Chemical and Microbiological Processes as Regulators of the Exchange of Substances between Sediments and Water in Shallow Eutrophic Lakes

It is generally believed that excessive P release from lake sediments, i. e. internal P load, is only a problem in deep lakes with stagnant anaerobic bottom waters. However, substantial amounts of P can also be released from sediments in shallow, well-mixed lakes. The dynamics and magnitude of P release from sediments in these types of lakes are affected primarily by physical factors, such as seasonal variations in water temperature and year-to-year differences in water renewal. These factors, in turn, induce chemical and microbiological processes which regulate the exchange of substances between sediments and water. The fractional distribution of sedimentary P and the chelating capacity of the water are also important factors that can provide insights to the processes involved and their quantitative impact on the P status in shallow, eutrophic lakes.     

Assessing factors underlying variation of CO2 emissions in boreal lakes vs. reservoirs

Reservoirs and lakes were compared to test the hypothesis that they are similar with respect to factors driving the variation in CO(2) emissions to the atmosphere. Understanding this variation is necessary for the assessment of the contribution of these freshwater ecosystems to the global carbon cycle. This study, in contrast to previous ones, included analyses of the relationships between CO(2) emissions and microbial communities. Pooled data (lakes and reservoirs) showed that variations in CO(2) emissions were strongly related to variations in temperature, dissolved organic matter (DOM) quality, and bacterial production (BP). Results also showed that lakes were characterized by higher water temperature, lower DOM quality, larger size of Daphnia, and enriched δ(13) C zooplankton compared to reservoirs. Moreover, interactions within plankton communities and relationships between CO(2) emissions and zooplankton δ(13) C signatures differed in lakes vs. reservoirs, indicating among-system type differences in food web structure and carbon cycling. As a result of these ecosystem-type characteristics, CO(2) emission variation was mainly explained by temperature and BP in lakes, and by DOM quality and the ratio of phytoplankton biomass to microheterotroph biomass in reservoirs. These results showed that differences in temperature and DOM quality between lakes and reservoirs translate into differences in microbial interactions and ultimately in the importance of factors driving CO(2) emissions to the atmosphere. They indicated that considering microbial communities and environmental variables such as temperature and DOM quality can help improve our understanding of the variation in CO(2) emissions from freshwater ecosystems.     

The nature of fish communities: A factor influencing the fishery potential and yields of tropical lakes and reservoirs

The discrepancy between high primary production and poor fish yields in some tropical reservoirs, especially in Souht East Asia, is apparently due to the fact that not all available trophic levels are utilized. Data analysis has shown that this is due to the riverline origin of fish communities which are not well adapted to lacustrine habitats in such lakes and reservoirs. These fishes are able to inhabit only a relatively narrow belt of the shallow inshore area. It has been shown that fish are rare in the deep water and pelagial area of geologically young lakes and reservoirs. Although most riverine fish are also able to inhabit the lacustrine habitat, only a few are preadapted to take advantage of deep or open water environments. In the tropics, Cichlidae and freshwater Clupeidae thrive in lakes and reservoirs. It is apparent that within these families suitable species can be chosen as potential candidates for introduction into young lakes and reservoirs. However, any fish introductions must be scientifically evaluated for desirability. Data from other lakes in the world have indicated that the present theory can be expanded to other than tropical lakes.     

Partitioning the influence of hydrodynamics-induced physical variables and nutrients on phytoplankton assemblages in a shallow tropical reservoir (Koka,Ethiopia)

Limnology - Ecological processes, population dynamics and species interactions in shallow lakes and reservoirs are affected by seasonal and inter-annual fluctuations in rainfall and runoff. The...     

Invertebrates in small shallow lakes and ponds: a new sampling method to study the influence of environmental factors on their communities

Aquatic Ecology - Small shallow lakes (SSL) are reservoirs of biodiversity and provide numerous ecosystem services. Therefore, tools to easily and rapidly assess the biological integrity and...     

Assessment of ecological risk in change of content of essential poluyunsaturated fatty acids in plankton of lakes during global warming

The ecological risk of changes in the content of essential polyunsaturated fatty acids (PUFAs) in plankton of lakes due to global warming is assessed. The analyzed hazards are temperature, dissolved phosphorus and nitrogen, and the phyto- and zooplankton structure. The main risks are related not only to the temperature increase, but indirect effects of warming. The critical link in PUFA risk assessment is the phytoplankton structure due to the particularly favorable growth conditions for cyanobacteria in nutrient rich waters in shallow lakes and reservoirs.     

Pico- and Nanoplankton in Aquatic Ecosystems in the Valley of the Lakes and Great Lakes Depression (Mongolia)

The abundance and biomass of bacterioplankton, phototrophic picoplankton, and heterotrophic nanoflagellates has been determined in lakes, rivers, and reservoirs located in the Valley of the Lakes and Great Lakes Depression (Mongolia). The species richness of the heterotrophic flagellates and their consumption of bacteria are estimated. Pico- and nanoplankton are the most abundant in shallow mineral lakes Orog and Tatsyn and in the freshwater Durgun Reservoir. Heterotrophic nanoflagellates consume 26–92% (on average 66%) of the daily bacterioplankton production. Thus, flagellates are important in the transfer of bacterial carbon to the higher levels of planktonic trophic webs. A total of 30 species and their forms of heterotrophic flagellates from 14 large taxa are identified. The highest species diversity of these protists are found in the Durgun and Taishyr reservoirs.     

Interannual and between-site variability in the occurrence of clear water phases in two shallow Mediterranean lakes

It is widely accepted that clear water phases constitute a regular stage in the seasonal succession of plankton in dimictic lakes and reservoirs (i.e. PEG Model). The occurrence of such a phenomenon in Mediterranean shallow lakes is characterised by a marked interannual variability, which makes it difficult to establish reliable predictions on the dynamics and functioning of plankton in these ecosystems. In the present paper we analyse the factors influencing the occurrence of the clear water phases in the two shallow lakes of the Albufera of Adra, a coastal wetland region of south-eastern Spain: Lake Honda and Lake Nueva. Despite their geographical proximity, both lakes depicted large hydrological and limnological differences. Lake Honda is an epigenic and recharge lake that is strongly influenced by the hydrological conditions in its watershed, while Lake Nueva can be classified as a hypogenic and discharge lake and, as such, is less affected by the hydrological regime. In contrast, the morphometry, exposure and fetch of Lake Nueva make this ecosystem especially sensitive to wind forcing. Clear water phases in these shallow lakes were linked with periods of low thermal stability and the dominance of small-edible algae in the phytoplankton community, both of which allowed a Daphnia magna population to grow up and induce the algae collapse by grazing. In Lake Honda, those conditions were met during the spring of 2002 under the influence of intense rainfall-events, while in Lake Nueva the clear water phase was induced in the spring of 2003 by the occurrence of strong and frequent wind events. In both lakes, a relatively high water column thermal stability and the abundance of cyanobacteria early in the spring prevented the development of the Daphnia magna population and the occurrence of the clear water phase.     

Relationship between epipelon,epiphyton and phytoplankton in two limnological phases in a shallow tropical reservoir with high Nymphaea coverage

Macrophytes and phytoplankton are recognized as having roles in determining alternative stable states in shallow lakes and reservoirs, while the role of periphyton has been poorly investigated. Temporal and spatial variation of phytoplankton, epipelon and epiphyton was examined in a shallow reservoir with high abundance of aquatic macrophytes. The relationships between algae communities and abiotic factors, macrophyte coverage and zooplankton density were also analyzed. Monthly sampling was performed in three zones of the depth gradient of the reservoir. Two phases of algal dominance were found: a phytoplankton phase and epipelon phase. The phase of phytoplankton dominance was characterized by high macrophyte coverage. Rotifera was the dominant zooplankton group in all the zones. Flagellate algae were dominant in phytoplankton, epipelon and epiphyton. Macrophyte coverage was found to be a predictor for algal biomass. Changes in biomass and species composition were associated with macrophyte cover variation, mainly the Nymphaea. In addition to the abiotic factors, the macrophyte coverage was a determining factor for changes to the algal community, contributing to the alternation between dominance phases of phytoplankton and epipelon. The macrophyte–phytoplankton–periphyton relationship needs to be further known in shallow reservoirs, especially the role of epipelon as an alternate stable state.

     

State of the art in the functioning of shallow Mediterranean lakes: workshop conclusions

Studies on shallow lakes from the north temperate zone show that they alternate between clear and turbid water states in response to control factors. However, the ecology of semi-arid to arid shallow Mediterranean lakes is less explored. Hydrological effects (e.g. water level fluctuations, water residence time) on major ions and nutrient dynamics and processes, and ecology of submerged macrophytes appear to have a crucial role for food webs in shallow Mediterranean lakes. Nutrient control may be of greater priority in eutrophicated warm shallow lakes than in similar lakes at higher latitudes. This will be relevant for the implementation of the European Water Framework Directive, and conservation and management of these ecosystems. Strong trophic cascading effects of fish resulting from dominance of omnivorous and benthivorous fish species, whose diversity is usually high, together with frequent spawning and absence of efficient piscivores, seem to be the reason for the lack of large-bodied grazers that could control phytoplankton. However, such effects may vary within the region depending on fish distribution and community. These factors need elaboration in order to allow shallow lake ecologists and managers to develop better restoration strategies for eutrophicated shallow Mediterranean lakes. Consequently, modifications for the implementation of the European Water Framework Directive for determining ecological status in shallow Mediterranean lakes appear to be necessary. Furthermore, the implications of climate warming may be even more challenging than in high latitude lakes since shallow lakes in the Mediterranean region are among the most sensitive to extreme climate changes. There is an urgent need for data on the ecology of shallow lakes in the region. An appeal is made for international cooperation, development of large-scale research and information exchange to facilitate this and a web-based discussion list has been implemented.     

Dominant species, functional assemblages and frequency of equilibrium phases in late summer phytoplankton assemblages in Hungarian small shallow lakes

Late summer phytoplankton associations were studied qualitatively and quantitatively in 80 Hungarian lakes altogether (mostly shallow salt lakes, reservoirs, oxbows, gravel pit lakes). Equilibrium phases sensu Sommer et al. (1993) were found only in 17 lakes. Most of them were under some kind (high salt content or very low level of nutrients) of stress factor. It is concluded that environmental stress forces phytoplankton communities towards equilibrium. No relationship between occurrence of equilibria and trophic state was found. Species number of non-equilibrated lakes was almost three times as high as those in equilibrium. Of the 31 recently described (Reynolds et al., 2002) phytoplankton assemblages most of those were recognized that are likely to occur in shallow lakes. Separation of a functional group W _S from W2 for Synura dominated lakes is suggested. It seemed also necessary to raise a group (Y _Ph) for lakes dominated by Phacotus. Sorting of Dinophyta species into different already described functional groups is desirable.     

The influence of geographic and morphometric factors on the distribution of water bird species in small high altitude tropical man made reservoirs,Central Rift Valley,Kenya

Variability in waterfowl characteristics among eight high altitude (2040–2640 m) small shallow (0.065–0.249 km²; 0.9–3.1 m) reservoirs in the escarpment zone along the central rift valley in Kenya between Naivasha and Nakuru towns were studied between 1998 and 2000. The aim of the study was to establish whether the geographic status of small reservoirs in terms of altitude and surface gradient can affect the characteristics of their birdlife in terms of bird counts and species numbers. The study also aimed at establishing whether reservoir bird counts and species number can be predicted by reservoir morphometric factors especially water depth, surface area, length of shoreline and area‐shoreline ratio. The other aim was to determine the influence of local environment especially distance from the nearest natural lakes, and house density on the birdlife. The findings showed that geographic location of the reservoirs in terms of altitude and landscape had a strong influence on birdlife whereby reservoirs in higher altitude and flat plateau landscape were found to support higher bird species and counts. Larger and deeper reservoirs were richer in water bird species but small and shallow reservoirs were superior in terms of both bird species and counts. Reservoirs with more coarse, irregular and highly erratic shorelines had higher species number than those with smooth and well‐rounded shorelines. The reservoir birdlife was found to be influenced by the number of farm houses near the waterbodies and also the distance from the nearby rift valley lakes. The results showed that both geographic and morphometric considerations are necessary in the establishment of new reservoirs especially for utilization in birdlife conservation and ecotourism.     

Physical and chemical aspects of Chew Valley and Blagdon Lakes, two eutrophic reservoirs in North Somerset, England

Chew Valley and Blagdon Lakes are two shallow, hard-water, lowland eutrophic reservoirs, situated near Bristol in the south-west of England. Chew Lake is more turbid and richer in plankton but poorer in macrophytes than Blagdon, and is more exposed to wind action. Both lakes show evidence of transient stratification in the summer coupled to deoxygenation of the bottom water, which has led to release of nutrients from the sediments. Severe algal blooms in Chew Lake in 1968 and the consequent filtration difficulties led to the establishment of a collaborative research programme between the University of Bristol and the Bristol Waterworks Company, to define the present biological status of the lakes, and to predict their possible future development. The work covers a wide range of measurements and observations on the limnological conditions of the lakes, which form an elegantly contrasted pair, and this paper describes their general physical and chemical features.     

Differences in the substrate spectrum of extracellular enzymes in shallow lakes of differing trophic status

Organic matter fluxes and food web interactions in lakes depend on the abilities of heterotrophic microbial communities to access and degrade organic matter, a process that begins with extracellular hydrolysis of high molecular weight substrates. In order to determine whether patterns of enzymatic hydrolysis vary among shallow lakes of different trophic status, we investigated the hydrolysis of six specific organic macromolecules (polysaccharides) in the spring and late summer in four adjacent shallow lakes of eutrophic, oligotrophic, and dystrophic status in coastal North Carolina, USA. The spectrum of enzyme activities detected differed strongly between lakes, with all six polysaccharides hydrolyzed in West Mattamuskeet in May, while only two substrates were hydrolyzed in Lake Phelps in August/September. Differences in the spectrum of enzyme activities, and therefore the capabilities of heterotrophic microbial communities, were likely driven by variations among lakes in primary productivity patterns, sediment–water interactions, and/or water chemistry. Our data represent a first step towards a better understanding of carbon substrate availability and differences in carbon cycling pathways in shallow lakes of different trophic status.     

Distribution and diversity of diatom assemblages in surficial sediments of shallow lakes in Wapusk National Park (Manitoba,Canada) region of the Hudson Bay Lowlands

The hydrology of shallow lakes (and ponds) located in the western Hudson Bay Lowlands (HBL) is sensitive to climate warming and associated permafrost thaw. However, their biological characteristics are poorly known, which hampers effective aquatic ecosystem monitoring. Located in northern Manitoba along the southwestern coast of Hudson Bay, Wapusk National Park (WNP) encompasses numerous shallow lakes representative of the subarctic zone. We analyzed the distribution and diversity of diatom (microscopic algae; class Bacillariophyceae) assemblages in surficial sediments of 33 lakes located in three different ecozones spanning a vegetation gradient, from NE to SW: the Coastal Fen (CF), the Interior Peat Plateau (IPP), and the Boreal Spruce Forest (BSF). We found significant differences (P < 0.05) in diatom community composition between CF and IPP lakes, and CF and BSF lakes, but not between IPP and BSF lakes. These results are consistent with water chemistry measurements, which indicated distinct limnological conditions for CF lakes. Diatom communities in CF lakes were generally dominated by alkaliphilous taxa typical of waters with medium to high conductivity, such as Nitzschia denticula. In contrast, several IPP and BSF lakes were dominated by acidophilous and circumneutral diatom taxa with preference for low conductivity (e.g., Tabellaria flocculosa, Eunotia mucophila, E. necompacta var. vixcompacta). This exploratory survey provides a first detailed inventory of the diatom assemblages in the WNP region needed for monitoring programs to detect changes in shallow lake ecosystems and ecozonal shifts in response to climate variations.     

Distribution of zooplankton community in Mediterranean-climate lakes

The sometimes sharp thermal variations and irregular precipitations and force concentrated over short periods characterize the Mediterranean climate. The structure of the zooplanktonic settlement was analyzed during one year in three Algerian reservoirs (lakes) with different geographical and climatic situation, in relation to abiotic factors (temperature, dissolved oxygen, pH, suspended matter, carbonates, nitrogenized and phosphorated nutritive salts). A canonical correspondence analysis was used to estimate the influence of the abiotic factors on the temporal distribution.The studied lakes are located, on the one hand, in northern Algeria, in a sub-humid area (Lake Boukourdane) and, on the other hand, in the South of the country, in the arid region (Foum El Ghorza and Djorf Torba). Analysis of the environmental parameters indicates that there is a seasonal variation in the three reservoirs. In Lake Foum El Ghorza, the temperature and hydrology variations, linked with the arid climate, affects the concentration of dissolved oxygen, which strongly decreases (1.5 mg/l), involving a pH reduction; suspended matters are sometimes high, coming from the stripped catchment area, causing a turbidity in this not very deep lake. The study of the distribution of the species allowed us to highlight a seasonal temporal variation. Lake Boukourdane, in the sub-humid zone, has an increased specific richness (SR=13). The various species evolve in alternation during the annual cycle. The representative species of this lake is Copidodiaptomus numidicus, characteristic of the rainy and endemic zone of the western Mediterranean; it is dominant (67%) in the spring. The Stenothermal species Diaphanosoma brachyurum, endemic of hot waters, is common to the two lakes; it evolves particularly in the summer (51.3%) at Boukourdane, whereas it is perennial and dominant (55%) in the spring at Djorf Torba. The specific richness is lower in Djorf Torba (SR=7) and in Foum El Ghorza (SR=6). The species collected in these two lakes are common and cosmopolitan, but they are adapted to the extreme conditions of the arid climate. Nevertheless, the species evolving in Lake Foum El Ghorza have undergone a significant decline, which has reduced the number of species and their density in the summer-autumn period. Thus, we can say that in the studied lakes, the hydrological factors and the temperature related to the Mediterranean climate would be two of the principal causes of the temporal distribution of the species. To cite this article: M. Cherbi et al., C. R. Biologies 331 (2008).     

Food-web studies in shallow eutrophic lakes by the Netherlands Institute of Ecology: Main results,knowledge gaps and new perspectives

For more than 20 years scientists of the ‘Food-chain studies’ Group of the former Limnological Institute have been studying interactions within the pelagic food web. Purpose of research was to explain the structure and dynamics of the zooplankton and fish communities in lakes and reservoirs in relation to biotic and abiotic environmental factors. A so-called multi-species approach was used, in which all common and abundant species within a specific ecosystem were studied on the individual and population level with the same degree of detail. The recent results and the scientific approach used are evaluated and the main gaps in knowledge about food-web dynamics in shallow eutrophic lakes are identified and discussed. It is concluded that instead of the purely functional approach used so far, future studies should also include evolutionary aspects which determine the success of an organism in a given environment and that more attention should be paid to central questions in ‘community ecology’. This paper is based on a lecture given by the first author for the Netherlands Society of Aquatic Ecology on May 12th, 1992, in Amsterdam, The Netherlands.     

Long-term phytoplankton changes in a shallow hypertrophic lake,Albufera of Valencia (Spain)

A long-term phytoplankton study was carried out in the Albufera of Valencia, a shallow hypertrophic lake (surface area 21 km², mean depth 1 m, total inorganic nitrogen load 155 g m^-2 y^-1, total inorganic phosphate load 15 g m^-2 y^-1) from 1980 to 1988. The lake functions as a reservoir for the surrounding rice cultivation. From 1940's to 1988, its phytoplankton assemblage has been altered from a mesotrophic to a hypertrophic character, as consequence of the increasing pollution. For 1980–88, annual variations in the phytoplankton were less pronounced than seasonal changes. The hypertrophic and morphometric features of the lake favoured the stability of the phytoplankton assemblage and chlorophyll a levels during the study period. Seasonal and horizontal distribution of the total phytoplankton abundance and biomass were highly influenced by the hydrological cycle of the lagoon. Compared with other shallow nutrient rich lakes, the Albufera of Valencia is similar to the shallow hypertrophic lakes of the Netherlands.     

Water level and fish-mediated cascading effects on the microbial community in eutrophic warm shallow lakes: a mesocosm experiment

Information on the effects of water level changes on microbial planktonic communities in lakes is limited but vital for understanding ecosystem dynamics in Mediterranean lakes subjected to major intra- and inter-annual variations in water level. We performed an in situ mesocosm experiment in an eutrophic Turkish lake at two different depths crossed with presence/absence of fish in order to explore the effects of water level variations and the role of top-down regulation at contrasting depths. Strong effects of fish were found on zooplankton, weakening through the food chain to ciliates, HNF and bacterioplankton, whereas the effect of water level variations was overall modest. Presence of fish resulted in lower biomass of zooplankton and higher biomasses of phytoplankton, ciliates and total plankton. The cascading effects of fish were strongest in the shallow mesocosms as evidenced by a lower zooplankton contribution to total plankton biomass and lower zooplankton:ciliate and HNF:bacteria biomass ratios. Our results suggest that a lowering of the water level in warm shallow lakes will enhance the contribution of bacteria, HNF and ciliates to the plankton biomass, likely due to increased density of submerged macrophytes (less phytoplankton); this effect will, however, be less pronounced in the presence of fish.     

持久性有毒物污染底泥修复技术进展

评述了底泥中持久性有毒污染物的危害。在分析持久性有毒污染物污染底泥修复技术现状及面临问题的基础上 ,指出浅水湖泊持久性有毒污染物污染底泥修复的发展方向是植物 -微生物联合修复 ,水库、深水湖泊等持久性有毒物污染底泥修复的发展趋势为物理化学 -生物协同修复 ,修复目标是在环保疏浚、生态清淤的基础上 ,实现持久性有毒污染物污染底泥的无害化和资源化处置