Arctic charr (Salvelinus alpinus) in Windermere (Cumbria)

The Arctic charr of the British Isles are all non-migratory and are near their most southernmost range. Windermere is one of the few lowland lakes at southerly latitudes to contain a substantial proportion of Arctic charr. The first recorded mention of charr in Windermere was made around 1540 but it was not till the 17th century that different "sons" of charr were recognized, based on differences in their breeding behaviour. In the 1960's, the presence of two distinct populations, autumn spawners and spring spawners were discovered. In the 1980's it was shown that there were at least four races of charr in Windermere, based on genetic characteristics. Recently, the lake has changed due to inputs of phosphorus from treated sewage released into the lake resulting in eutrophication particularly in the south basin. Since the mid-1980's the numbers of charr caught in the south basin have declined.

Limnological aspects of three man-made lakes in Sri Lanka

An investigation was undertaken to study the physicochemical characteristics, phytoplankton and fish fauna of three major deep lakes on the River Mahaweli: Kotmale, Victoria and Randenigala. These lakes were created mainly for hydroelectric purposes during the period 1984 to 1986. In all three lakes, thermoclines were present during most months of the year, but did not appear to be very stable. They tended to disappear during January - February but were well established in August - November. Fifteen species of blue-green algae were identified as well as 27 desmid species and 25 non-desmid green algae. Melosira granulata and M. undulata were the dominant diatom species. The family Cyprinidae dominated the fish fauna by number of species, but by biomass the exotic cichlids (tilapias) were dominant.

Plant nutrients and major ions in the Little Sea, Studland, Dorset

This short paper records some measurements made on the Little Sea, a shallow, coastal, acidic lake on Studland Heath, Dorset. The lake, formed about 100 years ago by dunes cutting off a sea inlet, has not received any input of agricultural fertilizers or other waste products for at least the last 30 years. It is a Site of Special Scientific Interest (SSSI). Samples of surface water were taken from the northern and southern ends of the lake at 3-monthly intervals, from July 1995 to April 1996. The first samples in July 1995 were taken during a period of drought; rain, sometimes very heavy, came in late September. With the exception of silicate, potassium and phosphate, there were no large changes in plant nutrient concentrations during the year. The concentration of nitrate-nitrogen was very low (close to the limits of analytical detection), but total phosphorus at ca. 30 mu g per litre was similar to concentrations found in some of the Cumbrian eutrophic lakes. The large number of algal species at low cell/colony concentrations suggested that the lake is mesotrophic. Sodium, chloride and magnesium in the lake water were close to the same proportions as those found in sea water. Dry and wet deposition of sea-salts on the lake surface and its catchment area probably is the major source of sodium, magnesium and chloride ions in the lake, and also accounts for about half of the mean potassium and sulphate concentrations.

A GEOPASS-NERC project on diatom deposition and sediment accumulation in Lake Baikal, Siberia

This new project is multidisciplinary, with physical and chemical palaeolimnological aspects mainly the responsibility of Swiss and Russian scientists, and the biological limnology and palaeolimnology components mainly undertaken by the British and Russian groups. The overall project aim is to improve palaeoclimate reconstructions using sedimentary diatoms by promoting better understanding of diatom ecology and sediment-forming processes. The initial work plan is divided into four main parts: To understand diatom phytoplankton ecology more fully, to assess taphonomic changes associated with the transformation of phytoplankton diatom communities into sediment assemblages, to demonstrate sediment core integrity and representativity and to calibrate modern diatom assemblages against contemporary climate records. The preliminary results from the interrelated studies of phytoplankton, sediment traps and sediment cores used in GEOPASS-NERC, demonstrate the complexity of links between the living and fossil systems. Furthermore, the nature of recent sedimentation in Lake Baikal is spatially variable and incompletely known. This poses a major challenge to palaeolimnological interpretation. Turbidite deposits and differential preservation of microfossils, combined with inadequate knowledge of the modern ecology of endemic diatoms, all conspire to obfuscate the sedimentary record of environmental change.

Monitoring and classification of lakes in Finland

In Finland, as in other member countries of the European Union, preparations for implementing the EC Water Framework Directive (WFD) have begun. The article describes the current monitoring and classification strategies for Finnish Lakes.

Monitoring fish populations in Lower Lough Erne, Northern Ireland: applicability of current methods and implications for future monitoring under the EC Water Framework Directive

The proposed EC Water Framework Directive (WFD) will require member states to monitor both biotic and abiotic components of lake environments. With adoption of the WFD some measurement of fish populations will also be required. This paper describes work carried out since 1971, and particularly since 1991, on the status of fish populations in Lower Lough Erne, Northern Ireland, with an emphasis on defining change over time due to human impacts on the lake. This offers a reasonable starting point from which to develop a monitoring programme suitable for the needs of the WFD in this lake. The implications for as yet unmonitored fish populations in lakes are also determined.

Symposium on Llangrose Lake: the ecology and conservation of a large nutrient-rich lake in South Wales

This paper summarises a meeting which discussed the ecology and conservation of Llangorse Lake in South Wales. The meeting was organised by the British Ecological Society (Aquatic Ecology Group), in association with the Countryside Council for Wales (CCW), Brecon Beacon National Park Authority (BBNPA) and Environment Agency Wales. It took place on 22 October 1998.

Some statistical aspects of the long-term gill net monitoring programme for pike Esox lucius in Windermere (English Lake District)

For more than 55 years, data have been collected on the population of pike Esox lucius in Windermere, first by the Freshwater Biological Association (FBA) and, since 1989, by the Institute of Freshwater Ecology (IFE) of the NERC Centre for Ecology and Hydrology. The aim of this article is to explore some methodological and statistical issues associated with the precision of pike gill net catches and catch-per-unit-effort (CPUE) data, further to those examined by Bagenal (1972) and especially in the light of the current deployment within the Windermere long-term sampling programme. Specifically, consideration is given to the precision of catch estimates from gill netting, including the effects of sampling different locations, the effectiveness of sampling for distinguishing between years, and the effects of changing fishing effort.

Heated aquatic microcosms for climate change experiments

Ponds and shallow lakes are likely to be strongly affected by climate change, and by increase in environmental temperature in particular. Hydrological regimes and nutrient cycling may be altered, plant and animal communities may undergo changes in both composition and dynamics, and long-term and difficult to reverse switches between alternative stable equilibria may occur. A thorough understanding of the potential effects of increased temperature on ponds and shallow lakes is desirable because these ecosystems are of immense importance throughout the world as sources of drinking water, and for their amenity and conservation value. This understanding can only come through experimental studies in which the effects of different temperature regimes are compared. This paper reports design details and operating characteristics of a recently constructed experimental facility consisting of 48 aquatic microcosms which mimic the pond and shallow lake environment. Thirty-two of the microcosms can be heated and regulated to simulate climate change scenarios, including those predicted for the UK. The authors also summarise the current and future experimental uses of the microcosms.

Aquaculture in tropical Mexican lakes and dams: achievements and perspectives

Mexico, with highly diverse physiography, geology, soils and climate, is a country with a broad mosaic of aquatic ecosystems within 320 watersheds. This paper presents a brief picture of Mexican fresh waters, the distribution of rainfall and the potential for aquaculture. The main fish species and water bodies, dams and lakes, are highlighted. The country faces problems of surface water shortage which requires better management.

A photographic record of a pre- and post-lake creation event from World War II at Valley, Isle of Anglesey, UK

The article compares a recent aerial photograph of the lowlands of the Isle of Anglesey area with a German surveillance photograph from 1941. The authors aim to infer the environmental changes made to this sand dune and lake system as a direct consequence of constructing the airfield. Part of Tywyn Trewan, the extensive sand dune system, was completely destroyed in order to create runways and the technical and domestic accommodation to house a strategic airfield. As part of the dredging, six new water bodies with a combined surface area of approximately 6 ha were created.

Littoral vegetation of Lake Tohopekaliga: community descriptions prior to a large-scale fisheries habitat-enhancement project

An extreme dry-down and muck-removal project was conducted at Lake Tohopekaliga, Florida, in 2003-2004, to remove dense vegetation from inshore areas and improve habitat degraded by stabilized water levels. Vegetation was monitored from June 2002 to December 2003, to describe the pre-existing communities in terms of composition and distribution along the environmental gradients. Three study areas (Treatment-Selection Sites) were designed to test the efficacy of different treatments in enhancing inshore habitat, and five other study areas (Whole-Lake Monitoring Sites) were designed to monitor the responses of the emergent littoral vegetation as a whole. Five general community types were identified within the study areas by recording aboveground biomasses and stem densities of each species. These communities were distributed along water and soils gradients, with water depth and bulk density explaining most of the variation. The shallowest depths were dominated by a combination of Eleocharis spp., Luziola fluitans, and Panicum repens; while the deeper areas had communities of Nymphaea odorata and Nuphar luteum; Typha spp.; or Paspalidium geminatum and Hydrilla verticillata. Mineralized soils were common in both the shallow and deep-water communities, while the intermediate depths had high percentages of organic material in the soil. These intermediate depths (occurring just above and just below low pool stage) were dominated by Pontederia cordata, the main species targeted by the habitat enhancement project. This emergent community occurred in nearly monocultural bands around the lake (from roughly 60–120 cm in depth at high pool stage) often having more diverse floating mats along the deep-water edge. The organic barrier these mats create is believed to impede access of sport fish to shallow-water spawning areas, while the overall low diversity of the community is evidence of its competitive nature in stabilized waters. With continued monitoring of these study areas long-term effects of the restoration project can be assessed and predictive models may be created to determine the efficacy and legitimacy of such projects in the future.

A study of the problems associated with Dalangdian reservoir, China

There are over 2,300 lakes over 1 km2 in China (total area 80 000 km2). In addition there are approximately 87 000 reservoirs with a storage capacity of 413 billion m3. These form the main supply of drinking water as well as water for industrial and agricultural production and aquaculture. Because of a lack of understanding of the frailty of lake ecosystems and poor environmental awareness, human activities have greatly affected freshwater systems. This article focuses on the problems of one water supply reservoir, Dalangdian Reservoir, and considers options for improving its management. Dalangdian Reservoir is described and occurrence of algal genera given. The authors conclude with remarks on the future of the Dalangdian Reservoir.

The impact of year-to-year changes in the weather on the seasonal dynamics of lakes

Year-to-year changes in the weather have a pronounced effect on the quality of the water abstracted from many reservoirs in the UK. In upland reservoirs, the most common weather-related problem is the appearance of coloured water following dry summers and the re-wetting of peat during the winter (Naden & McDonald 1989; George 2000). In lowland reservoirs, the most serious weather-related issue is the growth of bloom- forming species of algae during warm, calm summers (National Rivers Authority 1989). Both of these problems are likely to get worse as the climate becomes warmer and extreme variations in the weather become more common. In this article, the authors describe some of the ways in which recent changes in the weather have influenced the quality of the water stored in a large reservoir in the south-east of England. The reservoir selected for study is the Queen Elizabeth II (QEII), a bankside reservoir situated in the Thames valley. The quality of water stored in this reservoir is generally very good but summer blooms of algae have become increasingly common in recent years.

New challenges in lake and river monitoring

Freshwater ecosystems are highly dynamic and change on time-scales that range from a few hours to several months. The development of models that simulate these processes is often hampered by the lack of sufficient data to parameterize the processes and validate the models. In this article, I review some of the challenges posed by this lack of information and suggest ways in which they can be met by using automatic monitoring systems. One of these studies is the project tempQsim (EVK1-CT2002-00112) funded by the European Commission. In this project, detailed field and model analyses have been performed at eight catchment study sites in south and south-east Europe. A number of perceptual models for the study sites have been established, and results are being used to improve selected catchment models and provide a more adequate description of pollution dynamics. Results from the extensive field studies and model tests are now being used to derive recommendations for more tailored monitoring concepts in highly dynamic, but ‘data scarce’ environments, such as are frequently found in Mediterranean river basins. The author includes implications of the EU Water Framework Directive on monitoring methods.