the potential impacts of water erosion and …...the potential impacts of water erosion and...

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


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


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


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


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 18: Soil compositon of Site 5 sample ......................................................................40



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 30: Phosphate adsorption test on sample from Site 2..............................................55

LIST OF TABLES vii


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


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


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


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


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


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


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


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


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


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


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


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


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


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).



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).



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).



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



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



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



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).



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).



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



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



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).



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


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


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


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


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


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


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



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


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


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


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


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


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


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


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


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


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


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


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


SITE 2 - BREERA RD

0

10

20

30

40

50

60

70

80

90

100

10 100 1000 10000




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 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


SITE 4 - GT NORTHERN HWY

0

10

20

30

40

50

60

70

80

90

100

10 100 1000 10000




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



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


SITE 6 - RAILWAY PDE

0

10

20

30

40

50

60

70

80

90

100

10 100 1000 10000




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 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


0

10

20

30

40

50

60

70

80

90

100

10 100 1000 10000




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 5 250 µm – 500 µm


Site 7 250 µm – 500 µm

D50

RESULTS 43


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


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 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


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


Site 2


-25.00

-20.00

-15.00

-10.00

-5.00

0.00

5.00

0 50 100 150 200


Adsorbed Phosphate

(mg/L)


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


0.00

50.00

100.00

150.00

200.00

0 50 100 150 200


Adsorbed Phosphate

(mg/L)


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


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


0.00

50.00

100.00

150.00

200.00

0 50 100 150 200


Adsorbed Phosphate

(mg/L)


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


0.00

50.00

100.00

150.00

200.00

0 50 100 150 200


Adsorbed Phosphate

(mg/L)


RESULTS 49


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


0.00

50.00

100.00

150.00

200.00

0 50 100 150 200


Adsorbed Phosphate

(mg/L)


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


Site 7


0.00

50.00

100.00

150.00

200.00

0 50 100 150 200


Adsorbed Phosphate

(mg/L)


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


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


2 Adsorbed Phosphate (mg/L) -17.15 -15.28 -6.87











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


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


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


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


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 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


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


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


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


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APPENDICES 63


APPENDICES

A. The Investigated Sites and its Respective Soil Samples

Site 1

Site 2

APPENDICES 64


Site 3

Site 4

APPENDICES 65


Site 5

Site 6

APPENDICES 66


Site 7

APPENDICES 67


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


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



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


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


(mg/L)

Final Concentration

(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


(mg/L)

Final Concentration

(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


(mg/L)

Final Concentration

(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


Site 5


(mg/L)

Final Concentration

(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


(mg/L)

Final Concentration

(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


(mg/L)

Final Concentration

(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

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