investigation of eutrophication processes in the littoral zones of western irish lakes
TRANSCRIPT
Investigation of Eutrophication Processes
in the Littoral Zones of Western Irish Lakes
A Synthesis Report from the Project
Project Co-ordinator:
T.K. McCarthy (NUI, Galway).
Authors:
T.K. McCarthy, R. Barbiero, M. O’Connell, M. Guiry, D. Doherty, P. Cullen (all
NUI, Galway), J. King (CFB), B. O’Connor (Aquafact).
Project Participants
The National University of Ireland, Galway
The Central Fisheries Board, Dublin
Aquafact International Services Ltd., Galway
This project was part-funded by the European Regional Development fund through
the Operational Programme on Environmental Services, 1994-1999.
Environmental Protection Agency
Ardcavan, Wexford, Ireland
Telephone: +353-53-47120 Fax: +353-53-47119
© Environmental Protection Agency 1999
All parts of this publication may be reproduced without further permission, provided
the source is acknowledged
Although every effort has been made to ensure the accuracy of the material contained
in this publication, complete accuracy cannot be guaranteed. Neither the
Environmental Protection Agency nor the authors accept any responsibility
whatsoever for loss or damage occasioned or claimed to have been occasioned, in part
or in full, as a consequence of any person acting, or refraining from acting, as a result
of a matter contained in this publication.
Investigation of Eutrophication Processes
in the Littoral Zones of Western Irish Lakes
Published by the Environmental Protection Agency
ISBN:
Price:
Date:
CONTENTS
Page
Acknowledgements
Executive summary
Introduction 1
Background to the project 2
Main objectives of the project 4
Project management 5
Results 6
Recommendations 21
Contributions to the Environmental Monitoring 27
R and D sub-programme
References 28
Index of figures and tables 29
Appendix 1 31
ACKNOWLEDGEMENTS
This project has been undertaken as part of the Environmental Monitoring, R&D sub-
programme of the Operational Programme for Environmental Services, 1994-1999
and has been part financed by the European Union through the European Regional
Development Fund. The sub-programme is administered on behalf of the Department
of the Environment by the Environmental Protection Agency, which has the statutory
function of co-ordinating and promoting environmental research.
The authors gratefully appreciate the help given to them in compiling this report. We
would like to thank in particular the numerous students, assistants, technicians and
other staff of NUI, Galway who contributed to the research programme. We would
also like to thank the Western Regional Fisheries Board and its staff for their co-
operation and also the angling clubs and individual members of the public who helped
with fieldwork or provided information. Advice and information provided by Mr.
Martin McGarrigle (EPA, Castlebar) is also gratefully acknowledged.
EXECUTIVE SUMMARY
• This project was undertaken with a view to providing comprehensive
ecological assessments of the status of six large western Irish lakes (Loughs
Carrowmore, 960ha, Conn, 5000ha, Cullin, 1100ha, Carra, 1500ha, Mask,
8000ha and Corrib, 17000ha) and to make recommendations on how they
might be monitored in future.
• A multidisciplinary approach was adopted and the research programme
included: water quality monitoring; algal studies; aquatic plant surveys;
studies on littoral macroinvertebrates; analysis of non-biting midge species
assemblages; a special study of arctic char; investigations on lake sediments,
including evidence of historical changes in Lough Conn; studies on water
circulation patterns in Lough Mask and riverine discharges to the lakes.
• Water quality monitoring results indicated that that overall the water quality in
the six large western Irish lakes was generally very good. Trophic
classification of the six lakes on the basis of the OECD scheme, using mean
TP and maximum chlorophyll a values suggests that the lakes should be
classified as follows: Lough Carra, ultra-oligotrophic / oligotrophic; Lough
Carrowmore, mesotrophic; Lough Conn, mesotrophic; Lough Corrib, ultra-
oligotrophic / oligotrophic; Lough Cullin, mesotrophic and Lough Mask,
oligotrophic. Temperature and conductivity profiles, recorded at all sites
during water sampling, indicated that some transient summer stratification
occurred, but only in deeper lake basins.
• Results of limnological studies, including observations on periphyton,
filamentous algal accumulations, chironomid assemblages etc., did indicate
some localized effects of declining water quality, which were especially
evident in the areas where nutrient enriched rivers and streams were entering
the lakes. Lake wide enrichment was also noted in Lough Cullin, as evidenced
by extensive growth of filamentous algae on aquatic plants and the bottom of
this shallow lake. Indications of significant enrichment were also noted in
Lough Carrowmore.
• A more systematic approach to water sampling, for determination of lake
trophic status and for indication of changes in nutrient loading from particular
sub-catchments was recommended. More regular monitoring of lake outlet
water quality in conjunction with biological monitoring was also
recommended.
• A more comprehensive ecological approach to monitoring the lakes was also
recommended, with greater emphasis being placed on unique floral and faunal
characteristics of these, generally pristine, larger, western Irish lakes.
Suggestions on improvements to established biomonitoring protocols were
made and the potential of several new, cost effective, methods was evaluated.
• Detection of anthropogenic impacts, other than eutrophication should also be
an objective of future lake monitoring programmes. Likewise, the need to
prevent non-indigenous species introductions, coarse fish translocations and
other changes to the lake ecosystems should be promoted.
• The unique features of these lakes, such as relict populations of invertebrates
should be researched and highlighted. The feasibility of restocking Loughs
Conn and Corrib with arctic char should be explored and every effort should
be made to ensure the survival of this species in Lough Mask and in the other
Irish lakes in which it is still found. New information on the ecology of the
Lough Mask char was presented.
1
INTRODUCTION
Eutrophication, or nutrient enrichment, can refer to natural successional processes in
the historical development of lake ecosystems. However, nowadays this term is
usually synonymous with what was once referred to as artificial or cultural
eutrophication. Earlier in this century limnologists in their attempts to adopt a
classification system for lakes introduced the terms “oligotrophic”, “mesotrophic” and
“eutrophic” to represent lakes they found to be nutrient poor, moderately rich in
nutrients and rich in nutrients respectively. This terminology is now widely used,
though definitions can vary among authors. Likewise, the implied relationships to
primary production, by algae and other forms of aquatic plant life, are often somewhat
tenuously linked to the criteria used in defining lake ecosystems.
Changes in lakes that result from eutrophication can include direct effects on the
composition and productivity of planktonic algal communities. Likewise, indirect
effects on the various other elements of the ecosystem can include shifts in species
composition of microbial, plant and animal communities and effects on fundamental
ecological processes. Changes in the physico-chemical parameters, such as
deoxygenation of the deeper water layers, can occur in eutrophicated lakes if they
become thermally stratified in summer months. Effects of enrichment on lake littoral
zones have been less well researched generally, than have those in the open waters
and profundal areas of lakes.
In Ireland artificial eutrophication of lakes has become a significant problem since the
1960’s. Various management measures have been adopted to limit the environmental
consequences of enrichment of freshwater habitats. Control of many major point
sources of pollution is, for example through improved sewage treatment facilities,
being progressively achieved. However, diffuse sources of pollution, including
agricultural sources of phosphorus, have been less effectively limited. Consequently,
eutrophication still remains a major source of concern in Ireland, as it is similarly on a
global scale.
2
BACKGROUND TO THE PROJECT
The River Corrib (3139 km2 surface area, 83m3sec-1 mean annual discharge) and
River Moy (20851m2 surface area, 5lm3sec-1) catchment areas include a large number
of lakes of varying sizes and ecology in western Ireland. However, the major lakes
(Lough Corrib, 17000ha, Lough Mask, 8000ha, Lough Carra, 1500ha, Lough Conn
5000ha, Lough Cullin 1100ha) represent over 90% of the combined lake area of their
river networks. Together with Lough Carrowmore (960ha), in the smaller River
Owenmore system (337km2, 14.6m3sec-1), these larger lakes represent a major
national resource (Fig 1). Important salmonid recreational fisheries and commercial
eel fisheries exist on the lakes, which also harbour a variety of wildlife. Until
relatively recently lake water quality has not been a problem in the area and much of
the freshwater habitats are still in near pristine condition. However, the lakes are
increasingly subject to a variety of anthropogenic impacts including: lake level
regulation associated with flood control and water abstraction; increased recreational
activities; species introductions and in some instances eutrophication. A number of
sources of enrichment have been recognised including inadequate sewage treatment;
changing land use patterns such as increased afforestation; and intensification of
agriculture.
Prior to initiation of the present studies a considerable amount of information was
already available concerning the general limnology of these lake systems and surveys
of water quality undertaken by various state agencies (e.g. Champ 1994, Flanagan and
Toner 1975, McGarrigle et al 1993, and Toner et al 1986) have involved
investigations of hydrochemical and biological signs of eutrophication. However,
conflicts of opinion had arisen in respect of the extent of eutrophication and its effects
on the lake ecosystems and their fisheries (e.g. Santillo and Pocock, 1994). The
disappearance of Arctic Char from Lough Conn, and concerns expressed about
possible early warning signs of enrichment in some partially isolated bays in Loughs
Corrib and Mask, also resulted in an increased appreciation that a broadly based
ecological study of the larger western Irish lakes was urgently needed. The work
described in this synthesis report and in the Final Project Report, as well as in a range
of other associated technical documents and theses, was undertaken with a view to
addressing such issues
3
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5
MAIN OBJECTIVES OF THE PROJECT
The overall objectives of the research programme were:
1. To generally increase knowledge of the environmental characteristics of the
western Irish lakes and assess the role of such factors as determinants of littoral
community structure.
2. To undertake analyses of natural and anthropogenic variations in the composition
of the littoral communities, with particular reference to: (a) submersed aquatic
macrophytes, (b) periphyton, (c) chironomid midges, and (d) the overall macro-
invertebrate assemblages.
3. To attempt to relate variations in littoral community composition and trophic
structure to phosphorous inputs and assess the effects of nutrient enrichment on
habitat productivity.
4. To evaluate the significance of the reported disappearance of char and changes in
trout feeding habits in Lough Conn, and to use ecological parasitology methods to
investigate the trophic ecology of these fishes.
5. To analyse lake sediments, with a view to reconstructing the changes that have
taken place in the lake ecosystems in the past two centuries and to establishing
patterns of sediment mobility in relation to lake hydrodynamics and circulation.
6. To evaluate the potential role of littoral surveying of (a) macrophytes, (b) diatom
assemblages (c) macro-invertebrates and (d) chironomid exuviae, in monitoring
early stages of lake enrichment. To identify unique, or changing, aspects of lake
community structure and physico-chemical parameters that might be of use in
routine monitoring of the lakes in future.
6
PROJECT MANAGEMENT
The project was co-ordinated by the National University of Ireland, Galway (project
leader: Dr. T.K. McCarthy). Staff and students from the Departments of Zoology,
Botany and Oceanography, NUI, Galway, participated in all aspects of the research
programme in the six lakes studied. The Central Fisheries Board undertook
vegetation mapping surveys and char sampling in Lough Mask. Aquafact
International Services Ltd., provided SCUBA diving services and undertook
Sediment Profile analyses in Loughs Conn, Mask and Corrib.
Project outputs included a series of reports and theses (Appendix 1), as well as
computerised data bases on various quantitative studies undertaken. Photographic
images of sediment profiles and underwater video records of lake shorelines and
vegetation were also compiled.
7
RESULTS
Water Quality Monitoring
Water sampling undertaken at 34 stations distributed across the six lakes was
undertaken at least monthly, with increased sampling from April to September in
Loughs Mask, Conn and Cullin, from March 1996 to July 1997. Sampling stations
included both open water and inshore sites. At selected index sites in each lake
additional samples were obtained at 5m depth intervals, in other stations sampling
was generally restricted to top, middle and bottom layers. In shallow lake sites single
sub-surface samples were taken. During the sampling periods, a total of 884 water
samples were thus obtained for nutrient and chlorophyll a analyses. Summary data on
total phosphorus (TP), determined by the persulphate digestion method (APHA, 1995)
are presented (Table 1) together with similar data on epilimnetic chlorophyll a levels
which were fluorimetrically determined (APHA, 1995). Water clarity, (Secchi disk
readings) was also recorded in conjunction with water sampling, though variations in
water colour and suspended solids, especially in shallow lake basins, frequently
obscured the inverse relationship between water clarity and phytoplankton
productivity. Full details of the methodologies and results of the water quality
monitoring programme are presented elsewhere (Final Project Report, Chapter 2).
Trophic classification of the six lakes on the basis of the OECD scheme, using mean
TP and maximum chlorophyll a values suggests that the lakes should be classified as
follows: Lough Carra, ultra-oligotrophic / oligotrophic; Lough Carrowmore,
mesotrophic; Lough Conn, mesotrophic; Lough Corrib, ultra-oligotrophic /
oligotrophic; Lough Cullin, mesotrophic and Lough Mask, oligotrophic. Temperature
and conductivity profiles, recorded at all sites during water sampling, indicated that
some transient summer stratification occurred, but only in deeper lake basins.
Analyses of water samples also indicated extreme physico-chemical homogeneity of
most lakes on most sampling dates. Rapid loss of TP from major rivers to lake
sediments was noted, for example in Upper Lough Conn where higher chlorophyll a
levels reflected the localised effect of River Deel nutrient loading.
Phytoplankton
Integrated tube samples of phytoplankton (to twice the Secchi depth) were taken on
all occasions during water quality monitoring March 1996-July 1997 in the six lakes.
Chlorophyll a levels in the lakes which broadly reflected changing phytoplankton
8
Table 1a Trophic classification scheme for lake waters proposed by the O.C.E.D. (1982).
Total Phos. Chlorophyll TransparencyLake category mg/m3 mg/m3 m
Mean Mean Max. Mean Min.
Ultra-Oligotrophic <4 <1.0 <2.5 >12 >6
Oligotrophic <10 <2.5 <8.0 >6 >3
Mesotrophic 10-35 2.5-8 8-25 6-3 3-1.5
Eutrophic 35-100 8-25 25-75 3-1.5 1.5-0.7
Hypertrophic >100 >25 >75 <1.5 <0.7
Table 1b A summary of data on total phosphorus, chlorophyll a and water transparency for the
Total Phos. Chlorophyll TransparencyLake and site mg/m3 mg/m3 m
Mean Mean Max Mean Min
Cara 4.47 0.92 2.21 6.53 3.50
Carrowmore 24.90 4.89 24.08 0.96 0.70
Conn 10.40 2.08 9.65 3.25 1.75
Corrib 9.23 0.75 2.02 4.38 1.10
Cullin 18.06 2.51 10.27 0.97 0.20
Mask 8.39 1.83 5.94 5.39 2.50
Table 1c A summary of the trophic status of the six western lakes, based on the O.E.C.D. schemeand data in Table 1b
Total Phos. Chlorophyll TransparencyLake mg/m3 mg/m3 m
Mean Mean Max Mean Min
Cara Oligotrophic Ultra-Oligotrophic Ultra-Oligotrophic Oligotrophic Oligotrophic
Carrowmore Mesotrophic Mesotrophic Mesotrophic Hypertrophic* Eutrophic
Conn Mesotrophic Oligotrophic Mesotrophic Eutrophic* Mesotrophic
Corrib Oligotrophic Ultra-Oligotrophic Ultra-Oligotrophic Mesotrophic Eutrophic
Cullin Mesotrophic Mesotrophic Mesotrophic Hypertrophic Hypertrophic
Mask Oligotrophic Oligotrophic Oligotrophic Mesotrophic Mesotrophic
* Validity of this parameter questionable in these lakes due to water colour (dystrophy)
six western lakes (1996/1997 data).
9
abundances and biomass were typically low. Sites to site variations in lakes were
generally slight, with the exception of Lough Conn (Fig 2) where a longitudinal
gradient was apparent (attributable to a plug-flow component in the lake circulation
and River Deel nutrient inputs to the upper basin)
Most lakes exhibited bimodal phytoplankton maxima with large spring communities
and smaller more extended summer/autumn ones. Spring communities were
dominated by diatoms and declined in response to silica depletion. In Lough Corrib
little seasonal variation in phytoplankton biomass was evident, as is common in very
unproductive lakes. Loughs Mask and Conn exhibited patterns which were typical of
mesotrophic lakes (Fig 3) though the species composition of the summer/autumn
phytoplankton communities differed, with greater representation of cyanophytes in
Lough Conn. A striking feature of most lakes was the persistence of Oscillatoria
agardhii populations throughout the sampling period, which exhibited autumn peaks
in the deeper well-mixed Loughs Mask, Corrib and Conn. Full results of the
phytoplankton studies are presented elsewhere (Final Project Report, Chapter 4)
Fig 2 Comparison of chlorophyll a values at all sites, Lough Conn. Boxes indicate
median, 25th and 75th percentiles; whiskers indicate 10th and 90th percentiles,
points indicate 5th and 95th percentiles. Sample sites P1 to P5 are located
along the North-South axis of the lake with L1 and L2 being in enclosed
western bays. (See Chapter 2 of the main project report for location of
sample sites)
10
Fig 3 Seasonal variation in mean epilimnetic chlorophyll a levels in Loughs Mask
and Conn (January 1996 – April 1997).
Periphyton
Periphyton communities in Irish lakes have, with the exception of some taxonomic
check listing, not heretofore been scientifically investigated. For this reason, within
and between lake variations in biomass and taxonomic composition, with particular
reference to diatoms, was investigated in the six large western Irish lakes being
surveyed. In addition to producing base-line data, these studies aimed to evaluate the
potential of using diatom community structure and periphyton biomass as routine
water quality monitoring tools. In addition to natural substrates, periphyton was
sampled using artificial substrate samplers (Fig 4). Details of the methods employed
and a more comprehensive account of this research are presented elsewhere (Final
Project Report, Chapter 3) and a comprehensive bibliography on lake periphyton was
also compiled (Interim Project Report). Levels of periphyton biomass observed were
generally low and in most cases comparable to those reported from other oligotrophic
lakes (Jacoby et al, 1991). Overall values were comparable to those reported from a
survey of 21 oligotrophic lakes in British Columbia, using artificial substrates
(Shortreed et al 1984).
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11
Studies on aquatic plants
The distribution and composition of the aquatic flora was examined in mid-summer in
1995 (Lough Conn, Lough Cullin, Lough Mask) and l 996 (Lough Corrib, Lough
Carra). Sampling was carried out by boat along transects, specified by GPS
instrumentation, using grapnels following methods adopted by Krause & King (1994).
A flora dominated by species of the genus Chara dominated on the eastern, limestone
shores of Lough Corrib and Lough Mask and those areas in Lough Carra of sufficient
depth to support vigorous stands of submerged plants. Chara species colonised most
of the shallow (to 3m) basin of lower Lough Corrib and were also notable in those
parts of Lough Cullin most removed from the point of entry of the enriched R.
Castlebar system. The remainder of the Lough Cullin basin, another shallow littoral
area (to 3m), was heavily overgrown with filamentous algae. The partly-isolated
western arm area of Lough Corrib and upper Mask area of Lough Mask were
characterised by a flora dominated by isoetid growth forms - Littorella, Lobelia,
Eriocaulon and Juncus bulbosus growing in shallow water close to the shore with
Isoetes in deeper water (to 3.5m). Species of Potamogeton were best represented in
Lough Mask where stands of the broad-leaved P. lucens, P. perfoliatus, P. gramineus
and their hybrids grew at the foot of shoreline slopes on the lee shores of many of the
large islands present. These broad-leaved forms were also present in some of the
sheltered bay areas of Lough Conn. Charophytes were poorly represented in this latter
lake. This may be a consequence of its exposed nature and limited degree of shoreline
development. The flora of four of the five lakes had been previously examined by one
of the authors (J. King) in the 1984-87 period. The exception was Lough Carra which
had been studied in 1975 (Inland Fisheries Trust, unpublished data). While the status
and composition of aquatic plants has remained unchanged in the majority of areas
examined in all lakes, a number of changes were noted in the aquatic flora between
the present and previous studies. The findings do suggest that macrophytes reflect
changes in the parent water body but these changes may not be of sufficient subtlety
to allow their use as early-warning indicators of eutrophication onset.
12
Fig 4 Diagram of the artificial substrate sampler used in the diatom studies on the
western lakes.
Fig 5 Box plots of ash free dry weight measured on artificial substrate samplers,
for all lakes. Boxes indicate median, 25th and 75th percentiles; whiskers
indicate 10th and 90th percentiles, points indicate 5th and 95th percentiles.
Concrete block
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13
Macroinvertebrates
The littoral macroinvertebrate assemblages of the lakes were investigated, generally
by means of a combination of large core samplers (0.25m2) and pond nets. Some
special sampling programmes (Kelleher, 1997; Garry, 1998) also included artificial
substrate samplers (gravel filled wire baskets) or SCUBA sampling. Results of a DCA
analysis of some results of macroinvertebrate sampling at 66 lake sites are presented.
This data set initially comprised 36408 invertebrates belonging to 167 taxa. The DCA
analysis was run on a data set the invertebrates were assigned to 25 groups (Table 2)
on the basis of their presumed environmental sensitivities. The taxa associations
indicated by the ordination plot (Fig 6) did not reflect a definite gradient in lake
trophic status. Other attempts at defining such patterns were equally complicated by
the extent of within lake variations in macroinvertebrate species assemblages and the
similarity in the lake environments. Further details on the Macroinvertebrate
assemblages may be found in the Final Project Report (Chapter 6) and in theses of
Kelleher (1997) and Garry (1998).
In Table 3 results obtained by quantitatively SCUBA sampling along two transects of
increasing water depth from the western shore of Lough Mask are presented. These
can be used to illustrate the extent to which a variety of taxa, which would normally
be thought of as being characteristic of littoral rather than profundal benthic lake
communities, can occur in deep areas of lakes when environmental conditions are
suitable.
Sediments
The surface sediments from Lough Conn, north county Mayo, were investigated with
a view to reconstructing the environmental changes which have taken place in the
lake over the last century. A series of 1-metre cores was taken from the upper and
lower basins of the lake (Fig 7). Whole core magnetic susceptibility measurements
were made on all cores with a view to correlating cores from different parts of the
lake on the basis of similar patterns in susceptibility. One profile was selected for in-
depth study. This core, CON 4, was from the lower basin of the lake. Water content
was determined and pollen analytical investigations of the core were also conducted.
14
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16
Table 3 Transect studies of macro-invertebrates in Lough Mask (Devinish Island).
Distance from shore (metres) 3m 6m 10-11m
Depth (metres) 1m 5m 12m
Polycelis tenuis 2Dugesia polychroa 2Theodoxus fluviatilis 1 1Bithynia tentaculata 4Pisidium 51 85Oligochaeta 6 16 12Glossiphonia complanata 2Helobdella stagnalis 7Asellus aquaticus 5 11Crangonyx pseudogracillis 6 4Gammarus duebeni 57 12Niphargus kochianus 3Heptagenia sulphurea 2Ephemera danica 2Caenis luctuosa 41 1Caenis horaria 1Leuctra inermis 1Chloroperla torrentium 1Chloroperla tripunctata 2Esolus parallelepipedus 11 1Plectrocnemia conspersa 1Holocentropus picicornis 1Limnius volckmari 9 1Oulimnius tuberculatus 1Athripsodes aterrimus 2Athripsodes cinereus 7Lepidostoma hirtum 1Sericostoma personatum 2Chironomidae 2 32
Total no. of invertebrates 65 188 156
No. of species 4 23 13
17
Fig 7 Map of Lough Conn showing the locations of sites sampled during
sediment coring and SPI studies.
LC1
LC6
LC4
LC5
LC3
LC2
LC7
LC8
LC9
LC11
LC10
10
10A1117
12
1316
14 & 14A
15
1
2
3
4
5
6
78
1
LC1
LOUGH CONN
Sediment coring sampling sites
SPI survey sites
18
Attention was paid to the concentration of spheroidal carbonaceous particles (SCPs)
in the profile. More limited investigations were carried out on core, CON 14A, from
the upper basin.
The profile, CON 4, contains an important record of recent changes in the
limnological environment and, in particular, those associated with the arterial
drainage schemes of the late 1950s and early 1960s. The pollen analytical
investigations proved to be of particular value in that it provided clear evidence of
substantial inwash, firstly of peaty, organic-rich sediments and in more recent times of
mineral-rich sediments. Magnetic susceptibility measurements (Fig 8) did not
facilitate core correlation, but were useful indicators of periods of increased inwash of
mineral matter into the lake, which were linked to erosional processes occurring in the
catchment. The spheroidal carbonaceous particle (SCP) curve established for the
profile yielded evidence which provided important clues as to the age of the
sediments. Full details of the palaeoecological and sediment studies are given in the
Final Project Report (Chapter 9).
Sediment Profile Imagery (SPI) techniques, now widely employed in marine benthic
surveying, were evaluated during the surveys in Loughs Conn, Cullin, Mask and
upper Corrib and found to be effective in providing rapid assessments of sediment
characteristics. The methods involved deployed a special, diver operated, apparatus
(Fig 9) that photographically recorded a vertical section through the lake bottom
sediments. The varied sediment patterns, also noted during mini-Mackereth coring
work, of Lough Conn, were well illustrated in the SPI records. Redox profiles,
vegetation features and physical disturbance of the lake bottoms could also be
observed.
19
Fig 9 Diver operated sediment profile camera
Char
The biology of char, which were discovered during the course of the work to be now
largely present in Lough Corrib, was investigated. Shoreline and off shore SCUBA
studies of potential spawning sites in Loughs Conn, Mask and Carra showed that
conditions were poor in the case of Lough Conn due to accumulations of filamentous
algae and organic matter. However, no such effects were noticeable in areas of Lough
Corrib where they previously spawned. A comparison between Lough mask char and
those from Lough Eske, Co. Donegal was undertaken. A detailed study of the
morphometrics, growth rates, diets, parasites and reproduction of two char
populations were undertaken, full details of which are given in the Final Report,
Chapter 8 and in a thesis by Doherty (1999). The Lough Mask char were larger and
more fecund than those of Lough Eske (Fig 10). Differences in egg sizes (Fig 11) may
also reflect different life history strategies of the populations. Differences in diets, and
possibly also parasite burdens associated with difference in diet appear to affect char
growth. The studies on diet of char indicated their vulnerability to competitive
exclusion by a range of other freshwater fish and the decline of Corrib char seems to
be linked to the expansion of roach numbers in that lake.
20
Fig 10 Scatterplot illustrating the relationship between fecundity and length of
female char from Lough Mask and Lough Eske.
Fig 11 Percentage frequency distributions of egg diameters from female char
captured on Lough Mask and Lough Eske.
0
2
4
6
8
10
12
14
16
1
1.4
1.8
2.2
2.6 3
3.4
3.8
4.2
4.6 5
5.4
5.8
6.2
Egg diameter (mm)
%fr
equ
ency
L. Eske, 10/11/96 (n=8) L. Mask, 21/11/96 (n=41)
0
500
1000
1500
2000
2500
0 50 100 150 200 250 300 350
Length (mm)
Fec
un
dit
y
L. Mask, 21/11/96 (n=41) L. Eske, 10/11/96 (n=8)
21
Lake circulation patterns
Studies on the patterns of water movement and thermal stratification in Lough Mask
showed that wind can drive large topographic flows downwind in the shallow eastern
section of Lough Mask and counter to the wind in the deep parts of the lake. This flow
can mix the open lake rapidly and may destroy stratification in the Summer following
prolonged winds. There was also evidence of thermally driven diurnal frontal motion
in the eastern Lough Mask in calm summer periods.
Mapping of river plumes from the River Robe and River Deel showed seasonal and
between site variations that can affect distribution of nutrients within the lake basin.
In the case of the Rive Robe a generally northward dispersal of nutrients is suggested,
so that direct impacts of the rivers nutrient loading are unlikely to impact significantly
on a series of semi-enclosed bays in the south east part of the lake.
22
23
RECOMMENDATIONS
Water Quality
• Future monitoring programmes should focus on limnetic lake-wide mean
epilimnetic values of key water quality parameters, TP and chlorophyll a, for
purposes of lake classification Data fully representative of seasonal variations,
with at least monthly sampling, should be collected annually. In addition to open-
water sites conditions at river mouths should also be monitored for purposes of
detecting changes in P-loadings from particular sub-catchment areas. River mouth
sites could also be incorporated into biological monitoring programmes, and in
particular those that involve documentation of increased macrophyte and
filamentous algal growth. Care needs to be taken that normal diel variation in
oxygen levels etc., at such sites, and in areas where submersed macrophytes
extend into deeper water, are not misinterpreted.
• Ideally, future monitoring of the lakes should be based on periodic reviews of
their full external and internal nutrient budgets.
• Future monitoring, could focus on lake outlet points as areas of special interest.
Hydrometrical, physico-chemical and productivity linked data from these
ecologically interesting sites, compiled as time series, could be a cost effective
way of monitoring overall changes in the lake basins.
• Observations on selected isolated bays, for signs of enrichment, should become
part of future monitoring programmes. However, it may also be beneficial to
consider situations where due to thermal structures some inshore areas may
periodically become isolated from main water bodies and which may differ
ecologically.
Periphyton
• Long term monitoring of periphytic biomass and diatom community
compositions should be initiated in a series of lakes representing a broader range
of trophic states.
• Taxonomic training is required and ecological studies on the responses of
individual diatom species to nutrient levels, and other environmental factors, e.g.
light and pH need to be further researched.
24
Phytoplankton
• Future phytoplankton sampling be carried out at least monthly. Shorter interval
sampling would potentially miss important events in the seasonal cycle, in
particular spring and autumn maxima. Given the homogeneity of the lakes, a
single index station per lake or major basin is judged to generally be sufficient for
monitoring phytoplanktonic communities.
• Shoreline accumulations of cyanophytes in lower Lough Conn have been the
object of occasional complaints by the public. As has been shown, these
accumulation can result from relatively small populations of buoyant
cyanophytes in the water column. Their occurrence is dependent upon both the
presence of these populations, and the development of calm conditions, which
allow the algae to rise to the surface and be blown to shore. Monitoring
meteorological conditions can be used to predict the latter, but the potential for
the development of shoreline accumulations could be monitored through a regular
sampling program.
• The buoyancy of the cyanophytes forming shoreline accumulations could serve as
an aid to a future sampling program. It would be feasible to take large samples,
perhaps with the aid of a plankton net (mesh size < 75 µm), and allow the
samples to settle in a glass cylinder. Vacuolate cyanophytes would rise to the
surface and this should allow a reasonable estimate of their population densities
to be made. If done in a quantitative manner (i.e., known volume of water
sampled by plankton net), then a relationship could be developed between water
column populations and the potential for shoreline accumulations.
Macrophytes and filamentous algae
• Repeat surveys at, for example, five year intervals using similar methods would
be of value. Selected sites in each lake should in future be sampled quantitatively
by SCUBA divers. Responses of macrophytes to local enrichment events should
be better documented. Particular attention should be paid to effects of water
clarity on the depths to which particular plant species may colonise each lake.
25
• The sensitivity of unique floral features of the lakes (e.g. Eriocaulon in western
Loughs Corrib and Mask) to environmental change should be investigated and
particular attention should be paid to monitoring them.
• Observations, during macrophyte surveys, of benthic accumulations of
filamentous algae in the littoral zones of the lake should in future be more
systematic. Identification of species involved is important. Like-wise,
consideration of the significance of factors other than those linked to overall lake
eutrophication should not be neglected.
• Under water digital-video recording of macrophyte, and filamentous algal
accumulations along defined transects representative of depth-profiles and other
interesting features of individual lakes would be a cost effective way of
monitoring some general features of the aquatic floras of the lakes.
• Selection of sampling site locations at river mouths or in areas directly influenced
by river discharge plumes would be of value in identifying sources of increased
nutrient loading. Likewise, sampling specifically at lake outlets to would be
important if overall changes in the lake systems are to be monitored with limited
resources.
Macroinvertebrates
• Artificial substrate samplers could reduce some of the sampling and sorting
effort, but with some loss of detail, and could provide good replicates for
statistical purposes. Adoption of such protocols in lake invertebrate sampling
could be linked to use of artificial substrate sampling of periphyton for water-
quality monitoring purposes.
• Though not extensively utilised in the present research programme, initial studies
on the distributional patterns of macroinvertebrates along depth gradients in
Lough Mask and Corrib were promising. It seems likely that monitoring defined
transects, representative of individual lake basins or bays, by quantitative SCUBA
diver sampling of benthic invertebrates would be an effective way of
incorporating changes in macroinvertebrate assemblages into lake monitoring
programmes. The diversity of macroinvertebrates, typically considered to be
littoral zone inhabitants, that occur at considerable depths is a special feature of
the more pristine western Irish lake habitats. Monitoring this phenomenon on a
26
systematic basis, could contribute to an effective early warning system for
detection of eutrophication and other adverse environmental changes in lakes.
• Rare and unique taxa such as the amphipod Niphargus kochianus, the midge
Corynocera ambigua and the stone-fly Capnia atra, which occur in some of the
lakes should be further researched. Like the arctic char they are of special
conservation interest and research on their habitats may provide vital clues in the
identification of environmental factors, other than the normal water quality
parameters, that should be monitored in future
• Introduced species, such as amphipods Gammarus tigrinus and Eucrangonyx
pseudogracilis, are increasing their range in the western lakes, as are introduced
eel parasites and a wide variety of other organisms. Others, such as zebra, mussels
which are now wide spread in the Shannon and Erne catchments, could easily
arrive undetected. The potential that these organisms have to produce ecological
shifts in the lake communities represents a real threat to the biodiversity and
ecological integrity of the lake ecosystems such as those in the near pristine
Loughs Corrib, Mask and Carra. Future monitoring of the lakes should include
reference to such neozoon invertebrates.
Chironomid exuviae
• With access to better knowledge of the tolerance of individual taxa for
environmental conditions in lakes of different trophic status, exuvial sampling
could be a relatively simple, cost effective way of monitoring changes in Irish
lakes. However, a reasonable level of taxonomic expertise will be essential and it
is unlikely that simple indices (e.g. proportion of tolerant genera or numbers of
Chironomus sp.) will be of value in future lake monitoring.
• Improvements in sampling protocols, to ensure that samples are representative of
either main lake basins or targeted bay areas, can be made through: careful
selection of sampling sites; response to varying wind directions etc; ensuring
adequate sample sizes and by development of new sampling techniques.
• Further research on the dispersal of exuviae, from points at which emergence
occur, would appear to be justified by field observations and the general lack of
27
published data on this phenomenon in large lakes. The filtering and delaying
effects of dense aquatic macrophyte growth needs to be investigated.
Arctic char
• Further research on other populations of char in Ireland should be encouraged.
Genetical differences between lake populations of char and of their susceptibility
to known fish diseases are among the many topics that need to be researched.
• Lough Mask, as indicated by the presence of unusual relict invertebrates,
remarkably pristine limnetic algal communities and its extant char population, is a
most interesting lake. Conservation of the biodiversity aspects of the lake should
be a national priority. Multi-disciplinary research programmes, focused on this
lake, upper Lough Corrib and some of the other near pristine western lakes should
be encouraged, so that a better awareness of the importance of conserving, or
restoring, their char can be promoted.
• Restocking Loughs Conn and Corrib with char should be considered.
Improvements in water quality in Lough Conn and a reported decline in roach in
Lough Corrib in the past few years, may mean that some of the significant
environmental factors associated with their recent local extinction no longer
apply. Brood stock from Lough Mask, or other local lake like Lough Talt, could
be used with hatchery facilities for mass rearing of char fry to be released to the
lake areas from which the have disappeared. The recent development of char
farming in Ireland (Bass, 1998) means that technical advice is available locally to
assist in rearing of wild char for conservation purposes. Establishment of back up
populations of Lough Mask char is another conservation measure that may need to
be considered in the near future, possible reservoir sites need to be identified and
evaluated.
• Restricting species introductions to lakes with char should be a major fish
conservation goal. Translocations of common coarse fish species are as potentially
damaging to char as the introductions of exotic species (e.g. zebra mussels) that
can more easily capture the public imagination. The rapidity with which roach
was dispersed throughout most of Ireland’s river systems in recent times
28
illustrates the difficulty in protecting lakes like Lough Mask from such unwanted
new arrivals.
Sediments
• Further palaeoecological analyses of recent historical events affecting the western
lakes should be encouraged. Lakes should be recorded every 10 to 15 years for
palaeolimnological analysis.
• Lake coring (e.g. mini Mackereth technique) and/or Sediment Profile Imagery
(SPI) can be cost effectively used to rapidly map the heterogeneity of sediment
types that characterise the basins of the large topographically varied western
lakes. This would allow for selection of particular sites for more detailed analyses
of sediment chemistry, accumulation processes and nutrient recycling
phenomena.
Circulation studies
• Knowledge of the circulation patterns of the lakes is important if effective
modelling of the nutrient dynamics and sedimentation processes in the lakes is to
be achieved. Further research is required to provide the necessary data.
• An analysis of temperature structures of lake areas adjacent to shoreline
accumulations of cyanophytes and other filamentous algal, and in isolated bays is
recommended.
29
CONTRIBUTIONS TO THE ENVIRONMENTAL MONITORING
R AND D SUB-PROGRAMME
The project “Investigation of eutrophication processes in the littoral zones of western
lakes” will contribute to improving the environmental management of six large lakes
in the west of Ireland. This will have consequences for the future water quality in the
lakes themselves as well as minimising anthropogenic impacts elsewhere in the lake
catchments that affect eutrophication linked processes in the lake ecosystems.
Increased understanding of the littoral ecology of the lakes, analyses of current trends
in water quality and development of more effective monitoring protocols are among
the contributions the proposed R and D project has made to the Environmental
Monitoring R and D sub programme. The project addressed specific objectives of the
Environmental Sub-Programme. The participants in the project endeavoured to
involve local organisations, angling organisations and local environmentalists to
communicate R and D results locally. Improved management of the western Irish
lakes, that represent natural resources which are of immense potential value to the
expanding tourism industry of the area, will secure present employment and provide a
basis for sustainable growth in this economically important sector. The approach is
now one generally favoured by local authorities and development agencies, as well as
reflecting a generally increased environmental awareness among recreational users of
the lakes, tourist angling operators, and users of the water resources in the area.
In order to further involve the beneficiaries of the R and D project, through contacts
with representative individuals and organisations, they will be advised of the final
results of the project and they will get the opportunity to participate in a conference
organised at NUI, Galway. This conference, in addition to communicating the results
of the R and D project, will also seek to integrate the scientific findings within a
broader socio-economic framework.
30
31
REFERENCES
American Public Health Association (1995). Standard methods for the examination of water and
wastewater. 19th ed. American Public Health Association, Washington D.C.
Bass N. (1998) An introduction to farming arctic char in Ireland. Aquaculture Explained, Manual
No.18, BI.M, Dublin.
Champ, T. (1994). Lakes Report, April 1994. Central Fisheries Board, Dublin.
Flanagan, P. J. and Toner, P. F. (1975). A preliminary survey of Irish lakes. An Foras Forbartha, Water
Resources Division, Dublin.
Garry, Mairead R. (1998). The study of the littoral macroinvertebrate communities of the stony
shoreline of some western Irish lakes. Unpublished MSc thesis, NUI, Galway.
Jacoby, J.M., D.D. Bouchard and C.R. Patmont. (1991). Response of periphyton to nutrient enrichment
in Lake Chelan, WA. Lake and Reserv. Manage. 7(1):33-43.
Kelleher, Samantha (1997). Studies on the macroinvertebrate assemblages associated with aquatic
macrophytes in some western Irish lakes. Unpublished MSc thesis, NUI, Galway.
McGarrigle, M. Lough, Champ, W.S., Norton, R., Larkin, P. and Moore, M. (1993) The trophic status
of Lough Conn: an investigation into the causes of recent accelerated eutrophication. Report
prepared for the Lough Conn Committee. Mayo County Council, Castlebar.
Santillo, D. and I. Pocock. (1994). Water quality status of the Carra-Mask systems, Co. Mayo, Ireland.
Green Peace Exeter Research Laboratory Technical Note. No 02/94.
Shortreed, K.S., A.C. Costella and J.G. Stockner. (1984). Periphyton biomass and species composition
in 21 B.C. lakes: Seasonal abundance and response to whole-lake nutrient additions. Can. J.
Bot. 62:1022-1031.
Toner, P.F., Clabby, K.J., Bowman, J.J. and McGarrigle, M.Lough (1986). Water quality in Ireland.
The current position. Part 1: General assessment. An Foras Forbartha. WR/G15, Dublin.
32
33
FIGURES AND TABLES
Figures
Fig 1 Map of western Ireland showing the locations of the six western lakes
studies (Loughs Conn, Cullin, Carrowmore, Carra, Mask and Corrib). The
catchment areas are also outlined.
Fig 2 Comparison of chlorophyll a values at all sites, Lough Conn. Boxes
indicate median, 25th and 75th percentiles; whiskers indicate 10th and 90th
percentiles, points indicate 5th and 95th percentiles.
Fig 3 Seasonal variation in mean epilimnetic chlorophyll a levels in Loughs
Mask and Conn.
Fig 4 Diagram of the artificial substrate sampler used in the diatom studies on
the western lakes.
Fig 5 Box plots of ash free dry weight measured on artificial substrate samplers,
for all lakes. Boxes indicate median, 25th and 75th percentiles; whiskers
indicate 10th and 90th percentiles, points indicate 5th and 95th percentiles.
Fig 6 Ordination plots of A) lake sites (S indicates stony shore survey) and B)
associated macroinvertebrate groups resulting from a DCA analysis of 25
major macroinvertebrate groups from 66 individual sites distributed
among the six western lakes studied. (Details of the Macroinvertebrate
groups are given in Table 2)
Fig 7 Map of Lough Conn showing the locations of sites sampled during
sediment coring and SPI studies.
Fig 8 Whole core magnetic susceptibility curves (k) for 16 top-meter cores from
Lough Conn. Units are expressed as x10-5 SI units.
Fig 9 Diver operated Sediment Profile Imagery (SPI) camera.
Fig 10 Scatterplot illustrating the relationship between fecundity and length of
female char from Lough Mask and Lough Eske.
34
Fig 11 Percentage frequency distributions of egg diameters from female char
captured on Lough Mask and Lough Eske.
TABLES
Table 1 a) Trophic classification scheme for lake waters proposed by the O.C.E.D.
(1982). b) A summary of data on total phosphorus, chlorophyll a and
water transparency for the six western lakes. c) A summary of the trophic
status of the six western lakes, based on the O.E.C.D. scheme
Table 2 The 25 major groupings of invertebrates used in the DCA analysis
presented in Fig 4. In each case the abbreviated group name used to
identify individual data point in Fig 4 is given.
Table 3 Transect studies of macro-invertebrates in Lough Mask (Devinish Island)
35
APPENDIX
The following are reports and theses associated with this project:
Reports
Aqua-Fact (1996). A report on sediment profile imagery surveys of Loughs Conn,
Cullin and Mask. Aqua-Fact International Services Ltd., Galway
King, J. (1995). Macrophytes of Lough Mask, Lough Conn and Lough Cullin. July-
August 1995: An Interim Report. Central Fisheries Board, Dublin
King, J. (1996). Macrophytes of Lough Corrib and Lough Carra. July–August 1996:
An Interim Report. Central Fisheries Board, Dublin
McCarthy, T.K. (1996). Investigation of eutrophication processes in the littoral zones
of western lakes. An Interim report.
PhD theses:
Creed, Karen (1999). Studies on the metazoan parasites of Salmo trutta (Lough),
Anguilla anguilla (Lough) and Platichthys flesus (Lough) in the west of Ireland with
reference to Clare Island.
Doherty, Dennis (1999). Studies on the parasite assemblages and general biology of
some rare and endangered Irish fishes.
MSc theses:
Garry, Mairead R. (1998). The study of the littoral macroinvertebrate communities of
the stony shoreline of some western Irish lakes.
Kelleher, Samantha (1997). Studies on the macroinvertebrate assemblages associated
with aquatic macrophytes in some western Irish lakes.