Biomanipulation of lake ecosystems: an introduction

SUMMARY 1. This paper is an introduction to a special issue of Freshwater Biology containing selected papers from an international symposium on Food Web Effects of Fish in Lake Ecosystems: Research Progress, Water Quality and Fisheries Management held from 31 May to 3 June 2000 in Rheinsberg, Germany. The primary goal of the workshop was to enlarge the current view of fish-induced effects on lake ecosystems. An additional goal was to promote biomanipulation as a multiple-use tool for managing freshwater ecosystems.
2. The three main topics addressed at the workshop were: (i) mechanisms involved in biomanipulation, (ii) whole-lake case studies and (iii) management aspects in water quality and fisheries.
3. Mortality of Daphnia , nutrient recycling, habitat selection and fish predation are reported as important mechanisms governing food-web effects as a result of biomanipulation.
4. Whole-lake case studies indicate that repeated fish removal can help improve water quality of shallow lakes, but successful biomanipulation of deep, thermally stratifying lakes remains difficult.
5. In many cases, biomanipulation of lakes has proved to provide benefits in addition to improving water quality. As all lake users are potentially affected when biomanipulation is used as a lake management tool, their concerns need to be clearly recognised if biomanipulation is to be successful in practice.     

Remote European mountain lake ecosystems: regionalisation and ecological status

1. A survey of c. 350 remote high altitude and high latitude lakes from 12 different mountain regions across Europe was undertaken to explore ecosystem variability, climate forcing, environmental conditions and pollution threats at a scale not previously attempted.
2. Lakes were sampled for a range of contemporary and sub-fossil organisms including planktonic crustaceans, rotifers, littoral invertebrates, chironomids, diatoms and cladocerans. Survey and cartographic data were used to determine environmental characteristics at each site. Organic pollutants and trace metal concentrations were measured in the lake sediment.
3. A number of separate studies were undertaken which examined the environmental characteristics of the surveyed lakes (climate forcing and chemical composition), distribution of biota relative to local, regional and biogeographical factors and pollution threats (acidification, heavy metals and persistent organic pollutants) to these sensitive ecosystems.
4. There is a strong regional element to the way that environmental factors combine (including climate and pollution threats) and the biota responds in mountain lakes across Europe. From a management perspective it is clear that lake classification and the development of useful typologies and assessments of reference conditions should be undertaken at regional rather than pan-European scales.
5. There are some common features across lake districts related to the timing of industrialisation, but the studies carried out on metals, organic pollutants and nitrate deposition indicate that each lake district has distinct pollution threats. Climate warming already affects most of the lake districts and there are considerable uncertainties as to how this will modify conditions in remote European mountain systems.
6. The lake district concept goes beyond a geographical construct and merits further theoretical and experimental development as an ecological concept.     

The art and science of lake restoration

Science and art encompass understanding, through human hand and mind; both are applied in the form of creation by human hand and mind. Like Janus, the Roman god of doorways and bridges, they are two faces of the same thing. Great art requires great understanding and great understanding is wasted unless it is applied to create meaningful art, whether this is in the form of written works or paintings. These principles apply not least to the restoration of lakes and whole landscapes from the human-induced damage that is the antithesis of significant art and fundamental science. Because they lie at the lowest points of hydrologic basins, lakes reflect the balance of human activities in their catchments. If these activities are carried out well, they contribute greatly to the landscape and to the welfare of the human population. If carried out badly in the sole interests of exploitation of resources, both human and otherwise, they may become problems reflected, for example, in eutrophication, algal blooms and fish kills. Lake restoration involves first an understanding in a reductionist (scientific) way of the processes that drive lake ecosystems, but then of the ultimate reasons that create these proximate problems. Ultimate reasons lie in a much wider sphere of human nature and the organisation of society. Lake restoration, in its most trivial form, may be simply a form of gardening to allay the symptoms of problems and create the illusion of a solution. Lake restoration in its most profound form involves an understanding of cultural significance and the workings of human societies and forms an epitome for the solution of much greater, global problems. Only in this form does it become truly creative. Approval must come from both of the faces of Janus.     

Effects of a massive swarm of ants on ammonium concentrations in a subalpine lake

On two occasions in August 1979, massive aerial swarms of Lasius alienus (Foerster) (Hymenoptera: Formicidae) occurred over Castle Lake, California. Each event resulted in the delivery of millions of ants to the lake surface. Consumption and subsequent excretion by fish, in addition to direct release from ants, produced a brief, but marked increase in water column ammonium levels. Castle Lake phytoplankton are often nitrogen limited and possess a high affinity for ammonium. The events and effects are described and discussed with respect to nutrient limitation in an unproductive ecosystem.     

Micro‐scale structure in the chemistry and biology of a shallow lake

1. Repeat sampling in daytime within a lily (Nuphar lutea) bed and in open water showed distinct heterogeneities in the three‐dimensional distributions of water chemistry and planktonic organisms on centimetre to decimetre scales. 2. Vertical gradients of physico‐chemical variables that did not exist at dawn developed during the day in both sites, as available nutrients were released from the sediments and were consumed towards the surface. 3. Distributions of algal standing crop suggest limitation by both nutrients and grazing. 4. Marked variability in distributions may question the assumptions often made about the homogeneity of plankton and available nutrient distributions in open water and in macrophyte stands of shallow lakes. Although simple sampling regimes for monitoring of water quality may be adequate for many purposes, they miss a fine structure in the water that is inherently interesting in understanding the underlying processes of plankton function.     

A survey of the physiochemical characteristics and the zooplankton communities in an ephemeral karst lake

Chaney Lake State Nature Preserve is a 68 ha ephemeral karst lake in southern Warren County, Kentucky (USA). Chaney typically fills with water in the winter as groundwater levels rise and then slowly dries via evaporation and drainage back into the subsurface over the summer months. The lake contains several habitat types, identifiable by the dominant plant communities, which may have different physiochemical characteristics. Since these differences may result in an increase in habitat heterogeneity and niches available for colonization by resident zooplankton, a suite of physiochemical and nutrient parameters was monitored in these habitats from January 1997–August 1998. Zooplankton densities and community structure were assessed from January 1997 through May 1998. There were few significant differences among the habitats but there were significantly higher concentrations of NO_x and higher specific conductivities associated with some of the groundwater inlet areas in the lake. Zooplankton were abundant, but there were no differences in zooplankton densities among the areas sampled. These results suggest that the physiochemical properties in the lake are heavily influenced by the groundwater inputs and that land use patterns around Chaney Lake may be having an impact on the preserve.     

Relationship of trophic and chemical conditions to photobleaching of dissolved organic matter in lake ecosystems

Dissolved organic matter (DOM) is a major light-absorbing substance, responsible for much of the color in water bodies. When sunlight energy is absorbed by DOM, some color can be lost by the process of photobleaching. We measured rates of DOM photobleaching in thirty lakes that varied greatly in color, trophic status and ionic composition. Loss of color (measured as absorbance at 440 nm and expressed as absorption coefficients) was a first order function of sunlight dose, and rates were nearly identical for 0.2m- and GF/F-filtered samples suggesting that the process was predominantly abiotic. Photobleaching rates were rapid (color loss of 1–19% d^–1) and varied about seven-fold among lakes. Our method under-estimated the actual rate by 15–20% based on comparisons between the glass bottles we used in the survey and quartz containers. The large variation in photobleaching rates was examined in relation to lake trophy and chemical conditions. The best predictor of this variability was acid-neutralizing capacity (ANC) (r ²=0.94;p<0.001) such that photobleaching was most rapid in the most alkaline lakes. The relationship between ANC and photobleaching suggests that differences in ionic conditions among lakes may influence the solubility and configuration of humic and fulvic acids and hence their susceptibility to photobleaching.     

Community composition and activity of prokaryotes associated to detrital particles in two contrasting lake ecosystems

The composition, distribution and extracellular enzyme activities of bacteria attached to small (2-50 microm in size) transparent exopolymer and Coomassie-stained proteinaceous particles (TEP and CSP) were examined in two lakes of different trophic status located in the Massif Central of France. TEP concentrations (10(4)-10(6) particle per L) were significantly higher in the more productive lake and were significantly related to chlorophyll a concentrations. The majority of TEP and CSP were colonized by bacteria that constituted 2.6% and 7.4% of the total 4',6-diamidino-2-phenylindole-stained bacteria in lakes Pavin and Aydat, respectively. In both lakes, the composition of particle-associated bacteria was different from that of free-living bacteria, the Betaproteobacteria and Bacteroidetes (i.e. former Cytophaga-Flavobacteria group) being the dominant groups on particles. We also found that 2-5 microm TEP were more colonized than 2-5 microm CSP in the two lakes, and that TEP colonization was higher in the less productive lake. Measurements of Leucine aminopeptidase and alpha-glucosidase activities in fractionated lake water (0.2-1.2, 1.2-5 and >5 microm fractions) indicated that proteolytic activity was always higher and that particle-associated bacteria have higher enzymatic activities than free-living bacteria. The glycolytic activities in the 1.2-5 and >5 microm fractions were related to the abundance of TEP. We conclude that small freshwater detrital organic particles constitute microhabitats with high bacterial activities in pelagic environments and, undoubtedly, present significant ecological implications for the prokaryotic community structure and function in aquatic ecosystems.     

Restoration and recovery of shallow eutrophic lake ecosystems in The Netherlands: epilogue

During the symposium Restoration and recovery of shallow lake ecosystems in The Netherlands studies on restoration of eutrophic lakes were addressed and discussed. Many Dutch shallow lakes have received high external loadings of phosphorus through supply water that is influenced by the River Rhine and loadings in The Netherlands. Two important Action Plans (the Rhine Action Plan, the North Sea Action Plan) are now in operation to reduce nutrient emissions. The targets set are not likely to be fully reached, so that supplementary reduction of phosphorus supplied to inland fresh waters will be required. In several shallow lakes such a reduction has been achieved recently, but without leading to discernible recovery. The main causes of delay are phosphorus storage and its subsequent release from sediments and foodweb; however, the remaining extraneous phosphorus supply is often still too high. Supplementary actions are, therefore, called for. A further reduction of phosphorus inputs is suggested, besides supplementary measures proposed, viz. dredging, flushing, biomanipulation, chemomanipulation. Restoration to the past situation via upwelling groundwater appeares to be feasible in some cases. There is a common consensus that each lake behaves differently depending to its morphology, hydrology and history of eutrophication. Therefore each lake has to be studied before restoration measures can be applied. Besides, the ecosystem should not only be studied as a separate entity, but as a part of systems of a higher integration level.     

The bioenergetic basis for the decrease in metabolic diversity at increasing salt concentrations: implications for the functioning of salt lake ecosystems

Examination of the microbial diversity in hypersaline lakes of increasing salt concentrations shows that certain types of dissimilatory metabolism do not occur at the highest salinities. Examples are methanogenesis from hydrogen and carbon dioxide or from acetate, dissimilatory sulfate reduction with oxidation of acetate, and autotrophic nitrification. The observations can be explained on the basis of the energetic cost of haloadaptation used by the different metabolic groups and the free-energy change associated with the dissimilatory reactions. All halophilic microorganisms spend large amounts of energy to maintain steep gradients of Na⁺ and K⁺concentrations across their cytoplasmic membrane. Most Bacteria and also the methanogenic Archaea produce high intracellular concentrations of organic osmotic solutes at a high energetic cost. The halophilic aerobic Archaea (order Halobacteriales) and the halophilic fermentative Bacteria (order Halanaerobiales) use KCl as the main intracellular solute. This strategy, while requiring far-reaching adaptations of the intracellular machinery, is energetically more favorable than production of organic compatible solutes. By combining information on the amount of energy available to each physiological group and the strategy used to cope with salt stress, a coherent model emerges that provides explanations for the upper salinity limit at which the different microbial conversions occur in hypersaline lakes.     

A 2-year experimental study on nutrient and predator influences on food web constituents in a shallow lake of north-west Spain

1. A 2‐year study was carried out on the roles of nutrients and fish in determining the plankton communities of a shallow lake in north‐west Spain. Outcomes were different each year depending on the initial conditions, especially of macrophyte biomass. In 1998 estimated initial ‘per cent water volume inhabited’ (PVI) by submerged macrophytes was about 35%. Phytoplankton biomass estimated as chlorophyll a was strongly controlled by fish, whereas effects of nutrient enrichment were not significant. In 1999 estimated PVI was 80%, no fish effect was observed on phytoplankton biomass, but nutrients had significant effects. Water temperatures were higher in 1998 than in 1999. 2. In the 1998 experiment, cladoceran populations were controlled by fish and cyanobacteria were the dominant phytoplankton group. There were no differences between effects of low (4 g fresh mass m^?2) and high (20 g fresh mass m^?2) fish density on total zooplankton biomass, but zooplankton biomass was higher in the absence of fish. With the high plant density in 1999, fish failed to control any group of the zooplankton community. 3. Total biovolume of phytoplankton strongly decreased with increased nutrient concentrations in 1998, although chlorophyll a concentrations did not significantly change. At higher nutrient concentrations, flagellate algae became more abundant with likely growth rates that could have overcompensated cladoceran feeding rates. This change in phytoplankton community composition may have been because of increases in the DIN : SRP ratio. Both chlorophyll a concentration and total phytoplankton biovolume increased significantly with nutrients in the 1999 experiment. 4. A strong decline of submerged macrophytes was observed in both years as nutrients increased, resulting in shading by periphyton. This shading effect could account for the plant decline despite lower water turbidity at the very high nutrient levels in 1998.     

Microbial diversity and complexity in hypersaline environments: A preliminary assessment

The microbial communities in solar salterns and a soda lake have been characterized using two techniques: BIOLOG, to estimate the metabolic potential, and amplicon length heterogeneity analysis, to estimate the molecular diversity of these communities. Both techniques demonstrated that the halophilic Bacteria and halophilic Archaea populations in the Eilat, Israel saltern are dynamic communities with extensive metabolic potentials and changing community structures. Halophilic Bacteria were detected in Mono Lake and the lower salinity ponds at the Shark Bay saltern in Western Australia, except when the crystallizer samples were stressed by exposure to Acid Green Dye #9899. At Shark Bay, halophilic Archaea were found only in the crystallizer samples. These data confirm both the metabolic diversity and the phylogenetic complexity of the microbial communities and assert the need to develop more versatile media for the cultivation of the diversity of bacteria in hypersaline environments. Journal of Industrial Microbiology & Biotechnology (2002) 28, 48–55 DOI: 10.1038/sj/jim/7000175 Received 20 May 2001/ Accepted in revised form 15 June 2001     

Short-term variations in the abundance and cell volume of bacterioplankton in an artificial tropical lake

Circadian and spatial fluctuations in bacterioplankton abundance and cell volume were examined, for the first time, in the Municipal Lake located in the down town area of Yaoundé (Capital of Cameroon, Central Africa, ca 3° 52′ N, 11° 31′ E). Bacterial cell volumes (range, 0.05 to 0.2 μm3) were consistent with those reported for other aquatic systems while bacterial densities (0.8 to 2 × 108 cells ml-1) were among the highest values reported in pelagic systems. These variables and chlorophyll a and dissolved oxygen concentrations within a single depth-zone varied from 13 to 61%, while water temperature fluctuated only from 2 to 6%. Spatial fluctuations of physical-chemical and biological variables were generally higher during the day-time than during the night-time. A significant diel variation was provided for bacterial cell volume in the surface waters where synchronized cell division was occurring during the night. The measured bacterial abundances in this study were 4 to 17 fold higher than values known from other lakes of similar trophic status, and both cell abundance and volume were not correlated with chlorophyll. We conclude that this was due to the dependence of bacterial populations to different sources of allochthonous substrates, including untreated sewage from the major influents of the lake, resuspension of benthic material, and substrate releasing from macrophytes which are prevalent in the littoral zone of the lake. This revised version was published online in September 2006 with corrections to the Cover Date.     

Primate communities: Their structure and role in tropical ecosystems

The structure of primate communities living in a number of undisturbed areas is described and compared. Species richness is highest in tropical rain forests of Africa and South America, where up to 14 different species can share the same habitat. The number of sympatric primates in woodlands and savannas is always much lower. Some striking differences in community structure may be observed between communities living in apparently similar habitats. Three major factors may be held responsible for such discrepancies: history and paleoecology, present spatial heterogeneity of the vegetation, and competition with other taxonomic groups. The role of primates in the functioning of forest ecosystems is discussed. Though their trophic impact may be important, the role they play in seed dispersal appears to be more significant; they contribute greatly to homeostasis, as well as to regeneration, of the rain forests. A number of ecological traits are particularly developed among primates and may have contributed to the rapid evolutionary success of the order. Their predominantly vegetarian diet allows them to build up higher population densities than sympatric carnivorous mammals;their arborealism permits them to make use of all edible plant material available in a tridimensional environment; the opportunistic tendencies of some cebids, cercopithecids, and pongids enable them to take advantage of a variety of habitats and situations; and finally, an extended socialization period and a long life-span, allowing them to develop social traditions, give to many of them a further possibility to adapt quickly to novel situations. This paper is a revised version of the third Osman Hill Memorial Lecture delivered at the joint meeting of the Primate Society of Great Britain and the Association for the Study of Animal Behaviour, held in London on 2/3 December 1982.     

Effects of season and body-size on the distribution and diet of the Iberian chub Leuciscus pyrenaicus in a lowland catchment

Seasonal and ontogenetic variations in space and food use by Leuciscus pyrenaicus were analysed in a Portuguese lowland catchment. Large fish occurred mostly in deep permanent-flowing sites whereas small fish occurred mostly in the shallowest intermittent-flowing site. No seasonal or size-related changes in feeding intensity were found, but the diet changed both across seasons and throughout ontogeny. The diet was dominated by aquatic prey over all seasons, but during winter and summer more plant material and terrestrial prey, respectively, were eaten. Throughout ontogeny fish shifted from soft-bodied to hard-shelled prey and decreased animal prey breadth. Mean prey size increased with fish size but the prey size spectrum was more variable for medium-sized fish than for either small or large fish. It is suggested that: (i) large fish avoid shallow drying areas owing to the risk of mortality, either by thermal and respiratory stresses or increased predation by mammals and birds; (ii) seasonal changes in diet are a response to differences in prey availability; and (iii) morphological constraints, prey handling costs and habitat partitioning are responsible for size-related changes in diet.     

Monthly mass balances for compartments of the Loosdrecht Lakes system: Approach and preliminary results

Water quality modelling in the framework of the Water Quality Research Loosdrecht Lakes requires mass balances covering periods of one month or less for at least three of the lake compartments of the Loosdrecht Lakes system: the Loosdrecht Lakes, L. Vuntus and L. Breukeleveen. The hydrological system of the Loosdrecht area underlying these mass balances is described. Data available on the various mass balance items are surveyed, as well as the methods considered to calculate those items that do not lend themselves to direct measurement.The system will be modelled by means of a series of interdependent spreadsheets. Calibration of this model to the 1983–1986 data set should render it suitable to calculate the mass balances retrospectively,i.e. in the period 1975–1982. The model in its present form cannot be used to predict mass balances.Masses of Cl, P and N stored in the three main lake compartments of interest at consecutive sampling dates in 1983 and 1984 are graphically presented and compared with roughly estimated biannual balances of the same substances for the aggregate of the three lake compartments.Not unexpectedly, the distribution within the system of the conservative substance Cl is a function of the differences between the lake compartments in mixing ratios of high-Cl to low-Cl inputs.The amounts of the nutrients P and N stored in the lake water follow a rather erratic course. Though it is possible to idealize this to a seasonal cycle, the two-year period dealt with by this study is too short to identify such a cycle with certainty. From the large residual terms of the biannual nutrient balances it is obvious that the not directly quantifiable processes like sedimentation, release from the sediment and (presumably) denitrification that are lumped into those residual terms, are of major importance to the amounts of nutrients in the lake water.     

Vernal microstratification patterns in a meromictic saline lake: their causes and biological significance

Periodic high spring runoff, in addition to lake surface snow and ice melt, is shown to be a major cause of sharp secondary chemocline formation in a small (20 ha) lake arid and south-central British Columbia. Initially detected in 1982 at about 1 m and enhanced by high inflow of low salinity meltwater in spring 1983, the secondary chemocline gradually deepened and broke down over four subsequent years. Associated microstratification layers (major changes within a few cm of depth), exhibited very high temperatures (> 30 °C), and very high dissolved oxygen (> 200% saturation) as well as very low (close to 0% saturation) levels. Oxygen supersaturation resulted from photosynthetic production at the microstratification boundaries. In the springs of 1982 and 1983, formation of an anoxic layer between regions of high oxygen concentration, separated the phytoplankton and zooplankton communities into two layers above the primary chemocline. The several year persistence of the secondary chemoclines and associated interface processes (concentration of particulate organic matter, bacterial decomposition, nutrient regeneration, phytoplanktonic production) attest to their functional importance in this meromictic lake.     

Floodplain lake fish assemblages in the Amazon River: directions in conservation biology

The Neotropical region is renowned for its high biodiversity, and the Amazon River basin contains the highest number of fish species of any river system in the world. In recent years, habitat fragmentation and exploitation of biotic resources have threatened biological integrity and provoked to need for sustainable management and conservation of the Amazon River system. We studied 36 floodplain lakes along 2000 km of the Amazon River. The fish assemblages associated with flood forests are moderately diverse, with low species dominance and reduced populations. To detect nestedness of fish assemblage composition in floodplain lakes, a nested subset analysis was performed on species presence–absence. The incidence matrix (species × lakes) was maximally packed using the Nestedness Temperature Calculator software. The results of ranking lakes and species allow us to establish targets for conservation. Such strategy for sustainable management should be focused on maintaining the Amazonian biodiversity.     

Dominant diatoms in the interglacial lake sediments of the Middle Pleistocene in Central and Eastern Poland

Diatom studies carried out in Central and Eastern Poland have shown a diversified composition and considerable changes of relative frequency of dominant diatoms in profiles of lake sediments of the Mazovian and Ferdynandovian interglacials. Cyclotella spp. are dominant in a large part of the sediment profiles at Adamówka, awki-7 and Wola Grzymalina-59 and, at Krpiec and Podlodów, Stephanodiscus is also common while at Biaa Podlaska and Falcice, Aulacoseira is most abundant. Cyclotella comta var. lichvinensis and C. vorticosa are the typical diatoms in the Mazovian Interglacial. In the sediments representing the Ferdynandovian Interglacial, the characteristic diatoms are Cyclotella cf. reczickiae and the Stephanodiscus rotula/niagarae complex.