shane donaghy (2013) dissertation (full text)
TRANSCRIPT
‘A Study into the Abundance & Diversity of Phytoplankton Communities in a Phosphorus-rich Inter-
drumlin Lake on a Temporal (inter-seasonal) Dimension.’
Shane Donaghy,
Centre for the Environment, Trinity College Dublin, College Green, Dublin 2, Ireland
Email: [email protected]
Dissertation presented in partial fulfillment of the requirements for the Degree of Bachelor of
Environmental Sciences in the Faculty of Engineering, Mathematics & Science, at Trinity College,
Dublin University
Supervisor: Dr. Norman Allott
Co-supervisor: Lucy Crockford, MSc
March 2013
i
Declaration
By submitting this thesis, I declare that the entirety of the work contained therein is my own original
work, that I am the authorship owner thereof (unless to the extent explicitly otherwise stated) and
that I have not previously in its entirety or in part submitted it for obtaining any qualification.
Final Word Count:
Signature: _____________________
Date: _____/______/______
Copyright © 2013 Trinity College, Dublin University.
All rights reserved
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Abstract
This project had the primary aim of monitoring phytoplankton community dynamics in a eutrophic
inter-drumlin lake and its variance through a 6-month sampling period from 18/1/12 through to
18/7/12. Phytoplankton assemblages, and their changes, are very useful in monitoring water quality
in a wide range of habitats; aquatic, estuarine, marine and wetland. These ecotones make up the
vast majority of the earths surface (~70%, USGS, 1984) and are also critically important to terrestrial
life that depend on these surface waters as a water, food & recreational resource. The lake being
studied is located in Co. Monaghan, Republic of Ireland and has managed to maintain its almost
eutrophic status despite efforts by An Taisce’s (the National Trust for Ireland) ACP (Agricultural
Catchments Program) to rehabilitate the lake. This study monitors changes in phytoplankton
assemblages (through succession), extrapolates the changing growth conditions and examines the
literature to relate observed phytoplankton assemblage succession with lake health and trophic
status through the above-mentioned sampling period.
Phytoplankton assemblages were found to follow clear-cut and definite successional stages in line
with changing water quality parameters and were offered a considerable amount of support by
published authors to be indicative of a healthy lake bordering on mesotrophic/eutrophic border.
Their sensitivities and efficacy as biological indicators of ecological status for compliance with the
Water Framework Directive (WFD; 2000/60/EC) were explored and evaluated.
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Acknowledgements:
I would like to thank Dr. Norman Allott for all of his guidance, impressive wealth of knowledge and
expertise both in and out of the lab and in the preparation of this thesis in general.
I would also like to thank Lucy Crockford MSc, who facilitated the sampling effort and supplied
important background information on the lake, without which, interpretation of phytoplankton
assemblages could not be acheived.
Mark Kavanagh also deserves my most sincere thanks and praises for facilitating my research and
providing the equipment and space and of course trusting me with a key to the lab.
This dissertation was conducted as part of Lucy Crockford’s PhD on the trophic status of the Lake
(Lough Namachree, Co. Monaghan) and how it isn’t improving despite the reparative measures
implemented by the farmers on the lakes catchment and surrounding area.
She is conducting her PhD in close association with the ‘Rural Catchment Scheme’ of Teagasc. Their
cooperation in letting me use their boat to get out onto the lake along with access to data collated
from their data sondes is greatly appreciated and won’t be quickly forgotten.
The results & findings of this dissertation will be used for her PhD and could feature in her Thesis and
my only hope is that it is worthy and helpful.
This project was presented on the 20/03/2012 in poster format in fulfillment of the requirements for
the award of BSc. Env. Sci.
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Dedications:
I wish to dedicate this thesis to my late Uncle & Godfather, Arthur Donaghy, who sadly
passed away during the preparation of this dissertation (02/01/2013).
He leaves a grieving family and tight circle of friends behind, but thankfully he also left a lot
of memories of the good times.
Rest in Peace
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Table of Contents
Declaration i
Dedications: iv
List of Figures vi
List of Tables vii
List of Abbreviations viii
Glossary ix
Chapter 1: Introduction 11
1.1 - Eutrophication – What & How? 11
1.2 - Studies on Phytoplankton: 12
1.3 - The Water Framework Directive (WFD; 2000/60/EC): 14
1.4 - Species assemblages in Lakes: 17
1.5 - Seasonal Succession: 17
Chapter 2 - Methods: 19
2.1 – Chlorophyll ⍺ Depth Profile: 19
2.2 – Phytoplankton Community Analysis: 20
Chapter 3 - Results: 23
3.1 – Chlorophyll ⍺ Depth Profile: 23
3.2 – Phytoplankton Community Structure Analysis
Chapter 4 - Discussion 39
Chapter 5: Conclusions: 42
5.1 - Summary of Findings: 42
5.2 - Conclusions: 44
5.3 - Further Studies: 45
Appendices: 46
Appendix 1 – Formula relating Absorbance at 665nm and 750nm to Chl ⍺ levels in µg/L: 46
Appendix 2 - Table of Trait-seperated functional groups of phytoplankton. Taken from Reynolds
et al. 2002 47
Appendix 3 - A Copy of the Proposal for this Project: 49
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References: 57
List of Figures
Figure 1 – Satellite image of Namachree Lough showing boat launch site and sample site.
Page 22
Figure 2 – Depth profile of Chl ⍺ in the lake from 1-7m in µg/L
Page 26
Figure 3 – Annual variance in incident solar irradiation levels at a weather station in close
(~29km) proximity to the sample site.
Page 32
Figure 4 – Aulacoseira spp. abundances (measured as cell counts) throughout the sampling
period (18/1/2012 – 18/7/2012).
Page 33
Figure 5 – Asterionella formosa abundances (measured as cell counts) throughout the
sampling period (18/1/2012 – 18/7/2012).
Page 34
Figure 6 – Fragilaria crotonensis abundances (measured as cell counts) throughout the
sampling period (18/1/2012 – 18/7/2012).
Page 35
Figure 7 – Ceratium hirundinella abundances (measured as cell counts) throughout the
sampling period (18/1/2012 – 18/7/2012).
Page 36
Figure 8 – Abundances of Aulacoseira, Asterionella, Fragilaria & Ceratium spp. superimposed
to show seasonal succession pattern
Page 37
Figure 9 – Series of Pie-Charts showing seasonal variance through the 6-month sampling
period
Page 38
Figure 10 – Aulacoseira spp. abundances (measured as cell counts) throughout the sampling
period (18/1/2012 – 18/7/2012).
Page 40
vii
List of Tables
Table 1 – Chl ⍺ absorbance data and calculated Chl ⍺ levels in µg/L.
Page 24
Table 2 – Phytoplankton community structure analysis
Page 28 - 30
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List of Abbreviations
DO – Dissolved Oxygen
Chl ⍺ - Chlorophyll ⍺
HAB – Harmful Algal Bloom
N – Nitrogen, specifically, bioavailable Nitrogen
P – Phosphorous, specifically, bioavailable Phosphorous
K0 – Carrying Capacity
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Glossary
Plankton – small organisms of aquatic, estuarine and marine ecosystems, which are able to
float, (from Greek planktos meaning ‘errant’) often with no means of locomotion.
Phytoplankton – Planktic organisms containing pigments (primarily chlorophyll a, but often
chlorophyll c also), which enable photosynthesis; their only source of energy, and the basis of
the aquatic/estuarine/marine food web.
Phytoplankton Bloom – the annual ‘burst’ of phytoplankton growth in spring/summer as a
result of increased sunlight and nutrient-recharged water body. These blooms can increase
phytoplankton numbers by up to 10,000 times their original.
Harmful Algal Bloom – While phytoplankton blooms are natural and healthy (and often
predictable), harmful algal blooms, in which a bloom thrives at the expense of other aquatic /
estuarine / marine biota are an undesirable threat to ecological status.
Heterocyst(s) – Specialised cells of certain nitrogen-fixing cyanobacteria in which the enzyme
nitrogenase converts N2 into bioavailable forms of nitrogen (NO3, NO2 or NH3)
Zooplankton – Larger planktic organisms that graze on smaller phytoplankton. Their grazing
on phytoplankton cells is a major determining factor in phytoplankton’s’ population and
community dynamics.
DataSonde™ – a water-quality monitoring apparatus. There are two on the lake of focus in
this thesis (Namachree Lough) and they log parameters; %DO, Temperature, Chl ⍺,
Conductivity, pH, RedOx potential & Turbidity profiling using Hydrolab™ (5X-DS5X) data-
sondes. These have supplied continuously logged data, which proved very useful in this
project.
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Genera studied in this project:
Chlorophyta – Phylum of phytoplankton containing chlorophyll a & b which includes species
observed in this project;
1. Ankistrodesmus spp.
2. Melosira spp.
3. Sphaerocystis spp.
4. Stephanodiscus spp.
Cryptophyta – Phylum of phytoplankton which includes species observed in this project;
1. Chroomonas spp.
2. Cryptomonas spp.
Cyanophyta – A phylum of phytoplankton that take their name from their colour (kyanós
which is Greek for blue) and also posess the ability to convert atmospheric nitrogen into
ammonia, nitrates or nitrites. This is an important phylum for aquatic/estuarine/marine
ecosystems as this is where the vast majority of bioavailable nitrogen comes form. This
phylum includes species observed in this project;
1. Anabaena spp.
2. Aphanizomenon flos-aquae
3. Planktothrix spp.
Heterokontophyta – The final phylum observed in this lake who got their name from their
motile stage, during which motility is achieved through two differently shaped flagella. This
phylum contains over 100,000 known species (most of which are algae) and includes the
infamous Phytophthora, which caused the Irish potato famine. Genera encountered during
this project include;
1. Asterionella spp.
2. Aulacoseira
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Chapter 1: Introduction
1.1 - Eutrophication – What & How?
In general, eutrophication is caused by the increased loading of organic and inorganic
nitrogen / phosphorus to water bodies through both; point and diffuse sources originating
from agricultural run-off and industrial / domestic wastewaters. Point sources are the most
facile to manage because their routes to water bodies are straightforward to map and,
often, remediate. The challenge facing most water managers lies in the control of diffuse
sources, and indeed this is the case with the lake in current focus, Namachree Lough. They
can originate from a wide variety of sources over an, often large, spatial scale. Mapping their
routes of contamination is therefore a lot more complex. Controlling and remediating the
sources of contamination can also prove quite taxing; financially, systematically and, in the
case of lobbying policies which dictate farmers’ practice, diplomatically.
All activities in the catchment of the lake will be reflected, directly or indirectly, in the
nutrient status of the lake. This is not to say that surface waters only become eutrophied as
a direct result of human activities on the catchment area. Naturally high-fertility, rich soils
can leach nutrients into the water through run-off, etc., Wastewaters are typically the
principal suspect in the case of eutrophication, but in the case of Namachree Lough,
assurances have been made that wastewater is properly treated and discharged throughout
the catchment area (O’Dwyer et al, In press).
Climatic & geological catchment conditions are the primary drivers in the rates of nutrient
loading to lakes (Preston et al. 2011). Rainwater is the primary vector of nutrient loading and
the route to the water body is predicated on bedrock permeability. Atmospheric (wind-
borne) and precipitative deposition of nutrients and particulate matter (Lewis, 1981) often
acts to supplement the effects of nutrient loading by agricultural run-off. Due to the high
seasonal variability of environmental parameters, nutrient loading rates were found to vary
in line with these parameters (Preston et al., 2011).
High nutrient loading rates along with a resistance to recovery are common in freshwater
bodies throughout the drumlin belt of Ireland (Crockford et al, year not disclosed). The
Drumlin belt is characterized by moderate to intense levels of farming coupled with
impermeable clay-till that leaves the soil water-logged for most of the winter. This leaves
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the freshwater body catchments in this eco-region highly susceptible to flash floods and
consequent runoff from an agricultural soil with an anthropogenically-elevated nutrient
content. Seasonally anoxic conditions at the sediment-water interface which has been
characterized as a feature of the eutrophication process (Moss, 1990) especially in the case
of the drumlin belt of Ireland (Crockford et al, year not disclosed) prolongs the effects of
eutrophication by anoxia-influenced release of P from the sediment. The mixing of the water
column exacerbates this remobilization of P, which is largely wind-induced and causes an
upwelling of the freshly released nutrients (Wilkerson et al. 2006). Due to the landscape
characteristic of the Drumlin belt; vast and relatively flat, little protection is offered to
freshwater bodies from the effects of wind. The drumlin belt of Ireland is chararacterised by
intensive farming and it is this intensity that is being tipped as the root of the nutrient-
enrichment problem.
In summary, the majority of nutrient loading occurs during winter, mixed through the water
column during late winter/early spring in time for the phytoplankton growth season of
spring/summer. While this seems intuitive and logical, these claims have not been tested on
a large timescale (>10 years) owing to the fact that good-quality, high resolution water data
for testing have not yet been collected / made public on a large timescale. A paleolimnologic
study on the Lake on which this paper focuses (O’Dwyer et al., In Press) suggest
paleolimnology as the most effective way of hindcasting trophic status of the lake and found
that over the last 150-200 years, the lake could be regarded as being enrichment-sensitive
and resistant to recovery despite measures implemented to mitigate nutrient inputs. This is
reasoned to have a drastic and long lasting effect on the shaping of the phytoplankton
community supported by the lake.
1.2 - Studies on Phytoplankton:
Phytoplankton forms the basis of aquatic and marine ecosystems and fix all organic carbon
found therein. Therefore, their conservation and management is paramount to the
sustainability of these food webs (along with the terrestrial populations which they sustain
also). Phytoplankton also serve as extremely effective biological indicators which, when
properly interpreted, draw attention to environmental phenomena which can limit their
growth and the growth of organisms dependant on their primary production. Harmful algal
Blooms (HABs) are perhaps the most immediate ecological consequence of over-enriching
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surface water and are a prime example of phytoplankton’s application as a biological
indicator of ecological status. Algal blooms thrive when their growth rate is essentially
delimited when confounding nutrients, Nitrogen & Phosphorus in particular, are supplied in
excess. HABs have the ability to drastically increase the demand for dissolved oxygen that
organisms at higher trophic levels require for metabolism. Deoxygenation of surface waters
as a result of HABs can drastically impact the mortality of fish and other biota in the water
body. Leeching of toxic algal metabolites into the water is another dire ecological impact of
these blooms. A combination of these two phenomena is even offered as the reason to the
discoloration (to red) of the Nile and the resultant fish kills which were documented in
biblical times (Exodus 7:14-25).
HABs and their prevention/management, along with a myriad of other phenomena, which
pose a threat to ecological health of water bodies, are receiving increasing amounts of
interest in the EU as the Water Framework Directive (WFD) stipulates proper ecological
management of water bodies in all member states. Also, there is well-deserved concern that
the frequency and amplitude of these HABs will worsen with global change in eutrophic
aquatic, estuarine and marine water bodies due to their dominance over other
phytoplankton at higher water temperatures (O’Neil et al, 2011). This review went on to
highlight that the flexibility of cyanobacteria towards the nitrogen sources they fix can be a
real concern because cyanobacterial HABs can form in lakes with an ambient / low nitrogen
content. It is suggested also, that dinoflagellate species (the primary cause of HABs) may
introduce themselves earlier in the seasonal cycles as the Earths surface warms (Dale et al.
2006).
Perhaps more terrifying and potentially catastrophic than HABs is the fact that geo-
engineers are now controversially seeking to offset anthropogenic carbon emissions by
enriching the sea with Iron, along with other nutrients. This controversy is well placed and
justified, as not all phytoplankton respond in the same way to elevations in nutrient levels
and there is nothing to suggest that iron enrichment wouldn’t trigger harmful algal blooms
(HABs). Rickels et al (2012) highlight this as a concern and also point out that there is a
critical need to evaluate the ‘carbon-removal efficiency’ of iron fertilization along with a
‘detailed assessment of its distributional and dynamic aspects’.
It is important to remember also, that seasonal variations in phytoplankton numbers are
normal and healthy (Kim et al 2006; Liu et al 2010; Niu et al, 2011; Ramirez et al, 2005; &
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Silva et al 2008), and not indicative of anything apart from the fact that environmental
conditions in the lake are changing on a seasonal basis as light intensity increases in the
spring/summer and nutrient loading (primarily) from agricultural run-off is at its peak during
this time. Suitable considerations of this phenomenon should be taken in interpretation of
phytoplankton assemblages and their relative abundances, as phytoplankton abundances do
not mirror trophic status of the water body in a simple linear fashion.
There have been numerous studies conducted through recent decades on phytoplankton,
highlighting their massive importance, accounting for ~50% of global photosynthetic output,
but also their extreme susceptibility to a wide range of stressors; natural & anthropogenic.
The stressors phytoplankton are likely to become affected by span the biotic & abiotic
spectra, from physical lake properties including; temperature, pH to fluctuations in
zooplankton numbers and their exerted grazing pressure (Sinistro et al., 2006), and
internal/external nutrient loading from the lakes catchment areas (O’Dwyer, In Press),
resuspension from sediment, etc., Perhaps the biggest factors affecting phytoplankton
growth are; nutrient loading (specifically N, P and Si), incident light intensity, Carbon
availability and turbidity. Phytoplankton have evolved a certain tolerance to fluctuations in
these different parameters, with some authors finding that ‘pulsing’ of nutrient levels
(specifically N) are actually critically important in sculpting the biodiversity of phytoplankton
in water bodies (Hein & Riemann, 1994; Kroncang et al, 2004; Örnólfsdóttir, 2004).
1.3 - The Water Framework Directive (WFD; 2000/60/EC):
The Water Framework Directive (WFD; 2000/60/EC) was introduced in the EU in October
2000 in answer to decreasing water quality and increased demand and pressure on current
water stocks but also to replace the range of inconsistent European water legislations that
preceded it. The directive provides a simpler, more concise ‘all-in’ approach to improving
the [ecological] quality of water in the EU member states. It differs from the water quality
legislation which preceded its’ establishments in one key way; it provides ‘steps’ for reaching
water quality targets, as opposed to the limit value approach of old. The ecological and
chemical status of a surface water body is measured according to the following qualities;
biological [biodiversity], hydromorphological [bank structure, sediment characteristics],
physico-chemical [temp, pH, degree of oxygenation, etc.,], chemical [pollutants]. The
harmony of the above four will determine the ecological status of the lake.
15
Compliance to the Water Framework Directive (WFD; 2000/60/EC) in the EU is mandatory
for all states and requires ongoing monitoring of all surface (natural or artificial, with a
surface area of >0.5km2), ground and coastal waters with the objective of maintaining
healthy, non-deteriorating ecological status as dictated by a wide range of biological
indicators (Kaiblinger et. al. 2009) and artificially measured parameters. Typically, sampling
of water bodies is a compromise between cost, effort and the desired temporal resolution of
the monitoring. Because of this, under-sampling often prohibits accurate depiction of high-
frequency variables, which change significantly over time (e.g. Chl ⍺).
The WFD has five categories into which lakes may be placed; ‘bad’, ‘poor’, ‘moderate’,
‘good’ and ‘excellent’. The ‘excellent’ class is reserved for lakes, which have the biological,
chemical & morphological characteristics of a lake, which has (almost) no direct contact with
anthropogenic stressors. Because of the economic, recreational and social importance of
ground water aquifers and lakes/reservoirs, few remain untouched by humanity’s prolific
thirst and consequently ‘excellent’ ecological status is unfeasible. ‘Good’ ecological status is
perfectly achievable as it indicates that water is being utilized in a sustainable fashion with
little ‘downstream’ ecological effects.
Achieving the goals of the WFD require biological indicators, which among a wide range of
organisms, include phytoplankton. Kaiblinger et al (2009) describe the three indices, which
use phytoplankton-based parameters to indicate trophic and ecological status of the water
body. These are; the Brettum Index (BI) used in Austria and Slovenia, the ‘Phytosee’ (PSI)
Index used in Germany and the Phytoplankton Trophic Index (PTI) used in Italy. In freshwater
ecosystems, the nutrient to which phytoplankton are most sensitive to fluctuations is
Phosphorous (TP) and the species composition/abundance of phytoplankton along a TP
gradient is the basis of all three of the above-mentioned indices.
The German (PSI) Index is multi-metric and considers three metrics, with a fourth in the case
of lowland lakes; biomass index, algae classes (volume of algae: total biovolume), PTSI (a
core metric in PSI which stands for Phytoplankton Taxa Seen Index) and DIPROF (another
core metric; Profundal Diatomeen Index) and the index serves to quantify the effects of
eutrophication in temperate lakes. The Brettum index is calculated in a similar fashion to the
trophic index, which is based on taxon-specific trophic scores.
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The measurement of Chlorophyll ⍺ (Chl ⍺) is a very useful test and is widely used in
limnology. It provides a crude estimation of phytoplankton biomass (when properly
interpreted).
As the levels of phytoplankton increase (spring/summer bloom) the per capita concentration
of Chl ⍺ has been found to decrease which is reasoned, could be due to competition for light
(increased light attenuation by the rapid population increase), lake trophic status and
seasonal shifts in the phytoplankton community. This is the reason why it is so difficult to
relate Chl ⍺ to phytoplankton biomass, and so, Chl ⍺ remains should be a surrogate for
photosynthetic activity as opposed to a direct surrogate for phytoplanktonic cell counts.
There have been authors (Vollenweider, 1974; Wright et al., 1997) who suggest that
different solvents used in the extraction of Chl ⍺ can have varying efficiency in its’
extraction. The relationship between [Chl ⍺] and phytoplankton biomass is not a simple
linear relationship.
There have even been pioneering studies into the viability of using MERIS (Medium
Resolution Imaging Spectrophotometer) satellite imagery for the quantification of Chl ⍺ in
surface water bodies with authors brandishing reports of varying success (Bresciani et al.,
2011)
Kasprzak et al. (2008) describe the three established methods for counting phytoplankton;
particle counts (the method utilized in this dissertation), measurements of chemical
constituents and flow cytometry, which incorporates both of the above.
There are notable flaws in counting phytoplankton including; problems with the method,
inconsistent [Chl ⍺] through different phytoplankton spp., phytoplankton community
composition not being accounted for adequately and intense seasonal variation. An example
of methodological flaws is autotrophic picoplankton (APP) can contribute significantly
towards the total amounts of Chl ⍺ and yet not be counted by the particle counting
methodology adopted in this dissertation.
The worsening effects of climate change perhaps amplify the threat of human pressures on
surface waters and the knock-on effects of improper ecological management could spell
disaster for phytoplankton along with the higher trophic levels, which depend on their
productivity.
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1.4 - Species assemblages in Lakes:
Lakes are often extremely different in terms of ecological conditions and environmental
parameters, which causes a great deal of difficulty in comparing planktonic assemblages
from lake to lake. However, patterns are often predictable and characteristic of certain
groups of lakes. Reynolds (2006) achieves the feat of describing general phytoplankton
assemblages in lakes by grouping lakes together. An example of his categorization is ‘high
latitude eutrophic small lakes’ into which the lake in current study falls in. High latitude is
accepted as being an (approximate) surrogate for regional climate while the size of the lake
is deemed important due to coherences between phytoplankton assemblages and lake
morphometrics. Among small / moderately sized lakes phytoplankton abundance (K0) and
composition (favoring the most adapted genera) are constrained by nutrient supplies and
sub-aqua light environment.
A high planktonic biomass indicates alleviation of constraining factors, which in the case of
Namachree Lough is thought to have been achieved through its eutrophic status. In a
Nitrogen depleted lake, nitrogen-fixing cyanobacteria are expected to be present, and a lot
can be interpreted by their relative presence/absence/abundance.
1.5 - Seasonal Succession:
Phytoplankton assemblages reflect the conditions in which they are growing. Species make-
up is indicative of specific biotic and abiotic factors, which allow for heightened diversity,
while overall primary productivity levels are indicative of general growth conditions.
Phytoplankton assemblages changes as a direct result of changes in their environment. A
series of successional stages indicate a series of changes undergone by the lake. This can be
as a response to stressors, but also, it can simply be due to seasonality. The ability of
phytoplankton to change their community structure has practical applications in monitoring
water quality, especially as part of the WFD, as phytoplankton species, or groups of species,
are very efficient bioindicators. Their use as indicators of water quality is predicated on their
high sensitivity towards variances in water quality parameters along with their high
18
replication rates, which respond rapidly and allow for a speedy diagnosis of water quality
degradation.
Chrysophytes and certain diatom species are indicative of oligotrophic (nutrient-depleted)
lakes, while on the other and, cyanobacteria like Anabaena & Aphanizomenon thrive under
eutrophic (especially P-enriched as they can form heterocysts when Nitrogen is the nutrient
limiting growth) conditions and thus, their presence and abundance indicate the degree to
which a lake is a eutrophied. This is just a generalism however, and should not be taken
purely at face value. Moss (1972) found, through a series of manipulative experiments, that
the dynamic response of algae to a varied pH and Carbon source (CO2 levels) was more
notable than that to a simple manipulation of nutrient levels. Moss ended that paper by
concluding that the responses of natural phytoplankton assemblages to eutrophication are
not dependant on the amounts of nutrient in the lake, but on the ‘productivity demands on
the totality of resources’.
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Chapter 2 - Methods:
2.1 – Chlorophyll ⍺ Depth Profile:
On the 6th of June 2012, when Chl ⍺ was assumed to be at, or at least approaching its’
maximum, a Chl ⍺ depth profile from 0.5m – 7m was compiled using a Ruttner water
sampler. The design of the Ruttner water sampler makes it ideal for taking water samples a
discriminated depths as its chamber seals whilst submerged, ruling out discrimination by
water from the shallower depths.
Samples were taken at 0.5m increments to a depth of 4m and then another 3 samples were
taken at 5, 6 & 7m (beyond which, little photosynthetic activity was predicted). The samples
were preserved in Lugol’s Iodine solution (KI/I) to prevent biasing by post-collection
phytoplankton growth.
The solutions were homogenized by inverting the sample bottle several times before
filtration of 100mL of each sample through Whatmann GF/C with a pore size of 1.2µL with a
Buchner funnel. The funnel was left running until most of the water on the filter paper was
removed. The supernatant was poured off and, with a forceps, the filter paper was ‘rung-
out’ into a 50mL sample tube and the remainder of the filter paper was inserted into the
sample tube as well. 20mL of ethanol was added to each of the tubes. This methodology is
derived from Nicholls et al. (1996).
A water bath was heated to 60°C into which, the rack of sample tubes was placed for 1hr.
This is the stage where the Chl ⍺ was extracted form the phytoplankton cells. To remove the
cell matter and other potential suspended solids, which may alter the absorbance readings,
from the sample, each sample tube was centrifuged at 6300 rpm for 15 minutes.
The supernatant of each sample were then analyzed for [Chl ⍺] using a spectrophotometer
set to absorb at 665nm. To correct for turbidity of the water, the absorbance of each sample
at 750nm was subtracted from its absorption at 665nm.
Chl ⍺ levels were found (in µg/L) through utilization of the formula found in the appendix
and presented in the ‘Results’ section of this paper.
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2.2 – Phytoplankton Community Analysis:
A wealth of studies previously conducted by various authors provides a solid, peer-accepted
method for phytoplankton collection, preservation and analysis.
Kasprzak et al. (2008) describe three established methods for counting phytoplankton;
particle counts (the method adopted in this dissertation), measurements of chemical
constituents (often Chl ⍺) and flow cytometry, which incorporates both of the above.
Unfortunately, the time-intensive method of particle counts was the only method of
phytoplankton quantification, which was feasible for this study as interpretation of biomass
from Chl ⍺ measurements is so complex (and will most likely cause a loss in accuracy). Chl ⍺
data collated in this dissertation is for use as a rough illustration of phytoplankton activity
through varying water depths.
To compromise between efficiency and accuracy, this thesis incorporates the standard
method adopted by the US EPA (US EPA, 1994), which has been developed and refined for
water quality studies spanning two decades. A couple of modifications and deviations from
the published protocol have been implemented, mostly due to temporal constraints.
Sampling was conducted on a fortnightly basis for six months from 18/01/2012 through to
18/07/2012. Sampling was conducted with the use of a boat and taken from the centre of
the lake. The illustration below shows both; the boat launching site and the sampling site.
The sample site was taken to be close to the DataSonde™ water quality-monitoring buoy,
which is stationed near the centre of the lake. This was an effort to keep all water quality
parameters measured by the buoy as relevant to the phytoplankton samples as possible.
21
Figure 2 – Map of the lake showing locations of launch site and sampling site.
Samples were taken on a fortnightly basis, which is consistent with Nichols et al. (1996) from
the centre of the lake at elbow-depth (~0.35-0.40m) using a 1.7L Ruttner water sampler.
Elbow depth was found, through the above Chl ⍺ depth profile, to be approximately where
phytoplankton (through the proxy of Chl ⍺) were approaching their most productive /
densely populated. Making this assumption helped in assuring a moderate and statistically
significant cell density without being too dense to analyze in a time-efficient fashion. The
Ruttner water sampler was deemed the most suitable for sampling, as its design (a sealing
sample chamber) affords it the ability to discriminate against water from different depths.
Of the 1.7L water sample, 500mL was transferred to a glass bottle, along with a few drops of
Lugol’s Iodine solution for; preservation and for the staining of cells.
Prior to analysis under the inverted microscope, the sample bottles were inverted several
times to allow the phytoplankton to become evenly distributed, preventing any influences of
sample bias. 10mL was then abstracted from the center of the sample bottle using a 5mL
22
auto-macropipette and gently (to reduce the chances of air-bubbles forming) injected to the
settling chamber where it was left with a cover slip seal for a minimum of 24 hours.
The settling chamber was then placed onto the microscope stage and analyzed at 200X,
which is a deviation from the US EPA protocol for phytoplankton study that suggest a 600X
magnification. Using excessive magnification would cause the field of vision to be too
narrow to accurately represent the sample with 2 transects. An initial scout of the surface of
the chamber provided an accurate idea of the phytoplankton taxa present in the chamber.
Two linear diametrical transects were taken of the settling chamber during which; observed
taxa were recorded and accurate cell-counts were taken. The transects were found to be
100% representative of taxa present with no initially observed taxa (from spot-checks) not
being seen / recorded in the transects in any sample.
There were only three settling chambers available for this project, which left re-using the
settling chambers necessary. To avoid cross-contamination, a very meticulous cleaning
routine was paramount and strictly adhered to; the bottom of the settling chamber was
cleaned using distilled water and cotton swabs. The process was repeated until the chamber
was deemed clean by placing it back on the microscope stage and ensuring no residual
phytoplankton cells were to be seen. This often took 4-5 attempts. The outer perimeter of
the chamber trapped a significant amount of cells and special attention should be paid by
anyone adopting this methodology in cleaning these areas especially stringently. This is
especially important in the context of this project, owing to its intrinsic sensitivity towards
cross-contamination, as its primary objective is to map the succession of phytoplankton
taxa; even 1 foreign cell has the ability to skew the results significantly.
23
Chapter 3 - Results:
3.1 – Chlorophyll ⍺ Depth Profile:
The absorbance data at 665nm and 750nm are presented in Table 1 (overleaf). The table
also shows the Chlorophyll ⍺ levels at each discrete sample depth, which were derived from
the absorbance data in accordance to a simple equation abstracted from Morton (1993),
which can be found in Appendix 1.
The data is tabulated and presented (overleaf) and shows a very definite and salient
variance in Chl ⍺ as a function of depth. For clarity, this phenomenon is presented
graphically on the following page. It is clear to see that the maximum Chl ⍺ concentration is
observed at 1m depth (validating the assumption that this was the ideal depth at which to
abstract samples from the lake).
The slight increase in Chl ⍺ concentration at 7m is reasoned to be an error involved in the
experimental method adopted for the measurement of Chl ⍺. This author does not believe
there to be an increase in chlorophyll concentration at such depth, which is not in the
euphotic zone (limited to 4m depth) and is the most turbid of all the water samples (0.021
Absorbance units @ 750nm). The suspected cause of this anomaly is thought to be the
systematic method adopted by the researcher in extracting the pigment, which moved from
shallowest to deepest samples. This had the unfortunate consequence of meaning that the
last sample out of the water bath (which was the extraction phase) spent a larger amount of
time in its supernatant hot ethanol and thus its extraction efficiency was higher relative to
the other samples.
24
Table 1 - Chlorophyll ⍺ (μg/L) with respect to sample depth (m). Formula for calculations found in Appendix
Sample depth Total Absorbance Absorbance at 665nm Absorbance at 750nm Net absorbance [Chl ⍺]
(m) Arbitrary Absorbance Units (μg/L)
0.5 0.397 0.390 0.007 0.383 13.309
1 0.457 0.449 0.008 0.441 15.325
1.5 0.366 0.356 0.010 0.346 12.024
2 0.377 0.369 0.009 0.360 12.510
2.5 0.313 0.305 0.008 0.297 10.321
3 0.220 0.213 0.008 0.205 7.124
3.5 0.189 0.181 0.008 0.173 6.012
4 0.194 0.188 0.006 0.182 6.325
5 0.114 0.098 0.016 0.082 2.850
6 0.090 0.074 0.015 0.059 2.050
7 0.120 0.099 0.021 0.078 2.711
25
Figure 2 – Graphical representation of the Chlorophyll ⍺ variance through increasing water depths.
26
3.2 – Phytoplankton Community Structure Analysis
The data accrued during the analysis of these samples (especially the individual filament
lengths) is much too large to feasibly present in this paper. However, a compromise has
been reached in which total cell counts for the filamentous algal species is recorded along
with the total colony counts. This allows a ‘straight-forward’ calculation of mean filament
length to be found.
The Data tabulated in this fashion is presented on the next three pages.
As discussed in the methods section of this paper, 2 transects were studied along the
settling chambers diameter. With the 200X objective, the transect was found to be 100µm
wide. The settling columns have an internal diameter of 3.3cm and a tower height of 2.1cm.
A certain protocol, or set of rules, were imposed in order to not bias the analyses. These are
listed below:
Cells >15 μm are identified and counted using the 10X objective on transects that
cover 50% of the chamber surface.
Cells <15 μm are counted on a single transect, 100 μm wide, at the center of the
counting chamber using the 40X objective.
Cells must appear to be viable (i.e. chloroplasts intact).
Cell fragments are not counted.
Viable cells that are partially in a counting field on the right hand side are counted,
but those on the left are omitted.
For colonies, a small portion of the colony is counted, and the number of cells is
then estimated.
Filaments are counted individually, and their cells counted in full.
A minimum (400) amount of cells should be enumerated to assure that the count is
representative of the sample.
Be wary of reproductive cycles – cells can change size during reproductive stage.
Don’t use size as a fundamental genus characteristic.
27
28
Sample Date: 18/1 1/2 15/2 29/2 13/3
Transect # 1 2 1 2 1 2 1 2 1 2
SPECIES: CE CO CE CO CE CO CE CO CE CO CE CO CE CO CE CO CE CO CE CO
Anabaena flos-aquae 14 1 6 1 27 3 23 5
Ankistrodesmus 3 1 4 - 7 - 15 - 17 - 27 - 34 - 133 - 128 -
Aphanizomenon flos-aquae 308 10 293 11 571 18 476 17 242 7 561 16 637 19 592 16 593 21 498 23
Asterionella formosa 6 1 4 1 5 1 4 1
Aulacoseira spp. 55 4 67 6 49 5 76 7 67 10 78 12 60 11 46 9 83 11 87 11
Ceratium hirundinella
Chroomonas minuta 21 - 31 - 23 - 27 - 2 - 6 - 3 - 5 - 37 - 33 -
Cryptomonas ovata 19 - 17 - 11 - 13 - 4 - 13 - 18 - 16 - 17 - 16 -
Fragilaria crotonensis 14 3 11 2 5 1 13 3 16 5 2 1 11 -
Mallomonas spp. 1 - 5 - 3 - - -
Melosira 150 13 134 12 75 9 167 17 157 34 163 32 379 48 426 53 304 73 356 78
Peridinium spp.
Planktothrix 180um 5 140 3
Stephanodiscus
Sphaerocystis spp. 120 1
Synedra spp. 1 -
29
Sample Date: 27/3 11/4 26/4 8/5 23/5
Transect # 1 2 1 2 1 2 1 2 1 2
SPECIES: CE CO CE CO CE CO CE CO CE CO CE CO CE CO CE CO CE CO CE CO
Anabaena flos-aquae 67 7 57 7 50 4 63 5 87 7 83 8 134 11 128 12
Ankistrodesmus 3 - 4 - 3 - 5 -
Aphanizomenon flos-aquae 1840 59 1794 61 1651 56 1738 54 1953 63 1847 61 1306 48 1486 47
Asterionella formosa 47 11 56 13 444 89 503 97 503 117 489 112 368 72 436 74
Aulacoseira spp 257 32 346 41 898 113 927 116 206 21 183 17 70 7 68 9
Ceratium Hirundinella 1 - - - 1 - 3 - 4 - 5 - 7 - 12 -
Chroomonas minuta 16 - 12 - 1 - 2 - 3 - 1 -
Cryptomonas ovata 19 - 17 - 11 - 17 - 15 - 19 - 27 - 21 -
Fragilaria crotonensis 6 - 13 - 78 3 86 4 127 7 153 10 237 9 312 13
Mallomonas spp. 1 - - - - - 1 - -
Melosira 499 81 537 79 723 73 817 83 981 94 897 92 871 87 853 82
Peridinium spp. 1 - - -
Planktothrix 165um 5 195 4 165um 2 180 4 170 4 180 3 120 2 145 2
Stephanodiscus 8 - 3 - 13 - - - 11 - 9 - 7 - 6 -
Sphaerocystis spp. 40 5 34 4 97 4 89 5 94 - 89 -
Synedra spp. 14
30
Sample Date: 6/6 20/6 4/7 18/7
Transect # 1 2 1 2 1 2 1 2
SPECIES: CE CO CE CO CE CO CE CO CE CO CE CO CE CO CE CO
Anabaena flos-aquae 146 3 243 5 1873 64 1743 66 1482 47 1536
Ankistrodesmus
Aphanizomenon flos-aquae 1456 53 1527 56 1236 49 1398 47 1125 19 1254 12
Asterionella formosa - 28 4 32 4
Aulacoseira spp 52 - 12 2 13 3 72 1 67
Ceratium Hirundinella 13 - 11 - 48 - 38 - 9 - 10
Chroomonas minuta 26 - 33 - 7 - - - 1 -
Cryptomonas ovata 12 - 15 - 50 - 36 - 16 - 13
Fragilaria crotonensis 36 8 40 10 215 9 248 11 74 3 83
Mallomonas spp.
Melosira 103 11 128 10 67 7 71 8 3 1 8
Peridinium spp. 28 - 22 -
Planktothrix 244 2 270 4 55 2 320
Stephanodiscus 28 - 32 - 29 4 23
Sphaerocystis spp. 36 3 40 4 32 -
Synedra spp.
Table 2 – Tabulated data for the analysis of phytoplankton community
31
Figure 3 – Light intensity data through the year (in Joules/cm2) compiled from Met Éireann weather station data at
Ballyhaise (~29km from Namachree Lough sampling site). Note the ‘dip’ in solar irradiance in midsummer.
32
Figure 4 – Aulacoseira Abundance through sampling effort. Graph shows very definite establishment
beginning at sample taken from 13/3/2012. This genus was expected to be the first to bloom
33
Figure 5 – Asterionella formosa succeeds Aulacoseira towards the end of March through to late April.
34
Figure 6 – Fragilaria establishes itself during Asterionella’s demise.
35
Figure 7 – Ceratium hirundinella is the final successor in the 4-part successional pattern found by Talling (1976). Its individual
cell counts are larger as a result of their much larger sizer and the finite amount of resources in the lake.
36
Figure 8 – Abundance (cell counts) of the four species, which typically succeed each other in eutrophic lakes (Talling 1976)
37
Figure 9 – Pie-chart series showing changes in phytoplankton
species composition throughout sampling effort
38
Chapter 4 - Discussion:
Talling (1976) ordered freshwater phytoplankton into a series of increasing tolerance to CO2
depletion. This succession is strongly observed in this lake and takes the form:
This succession was observed in the results collated from this project (figure 7, page __) and
is indicative of a healthy eutrophic lake. When compared against phytoplankton
assemblages characteristic of oligotrophic lakes (lakes with low nutrient content) we see
that there are some common genera during the spring bloom (Aulacoseira spp., synedra
spp., stephanodiscus spp.) there are also a myriad of other genera, which are lacking in this
particular lake (e.g. Nitzchia spp.). The common genera, as defined by Reynolds (2006) are
present in such low quantities that their presence is deemed not to be overly significant and
attributed to seasonal decreases in lakes nutrient load (autumn/winter). This is, in essence a
reinforcement of the documented (O’Dwyer et al. 2013) findings of the lakes’ eutrophic
status.
A table of phytoplankton sensitivities abstracted from Reynolds et al (2006) is presented in
Appendix 2 and summarizes the link between genera present and what habitat
characteristics they represent. From the data collated in this project ‘vertically mixed,
mesotrophic small-medium lakes’ are represented by the Aulacoseira genus (‘Group B’ in
Ceratium hirundinella
Fragilaria crotonensis
Asterionella formosa
Aulacoseira subartica
39
the table found in Appendix 2) which is a species that is observed in this lake. The lake is on
the border between meso- and eu- trophic status, so representative genera from both
statuses is to be expected within. Aulacoseira spp. presence in the lake offers support to the
statement that the lake is Mesotrophic, while their relatively low abundance in the lake
suggests that the lake recovers from Mesotrophic status and turns eutrophic.
Figure 10 – Graphical representation of Aulacoseira spp. rise and fall in spring/summer
As can be seen from the above figure (Figure 10), Aulacoseira, which is indicative of
mesotrophism, suffers a great decline during the summer period where increased diffuse-
source nutrient loading (suspected to be primarily through artificial fertilization of
catchment). This genus is sensitive to changes in pH, silicon exhaustion and lake
stratification, but has a high tolerance for light deficiency. This is an important consideration
for water managers, and deviation from equilibrium levels of Aulacoseira spp. can indicate
either of the above lake characteristics to which this genus is most sensitive.
Hopefully not contradicting this point, ‘Group C’, which is a grouping of genera
representative of ‘Mixed, eutrophic small-medium lakes’ contains the species; Asterionella
formosa, Stephanodiscus rotula & Aulacoseira ambigua. Aulacoseira ambigua and
Asterionella formosa are both species that are observed in this lake and forms a critical role
in Talling’s (1976) succession pattern for a lake that is losing carbon (Aulacoseira
Asterionella Fragilara Ceratium). Half of these species (Aulacoseira & Asterionella) are
40
indicative of eutrophic status. This group (‘C’) shares the same sensitivities towards silicon
exhaustion and lake stratification, but differ from group B in their tolerance of changes in
pH. Group B were mentioned to have been tolerant to light deficiencies which is common to
Group C also. Yet on top of this, ‘Group C’ organisms are also tolerant of Carbon deficiencies.
Yet another group of organisms in this table, which are observed in this lake (Group ‘P’)
include Fragilaria crotonensis & Aulacoseira granulata. Both of these species are observed in
this lake and are indicative of eutrophic epilimnia (uppermost layer of a thermally stratified
lake). This might sound like a tired reinforcement of the last point made in this discussion,
but a eutrophic stratified lake does not necessarily imply a eutrophic epilimnion, as to do so
would mean a very high rate of vertical mixing of the water column. Fragilaria crotonensis
forms the third successional stage of Talling’s (1976) model and is thus more tolerant
towards carbon depletion than its two predecessors. Both ‘Group P’ species observed in this
lake share the same standard sensitivity towards Stratification of the lake and silicon
depletion that the previous two groups also shared. They are however less tolerant of light
deficiency than the other two groups which means that their cell numbers could be
indicative of a turbid or humic lake.
The Group ‘S1’, which is characteristic of ‘turbid, mixed layers’ contains the genera
Planktothrix, which was observed in Namachree Lough. This genus establishes itself in the
lake (first observed) on the 13/3/12 and continues to thrive throughout the summer,
reaching its maximum during the final sample (18/7/12) at 320 µm. The literature commonly
cites Planktothrix spp. as total filament lengths as their cell walls, under light microscopy
with iodine staining, are often hard to visualize and excessively tedious to count. While the
original aim was to record total filament lengths and, at a later stage, find an average cell
length from other authors, it proved unfeasible, as there doesn’t seem to be agreement
among the publishing authors on just how long a mature Planktothrix cell is. Their presence
is understandable as they (according to Reynolds, 2006) have a high tolerance to dwindling
light levels as caused by turbidity. Turbidity in lakes during spring / summer is a well-
documented phenomenon and arises from the increased algal growth and consequent light
attenuation during the peak growth season.
Planktothrix is also grouped into the group ‘R’ which is characteristic of the ‘Metalimnia of
Mesotrophic stratified lakes’. This lake, as already discussed in the ‘Introduction’ section of
this paper is bordering between mesotrophic and eutrophic status and a representative
genus of taxa characteristic of a mesotrophic lake reinforces that point.
41
The final group of phytoplankton in Reynold’s (2006) table that bear relevance to this lake is
the group named ‘H1’, the dinitrogen-fixing nostocaleans. This entire group of organisms
(Anabaena flos-aquae & Aphanizomenon) is observed in this lake and are present in quite
large numbers. Colony sizes increase on progression through the six month sampling period,
which is reasoned to be due to grazing by Daphnia (zooplankton) spp. (Lynch, 1980) Both
species have the ability to form heterocysts, where inorganic N2 is converted to one of three
bioavailable forms for protein synthesis and other cell metabolites. The ability of these cells
to make nitrogen bioavailable allows for the diversity of phytoplankton supported by these
underwater ecosystems. While this is where the majority of bioavailable nitrogen originates,
it is important (as Bautista & Pearl, 1984 remind us) of the significant contribution to
bioavailable nitrogen levels made by non-photosynthetic (heterotrophic) bacteria.
Namachree Lough, while not low on Nitrogen (O’Dwyer et al, In press) suffers an increasingly
high demand for nitrogen during the growth season. Not surprisingly, it is during this season
that we notice both nitrogen-fixing species climbing toward their maxima.
Due to the enormous complexity of phytoplankton growth and the variance in
environmental parameters in lakes of certain regions, even in temperate zones,
extrapolations of phytoplankton assemblage data can only be treated as generalizations and
representative of a broad range of lakes. Within the comparison of temperate lakes, nutrient
loading and light penetration are the principal drivers of planktic diversity.
Reynolds (2006) found that water column mixing and light harvesting efficiency are inversely
related and concluded that the more light-sensitive taxa were outcompeted by the more
robust and adaptable to light interception and harvest. Summer mixing therefore selects for
what he has termed ‘P-group’ plankton, which include Aulacoseira granulata and Fragilaria
crotonensis. This was observed from the collated data and supports the notion that this lake
is eutrophic and well mixed.
42
Chapter 5: Conclusions:
5.1 - Summary of Findings:
Late winter:
In late winter (samples 18/1/12 – 1/2/12) planktic diversity and taxa cell counts are
unquestionably at their lowest. There are 7 species present in very modest numbers. This is
characteristic of a winter planktic assemblage due to reduced light conditions, but also
nutrient leaching from the soils of the catchment (which has been highlighted as the
principal source of diffuse nutrient loading) are at their minimum. Nutrient loading rates are
at their minimum due to the timing with which artificial fertilizers are spread on the land
(spring).
Early spring:
The start of the spring growth season for phytoplankton in the lake seems to be begin from
sample 13/3/12 onwards. There is a marked increase in diversity and the genera already
established before spring undergo a similarly drastic increase in abundance. Although, in the
case of Aphanizomenon spp. spring appears to begin on the 1/2/12 where is cell numbers
almost double (from an average of 301 cells to an average of 524 cells). Aphanizomenon spp.
have a high tolerance for fluctuations in water temperature and can be expected in the lake
all year round (although, in winter, at much reduced numbers). Anabaena flos-aquae
establishes itself on the 29/2/12, but only in reduced numbers. No examples of non-
heterocystous Anabaena were observed throughout the sampling period. Their presence
marks an increase in demand for bioavailable nitrogen. Planktothrix spp. also establish
themselves on the 13/3/12 and their presence is attributed to their high tolerance for
turbidity which results from increased lake productivity.
Mid-Late spring:
The most diversity in the lake sample is noted on the 27/3/12 & 11/4/12 where a mighty 14
genera are recorded. Asterionella formosa establishes itself in its newly carved ecological
43
niche (following on from its predecessor, Aulacoseira spp.). This succession forms part of
Talling’s (1976) seasonal succession of eutrophic lakes in response to depleting Carbon levels
(as a result of heightened productivity).
Summer:
The heightened biodiversity of the lake achieved in spring maintains throughout the
summer. The nitrogen-fixing nostocaleans (Aphanizomenon & Anabaena) reach their
maximum abundance during mid-summer (20/6/12) and begin to fall through July. Although,
because sampling stopped in July, it is impossible to tell whether this is an actual decrease in
numbers or just a temporary fluctuation from which they recover. Also, Figure 2 shows
annual light irradiance for the year and there is a distinct decrease in light intensity during
June from which recovery only begins in July. There could be a decrease in abundances
associated with this dimming effect.
44
5.2 - Conclusions:
Chl A Analysis
Chlorophyll A varies drastically with water depth.
Chlorophyll A reaches its maximum at 1m depth in this lake.
This maximum is not a desirable depth for analyzing phytoplankton community
structure as the settling column’s bottom surface is too densely lined with cells.
Phytoplankton Community Structure Analysis
Phytoplankton community structure analyses show great diversity (up to 14 spp.
during spring/summer bloom) – indicative of healthy ecological status.
Phytoplankton are present in relatively high densities which indicates that micro-
niches are established for each genera / group of genera (low interspecific
competition).
Phytoplankton assemblages change in a definite fashion and do so in a previously
documented fashion.
Talling (1976) provides support for the statement that the lake suffers from
depleting Carbon throughout the growth season.
The fact that we are able to make such well-reasoned extrapolations from
phytoplankton assemblages suggest that phytoplankton are very effective biological
indicators of ecological and environmental status.
45
5.3 - Further Studies:
Unfortunately, through sloppy and unfortunate management of the samples, two got
misplaced and were unable to be relocated. This leave a month-long hole in our knowledge
of the lake and would be especially useful in finding out more about Ceratium hirundinella’s
succession from Fragilaria crotonensis.
It would, certain limitations notwithstanding, be deeply desirable for data to remain being
collected and analyzed for a much longer period to get an idea of how phytoplankton are
responding to long-term fluctuations in nutrient loading and other environmental
parameters critical to their success.
I would like to take this opportunity to wish Lucy Crockford every great success in her PhD
dissertation, and that the phytoplankton data collated as part of this project prove useful to
her.
46
Appendices:
Appendix 1 – Formula relating Absorbance at 665nm and 750nm to Chl ⍺ levels in µg/L:
Chl ⍺ (µg/L) = ([Absorbance @ 665 nm] - [Absorbance @ 750 nm]) * (13.9 * v)
V * d
Where:
v = Volume of Extract
V = Total Volume of Filtered Lake Water
d = Optical Path Length (Length of Spec. Cell)
13.9 = Chl ⍺ Coefficient
Abs @ 665nm = Absorbance Maximum for Chl ⍺
Abs @ 750nm = Correction for Turbidity
47
Appendix 2: Table of Trait-separated functional groups of phytoplankton. Taken from Reynolds et al.
2002
48
49
Appendix 3 - A Copy of the Proposal for this Project:
Proposal for the Project entitled:
“The study of the variations of abundance and diversity in phytoplankton communities in a
phosphorous-enriched (borderline eutrophic) inter-drumlin lake (Namachree / Sreenty) on
a spatial (species variance with depth) and temporal scale (fortnightly basis throughout a
one-year period).”
Shane Donaghy
Trinity College Dublin,
College Green,
Dublin 2,
Ireland
Submitted: Friday 13/04/2012
This Project proposal is submitted for the degree of Environmental Sciences to the University
of Dublin, Trinity College 2012
50
PROJECT TITLE:
A study of the variations of abundance and diversity in phytoplankton communities in a
phosphorous-enriched (borderline eutrophic) inter-drumlin lake (Namachree / Sreenty) on a
temporal scale (fortnightly basis throughout a 6-month period).
PROJECT ABSTRACT:
The proposed project is going to study the population dynamics of the phytoplankton
species present in the lake and monitor the species present, their numbers especially around
the timing of the anticipated spring/summer bloom (growth season).
It is expected that the lake, given its current meso-eutrophic state, is playing host to many
phytoplankton individuals spanning a large number of taxa, and it is the validation/rejection
and quantification of this hypothesis that the project aims to address.
This hypothesis is one that has long needed addressing as it may suggest reasons why the
trophic status of this lake is not improving despite a myriad of policies and improvisational
measures implemented by the Agricultural catchment program (herein abbreviated to
'ACP'). A PhD student in the centre for the environment (Lucy Crockford) is currently
studying this question and her biggest handicap in progressing her research is the lack of
information published about the lake. For her, and others, to continue to work on this lake,
a clear and concise description of the phytoplankton communities present is essential.
SECTION 1: MAIN PROPOSAL:
The hypothesis being tested in this proposal is; 'does species composition and abundance of
phytoplankton vary spatially & temporally throughout a ~1 year period in a meso-eutrophic
lake in Co. Monaghan'. This hypothesis will comprise the testing of two variables; the
relative abundance of each phytoplankton species and the overall phytoplankton biomass
present.
The study will focus on the population dynamics of phytoplankton species on two scales;
temporal and spatial. Data will be collected for a 1-year period and its [anticipated] variance
will be analyzed. The spatial dimension of this project will consist of analyzing
phytoplanktonic population dynamics as a function of depth. This is of interest, as there is a
thermocline at ~6-7m below the surface of the lake (see Figure 2 below). Special attention
51
on both studies will be afforded to the key season; the growing season. This growing season
spans from spring to early/late summer and defines the number of other animal species that
the lake can afford to maintain through establishing the aquatic food web.
SECTION 2: WHY IS THIS PROBLEM SIGNIFICANT / OF INTEREST?
Phytoplankton are the primary producers in open waters and their abundance in lakes is
especially high in shallow parts of, in this case, a lake.
This problem is very significant, as it will provide others with a better understanding of the
biological activity of the lake. Lucy Crockford, a PhD student with the school of
environmental sciences is working on a lake without a strong published background. Very
little information is available about the lake, and the intent is to increase the amount of data
available to her, and others, in order for future study to be conducted. Temporal and
financial constraints prevent Lucy from undertaking this research herself. With time and
increased funding, perhaps my role in her research would be unnecessary.
Lucy is endeavoring to discover why the tropic status of the lake isn't improving, given the
current policies in place. There are gaps in the knowledge that exists about the lake, and a
set of Senior Sophister Environmental sciences research projects are hopefully going to fill in
some of those gaps. There is very little information available on inter-drumlin lakes in
general, and almost nothing on this one in particular. Yet they remain very prone to
eutrophicaton due to drumlin landscape often being exploited by farming and other primary
industries where synthetic phosphates are commonly spread across the landscape and
drained into the lake.
By studying the abundance and diversity of phytoplankton in the lake, a clearer picture will
be obtained of the primary production [of biomass] of the lake. Primary production by
phytoplankton is the basis of the aquatic food web, and given that Lucy is addressing the
issue of the lakes trophic status, a clear insight into the foundation of the food web is
essential.
There are many reasons why the results of this project are important. Firstly, general
knowledge of the lakes primary production is a very important starting point in terms of
gathering information on the lakes trophic structure. Fluctuations in phytoplankton
abundances and diversities in the lake in future could be indicative of pollution of various
sorts. In this regard, my research will serve as a benchmark, or standard, of the
52
phytoplankton community.
This project is interesting, as it serves to address a very intriguing question: 'why is the
trophic status of this lake not improving, given the policies in place?'. The lake is
mesotrophic, yet it remains on the verge of turning eutrophic despite best efforts to control
the total phosphorous concentrations. The sources of the contamination, both point and
diffuse sources, have been identified. They are; industrial run-off & septic tank leakage
(point sources) and the main diffuse source is agricultural run-off, although, atmospheric
and particulate sources are also at play. Despite close co-operation between the ACP
(agricultural catchment program) and farmers whose land lies within the catchment (Figure
1, below), the concentration of total phosphorous is still increasing.
The lake itself is located near Carrickmacross, Co. Monaghan, with a North-lying ~650ha
drumlin grassland catchment. The primary land-use within the catchment is beef production
with some dairy farming and sheep-production present in the catchment also. Given the
land-use, the nutrient most at risk of draining into the lake is P which is validated through its
meso-eutrophic status.
Figure 1 – The land use of the Lakes catchment.
There are 3 factors that can act alone, or in concert, to influence total phosphorous
concentration:
Internal Loads
External Loads
Wind-induced resuspension (in shallow areas)
Examples of internal loads to phosphorous (P) concentration would include the release of P
from sediment in anoxic waters (Niirnberg, G.K. 1994). This is the subject of another
students project, and his findings shall, I anticipate, prove both interesting and relevant to
my own project. External loads, as discussed previously, include the diffuse and point
sources of dissolved and particulate phosphorous. Wind-induced resuspension of P from
sediment has proven to be quite significant (Laenan, A & LeTourneau, A.P, 1996) and is
highly dependent on lake morphology, (especially bathymetry), prevailing winds (and
severity) along with waves on the lake. This effect was studied by the aforementioned A.
Laenan & A.P. LeTourneau in 1996 on a lake in Oregon (the Upper Klamath lake). The lake
53
has a surface area of 207.976 km² and it was found that during a single wind event,
between 220-1200 tons of sediment was resuspended with a median value of 530 tons. The
result of this is that, higher P concentrations will lower the N:P ratio (where N = Nitrogen).
This can transform a lake (depending on degree of contamination) from being N-limiting (of
biomass production) to being P-limiting which will impact Phytoplankton growth as
phytoplankton species are primarily N-limited (Lagus, A et. al. 2004). At this point, one
author suggests that Nitrogen containment is vital, and perhaps even more important that P
containment (Lewis, W. M. 2000). Phytoplankton (more accurately, chlorophyll a) has been
correlated significantly to total Nitrogen and total P in studies conducted previously (Philips
et. al. 2008).
It is important, at this point, to mention and define the bathymetry of the lake, especially in
the context of resuspension of P in sediment. The prevailing wind comes from the West, and
we can see below (Figure 2) that this wind is blowing directly into the shallower regions of
the lake. It is thus anticipated that there will be an increase in the amount resuspension of P
from sediment in shallower areas of the lakes and perhaps even a detectable / statistically
significant variance in the phytoplankton populations in the shallower areas.
Figure 2 – Bathymetry of the lake. Note thermocline at ~6m.
Section 3: How will the question be answered?
Experimental Design & Statistical Analysis:
Collection of samples:
Sampling of the lake will take place on a fortnightly basis. It will be achieved by means of a
modified 5L water bottle (i.e. sample size = 5L) which will allow a weight to be attached to
the bottom (to counteract the buoyancy of the air in the bottle) and a rope to be fitted to
the top (for lowering into the open water and recovery). The collection of samples from the
lake will be a largely non-invasive process, i.e. due care will be taken so as not to disturb the
sediment or the lakes flora & fauna. The depth will be recorded and kept as constant as
possible throughout the sampling.
54
The sampling will be replicated once i.e. 2 samples will be taken at each site. The purpose of
this is to get an average of the two values (assuming populations are within 5% of each-
other). If the larger sample is >105% of the smaller one, then the data will become distorted
due to outliers in the dataset. Every effort will be made to keep the sampling methods
(described briefly above) as close to being constant as possible.
An unpaired Students t-test would be suitable for this study and would show us the
probability of our hypothesis being correct (or our null hypothesis being incorrect). The
assumption is that the data collected will be normally distributed, which is a requirement of
this test.
Analysis of samples:
The phytoplankton will be preserved in Lugol's Iodine solution until they are ready to be put
into a sedimentation column for 24hrs to flocculate the phytoplankton species. The samples,
once flocculated, will be studied under an inverted microscope and the phytoplankton
species, and their counts, will be recorded.
Identification of species will require the use of a suitable key. One suitable for all aquatic
phytoplankton species has yet to be identified, but I trust that collabaration with Norman
Allott will solve this problem. However, from the offset it is important to be realistic and
realise that there is a strong possibility that not all taxa will be identified. In many cases, the
family of species will be as far as identification can go. The reason for this unfortunate
limitation to the study is common inter-species morphologies.
Section 4: Requirements for resources:
The proposed project will not be overly intense on resources. I will require very little in
terms of consumables for the collection of samples for this project (reusable plastic bottles).
The primary resource required will be the inverted microscope (i.e. lab time) and the use of
a boat to collect the samples.
All of the samples required for this project will be collected from the lake on a fortnightly
basis. To this end, the greatest expense will be transport to the lake. As shown below (Figure
3), the distance is ~45.1km and the estimated fuel consumption for my car equates to
approximately €8 each way.
Figure 3 – Google Map excerpt highlighting (in purple) the proposed route to the lake
55
The ongoing support and guidance from my supervisor, Dr Norman Allott[Email:
[email protected]] along with the aid and facilitation of access to the lab granted to me by the
chief technical officer of the Centre for the Environment, Mr. Mark Kavanagh[Email:
[email protected]] are resources I will not be taking for granted over the coming months,
and to them both I already owe a lot.
Careful time management and planning will be key in ensuring that all of the projects aims
are accomplished on time. Below is a schematic of how (roughly) the time will be spent
(Figure 4). Once this proposal is completed, end of year exams and their preparation are all
that will delay the commencement of the project until the 21st of May 2012 (as shown in
Figure 4).
Figure 4 – Gantt diagram showing primary aims and roughly how time will be spent during
project
References:
Graphics (Figures 1 & 2):
Lucy Crockford – FBA Public Presentation.
Web References:
http://www.epa.gov/med/grosseile_site/indicators/plankton.html
http://www.teagasc.ie/agcatchments/publications/2011/Lucy_Environ2011.pdf
http://www.teagasc.ie/agcatchments/locations/corduff.asp
56
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