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 subprogramme 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 cooperation 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, ultraoligotrophic / 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. 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. 1 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 2 Fig 1 Corrib). The catchment areas are also outlined. 3 Map of western Ireland showing the locations of the six western lakes studies (Loughs Conn, Cullin, Carrowmore, Carra, Mask and 4 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 macroinvertebrate 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. 5 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. 6 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 7 Table 1a Trophic classification scheme for lake waters proposed by the O.C.E.D. (1982). Total Phos. 3 mg/m Mean Mean Max. 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 >100 >25 >75 <1.5 <0.7 Lake category Hypertrophic Chlorophyll 3 mg/m Transparency m Mean Min. Table 1b A summary of data on total phosphorus, chlorophyll a and water transparency for the six western lakes (1996/1997 data). Total Phos. 3 mg/m Mean Mean Max Transparency m 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 Lake and site Chlorophyll 3 mg/m Table 1c A summary of the trophic status of the six western lakes, based on the O.E.C.D. scheme and data in Table 1b Total Phos. 3 mg/m Mean Mean Max Transparency m 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 Lake Chlorophyll 3 mg/m * Validity of this parameter questionable in these lakes due to water colour (dystrophy) 8 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) 9 4.5 4 Chl a (µg l -1) 3.5 3 2.5 2 1.5 1 0.5 0 J F M A M J J A L. Mask S O N D J F M A L. Conn 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). 10 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. 11 Rubber bung Glass slides Cover to prevent grazing (optional) Concrete block 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. 12 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 indepth 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. 13 350 A Axis 2 (10.51%) 300 250 200 150 100 50 0 0 50 100 150 200 250 300 350 Axis 1 (17.73%) Corrib - S Corrib Mask - S Mask Cara - S Cara Cullin - S Cullin Conn - S Conn Carrowmore - S Carrowmore 450 B Plecop 400 350 Col A Axis 2 (10.51%) 300 Gam Ephem A 250 Mys Aphel Trich B Chiron 200 Col B Gast A Ephem C Gast C Triclad As Het 150 Arachnid H Trich A 100 Biv Ephem B Ephem D Odon Gast B 50 Si 0 Oligo -50 -100 -50 0 50 100 150 200 250 300 350 400 Axis 1 (17.73%) 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) 14 danica ae - Gam s duebeni s lacustris s tigrinis pseudogracilis s pulex raria tuosa ulorum usta dani m pennulatum spp. (adult) dae spp. indet spp. ermanni ovatus p. ctuus depressus maculatus ptera - Ephem a s insignis s venosus a fuscogrisea a lateralis a sulphurea ia vespertina maculatus p. 13 Gastropoda - Gast a Ancylus fluviatilis Theodoxus fluviatilis 14 Gast b Ancylus lacustris Lymnaea palustris Lymnaea stagnalis Lymnaea glabra Lymnaea peregra Planorbis contortus Potamopyrgus jenkinsi Succinea putris Valvata cristata Valvata macrostoma Valvata piscinalis Physa fontinalis Gast c 15 Planorbis leucostoma Bithynia tentaculata Planorbis carinatus Planorbis corneus Segmentia complanata Hirudinea - H 16 Erpobdella octoculata Glossiphonia complanata Glossiphonia heteroclita Haemopis sanguisuga Helobdella stagnalis Piscicola geometra 17 Heteroptera - Het 21 Corixa iberica Corixa panzeri Corixa punctata Arctocorisa germari Corixa distincta Corixidae spp. indet Notonecta spp. 22 Sigara distincta Sigara dorsalis Sigara falleni 23 Sigara fallenoidea Sigara fossarum Velia caprai 18 Mysidae - Mys Mysis relicta 19 Odonata - Odon Ischnura elegans Coenagrion spp. Coenagrion pulchellum Coenagrionidae spp. Indet Cordulia aenea Cordulia linaenea Enallagma cyathigerum Erythromna najas Lestas dryas Nymphula nympheata Platycnemis pennipes Pyrrhosoma nymhula 20 Oligochaeta - Oligo Oligochaeta spp. indet Eisenella tetrhaedra Plecoptera - Plec Capnia bifrons Chloroperla torrentium Dinocras cephalotes Diura bicaudata Nemoura cinerea Nemoura erratica Sialidae - Si Sialis spp. indet Sialis lutaria Trichoptera - Trich a Agapetus fuscipes Agrypnia obsoleta Agrypnia pagetana Anabolia nervosa Apatania wallengreni Athripsodes aterrimus Athripsodes cinereus Beraeodes minutas Chaetopteryx villosa Goera pilosa Goeridae spp. indet Goeridae clavicornis Halesus radiatus Lepidostoma hirtum Limnephilidae spp. indet Limnephilus affinis / incisus Limnephilus extricatus Limnephilus flavicornis Limnephilus lanatus Limnephilus marmoratus Limnephilus rhombicus Limnephilus vittatus identify individual data point in Fig 6 is given. Micropterna lateralis Micropterna sequax Molanna angustata Molannidae spp. indet Mystacides longicornis Paraponyx stagnata Paraponyx statiolata Phryganea bipunctata Psychomia pusilla Sericostoma personatum Tinodes waeneri Lepidostomatid spp. indet Micropterna spp. indet 24 Trich b Ecnomus tenellus Holocentropus picicornis Metalype fragilis Plectrocnemia conspersa Polycentropus flavomaculatus Polycentropus irroratus Polycentropus kingi 25 Tricladia - Triclad Dendrocoelum lacteum Dugesia lugubris Dugesia polychroa Planaria torva Planorbis planorbis Polycelis nigra Polycelis tenuis Table 2 The 25 major groupings of invertebrates used in the DCA analysis presented in Fig 6. In each case the abbreviated group name used to 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 Dugesia polychroa Theodoxus fluviatilis Bithynia tentaculata Pisidium Oligochaeta Glossiphonia complanata Helobdella stagnalis Asellus aquaticus Crangonyx pseudogracillis Gammarus duebeni Niphargus kochianus Heptagenia sulphurea Ephemera danica Caenis luctuosa Caenis horaria Leuctra inermis Chloroperla torrentium Chloroperla tripunctata Esolus parallelepipedus Plectrocnemia conspersa Holocentropus picicornis Limnius volckmari Oulimnius tuberculatus Athripsodes aterrimus Athripsodes cinereus Lepidostoma hirtum Sericostoma personatum Chironomidae 2 2 1 6 1 4 51 16 57 7 5 6 12 85 12 2 11 4 3 2 2 41 1 1 1 1 2 11 1 1 1 1 9 1 2 7 1 2 2 32 Total no. of invertebrates 65 188 156 No. of species 4 23 13 16 10 LC5 LC4 11 17 10A LC3 LC2 LC6 LC1 12 LC7 16 13 14 & 14A 15 LC8 1 2 LC9 1 Sediment coring sampling sites LC1 SPI survey sites 3 4 LOUGH CONN 5 LC11 6 7 8 LC10 Fig 7 Map of Lough Conn showing the locations of sites sampled during sediment coring and SPI studies. 17 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. 18 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. 19 2500 Fecundity 2000 1500 1000 500 0 0 50 100 150 200 250 300 350 Length (mm) L. Mask, 21/11/96 (n=41) L. Eske, 10/11/96 (n=8) Fig 10 Scatterplot illustrating the relationship between fecundity and length of female char from Lough Mask and Lough Eske. 16 14 % frequency 12 10 8 6 4 2 6.2 5.8 5.4 5 4.6 4.2 3.8 3.4 3 2.6 2.2 1.8 1.4 1 0 Egg diameter (mm) L. Eske, 10/11/96 (n=8) L. Mask, 21/11/96 (n=41) Fig 11 Percentage frequency distributions of egg diameters from female char captured on Lough Mask and Lough Eske. 20 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. 21 22 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 openwater 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. 23 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. 24 • 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 waterquality 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 25 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 26 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 27 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. 28 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. 29 30 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. 31 WR/G15, Dublin. 32 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. 33 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) 34 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. JulyAugust 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. 35