff will depend on runoff
velocity and turbulence, which increases as slope steepens and flow increases. The impact
of rainfall in conjunction with runoff is known to cause more erosion than when either acts
alone (Brady and Weil, 1996, Charman and Murphy, 1991).
Riparian vegetation has been recognised to reduce bank erosion because tree roots add
substantial strength to the bank, effectively preventing them from slumping or
experiencing other forms of collapse. Moreover, overhanging and emergent vegetation is
able to reduce flow velocities and the scouring of banks. In areas where its protective
vegetation cover is removed or degraded, the risk of erosion is increased and rill and gully
erosion could occur. In America, it was found that undisturbed forest and grass provide the
best natural protection for soil, while bare areas are most subjected to erosion (Brady and
Weil, 1996, National Land and Water Resources Audit, 2001).
LITERATURE REVIEW 6
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
2.2. Known Impacts of Water Erosion
Water erosion has the potential to bring about beneficial or detrimental effects both on-site
and off-site. In many regions of the world, the movement and deposition of soil is essential
to maintain soil fertility. However, high levels of erosion could disrupt the ecological
health of the environment. The loss of nutrient caused by erosion made it necessary to
increase fertiliser application and to implement effective land managements. The
transported sediment will increase water turbidity and smother the floor of a water body.
These will then reduced the amount of light needed for photosynthesis and inhibit
respiration and feeding of aquatic organisms. Moreover, the desorption of nutrients and
other chemical compound from eroded sediment could lead to eutrophication and pollution
of the receiving water bodies (National Land and Water Resources Audit, 2001, Zheng et
al., 2005, Ashman and Puri, 2002).
Eutrophication refers to a condition where a body of water is rich in nutrient. It was
recognised as early as 1960s that eutrophication would accelerate growth of aquatic plants
and caused disruption to the surrounding ecosystem. This phenomenon is evident in
Western Australia where excessive input of nutrients, predominantly nitrogen (N) and
phosphorus (P), have been responsible for potentially harmful algal blooms in upper
Swan-Canning River estuaries. The algal blooms have caused occasional fish deaths and
its potential toxicity made it necessary to warn the community to avoid direct contact with
the affected waters and not to consume organisms taken from the river during the blooms
(PPK Environment and Infrastructure, 2000, Smith, 2001, National Academy of Sciences,
1967).
2.3. The Impacts of Water Erosion in Australia
A national land audit done in Australia revealed that erosion transported a significant
amount of sediment and nutrients. On average, the total erosion rate is 4.4 tonnes/ha per
year within the areas assessed with gully, riverbank and sheetwash erosion delivered over
120 million tonnes of sediment to the streams yearly. It was found that up to 85% of
phosphorus (P) and nitrogen (N) sourced from hill slope erosion, and up to 59% of
nutrient load to Indian Ocean region was caused by gully erosion. Even though the survey
showed that much of the soils in the south-west of Western Australia were less susceptible
LITERATURE REVIEW 7
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
to water erosion, there were 30,000 streams, of which 30% is located in south Western
Australia, that received sand and gravel derived from erosion to the extent that its in-
stream ecological health was impaired (National Land and Water Resources Audit, 2001).
The deposition of sand and suspended sediments in streams and rivers were found to be
greater in areas with significant vegetation clearance and high rainfall intensity. The
degradation of riparian vegetation has accelerated erosion of creeks and river banks whilst
reduced vegetation cover in arid and semi-arid landscapes has also accelerated wind-borne
erosion. Hence, it was deemed necessary to maintain adequate vegetation cover and to
implement a good riparian management (National Land and Water Resources Audit,
2001).
2.4. Interactions Between Nutrient and Soil
Soil possesses electrostatic charge and this determines its ability to hold certain chemical,
such as nutrients, acidity and toxins. Some soil have ‘permanent’ and ‘variable’ charge
while others mainly have ‘variable’ charge. A permanently charged soil is not affected by
acidity and most of the time it is negatively charged. The charge in a variably charged soil
could be positive, negative or neutral, depending strongly upon the acidity of the soil
(Ashman and Puri, 2002).
Most soils that are not too acidic or alkaline are negatively charged and will attract cations
and repel anions. This soil property causes many anions, such as nitrate (NO3-),
susceptible to leaching while cations, such as potassium (K+), calcium (Ca
2+) and
magnesium (Mg2+) ions, are adsorbed (Ashman and Puri, 2002).
Soil may also have some positive charges even though its particles are predominantly
negatively charged. Edges of clay soil and surfaces of oxide minerals, especially iron (Fe)
and alumunium (Al) oxides/ hydroxides, are likely to be positively charged at pH below
seven and hence able to adsorb anions. Moreover, clay minerals and sesquioxides/
hydroxides have a stronger preference for phosphate (PO4-) anions compared to other
anions. It was found that as the content of soil’s sesquioxides increases, so does its
adsorption capacity for phosphate. This indicate that there exist chemical bonding in
LITERATURE REVIEW 8
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
addition to electrostatic attraction between the soil particles and the phosphate ions (Bolt,
1976).
The previously mentioned soil responses to phosphate ions can be utilised to increase
phosphate retention in soil. It was suspected that coatings of Fe and Al- oxides/ hydroxides
on sand grains contribute to the observed retention of phosphate in sandy soils. Sandy soils
have higher capacity to retain water and if its adsorption capacity can be increased,
inorganic phosphate ions would be rather immobile in these soils. This could reduce
eutrophication problems of the adjacent water bodies (Bolt, 1976).
There are also other factors that could affect the soil ability to hold or release nutrients.
Some of these factors are pH, bioturbation and temperature. High temperature would
intensify chemical reaction and biological activity, which will promote nutrient being
released from sediment. A high pH in water column, especially pH nine or higher, was
mentioned on previous studies as a factor that increased phosphorus release from
sediment. Bioturbation by sediment-dwelling macro-fauna may disturbed soil deposition
and promote nutrient release (Suomela et al., 2005).
Amongst the wide range of nutrients, there are three most important soil macro-nutrients.
These are nitrogen (N), phosphorus (P) and potassium (K). The behaviour of these
nutrients in soil is discussed.
2.4.1. Nitrogen (N)
Nitrate (NO3-) anions are one of the main forms of inorganic nitrogen existing in soil.
These negatively charged ions are not adsorbed by negatively charged soil colloidal
particles that dominate most soils. As a consequence, this nutrient leaches readily from the
soil unless utilised by plants. The amount of nitrate leached from tsoil depends on the
amount of water draining through the soil and the amount of available soluble nitrate in
soil solution (Brady and Weil, 1996).
Leached nitrate ions are generally carried by drainage water to the groundwater or surface
water. It may also eventually flow underground to the surface waters such as streams,
LITERATURE REVIEW 9
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
lakes and estuaries. This may contaminate drinking water, causes eutrophication and other
associated environmental problems. Only if the input is balanced by removal via plant or
denitrification will it be possible to stabilise the leaching (Brady and Weil, 1996, de Haan
and Zwerman, 1976, Ashman and Puri, 2002).
The quantity of nitrate that leached will depend on some factors such as the amount of
water draining through the soil profile and the amount of nitrate available for leaching. For
example, leaching potential will be low on non-irrigated semiarid and arid region as there
is insufficient water to carry nitrate ions. In areas where there is sufficient water for nitrate
transport, the texture and structure of soil horizons will affect the rate of which water will
go through. The amount of nitrate available for leaching depends on the balance of
nitrogen input and output, which also include fertilisation, nitrification-denitrification rate
and plant nitrate uptake (Brady and Weil, 1996).
There were several major sources of nitrogen that generally found in agricultural areas.
These sources were: (1) constituents of leaves, stems and roots of crops, (2) soil
constituents whether they are in organic and inorganic form, (3) decaying plant residues
and (4) fertiliser (de Haan and Zwerman, 1976).
2.4.2. Potassium (K)
Potassium exists in form of K+ ions in soil and is stored in three forms: (1) K
+ in solution,
(2) exchangeable K+ and (3) non-exchangeable K
+. They are generally attracted to
negatively charged soil colloids and can be hold in soil solution, attached on soil’s
exchange sites or fixed in a non-exchangeable form by certain clay minerals. Potassium is
more readily lost by leaching than phosphorus and this losses will be higher if it is not
slowed by attraction between this positively charged ions to the negatively charged soils
(Ashman and Puri, 2002, Brady and Weil, 1996).
Liming an acidic soil to raise its pH may reduce the amount of potassium leaching. Limed
soils have higher levels of exchangeable calcium (Ca) and magnesium (Mg). In this type
of soils, K+ ions have better ability to replace Ca and Mg and be adsorbed. However, if
LITERATURE REVIEW 10
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
other ions such as exchangeable alumunium (Al) are present, K+ ions are less likely to be
adsorbed (Brady and Weil, 1996).
2.4.3. Phosphorus (P)
Phosphorus (P) exists in soil as phosphate anions. It can exist in several different forms
depending on the soil pH and its anionic character can be altered by other soil chemicals.
The alteration of the anionic character leads to formation of phosphorus compounds that
attracted directly to negatively charge colloidal particles, which will lead to ligand
formation. Insoluble phosphate compounds will form when the pH is outside the narrow
range of six and seven (Ashman and Puri, 2002).
The combination of insoluble compound and ligand formation resulted in P being bind to
soil constituent and hence the P leaching potential is reduced. This was thought to be the
reason behind why previous studies shown that on worldwide scale, contribution of P from
erosion was larger than leaching through soil profile. However, P bonding to soil particles
is not permanent. It is frequently mentioned that pH of 9 or higher may contribute to the
increase of P flux from sediments (Ashman and Puri, 2002, Suomela et al., 2005, de Haan
and Zwerman, 1976).
There is a method that can be used to measure the P fixing capacity of a particular soil. In
this method, a known quantity of soil is mixed in a P solution with known concentration.
The equilibrium state of the soil-water interaction will be achieved after about 24 hours
and the remaining concentration can be measured. This remaining concentration is known
as the Equilibrium Phosphorus Concentration (EPC). By extracting the amount of
remaining P concentration from the initial concentration, the amount of adsorbed nutrient
can be determined. When this procedure is repeated using a series of solutions with
different initial P concentration, the results can be plotted as a phosphorus-fixation curve.
The maximum phosphorus-fixation capacity can be extrapolated from the value at which
the curve levels off. The P adsorption capacity for most soils would be in the order of 100
kg of P per ha per 10 cm of soil (Brady and Weil, 1996, Gerritse, 1992).
LITERATURE REVIEW 11
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
2.5. Erosion and Nutrient Budget
Eroded soil particles often carry with them a much greater concentration of adsorbed
nutrients than the original soil. This process was thought to come about due to the fact that
erosion tends to transport the smaller soil particles, which are relatively rich in nutrient.
This process left behind the coarser materials with lower nutrient concentration, which
made it necessary to increase fertiliser application in agricultural areas (McDowell and
Sharpley, 2003).
A number of studies have been conducted to investigate various factors that influence
nutrient transport due to erosion and these factors will be discussed further.
Change of soil conditions will changes the organic matter quality, decrease/increase soil
moisture and hence affected the soil’s erodibility. For example, it was found that the
amount and type of soil’s carbon content and exchangeable cation influenced the loss of
phosphorus (P) in sediment. P-rich particles were lost during the start of runoff event and
gradually decrease with time. This decrease was found to be correlated to soil’s
carbohydrate concentration. This result inferred that increasing soil carbohydrate content
increase soil binding capacity and made P less available for loss by runoff (McDowell and
Sharpley, 2003).
Storm events and soil particle size affect the amount of nutrients being transported. A
study on storm events effects found that during these events, the eroded sediments were
significantly enriched in nitrogen (N) and phosphorus (P). The particulate matter load
duration curves showed that more sediment transport occured during the infrequent storm
events. This was more extreme on particulate organic matter than inorganic matter.
Another study reported that N and P concentration in eroded sediment in runoff decreased
as the soil size fraction increased. The highest N and P concentrations were found in
particles less than 2µm in diameter. This confirmed other studies that found only 10% of
transported particulates were in silt and clay size but they contained over half the total P
load and 25% of other pollutants. An experiment conducted in 1993 recorded the highest
concentration of copper, zinc and phosphorus were associated with sand particles between
75µm to 250µm in size (Alberts and Moldenhauer, 1981, Flanagen and Foster, 1989,
Kronvang, 1992, Vaze and Chiew, 2004).
LITERATURE REVIEW 12
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
It was found that conditions in the environment affected the particle size to which majority
of the nutrients adsorbed to. In this study, nutrient load across different particle sizes were
determined for dry samples, dry samples dissolved in water and samples from storm
events wash off. The dry samples represented the availability of nutrients in dry surface
pollutants. Dry samples which were dissolved in water represented the potential amount of
nutrients that can be washed off if there was sufficient water to dissolve the pollutants.
Samples from storm events represented the actual amount of nutrients that would be
washed off under different storm events. The dry samples had almost all of total P and
total N attached to particles with diameter between 53µm and 300µm. A similar result was
observed on the wet samples. Storm events samples had almost all of its particulate P and
N attached to particles with diameter between 11µm and 150µm (Vaze and Chiew, 2004).
A recent study conducted in Loess Plateau, China, confirmed the role of erosion in
reducing the concentration of nutrient in the original soil and enriching nutrients in eroded
sediment. The P content of the original soil had the highest reduction followed by
ammonium – nitrogen (NH4 – N) and organic matter. This observation could be attributed
to the fact that these nutrients were strongly adsorbed by clay soil, which has high
likelihood to get eroded. It was also found that nutrient enrichment in eroded sediment was
significantly affected by total rainfall and intensity. This relationship was thought to be
caused by the influence of total rainfall and intensity on runoff, which would affect soil
detachment by runoff, transport capacity and erosion rate (Zheng et al., 2005).
Another study in Queensland, Australia, found that there were relationships between
eroded sediment and nutrient loss. There was a significant correlation (R2 = 0.77) between
loss of total N and total erosion. A stronger correlation (R2 = 0.87) between loss of total N
and eroded sediment of less than 50 µm diameter was observed. There was a poor
correlation between loss of total P and total erosion. However, a significant correlation
(R2 = 0.7) between loss of P and eroded sediment particles with diameter bigger than 100
µm was observed. Overall, the study found that nutrient loss was highly correlated with
weights of the finer components of the eroded sediment, including organic matter. The
detached coarser soil fractions were generally found to be deposited in the nearby furrows
whereas nutrient-rich fine sediments were transported off-site (Costantini and Loch,
2002).
LITERATURE REVIEW 13
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
Similar results on erosion and nutrient load were observed in a study conducted in Japan.
The results from this study indicated that total N and P concentrations in water with
eroded suspended solids were higher than surrounding water. This study found that total N
and P in suspension tends to increase with the increasing concentration of eroded
materials. This showed that N and P were dominantly transported by soil particles and
organic matter to water bodies. Furthermore, the N and P loss in surface runoff would
increase with the increasing soil loss and fertiliser application level (Mihara and Ueno,
2000).
Even though there were a number of studies confirming the effect of erosion to nutrients
input to water bodies, the significance of this process and the availability of these nutrients
to aquatic organisms are still debateable.
Phosphorus losses through erosion are insignificant in some areas. A study conducted in
the Peel Inlet and Harvey Estuary system, Western Australia, showed that river and creek
bank erosion were likely to be a minor contributors of P loss from soil. Throughout the
investigation, the P losses due to erosion in these areas were probably less than 10%.
Another study in Western Australia concluded that the sandy soil had little phosphate
adsorption capacity and losses of P mainly occurred through leaching (Weaver et al.,
1999, Gerritse, 1992).
There is uncertainty on whether effort to reduce erosion will concurrently reduce nutrient
load. Results from an experiment on nutrient adsorption by soil particles implied that
effective reduction in eroded sediment or total suspended solid (SS) did not necessarily
reduce nutrient loads in the same magnitude (Vaze and Chiew, 2004).
A study conducted in 2003 concluded that the significance of eroded particulate P (PP) to
the eutrophying P load is unclear. This study investigated the amount of bioavailable P
that could be transformed from PP. The bioavailability of particulate P can be assessed by
bioassays and chemical methods. In this experiment, the amount of bioavailable P was
represented by the sum of Dissolved molybdate-Reactive Phosphorus (DRP) and Anion
Exchange Resin extractable Particulate Phosphorus (AER-PP). The maximum
concentration of bioavailable P was represented by the sum of DRP and Bicarbonate
Dithionite extractable Particulate Phosphorus (BD-PP). It was found that only a fraction of
LITERATURE REVIEW 14
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
PP can be transformed to bioavailable P, depending upon the geochemical properties and
oxygen level. It was reported that sediment in anoxic condition released greater amount of
P than oxic state. This process is often reversible and P may be readsorb to the sediment in
freshwater, but it is done less effectively in marine water (Uusitalo et al., 2003).
It was found that the amount of bioavailable P in the smaller soil size fraction was lower
compared to other size fractions. There were studies which showed the tendency of
erosion to erode P-rich fine sedimens. However, a specific study on the amount of
bioavailable P had found that the content of bioavailable P in less than 100µm size
fraction was lower compared to other size fractions. There were two possible causes that
were thought to attribute to this matter: (1) smaller size fraction has higher P adsorption
capacity and hence P binding is stronger and (2) P extractability has decreased due to
drying process conducted to retrieve these particles from suspension. It was concluded
then, that P-rich aggregates carried into surface water should not contribute immediately to
eutrophication (He et al., 1994).
Even though P-rich aggregates should not immediately cause eutrophication problems, this
does not mean this condition will continue after these particles are deposited. Deposited
particulate P increases P storage in the sediment. It has been confirmed that the amount of
phosphate stored in sediments is often an order of magnitude greater than amount of
phosphate present in water column. This stored phosphate may be released when there are
changes to the environmental conditions or there are micro-organisms activities occurring.
Changes in pH or algal and bacterial activities have been known to mobilise phosphate
from sediment and add it to the water column (Gerritse, 1992, Suomela et al., 2005)
2.6. Phosphorus and its Importance
Phosphorus (P) is often found to be the limiting element to the growth of aquatic
organisms in fresh water. Although there are other essential nutrients such as nitrogen (N)
and carbon (C), the amount of N and C exchange between atmosphere and water made
more attention being put to P as there is no exchange of this nutrient in the atmosphere-
water interaction. The significance of P in profileration of algal bloom was confirmed by
environmental surveys conducted in Peel Inlet and Harvey Estuarine system, Western
LITERATURE REVIEW 15
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
Australia, which showed that the growth of algae has been stimulated by P load from
surrounding catchment. This made P control important in reducing eutrophication in fresh
water. As the condition change from fresh water to saline ocean water, N becomes the
element controlling aquatic productivity (Summers et al., 1999, Daniel et al., 1998).
The loss of phosphorus from soil surface to the surrounding water bodies is of concern due
to the resulting effects on surface water quality. P can be loss to surface runoff and
subsurface drainage in particulate and dissolved forms. Surface runoff was thought to be
the main mechanism by which P is exported from most watersheds. P in runoff from
agricultural lands is one of the major non-point sources of pollution that can accelerate
eutrophication. The potential loss of P from these areas is dependent on different factors
such as surface and subsurface runoff, land management and the amount, form and
availability of P in soil (Daniel et al., 1998).
Dissolved P is often found to be immediately available for biological uptake, while
particulate P has the potential in becoming long term storage of P for aquatic biota. In
some areas, the loss of particulate P (PP) accounts for 70% to 90% of total P loss from
agricultural areas. Small P concentration, ranging from 0.01 to 0.03 mg/L, can cause
eutrophication. Hence, the efforts to reduce the amount of P input to water bodies need to
continue (McDowell and Sharpley, 2001, He et al., 1994).
Runoff could erode soil material and this material may be a sink for soluble P. As there is
size selective nature of erosion, soil aggregates are not transported equally and it tend to
erode smaller sized soil aggregates. The role of suspended solid as a sink for Dissolved
Reactive Phosphorus (DRP) is depending on the Equilibrium Phosphorus Concentration
(EPC). The EPC is determined by the physical and chemical properties of the solution and
the suspended sediment. Suspended sediment was known to act as a sink in an
environment where the soil’s P level was very low (Maguire et al., 2002, Bjorneberg et al.,
2006).
Phosphorus fixation by soil is not easily reversible but certain environmental conditions
can make it to occur. The release of P from soil to solution is often called desorption
process. This process may occur when a portion of the fixed P is present in a relatively
soluble form and most of the fixation sites are already occupied with P ions. The release of
LITERATURE REVIEW 16
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
fixed P is very important in determining losses of dissolved P to the surface runoff. The
point where P is neither released nor retained is often called Equilibrium Phosphorus
Concentration (EPC). This is an important soil parameter because it indicates both the
level of P needed for soil fertility and the alarming level of P loss by solution in runoff
water (Brady and Weil, 1996).
2.7. Remediation Effort to Reduce Phosphorus
Erosion control, effective land management and other effort to increase P retention in soils
will bring about significant benefits in managing supply of nutrient from sediment.
Conservation tillage, buffer strips and putting in riparian zones vegetation are some of the
available options that can reduce P loss via erosion and runoff. Control on fertiliser
applications on agricultural area may be implemented to reduce point source discharge of
P. Soil amendment to increase P retention is currently being looked at to reduce P load to
water bodies (Daniel et al., 1998, National Land and Water Resources Audit, 2001).
Red mud application was proven to be successful to enhance P retention ability of sandy
soil. Red mud is the fine fraction of bauxite residue, mainly silica, iron (Fe) and
alumunium (Al) oxides, that has been treated with caustic soda to remove alumina. A
study conducted at Peel-Harvey estuary, Western Australia, shown that red mud
application enhanced P retention ability of the sandy soil when it was neutralised with
gypsum. The treated areas experienced significant reduction in P loss and leaching
compared with untreated areas. Moreover, the P concentration in the treated areas
gradually declined during the five years investigation period. This indicated that the P
retention ability increases with time. This was suspected to be caused by the gradual
decrease of pH, which lead to the increase of soil’s affinity for P (Summers et al., 1992).
Red mud application produced minimal environmental impact on the Peel-Harvey estuary
study. The amount of soluble salts in the treated areas was consistently higher than the
untreated areas. However, this increase was still within the guideline range for most of the
Swan Coastal Plain water. Red mud has a pH of about 11 due to its sodium hydroxides
and sodium carbonate content, however the pH fell to about 8.5 after it was treated with
gypsum (Summers et al., 1992).
LITERATURE REVIEW 17
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
Riparian vegetation may increases nutrient and sediment entrapment and hence increases
the stream water quality. Riparian vegetation has the potential to reduce the environmental
issues connected with stream water quality by: (1) physically filtering and trapping
sediment, nutrient and chemicals in surface runoff, (2) providing suitable subsurface
conditions for plant uptake and chemical activities such as denitrification and (3)
displacing sediment and nutrient-producing activities away from streams. The
effectiveness of grass and eucalyptus as riparian vegetation were tested. Grass coverage
was able to reduce nutrients and suspended solid concentration in surface runoff by 50%
to 60%. Lower percentage reduction was observed with the eucalyptus type of riparian
vegetation. The trapping of nutrients and suspended solid were generally positive and were
at its highest during the wettest year monitored. Low and negative trapping of nutrients
and suspended solid were typically observed in the driest year monitored. A limitation on
the functionality of vegetation cover was observed in areas where subsurface flow
dominated (McKergow et al., 2006).
The effectiveness of riparian vegetation might be limited in sandy areas with low P
adsorption capacity. A ten years monitoring program in a 6 km2 catchment near Albany,
Western Australia, was conducted to monitor stream flow, nutrient and sediment
concentration in order to investigate the effectiveness of riparian vegetation. These data
were collected at the downstream end of fenced riparian areas to get before and after data
on the improved riparian management. Before the implementation of riparian vegetation,
around half of the total P is particulate P. However, after riparian management was
implemented the level of P exports remain the same, despite significant decrease in
suspended solid. The data indicated that there were additional P sources and only a little
amount of particulate P derived from the investigated channels. There were also other
suspected reasons that could contribute to why the vegetation cover did not reduce P
exports. If the P losses were dominated by soluble P, then it would be less amenable to
reduction by vegetation cover. Subsurface-flow paths may dominate over surface runoff in
some soils, and soils in this particular catchment could not retain large amount of P
(McKergow et al., 2002).
LITERATURE REVIEW 18
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
2.8. Site of Study Background
2.8.1. Swan – Canning River
The estuaries ecology and water quality of the south coast of Western Australia (WA) has
been disrupted by increased nutrient and sediment load. Input of nutrients from rural
catchments is a major source of non-point source of pollution that can accelerate
eutrophication in lakes and streams. This had been identified as the greatest threat to
estuarine ecosystem health. The excess of nutrient inputs were first thought to derive from
sewage effluent but when this was stopped, the water was still enriched. It was then
suspected that the nutrients had came from diffuse resources in urban and agricultural area
A recent review of south-western estuaries of WA suggested that reducing external
nutrient load up to 70% might be required in order to handle this eutrophication issue. In
addition to this, an even greater reduction might be required to handle internal loading of
nutrients (Weaver et al., 2005, Daniel et al., 1998, Donohue et al., 1994).
The effect of eutrophication has been observed in Swan-Canning estuary, W.A., for some
time. Eutrophication may causes unpredictable changes in the distribution and biomass of
macrophyte. This nutrient enriched condition manifested in occasional algal blooms in the
Swan-Canning River estuary. The urban wetlands in the catchments within the estuary
were dominated with blue-green algae and green algae. This aquatic biota fouled the
estuary beaches and had to be removed. It also reduced the light needed by other plants to
photosynthesise, which was manifested by the loss of more than 80% of seagrass cover in
Oyster Harbour, W.A. Moreover, it consumes oxygen necessary for fish and caused
occasional fish deaths. The potential toxicity of algal blooms made it necessary to warn
the community to avoid direct contact with the affected waters and not to consume any
organisms taken from these areas. (Donohue et al., 1994, PPK Environment and
Infrastructure, 2000, Elliott et al., 2005).
Swan-Canning River estuary receives about 589 million m3 of fresh water yearly, which
contains about 740 tonnes of nitrogen (N) and 70 tonnes of phosphorus (P). Ellen Brook
and Avon River catchment are the biggest P and N load contributors out of the
investigated 15 major tributaries to Swan-Canning River estuary. They deliver 45 tonnes
LITERATURE REVIEW 19
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
of P and nearly 500 tonnes on N, which is about 65% of the total external P and N load to
the estuary. Between these two catchments, Ellen Brook discharges the highest
concentration of P to the estuary (Donohue et al., 1994, Deeley et al., 1993).
This study chose Ellen Brook as its case study due to two important factors. Firstly,
phosphorus load has been known as one of the major contributors to eutrophication
problems occurring in Swan-Canning River system. Secondly, reducing the amount of P
load from Ellen Brook has the potential to reduce the environmental issues within the
catchment itself and Swan-Canning River estuary.
2.8.2. Ellen Brook Catchment
Ellen Brook is the largest coastal sub-catchment of the Swan-Canning River estuary. It has
an area of approximately 720 km2 and it experiences Mediterranean climate of hot dry
summers and cool wet winters. Average annual rainfall for southern region of the
catchment is about 868 mm and less than 660 mm in the northern region. About 90% of
this rainfall falls between May and October, with significant falls occurring in April. The
catchment consists of three distinct regions: the Darling Plateau, the Dandaragan plateau
and the Swan Coastal Plain. It has an extensive area of annual clover based pastures
located at low lying Bassendean sand and horticulture area located on the heavier soils on
the eastern side (PPK Environment and Infrastructure, 2000, Deeley et al., 1993, Banfield,
2001).
Ellen Brook catchment contributes an average of 37 million m3 of fresh water runoff, 77
tonnes of nitrogen (N) and 26 tonnes of phosphorus (P) to Swan-Canning estuary
annually. This represents about 6% to 10% of total flow, 36% to 39% of total P and 7% of
total N to Swan-Canning system. This high nutrient loading might be underestimated as it
excludes the load during storm event (PPK Environment and Infrastructure, 2000, Viney
and Sivapalan, 2001, Donohue et al., 1994).
The N to P ratio in Ellen Brook was found to be significantly lower from the idealised
Redfield ratio. As it was mentioned earlier, the annual total N and total P of Ellen Brook
are about 77 tonnes and 26 tonnes respectively. This would mean that its N to P ratio is
LITERATURE REVIEW 20
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
close to 6 to 1 whereas the idealised N: P ratio according to Redfield ratio is 16 to 1. The
low N to P ratio and high nutrient loads may encouraged the growth of blue-green algae.
Blue-green algae are currently regular but relatively unimportant in the upper
Swan-Canning River phytoplankton community. However, the conditions in Ellen Brook
may encourage a shift in the phytoplankton community (Deeley et al., 1993).
The central portion of the catchment has been cleared extensively to accommodate its
main land uses. The main land uses within the catchment include grazing, forestry, annual
and perennial horticulture, mining and extractive industries, and expanding region of
urban and rural residential development. The clearance of this catchment leaves only about
35% of its natural vegetation (PPK Environment and Infrastructure, 2000, Viney and
Sivapalan, 1999).
The land clearance has created a considerable impact to the hydrology of the streams and
the estuaries. The replacement of deep-rooted vegetation by seasonal, shallow-rooted
crops has led to reduced evapotranspiration, increased surface runoff and increases in
groundwater recharge. All these factors have increased land degradation potential. Some
of the land degradation indicators found in Ellen Brook were wind and water erosion,
waterlogging, flooding and nutrient export to waterways. A study conducted at Peel Inlet
and Harvey Estuary system supported this statement as it found that the uncleared native
forest contributed very little phosphorus to the estuary compared with the cleared area of
the coastal plain (Summers et al., 1999, PPK Environment and Infrastructure, 2000, Viney
and Sivapalan, 2001).
Wide range of erosion is evident in Ellen Brook catchment. The type and significance of
erosion found in this catchment is often related to landforms, but also in conjuction with
soil type, land management, local development, and so on. Infrastructure disturbances,
such as pipeline excavation, found to be a common factor influencing erosion along the
surveyed route. Some of the observed erosion processes were due to poor subdivision
design, development or practices. For an example, many drainage line embankments were
significantly degraded, often by stock access. This had diminished vegetation cover and
exacerbate bank erosion (Llyod, 2000).
LITERATURE REVIEW 21
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
The movement of sediments and adsorbed nutrients are one of the main management
issues in Ellen Brook catchment. Two areas in this catchment, Bulls Brook and Ki-it
Brook, were investigated. Bulls Brook represented the coastal plain catchment while Ki-it
Brook represented the upland catchment. The results showed that the movement of
adsorbed phosphorus (P) during erosion and the leaching of soluble P from the sandy
coastal catchment were the main mechanisms of P movement. It also showed that
sediment loss was greater in the upland catchment than in coastal catchment, with
suspended sediment concentration at its highest during high stream flows (Banfield, 2001).
A study on the Darling Plateau showed that erosion did not seem to be significant in
nutrient export. In this study, the effect of erosion was measured by looking at the amount
of transported particulate matter in streams. The total annual quantities of particulate
matter in the subcatchments were found to be small and ranged from 100 kg to 500 kg of
dry weight. However, the level of phosphorus, organic carbon and other substances such
as manganese, copper and zinc were much higher in the suspended particulate matter than
in the associated soil. This finding agrees with other studies that stated nutrients in eroded
particles were higher than its original soil. As some part of Ellen Brook is on the Darling
Plateau region, this study may be applicable to the catchment (Banfield, 2001).
There is a possibility that suspended particles have considerable ability to adsorb
phosphorus from the surrounding water. A study on Ellen Brook catchment found that
concentrations of total phosphorus (TP) were high at all investigated sites except Lennard
and Ki-it Brook. The suspended solid (SS) concentrations were very low at all sites except
Ki-it Brook. This site drains reddish clayey (lateritic) and milky colloidal clay material,
which have considerable phosphate retention capacity. The low P concentration and high
sediment load at Ki-it Brook suggested that the suspended load may have adsorb P after
mixing with the dissolved P-rich waters of Ellen Brook. Traces of suspended solids from
this site were observed immediately downstream in the main channel of Ellen Brook at
Warbrook. Warbrook has a lower proportion of dissolved P than other sites. This might be
caused by the adsorption of dissolved P by the suspended solids coming from Ki-it Brook
(Deeley et al., 1993).
METHODS 22
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
3. METHODS
This chapter will discuss in detail the methods and instruments used to determine the
following:
i. The likelihood of Ellen Brook soils to erode under its present bankfull and
baseflow current velocities;
ii. The ability of the bank soil to retain water and hence determine its chances to
adsorb phosphate;
iii. The maximum phosphate adsorption capacity of the bank soils;
iv. The phosphate adsorption capacity of the different soil size fractions of each
sample in order to find out whether or not adsorption capacity is affected by soil
particle size;
v. The phosphate adsorption of the original soil under simulated condition of Ellen
Brook catchment; and
vi. The phosphate adsorption of the amended soil under simulated condition of Ellen
Brook catchment.
3.1. Sites and Samples Description
The samples were taken from seven different banks of various water bodies along Ellen
Brook catchment transection. These sites were chosen such that there would be a
representation of soils from different locations in Ellen Brook catchment. The sites were
originally intended to represent the different types of soil along the catchment’s main river
channel. However, lack of access to the previously intended areas made it necessary to
choose other sites closest to the ones intended.
The following are the locations of the investigated banks:
Site 1: Gingin Access Road
Site 2: Breera Road.
Site 3: Brand Highway.
Site 4: Great Northern Highway.
Site 5: Rutland Road.
Site 6: Railway Parade.
METHODS 23
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
Site 7: West Swan Road
The relative positions of these sites in the Ellen Brook catchment can be observed in the
map of the catchment (Figure 2). The numbers on the map show the locations of the sites.
Figure 2: Ellen Brook catchment map with the location of the investigate sites
The samples consist of three to five cm of the bank’s top soil, which were taken using a
small shovel. The top soils were sampled due to the assumption that they are the part of
the bank soil that would most likely be affected during runoff events. The amount of soil
taken from each site was approximated such that there was enough samples to find out: (1)
the composition of each soils, (2) the hydraulic conductivity of the major particle sizes and
(3) phosphate adsorption capacity. The amount of soil taken ranged from three to about
five kg. It was necessary to take more sample from a sandy type of soil to ensure there was
an adequate amount of the bigger soil particles to be tested.
The seven investigated banks have relatively different surrounding environment, bank
conditions and soil types. These will be discussed in the following:
1
2
3
4
5
6
7
METHODS 24
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
Site 1
The sample from Site 1 was taken from a modified roadside drainage, which apparently
was experiencing its baseflow or near to baseflow condition. The bank has poor vegetation
cover and hence has the potential of experiencing erosion under moderate to high flow
regime. The sample seems to be composed of reddish brown soil, with the bigger soil
particles dominating. There is a little amount of organic materials observed in the sample.
Site 2
The sample from Site 2 was taken from a modified land drainage. The bank has poor
vegetation cover and was experiencing no flow. The erosion process is most likely to be
caused by wind erosion under this condition. However, as rainfall condition changes,
water erosion could take place. The sample is observed to be dominated with fine sandy
particles, with a fair amount of organic materials.
Site 3
The sample from Site 3 was taken from a river bank, experiencing what seemed to be
moderate flow. The bank has good vegetation cover, which will give resistance to erosion
and create good opportunity for water-soil interaction between the channel’s water and the
riparian zone. This also means that there is a good opportunity for nutrient in the water to
be adsorbed by the bank’s soil. The sample seems to be composed of a mixture of sandy
soil and bigger brown-coloured soils. A little amount of organic materials is present.
Site 4
The sample from Site 4 was taken from a land drainage. At the time sampling was done,
this water body seemed to be experiencing baseflow or near baseflow condition. It has
moderate vegetation cover, which will protect it to some degree from erosion and provide
opportunity for water-soil interaction under medium to high flow condition. The sample is
observed to be composed of uniformly fine sandy soil with little amount of organic
materials.
Site 5
The sample from Site 5 was taken from a river bank with good vegetation cover. At the
time sampling was done, the bank was experiencing moderate flow. This site has good
vegetation cover and it seems that nutrient assimilation will be encouraged in this
METHODS 25
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
environment. The soil sample is observed to be mainly composed of sandy soil with a little
amount of organic materials.
Site 6
The sample from Site 6 was taken from a river bank experiencing near bankfull condition.
This area has good vegetation cover and should encourage water-soil interaction, which
will lead to nutrient assimilation. The soil sample seems to be dominated by brownish soil
particles with some bigger particle size fractions exist. A little amount of organic materials
is observed.
Site 7
The sample from Site 7 was taken from a river bank experiencing baseflow or near
baseflow condition. This area has poor vegetation cover and bank erosion is evident.
However, as the river moves on to the flood plain where it has good vegetation cover,
there could be opportunity for nutrient exchange. The soil sample is dominated by fine
sandy particles with very few organic materials.
3.2. Soil Erodibility Potential
The likelihood of the soil in the catchment to erode was examined using the current
velocities and sediment particle sizes for erosion, sedimentation and transport chart
(Figure 3). This chart contains information on which processes (erosion, sedimentation
and transport) is most likely to occur under certain current velocities and soil particle
sizes.
METHODS 26
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
Figure 3: Current velocities for erosion, sedimentation and transport chart (Hezen and
Hollister, 1964)
The soil samples were separated to different size fractions utilising sieves with mesh size
of 4.75mm, 2mm, 1mm, 500µm, 250µm, 106µm and 53µm to find out the soil
composition. To ease the effort of sieving and to ensure accuracy, the samples were sieved
in about 200g batch of sample at a time. Too much sample would clog the mesh and
smaller particles could not sieve through. The sieving process was done repeatedly for a
sample batch, especially starting from the 500µm mesh size. It was found that as the mesh
size gets smaller, it was easier to get clogged. Repetition and soft brush were used in this
process to unclog the mesh and obtain a more accurate soil composition. However, it
needs to be kept in mind that sieving a sample batch too much could cause the soil
particles to erode due to force from soil particles collision and the brush. In this
experiment, each sample batch went through about three repetitions on average.
METHODS 27
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
Figure 4: Sieves stack used to separate soil samples to different size fractions
The bankfull and baseflow current velocities for each site were gotten from discussions
with Associate Professor Keith Smettem, who has worked on different projects on Ellen
Brook catchment (Table 1).
Table 1: Bankfull and baseflow current velocities of each site (Smettem, 2006)
Site No. Current Velocities
Site 1 and 2 Bankfull: higher than 50 cm/s
Site 3 Baseflow: 10 cm/s
Bankfull: 50 cm/s
Site 4 and 5 Bankfull: higher than 60 cm/s
Site 6 and 7 Bankfull: higher than 80 cm/s
The main soil particle size fraction that made up each soil sample, known as the D50 value,
and the current velocities are used to find out the likelihood of the tested soil samples to
experience erosion, sedimentation and transport. The range of bankfull and baseflow
current velocities and the D50 values were plotted in the current velocities for erosion,
sedimentation and transport chart. The chart was then examine to find out the most likely
process to occur.
METHODS 28
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
3.3. Hydraulic Conductivity
Hydraulic conductivity gives the water retention ability of the soil sample, which indicates
the potential of water-soil interaction. It is assumed that the longer water can be retained,
the more opportunity for nutrient to be assimilated by the soil particles.
The soil size fractions being tested for hydraulic conductivity were: 500 µm – 1mm, 250
µm – 500 µm and 106 µm – 250 µm. This was done as there were not enough samples of
the smaller size fractions to do the experiment and the bigger size fractions were assumed
to have low water retention ability, which would not be adequate for nutrient assimilation
by soil particles.
The hydraulic conductivity test for each sample was done utilising cylindrical tubes with
diameter of five cm of which its bottom was covered with filter paper. The soil sample
was put into the cylinders until it form four cm thick layer of soil. The weight of the
sample needed to form four cm thick of soil inside the tubes was measured. The sample
was then immersed in water and let to settle to release trapped air within the soil. The
thickness of the soil layer after the soil settled was measured to calculate saturated
hydraulic conductivity (Ksat).
Figure 5: Sample preparation to conduct hydraulic conductivity test
4cm
METHODS 29
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
Syringes filled with 30cc of water, a stop watch and a stand to hold the cylindrical tubes
were prepared. The tube was held by the stand in order to drain water from it. The filter
paper prevented soil particles leaving the tube as the water drained away. Once the water
reached six cm level, i.e. about two cm above the soil sample, water from the syringes was
flowed into the tube to maintain the water level at six cm. The time taken to empty a
syringe was recorded and this process was done three times for each sample. The resulting
three time records were averaged to calculate the saturated hydraulic conductivity.
Figure 6: Equipments used for hydraulic conductivity test
Figure 7: Maintaining water level at six cm for hydraulic conductivity test
6 cm
METHODS 30
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
h
The saturated hydraulic conductivity is calculated using Equation 1.
Equation 1: Ksat (cm/min) = Q x (h - L/L)
Q : inflow of water from the syringes (cm/min)
h : water level (cm)
L : thickness of soil in saturated condition (cm)
Figure 8: Schematic diagram on the different variables used in calculating Ksat.
In order to calculate the inflow, Q, the following equation is used:
Equation 2: Q (cm/min) = (vol / Π r2)/ t
Vol : volume of water in the syringes, which is 30 cc.
r : radius of the cylindrical tubes used for hydraulic conductivity test,
which is 2.5 cm.
t : time taken to empty a 30 cc syringe filled with water (minute)
3.4. Phosphate Adsorption Capacity of the Soil Samples
The phosphate adsorption capacity tests were conducted in order to find out:
1. The maximum phosphate adsorption capacity of the sampled bank soils;
L
Q
Q
METHODS 31
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
2. The phosphate adsorption capacity of the different soil size fractions of each
sample and utilise it to determine whether or not adsorption capacity is affected by
soil particle size;
3. The phosphate adsorption of the original soil under simulated site condition of
Ellen Brook catchment; and
4. The phosphate adsorption of the amended soil under simulated site condition of
Ellen Brook catchment.
The phosphate adsorption capacity tests were done using tri-potassium orthophosphate. In
order to find out the maximum phosphate adsorption capacity, the soil samples were
immersed in five different phosphate concentrations. Three different soil size fractions
from each sample were immersed in the same phosphate concentration to determine the
relationship between soil particle size and phosphate adsorption. The ability of the bank
soils and the amended soils to adsorb nutrient under the catchment’s natural conditions
were determined using transient wetting/ drainage experiment, utilising 0.5 mg/L
phosphate concentration. This concentration is the typical phosphate concentration of
Ellen Brook catchment as per discussion with Associate Prof. Keith Smettem. All of the
phosphate adsorption tests conducted allowed more than 24 hours of water-soil interaction
before the final phosphate solutions were extracted from each test. The extracted solutions
were then analysed for its phosphate concentration, which would give the amount of
phosphate adsorbed in each test.
A stock solution containing 10,000 mg/L of tri-potassium phosphate was utilised to make
the different phosphate concentrations by diluting the stock solution with de-ionised water.
An automated adjustable pipette with varying suction pressures was utilised to ensure the
accuracy of the amount of solution being mixed. Prior to use, the stock solution was kept
in the fridge to prevent possible chemical reactions caused by heat.
All of the equipments used have been washed using Decon 90, a powerful detergent, and
were rinsed twice using deionised water. This step was done to prevent any contamination
from possible chemical residues left on the equipments being used. The detergent,
Decon 90, does not contain phosphates, enzymes or chlorine bleaches and totally rinsable.
Hence, the potential of chemical contamination due to the use of this detergent can be
deemed insignificant.
METHODS 32
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
Figure 8: The automated adjustable pipette and stock solution
The following equation was used to make the different phosphate concentration solution:
Equation 3: Final concentration (mg/L) = initial concentration x vol
final volume
Initial concentration: the concentration of the phosphate solution used to
make the phosphate solution with different concentration (mg/mL).
vol : volume of the initial concentration (mL)
final volume : volume of phosphate solution required for the tests (L)
The amount of adsorbed phosphate by soil was calculated with the following equation:
Equation 4: Phosphate adsorbed = P original – P final
P original: the phosphate concentration in the solution before the tests were
conducted
P final: the phosphate concentration in the solution after the tests were
conducted
In order to get the final phosphate concentration, the extracted phosphate solutions were
sent to a chemical analysis laboratory in Albany, Western Australia. They used the
ammonium molybdate method, which is a nationally recognised method for phosphate
analysis.
METHODS 33
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
It is assumed that processes contributing to the diminishing or increasing phosphate
concentration other than adsorption or desorption of phosphate by the soil sample are
negligible.
3.5.1. Phosphate Adsorption Test with Varying Concentration
The maximum phosphate adsorption capacity of each sample was determined by using
adsorption distribution isotherm at 1:2 soil to solution ratio. Adsorption capacity of each
sample was tested against five different phosphate concentrations. The amount of
adsorbed phosphate from each of the different concentrations was plotted and produced
phosphate adsorption curve. The maximum phosphate adsorption capacity was then
determine by extrapolating the value at which the curve level off.
Using the stock solution, two litres of 200 mg/L phosphate solution was made. This was
then used to make phosphate solutions with concentration of 10, 50, 100, 150 and 200
mg/L. The amount of phosphate solution and de-ionised water used to make the different
phosphate concentrations using Equation 3 is summarised (Table 2).
Table 2: The volumes and concentrations to make different phosphate concentration solution
Intended concentration (mg/L) 200 150 100 50 10
Vol. of intended concentration (L) 2 0.3 0.3 0.3 0.3
Initial concentration (mg/mL) 10 0.2 0.2 0.2 0.2
Vol. of initial concentration needed (mL) 40 225 150 75 15
Vol. of de-ionised water needed (mL) 1960 75 150 225 285
A total of 100g of soil sample from each site was used to test phosphate adsorption against
phosphate solution with concentration of 10, 50, 100, 150 and 200 mg/L. In each test, 20g
of soil sample was put into a plastic container and immersed with approximately 40mL of
phosphate solution with different concentrations. This was done for all soil sample and
they were then shook to create maximum soil particles-phosphate solution interaction.
Each sample were let to settle for more than 24 hours to reach equilibrium state, a state
where phosphate is neither released nor retained. An approximately 10mL of phosphate
solution from each sample was taken out afterwards using glass pipette and was put into
METHODS 34
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
small plastic tubes. The use of glass pipette instead of the previously used automated
pipette was done to reduce the amount of suspended particles being put into the analysed
solution. This can be achieved as the opening of the glass pipette is smaller than the
automated pipettes.
Figure 9: Soil samples immersed in different phosphate concentration
Figure 10: Glass pipette used to extract solution from the soil-phosphate test
3.5.2. Phosphate Adsorption Test with Constant Concentration
This test is aimed to determine whether the amount of phosphate adsorbed by soil particles
is related with the size of the soil particles. In doing this, three different soil size fractions
from each sample were tested for its adsorption of 50 mg/L phosphate concentration.
The soil size fractions being tested for phosphate adsorption capacity were: 500µm–1mm,
250µm–500µm and 106µm–250 µm. This was done as there was not enough samples of
the smaller size fractions to do the experiment and the bigger size fractions were assumed
METHODS 35
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
to have insignificant phosphate adsorption capacity due to its low surface area to volume
ratio. For the same reason, the smallest soil size fraction was predicted to have the highest
adsorption capacity due to its higher surface area to volume ratio.
A litre of 50 mg/L was prepared using 5mL of stock solution mixed with 955mL of
deionised water. For each of the three different soil size fractions, 20g of sample was put
into a plastic container and immersed in 40mL of 50 mg/L phosphate solution. This was
done for all of the seven different soil samples and they were shook to create maximum
soil particles-phosphate solution interaction. They were then let to settle for more than 24
hours afterwards. Glass pipette was used to extract about 10mL of the resulting phosphate
solutions and they were then put into small plastic tubes.
Figure 11: Different soil size fractions are tested for its adsorption
3.5.3. Phosphate Adsorption under Simulated Site Conditions
Transient wetting/ draining experiment was performed to determine the phosphate
adsorption of the original bank soil under the Ellen Brook catchment site condition. This
method intends to simulate actual site condition where the bank of a water body
experiences flooding and drainage events. The initial phosphate concentration of 0.5 mg/L
was chosen as it is the typical phosphate concentration of Ellen Brook catchment.
To simulate soil-water interaction during the bank flooding event, 100g of soil from each
site was put into a cylindrical tube, which has little cavities at its bottom for drainage. To
prevent soil particles escaping from the tube during the experiment, filter papers were put
METHODS 36
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
at its base. The tube was then placed into another container with a closed end and plastic
lining. Phosphate solution with 0.5 mg/L concentration was poured at the space between
the cylindrical tube and plastic lining. This solution then went into the cylindrical tube
through the cavities and immersed the soil within the tube. It was immersed for more than
24 hours and drained afterwards. The drained solution was collected and about 10mL of
the resulting phosphate solution was extracted and put into a small plastic tubes. This
method was done for all of the seven different samples.
Figure 12: Soil column experiment simulating wetting and drainage event
3.5.4. Phosphate Adsorption Capacity of the Amended Soils
The transient wetting/ draining experiment was repeated after the soils were amended with
crushed laterite. It was expected that the phosphate adsorption capacity would increase due
to this action. If the soil amendment is proven to increase phosphate adsorption, this
method may be used as a management option to decrease the amount of phosphate in
water column of Ellen Brook catchment by increasing the potential of bank soil and
eroded bank sediment to act as a sink for phosphate.
Each of the soil sample was mixed with crushed laterite with particle size of less than or
equal to 500µm. The composition of the 100g soil samples used in this experiment were
75g of original sample and 25g of crushed laterite. The samples were immersed with 0.5
mg/L phosphate concentration and drained after they were let to settle for more than 24
METHODS 37
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
hours. About 10mL of phosphate solution from each sample was extracted and put into
small plastic tubes.
3.5. Measuring Phosphate Concentration
The solution from each phosphate adsorption tests was tested for its Filterable Reactive
Phosphate (FRP) concentration. The results from this test would give the concentration of
dissolved phosphate, excluding phosphate content of possible biological organisms and
soil particles in the sample. In order to get FRP, each of the solution was filtered by 45µm
filter before it was analysed.
Centrifugation was conducted for each sample in order to ease the filtration process.
Solutions from phosphate adsorption tests, which were put into plastic tubes, were
centrifuged to settle out any suspended particles. The centrifugation process was done
using 4800 rpm speed for 20 minutes.
Figure 13: Extracted solutions undergoes centrifugation process
The solutions were then analysed for FRP using the ammonium molybdate colorimetric
method on a segmented flow auto-analyser. The ammonium molybdate method is the
nationally recognised standard method for analysis of FRP in solution (Rayment and
Higginson, 1992, Murphy and Riley, 1962).
RESULTS 38
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
4. RESULTS
4.1. Soil Composition and its Erodibility Potential
The soil composition of each investigated site in Ellen Brook catchment is described in the
following graphs. The D50 value, which indicates the main soil size fraction that makes up
the soil sample, is shown by the deep blue line.
SITE 1 - GINGIN ACCESS RD
0
10
20
30
40
50
60
70
80
90
100
10 100 1000 10000
Soil size fraction (micro metre)
Percentage Passing (%)
Figure 14: Soil composition of Site 1 sample
Soil sample from Site 1 is dominated by soil particle fraction of 1mm-2mm. This sample
contained the most of bigger than 4.75mm soil particle size amongst the seven different
samples. There is a little amount of less than 106µm particles in this sample.
D50
RESULTS 39
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
SITE 2 - BREERA RD
0
10
20
30
40
50
60
70
80
90
100
10 100 1000 10000
Soil size fraction (micro metre)
Percentage Passing (%)
Figure 15: Soil composition of Site 2 sample
Soil sample from Site 2 is dominated by soil size fraction of 500µm-1mm. This sample
contains a little amount of the bigger and the finer particle sizes and is mainly composed
of two size fractions, 250µm-500µm and 500µm-1mm.
SITE 3 - BRAND HWY
0
10
20
30
40
50
60
70
80
90
100
10 100 1000 10000
Soil size fraction (micro metre)
Percentage Passing (%)
Figure 16: Soil composition of Site 3 sample
Soil sample from Site 3 is dominated by soil size fraction of 500µm-1mm. This sample
contains a little amount of finer than 106µm soil particles. The domination of just one size
fraction is not evident in this sample.
D50
D50
RESULTS 40
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
SITE 4 - GT NORTHERN HWY
0
10
20
30
40
50
60
70
80
90
100
10 100 1000 10000
Soil size fraction (micro metre)
Percentage Passing (%)
Figure 17: Soil composition of Site 4 sample
Soil sample from Site 4 is dominated by soil size fraction of 500µm-1mm. Again, the
domination of just one particle size fraction is not evident. This sample contains a little
amount of finer than 106µm particles.
SITE 5 - RUTLAND RD
0
10
20
30
40
50
60
70
80
90
100
10 100 1000 10000
Soil size fraction (micro metre)
Percentage Passing (%)
Figure 18: Soil compositon of Site 5 sample
Soil sample from Site 5 is dominated by soil size fraction of 250µm-500µm. The
domination of one soil size fraction is evident in this sample. There is very little amount of
less than 106µm particles and bigger than 500µm particles.
D50
D50
RESULTS 41
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
SITE 6 - RAILWAY PDE
0
10
20
30
40
50
60
70
80
90
100
10 100 1000 10000
Soil size fraction (micro metre)
Percentage Passing (%)
Figure 19: Soil composition of Site 6 sample
Soil sample from Site 6 is dominated by soil size fraction of 500µm-1mm. There is a very
little amount of particles smaller than 106µm exists in this sample.
SITE 7 - WEST SWAN RD
0
10
20
30
40
50
60
70
80
90
100
10 100 1000 10000
Soil size fraction (micro metre)
Percentage Passing (%)
Figure 20: Soil composition of Site 7 sample
Soil sample from Site 7 is dominated by soil size fraction of 250µm-500µm. The
domination of one soil size fraction is evident in this sample. There is a very little amount
of soil which is smaller than 106µm and bigger than 500µm.
D50
D50
RESULTS 42
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
0
10
20
30
40
50
60
70
80
90
100
10 100 1000 10000
Soil size fraction (micro metre)
Percentage Passing (%)
SITE 7 - WEST SWAN RD
SITE 6 - RAILWAY PDE
SITE 5 - RUTLAND RD
SITE 4 - GT NORTHERN HWY
SITE 3 - BRAND HWY
SITE 2 - BREERA RD
SITE 1 - GINGIN ACCESS RD
Figure 21: The soil composition of all the sites
There are differences and similarities of soil composition for samples from different sites.
Samples from Site 5 and Site 7 have the most similarity in its composition compared to
other samples. They both show the domination of one soil size fraction and have a little
amount of other size fractions. This similarity in composition is also observed with
samples from Site 3, 4 and 6. Samples from these sites do not have clear domination of
just one size fraction and more of the bigger size fractions exist. Soil composition of Site 1
sample is very different from other samples as it has more of the bigger soil size fraction.
All of the samples have a little amount of the smaller than 106µm particles with sample
from Site 2 having the highest amount of soil particles which size is smaller than 106µm.
The different D50 values of the samples is summarised in Table 3.
Table 3: The main size fractions for each soil sample
Site No. D50 soil size fraction
Site 1 1 mm – 2 mm
Site 2 500 µm – 1 mm
Site 3 500 µm – 1 mm
Site 4 500 µm – 1 mm
Site 5 250 µm – 500 µm
Site 6 500 µm – 1 mm
Site 7 250 µm – 500 µm
D50
RESULTS 43
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
Figure 22: The bankfull - baseflow velocities and D50 values for Ellen Brook samples
The range of bankfull and baseflow current velocities is plotted on the current velocities
for erosion, sedimentation and transport chart along with the D50 value for each site
(Figure 22). The range of bankfull current velocities is indicated with yellow box and the
range of baseflow current velocities is indicated with clear-blue box. The range of the
different main size fractions (D50 values) are indicated by the black line with an
explanation of which site/ sites the D50 value belong to.
It is observed from the chart that soil from all sites have the potential to experience erosion
as the current velocities approaches the bankfull condition. They also have the potential to
be transported and sedimented as the current approaches the baseflow velocity.
Range for Bankfull velocities
Range for recession velocities
Site 1
Site 2,3,4,6
Site 5,7
RESULTS 44
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
4.2. Hydraulic Conductivity Test
The flow rate (Q) and saturated hydraulic conductivity (Ksat) for soil samples from each
site for three different size fractions (500 µm - 1 mm, 250µm - 500µm and 106µm -
250µm) were determined and the results is summarised (Table 4).
Table 4: Hydraulic conductivity of each sample
Particle Size
Site No. 500 µm - 1 mm 250 µm - 500 µm 106 µm - 250 µm
Q (cm/min) 1.425 1.608 0.393
Site 1 Ksat (cm/min) 0.767 0.804 0.131
Q (cm/min) 5.979 4.509 1.022
Site 2 Ksat (cm/min) 3.461 1.639 0.341
Q (cm/min) 3.056 2.236 0.975
Site 3 Ksat (cm/min) 1.900 0.745 0.418
Q (cm/min) 8.872 1.687 0.085
Site 4 Ksat (cm/min) 4.436 0.562 0.034
Q (cm/min) 5.851 2.723 1.180
Site 5 Ksat (cm/min) 3.637 1.361 0.734
Q (cm/min) 1.647 0.203 0.123
Site 6 Ksat (cm/min) 1.176 0.135 0.061
Q (cm/min) 4.044 2.132 1.074
Site 7 Ksat (cm/min) 2.889 1.234 0.716
Hydraulic conductivity of Site 1 sample shows that there is no significant difference of
hydraulic conductivity between the different soil size fractions. The 250µm-500µm size
fraction has the highest value while the 106µm-250µm size fraction has the lowest value.
Overall, the hydraulic conductivity for this sample is on the lower range and it has the
lowest hydraulic conductivity value for 500µm-1mm size fraction.
Results on Site 2 sample shows that there is a marked difference of the hydraulic
conductivity between the different size fractions. As the soil size fraction decreases, so
does the hydraulic conductivity.
Site 3 sample shows decreasing hydraulic conductivity along with the decreasing soil
particle size. The hydraulic conductivity difference between the different soil size
fractions is not as marked as sample from Site 2.
RESULTS 45
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
The test results on Site 4 sample shows significant decrease in hydraulic conductivity as
the soil particle size decreases. The hydraulic conductivity decreases in a factor of 10 for
each decrease in the soil size fraction. This confirms that the smaller size fractions retain
water much better than the bigger size fractions. The 106µm–250µm size fraction of this
sample has the lowest hydraulic conductivity value amongst all other samples.
Site 5 sample also shows decreasing hydraulic conductivity as the soil particle size
decreases. The decrease of the hydraulic conductivity is quite notable, even though it is
not as marked as the other samples.
Similar to Site 4 sample, Site 6 sample shows significant decrease of hydraulic
conductivity as the soil particle size decreases. As the size fraction decreases, the
hydraulic conductivity decreases by a factor of 10. This sample has the lowest hydraulic
conductivity for 250µm – 500µm size fraction.
The results from Site 7 sample shows decreasing hydraulic conductivity as the soil size
decreases. Its decrease of hydraulic conductivity and its values are similar to Site 5
sample.
There is a general trend of decreasing saturated hydraulic conductivity as the soil particle
size decreases, with exception of Site 1 sample. There are some samples where the
decreases of hydraulic conductivity are quite marked, which can be observed on samples
from Site 4 and 6. The decreases from other samples are not as distinguish, however it still
shows that hydraulic conductivity decreases as the soil particle size gets smaller.
RESULTS 46
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
4.3. Phosphate Adsorption Tests
4.3.1. Phosphate Adsorption Test with Varying Concentration
The phosphate adsorption of five different phosphate concentrations of each site was
determined and the phosphate adsorption curves are graphed.
Site 1
Phosphate Adsorption Curve of Site 1
0.00
50.00
100.00
150.00
200.00
0 50 100 150 200
Initial Phosphate Concentration (mg/L)
Adsorbed Phosphate
(mg/L)
Figure 23: Phosphate adsorption curve of Site 1 sample
It is observed from Site 1 sample that as the concentration of phosphate in solution
increases, so does the amount of adsorbed phosphate. The almost linear relationship
between initial phosphate concentration and adsorbed phosphate shows that this sample
adsorbed almost all of the phosphate existing in the solution. The resultant curve (Figure
23) shows that the maximum phosphate adsorption capacity of this soil is beyond 200
mg/L phosphate concentration. Hence, higher concentrations need to be tested in order to
find out the maximum adsorption capacity.
RESULTS 47
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
Site 2
Phosphate Adsorption Curve of Site 2
-25.00
-20.00
-15.00
-10.00
-5.00
0.00
5.00
0 50 100 150 200
Initial Phosphate Concentration (mg/L)
Adsorbed Phosphate
(mg/L)
Figure 24: Phosphate adsorption curve of Site 2 sample
Phosphate adsorption of Site 2 sample shows that the soil is desorbing phosphate instead
of adsorbing it. There is a trend observed where the amount of phosphate desorbed
increases as initial concentration increases. As this sample does not seem to adsorb
phosphate, the maximum phosphate adsorption can not be determined.
Site 3
Phosphate Adsorption Curve of Site 3
0.00
50.00
100.00
150.00
200.00
0 50 100 150 200
Initial Phosphate Concentration (mg/L)
Adsorbed Phosphate
(mg/L)
Figure 25: Phosphate adsorption curve of Site 3 sample
The amount of adsorbed phosphate from Site 3 sample increases as the amount of
phosphate in solution increases. It is observed the curve starts to level off at the higher
range of initial phosphate concentration. This indicates that the maximum phosphate
RESULTS 48
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
adsorption capacity was almost reached. As the curve is extended further, the maximum
adsorption capacity is predicted to be about 224 mg/L.
Site 4
Phosphate Adsorption Curve of Site 4
0.00
50.00
100.00
150.00
200.00
0 50 100 150 200
Initial Phosphate Concentration (mg/L)
Adsorbed Phosphate
(mg/L)
Figure 26: Phosphate adsorption curve of Site 4 sample
There is a close to linear relationship between initial concentration of phosphate in
solution and amount of adsorbed phosphate of Site 4 sample. The results from this sample
are similar to Site 3 sample. However, as the adsorption curve does not seem to level off
(Figure 26), more tests need to be conducted in order to find out the maximum phosphate
adsorption capacity.
Site 5
Phosphate Adsorption Curve of Site 5
0.00
50.00
100.00
150.00
200.00
0 50 100 150 200
Initial Phosphate Concentration (mg/L)
Adsorbed Phosphate
(mg/L)
Figure 27: Phosphate adsorption curve of Site 5 sample
RESULTS 49
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
The amount of adsorbed phosphate of Site 5 sample indicates that the maximum phosphate
adsorption capacity is reached at initial phosphate concentration between 150 mg/L – 200
mg/L. The amount of adsorbed phosphate increases as the initial phosphate concentration
increases from 10 mg/L to 150 mg/L and peaked at 150 mg/L. As the initial concentration
increases to 200 mg/L, the amount of adsorbed concentration decreases. This could due to
desorption after the maximum adsorption capacity satisfied. The levelling of the phosphate
adsorption curve is observed for this sample (Figure 27). As the curve is extended, the
maximum adsorption capacity is approximated to be about 48 mg/L.
Site 6
Phosphate Adsorption Curve of Site 6
0.00
50.00
100.00
150.00
200.00
0 50 100 150 200
Initial Phosphate Concentration (mg/L)
Adsorbed Phosphate
(mg/L)
Figure 28: Phosphate adsorption curve of Site 6 sample
The phosphate adsorption curve of Site 6 sample shows that the amount of adsorbed
phosphate levels off at initial phosphate concentration 100 mg/L – 150 mg/L. The amount
of adsorbed phosphate peaks at 200 mg/L initial concentration. This could indicate that the
maximum adsorption capacity is beyond the 200 mg/L concentration. However, similar to
Site 5 sample, this could be caused by desorption after the adsorption capacity has reached
its maximum. Utilising the available data, the adsorption curve is extended and the
phosphate adsorption capacity is approximated to be about 180 mg/L.
RESULTS 50
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
Site 7
Phosphate Adsorption Curve of Site 7
0.00
50.00
100.00
150.00
200.00
0 50 100 150 200
Initial Phosphate Concentration (mg/L)
Adsorbed Phosphate
(mg/L)
Figure 29: Phosphate adsorption curve of Site 7 sample
Sample from Site 7 gives quite distinct level of maximum phosphate adsorption. It is
observed that this level of maximum phosphate adsorption of about 50 mg/L is reached at
initial phosphate concentration of 150 mg/L. The phosphate adsorption is observed to level
off at 50 mg/L and hence the phosphate adsorption capacity is approximated to be about
50 mg/L.
RESULTS 51
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
4.3.2. Phosphate Adsorption Test with Constant Concentration
The phosphate adsorption test results using initial phosphate concentration of 50 mg/L on
the different soil size fraction are summarised (Table 5).
Table 5: Phosphate adsorption of 50 mg/L initial phosphate concentration
Site no. Particle Size
500µm - 1mm
250µm - 500µm
106µm - 250µm
Final Concentration (mg/L) 1.41 0.54 0.91
1 Adsorbed Phosphate (mg/L) 48.59 49.46 49.09
Final Concentration (mg/L) 67.15 65.28 56.87
2 Adsorbed Phosphate (mg/L) -17.15 -15.28 -6.87
Final Concentration (mg/L) 3.07 2.26 0.74
3 Adsorbed Phosphate (mg/L) 46.93 47.74 49.26
Final Concentration (mg/L) 30.71 27.55 2.7
4 Adsorbed Phosphate (mg/L) 19.29 22.45 47.3
Final Concentration (mg/L) 2.99 44.54 43.07
5 Adsorbed Phosphate (mg/L) 47.01 5.46 6.93
Final Concentration (mg/L) 22.63 19.62 2.42
6 Adsorbed Phosphate (mg/L) 27.37 30.38 47.58
Final Concentration (mg/L) 1.49 32.08 33.75
7 Adsorbed Phosphate (mg/L) 48.51 17.92 16.25
There is no notable difference on the phosphate adsorption between different soil size
fractions for Site 1 sample. The amount of phosphate being adsorbed by the different soil
size fractions is very similar, with the highest difference being 0.87 mg/L.
Similar to the adsorption test using five different phosphate concentration, it is observed
that sample from Site 2 desorbed phosphate instead of adsorbing it. It is observed that the
amount of desorbed phosphate decreases as the soil size fractions decreases.
The phosphate adsorption for Site 3 sample increases as the soil particle size decreases.
This increase is considered minor with the biggest difference of 2.33 mg/L between the
tested soil size fractions.
Site 4 sample displays a marked increase on the amount of adsorbed phosphate as the soil
particle size decreases. The amount of adsorbed phosphate of the smallest soil size fraction
is more than double the amount of adsorbed phosphate for the other two soil size fractions.
RESULTS 52
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
Unlike samples from other sites, the highest amount of adsorbed phosphate for Site 5
sample is observed at the biggest soil size fraction. The difference is quite significant with
more than 40 mg/L difference of adsorbed phosphate between the biggest size fraction and
the others.
There is a continual increase of phosphate adsorption as the soil size decreases for sample
from Site 6. Significantly higher amount of adsorbed phosphate is observed for the
smallest soil size fraction compared to other sizes.
Similar to sample from Site 5, the amount of adsorbed phosphate is observed at the biggest
soil size fraction for Site 7 sample. This difference is quite significant with more than 30
mg/L difference of adsorbed phosphate between the biggest soil size fraction and the other
two soil size fractions.
4.3.3. Phosphate Adsorption Under Simulated Site Conditions
The results of the transient wetting/ drainage experiment of the original and the amended
soil with 0.5 mg/L of initial phosphate concentration are shown (Table 6).
.
Table 6: Phosphate adsorption capacity of the original and amended soil
Original Soil Amended Soil
Site No.
Final Concentration
(mg/L)
Adsorbed Phosphate
(mg/L)
Final Concentration
(mg/L)
Adsorbed Phosphate
(mg/L)
1 0.56 -0.06 0.12 0.38
2 1.36 -0.86 0.15 0.35
3 0.39 0.11 0.11 0.39
4 0.13 0.37 0.06 0.44
5 0.53 -0.03 0.02 0.48
6 0.14 0.36 0.01 0.49
7 0.29 0.21 0.04 0.46
Desorption of phosphate is observed in the original sample of Site 1, 2 and 5. However,
the amount of desorption from Site 1 and 5 sample is very minute and can be said that the
phosphate concentration stays the same with no desorption or adsorption taking place.
Highest adsorption is observed in Site 4 and Site 6 sample.
RESULTS 53
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
Amended soils from all the seven sites have adsorbed almost all of the phosphate initially
in the solution. The amount of phosphate being adsorbed by the amended soils are very
similar, with the difference between the least adsorbing and the most adsorbing sample
being 0.14 mg/L. Amended soil sample from Site 6 has the highest phosphate adsorption
and Site 2 has the least phosphate adsorption.
DISCUSSION 54
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
5. DISCUSSION
Under the current flow regimes, erosion is likely to occur in all the investigated sites of
Ellen Brook catchment. The chart of current velocities for erosion, sedimentation and
transport (Figure 22) shows erosion should occur during bankfull or near to bankfull
condition. This is likely to happen between May and October as about 90% of the rainfall
occurs in this catchment in this period, significantly in April (Banfield, 2001). The chart
also shows that soils from Site 2, 3, 4 and 6 are the ones most likely to experience erosion.
As erosion is likely to occur, this confirms the importance of finding out whether eroded
sediment would act as sink or source of phosphate in water bodies.
Phosphate is being adsorbed by almost all of the tested samples, with an exception of
sample from Site 2. Sample from Site 1 adsorbed the most amount of phosphate amongst
the tested samples. The maximum phosphate adsorption capacity of this sample is
predicted to be higher than 200 mg/L because its phosphate adsorption curve does not
seems to be levelling off at this point. High adsorption capacity is also observed in
samples from Site 3 and 4, which have very similar phosphate adsorption curve. Samples
from Site 5 and 7 adsorbed the least amount of phosphate amongst the tested samples.
These samples have similar phosphate adsorption curve and maximum phosphate
adsorption capacity. If erosion process transports sediment which composition is close to
the investigated soils, eroded sediment from Site 1 will be acting as the most effective sink
for phosphate while sediment from Site 5 and 7 are the least effective.
A variety of results is observed while investigating the impact of soil particle size to
phosphate adsorption. There is trend in samples from Site 3, 4 and 6 where the amount of
adsorbed phosphate increases as the soil particle size fraction decreases. This agrees with
other studies on the effect of particle size to nutrient adsorption where the amount of
nutrient adsorbed increases as the soil particle size decreases (Kronvang, 1992, Vaze and
Chiew, 2004). There is no significant difference on the amount of phosphate adsorbed by
the different size fractions of Site 1 sample. Highest phosphate adsorption is observed in
soil size fraction 106µm-250µm of Site 3 sample while the lowest phosphate adsorption is
observed in the 250µm-500µm of Site 5 sample. Sample from Site 2 is again observed to
DISCUSSION 55
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
be desorbing phosphate. As its soil particle size decreases so does the amount of desorbed
phosphate.
Phosphate adsorption of Site 5 and 7 is at its highest in the largest tested soil size fraction
(500µm-1mm). This could come about due to the fact that smaller particle size has almost
reached its maximum phosphate adsorption capacity prior to the test. This could explain
the lack phosphate adsorption by samples from these sites. Site 5 and 7 samples are both
dominated by soil size fraction 250µm-500µm, which has low phosphate adsorption for
these samples.
Sample from Site 2 has desorbed phosphate in all of the experiments. This could be caused
by the fact that this soil sample contained the highest amount of organic material. The
presence of organic materials can be observed by the colour it produced as the sample was
immersed in phosphate solution (Figure 30). This organic material could be containing
phosphate of which get desorbed in the experiment. This possibility combined with the
low phosphate adsorption capacity of sandy soil, could be the reason of this phenomenon.
There are possibilities of laboratory error involved that causing this, however due to the
consistency of phosphate desorption in all of the tested soil sample of Site 2, this factor
can be considered minor and should not affect this finding significantly. If erosion process
is experienced by Site 2 soil, the eroded sediment is more likely to act as a source of
phosphate instead of as a sink. More desorption will occur if erosion transports sediment
which composition is close to the original composition of Site 2 sample. However, least
desorption of phosphate and other possible nutrients will be observed if erosion transports
the smallest size fraction as this size fraction desorbed the least amount of phosphate.
Figure 30: Phosphate adsorption test on sample from Site 2
DISCUSSION 56
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
The water retention ability generally increases as the soil particle size decreases, which
can be seen from the decreasing hydraulic conductivity as the soil particle size decreases.
This indicates that water-soil interaction between a bank soil and its adjacent water body is
likely to be more effective as the soil is composed more of the smaller soil particles. The
longer water is being retained within the soil, the higher is the opportunity for phosphate
to be adsorbed by the soil particles. As a result, the amount of phosphate transported to a
water body can be reduced. The best water retention ability is observed in 106µm-250µm
size fraction of Site 4 soil and the least water retention is observed in 500mm-1mm of the
same soil sample.
Soil from Site 1 does not show significant difference of hydraulic conductivity between
the different soil size fractions. However, its low range of hydraulic conductivity shows
that this soil type has good water retention ability across the different soil particle sizes.
Combine this characteristic with its high phosphate adsorption capacity, Site 1 soil type
has a strong potential to act as a sink for phosphate both as eroded sediment and as bank
soil.
Site 4 soil has significantly increased water retention ability as the soil particle size
decreases. It also has a high phosphate adsorption capacity, especially with its smallest
tested soil size fraction (106µm-250 µm). Similar to Site 1 soil, this soil type has a strong
potential to act as a sink for phosphate either as eroded sediment or as bank soil. Similar
result is observed with soil from Site 3, even though its increase in water retention ability
is not as marked as Site 4 soil. However, this does not diminish the potential for Site 3 soil
to act as a sink for phosphate, both as eroded sediment and as bank soil.
The effectiveness of soil amendment in increasing soil potential to act as a sink for
phosphate is evident in this study. Results from the transient wetting/ drainage
experiments indicate that sediment have the potential to act as a sink for phosphate in
Ellen Brook catchment present conditions. This is observed to naturally exist in some soil
types. However, amending the soil with crushed laterite uniformly increases the phosphate
adsorption capacity. The amendment of the bank soil will not just increase the potential of
eroded sediment to be a sink for phosphate, it will also increase the ability of the bank soil
itself to adsorb phosphate and hence reduce the amount of phosphate in water bodies.
DISCUSSION 57
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
There are possible errors that could occur while conducting the experiments. The precision
of the results could be affected by various factors such as contamination, evaporation and
other unpredicted chemical and biological reactions. Contamination could come about
from residues left on the equipments that were used. Some of the phosphate solutions that
were analysed might have evaporated during the study period before they were analysed.
Other unpredicted chemical and biological reactions might have occurred and caused the
increase or decrease of phosphate, which are not caused by soil particles adsorption or
desorption of phosphate.
The experimental errors in this study are not likely to affect the general findings of this
study. Due to the precautions taken when conducting the experiments, it is not likely that
the previously mentioned factors will significantly alter the findings. The possible
contamination from the equipments used was minimised by cleaning them prior to use.
The analysed phosphate solutions were kept in closed containers before they were
analysed and hence evaporation should be minor. Different to nitrogen and carbon,
phosphate does not react easily and is less likely to be affected by the change of
environmental conditions. The errors in this experiment would most likely to affect
accurate amount of phosphate being adsorbed or desorbed. However, this does not affect
the potential of Ellen Brook catchment soils to experience erosion and that the eroded
sediments could act as a sink for phosphate.
CONCLUSION 58
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
6. CONCLUSION
The bank soils in Ellen Brook catchment are liable to experience erosion and their eroded
sediments have the potential to act as sink for phosphate. Under the present flow regimes
of Ellen Brook catchment water bodies, the soil composition analysis of the seven
different soil samples shows that erosion is likely to occur. Phosphate adsorption capacity
analysis then discovers that most of the investigated soils have a natural ability to adsorb
phosphate. Hence, eroded sediments from these soils should also have the ability to adsorb
phosphate.
Phosphate adsorption capacity of the bank soils could be increased by amending it with
crushed laterite. The experiments conducted have shown that crushed laterite uniformly
increases phosphate adsorption for all of the investigated soils. This method could be used
as a management option to reduce environmental issues caused by excess of phosphate
load to the water bodies. Further research on the costs and benefits on the implementation
of this method needed to be done.
RECOMMENDATIONS FOR FUTURE WORK 59
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
7. RECOMMENDATIONS FOR FUTURE WORK
There are some factors that need to be pursued further to validate the findings of this
study. Some of them are:
i. In order to find out the maximum phosphate adsorption capacity more accurately,
more range of phosphate concentrations need to be tested.
ii. Soil samples need to be check for its pH because high pH values could causes
nutrients desorption.
iii. Initial phosphate content of the bank soils need to be determined as this may affect
their phosphate adsorption capacity.
iv. More bank soils need to be investigated in order to find out whether or not the
findings in this study applies to most soils in Ellen Brook catchment.
v. The experiments need to be done with better instruments in a more controlled
environment to increase the accuracy of the findings.
vi. The phosphate adsorption capacity tests were conducted in more than 24 hours
timescale. Varying the timescale could give more understanding on the effect of
timescale to phosphate adsorption.
vii. The environmental impact of amending bank soils with crushed laterite need to be
further investigated before this method is used.
Further study need to be conducted to confirm the potential of eroded sediment to act as a
sink for phosphate. The effectiveness of soil amendment should also be further
investigated as it may causes disruption to the surrounding ecosystem and other
unforeseen consequences. This method should not be utilised until further investigations
are conducted.
REFERENCES 60
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
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APPENDICES 63
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
APPENDICES
A. The Investigated Sites and its Respective Soil Samples
Site 1
Site 2
APPENDICES 64
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
Site 3
Site 4
APPENDICES 65
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
Site 5
Site 6
APPENDICES 66
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
Site 7
APPENDICES 67
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
B. Soil Composition of Each Sample Taken
Table 7: Soil composition of the soil samples taken from Ellen Brook catchment
SITE 1 - GINGIN
ACCESS RD SITE 2 – BREERA
RD SITE 3 - BRAND
HWY
Particle size (µm) Weight of soil (g) Weight of soil (g) Weight of soil (g)
> 4750 1112.3 123.2 1014.3
2000 - 4750 460.2 55.8 514.4
1000 - 2000 695 298.9 457.5
500 - 1000 517.4 1137.1 1034.2
250 - 500 267.4 873.8 1183.9
106 - 250 186.9 260.5 345.7
53 - 106 37.3 141.3 94
<53 32.7 49.1 39.9
Total 3309.2 2939.7 4683.9
% passing % passing % passing
> 4750 66.388 95.809 78.345
2000 - 4750 52.481 93.911 67.363
1000 - 2000 31.479 83.743 57.595
500 - 1000 15.844 45.062 35.515
250 - 500 7.763 15.338 10.239
106 - 250 2.115 6.477 2.859
53 - 106 0.988 1.670 0.852
<53
% composition % composition % composition
2000 - 4750 33.612 4.191 21.655
1000 - 2000 13.907 1.898 10.982
500 - 1000 21.002 10.168 9.768
250 - 500 15.635 38.681 22.080
106 - 250 8.081 29.724 25.276
53 - 106 5.648 8.861 7.381
<53 1.127 4.807 2.007
APPENDICES 68
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
SITE 4 - GT
NORTHERN HWY SITE 5 - RUTLAND
RD SITE 6 - RAILWAY
PDE
Particle size (µm) Weight of soil (g) Weight of soil (g) Weight of soil (g)
> 4750 954.8 60.8 782
2000 - 4750 267.9 43 355.9
1000 - 2000 204.4 40.6 341.4
500 - 1000 885 114.3 1515.7
250 - 500 1665.2 3316.4 1730.7
106 - 250 384.3 786.8 344.4
53 - 106 72.2 50.7 36.9
<53 17.9 7.7 21.5
Total 4451.7 4420.3 5128.5
% passing % passing % passing
> 4750 78.552 98.625 84.752
2000 - 4750 72.534 97.652 77.812
1000 - 2000 67.943 96.733 71.155
500 - 1000 48.063 94.147 41.601
250 - 500 10.657 19.121 7.854
106 - 250 2.024 1.321 1.139
53 - 106 0.402 0.174 0.419
<53
% composition % composition % composition
2000 - 4750 21.448 1.375 15.248
1000 - 2000 6.018 0.973 6.940
500 - 1000 4.592 0.918 6.657
250 - 500 19.880 2.586 29.554
106 - 250 37.406 75.027 33.747
53 - 106 8.633 17.800 6.715
<53 1.622 1.147 0.720
APPENDICES 69
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
SITE 7 - WEST SWAN RD
Particle size (µm) Weight of soil (g)
> 4750 164.124
2000 - 4750 51.341
1000 - 2000 56.579
500 - 1000 232.569
250 - 500 2253.301
106 - 250 1240.349
53 - 106 70.417
<53 11.91
Total 4080.59
% passing
> 4750 95.978
2000 - 4750 94.720
1000 - 2000 93.333
500 - 1000 87.634
250 - 500 32.414
106 - 250 2.018
53 - 106 0.292
<53
% composition
2000 - 4750 4.022
1000 - 2000 1.258
500 - 1000 1.387
250 - 500 5.699
106 - 250 55.220
53 - 106 30.396
<53 1.726
APPENDICES 70
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
C. Phosphate Adsorption for each Sample
Table 8: Phosphate adsorption capacity of five different phosphate concentrations
Site 1
Initial Concentration
(mg/L)
Final Concentration
(mg/L)
Phosphate adsorbed (mg/L)
10 0.02 9.98
50 0.23 49.77
100 1.15 98.85
150 2.68 147.32
200 2.58 197.42
Site 2
Initial Concentration
(mg/L)
Final Concentration
(mg/L)
Phosphate adsorbed (mg/L)
10 15.31 -5.31
50 55.43 -5.43
100 98.64 1.36
150 154.79 -4.79
200 223.37 -23.37
Site 3
Initial Concentration
(mg/L)
Final Concentration
(mg/L)
Phosphate adsorbed (mg/L)
10 0.22 9.78
50 1.03 48.97
100 2.69 97.31
150 19.67 130.33
200 34.31 165.69
Site 4
Initial Concentration
(mg/L)
Final Concentration
(mg/L)
Phosphate adsorbed (mg/L)
10 0.32 9.68
50 1.87 48.13
100 13.44 86.56
150 33.58 116.42
200 39.68 160.32
APPENDICES 71
The Potential Impacts of Water Erosion and Assimilation Processes on Phosphate Budget in Water Bodies
Site 5
Initial Concentration
(mg/L)
Final Concentration
(mg/L)
Phosphate adsorbed (mg/L)
10 2.73 7.27
50 27.73 22.27
100 65.09 34.91
150 85.56 64.44
200 165.06 34.94
Site 6
Initial Concentration
(mg/L)
Final Concentration
(mg/L)
Phosphate adsorbed (mg/L)
10 0.12 9.88
50 7.65 42.35
100 26.72 73.28
150 73.56 76.44
200 83.26 116.74
Site 7
Initial Concentration
(mg/L)
Final Concentration
(mg/L)
Phosphate adsorbed (mg/L)
10 1.48 8.52
50 22.76 27.24
100 59.11 40.89
150 99.58 50.42
200 155.21 44.79