Structure of plankton communities in Ilchir, an alpine lake in eastern Siberia

 Lake Ilchir is an alpine lake located 1963 m above sea level in the mountain ranges of eastern Sayan, eastern Siberia. Observations are presented from October 1998 to September 1999 in order to provide the phytoplankton and zooplankton community structures. Sixty-six taxa of phytoplankton and 66 taxa of zooplankton were recorded. Of much interest was the finding of rare species, such as the dinoflagellate Gymnodinium coeruleum, the diatoms Pliocaenicus costatus and Cyclotella tripartita, and the calanoids Acanthodiaptomus tibetanus and Arcthodiaptomus (S.) paulseni. Received: August 24, 2001 / Accepted: April 13, 2002     

Diversity of Actinobacterial community in saline sediments from Yunnan and Xinjiang, China

The diversity and community structures of actinobacteria in saline sediments collected from Yunnan and Xinjiang Provinces, China, were investigated with cultivation and 16S rRNA gene analysis. A total of 163 actinobacterial isolates were obtained, and they were affiliated with the order Actinomycetales (distributed into five suborders: Streptosporangineae, Micrococcineae, Streptomycineae, Pseudonocardineae, and Glycomycineae). A total of 748 actinobacterial 16S rRNA gene clones were examined, and they could be classified into Actinomycetales, Acidimicrobiales, and unclassified actinobacteria. The Actinomycetales sequences were distributed into nine suborders: Streptosporangineae, Glycomycineae, Micromonosporineae, Pseudonocardineae, Corynebacterineae, Frankineae, Propionibacterineae, Streptomycineae, and Micrococcineae. The unclassified actinobacteria contained three new clusters at the level of subclass or order. Our 16S rRNA gene phylogenetic data indicated that actinobacterial communities were very diverse in the investigated saline sediments (salinity 0.4–11.6%) and some actinobacterial members may be halotolerant or halophilic. The actinobacterial community structures in the saline sediments were different from those in marine and freshwater environments. Our data have implications for a better understanding of the distribution of Actinobacteria in saline environments. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Peracarid composition,diversity and species richness in the area of the Northeast Water polynya,East Greenland (Crustacea,Malacostraca)

During the ARK XI-2 expedition with RV Polarstern in September/October 1995, a transect of epibenthic sledge (EBS) samples was taken in the area of the Northeast Water Polynya off the Greenland coast, from the shelf down into the deep sea. A total of 85,304 specimens of Peracarida were collected at seven stations. These individuals comprised 45 families, 103 genera and 180 species. With regard to abundance, Cumacea occurred with highest numbers, 31,269, followed by Isopoda, Amphipoda, Mysidacea and Tanaidacea. Species richness was highest in Amphipoda with 94 species, followed by Isopoda with 43 species, Cumacea with 20 species, Tanaidacea with 15 and Mysidacea with 8 species. Species richness was highest at the shallowest station 37-016 and lowest at the deepest station 37-021, whereas the opposite pattern was found for abundance. Diversity and eveness were highest at the southernmost station and lowest at the deepest station. Amphipoda occurred more frequently at the shallower stations, while Cumacea were very frequent at the deepest station. Numbers of species were lowest for Cumacea at the deepest station, while Amphipoda and Isopoda generally occurred with high species richness at all stations. On the basis of the species composition stations were compared.     

The relationship between phytoplankton species dominance and environmental variables in a shallow lake (Lake Vrana,Croatia)

The shallow Lake Vrana was studied over a 1-year period, special attention being paid to the phytoplankton. Phytoplankton was investigated monthly with respect to temporal variability of selected environmental factors. The regular annual development observed was in species contribution to total biomass rather than in seasonal changes in species composition. The assemblage was dominated by Cosmarium tenue Arch. and Synedra sp. In winter and in spring the phytoplankton assemblage was dominated by Cosmarium tenue and high contribution of Synedra sp. was observed during the summer and autumn. Results suggest that concentrations of inorganic nitrogen and phosphorus were critical in regulating phytoplankton biomass and species dominance.     

A comparative analysis of cladoceran communities from different water body types: patterns in community composition and diversity

To develop strategies for the management and protection of aquatic biodiversity in water bodies at the landscape scale, there is a need for information on the spatial organization of diversity in different types of aquatic habitats. In this study, we compared the cladoceran composition and diversity between wheel tracks, pools, ponds, lakes, ditches, and streams, in 18 different areas of Flanders (Belgium). Multivariate analysis revealed significant differences in the composition of cladoceran communities among the different water body types. Average local and total diversity tended to be highest for lakes and lowest for streams. Despite the relatively high number of species supported by lakes, small water bodies seem to contribute considerably more to the total cladoceran richness of an average landscape in Flanders than lakes, because of their high abundance. With respect to biodiversity conservation at the landscape scale, our results point to the importance of maintaining a diversity of water body types of different size, permanence and flow regimes. Guest editors: R. Céréghino, J. Biggs, B. Oertli & S. Declerck The ecology of European ponds: defining the characteristics of a neglected freshwater habitat     

Effects of the halocline on water quality and phytoplankton composition in a shallow brackish lake (Lake Obuchi, Japan)

The relationships of the halocline to both water quality and phytoplankton composition in Lake Obuchi, a shallow brackish lake in northern Japan, were investigated from April 2001 to December 2004. The halocline in this lake became stronger in summer (July–September, mean maximum density gradient 4.3–5.8 ρ_tm⁻¹) but weaker in spring, fall, and winter (1.9–3.3 ρ_tm⁻¹). Although the difference in water quality between the upper and lower layers separated by the halocline was high in summer, nutrients (PO₄³⁻-P and NH₄⁺-N) were eluted from the bottom sediment as levels of dissolved oxygen decreased in the bottom layer because of the strong stratification caused by the halocline formed over the long term. Moreover, phytoplankton taxa composition also differed between the upper and lower layers in summer, but was similar in other seasons. The dominant phytoplankton taxa in the upper layer in summer were Skeletonema costatum and Cyclotella spp., whereas in the lower layer, Gymnodinium spp. (Dinophyceae) and Chlorophyceae, which prefer eutrophic and low dissolved oxygen conditions, dominated. This suggests that the halocline was related to differentiations in both water quality and ecosystem components between the upper and lower layers in the brackish lake water.     

The plankton community of Lake Matano: factors regulating plankton composition and relative abundance in an ancient,tropical lake of Indonesia

Recent evidence reveals that food webs within the Malili Lakes, Sulawesi, Indonesia, support community assemblages that are made up primarily of endemic species. It has been suggested that many of the species radiations, as well as the paucity of cosmopolitan species in the lakes, are related to resource limitation. In order to substantiate the possibility that resource limitation is playing such an important role, a study of the phytoplankton and zooplankton communities of Lake Matano was implemented between 2000 and 2004. We determined species diversity, relative abundances, size ranges, and total biomass for the phytoplankton and zooplankton, including the distribution of ovigerous individuals throughout the epilimnion of Lake Matano in three field seasons. The phytoplankton community exhibited very low biomass (<15 μg l^?1) and species richness was depressed. The zooplankton assemblage was also limited in biomass (2.5 mg l^?1) and consisted only of three taxa including the endemic calanoid Eodiaptomus wolterecki var. matanensis, the endemic cyclopoid, Tropocyclops matanensis and the rotifer Horaella brehmi. Zooplankton were very small (<600 μm body length), and spatial habitat partitioning was observed, with Tropocylops being confined to below 80 m, while rotifer and calanoid species were consistently observed above 80 m. Less than 0.1% of the calanoid copepods in each year were egg-bearing, suggesting very low population turnover rates. It was concluded that chemical factors as opposed to physical or biological processes were regulating the observed very low standing crops of phytoplankton which in turn supports a very minimal zooplankton community restricted in both species composition and abundance. As chemical factors are a function of the catchment basin of Lake Matano, it is predicted that resource limitation has long played an important role in shaping the unique endemic assemblages currently observed in the food web of the lake.     

Seasonal dynamics of zooplankton in a shallow eutrophic,man-made hyposaline lake in Delhi (India): role of environmental factors

Old Fort Lake, a small (1.6 ha), shallow, and recreational water body in Delhi (India) was studied through monthly surveys in two consecutive years (January, 2000–December, 2001). Precipitation is the major source of water for this closed basin lake. In addition, ground water is used for replenishing the lake regularly. This alkaline, hyposaline hard water lake contains very high ionic concentration, especially of nitrates. Based on overall ionic composition, this lake can be categorized as chloride–sulfate alkaline waters with the anion sequence dominated by SO₄ ²⁻ > Cl⁻ > HCO₃ ⁻, and the cations by Mg⁺⁺ > Ca⁺⁺. The overall seasonal variability in physicochemical profile was largely regulated by the annual cycle of evaporation and precipitation, whereas the ground water largely influences its water quality. The lake exhibited phytoplankton-dominated turbid state due to dominance of the blue green alga, Microcystis aeruginosa. The persistent cyanobacterial blooms and the elevated nutrient levels are indicative of the cultural eutrophication of the lake. This study focuses on the relative importance of eutrophic vis-à-vis hyposaline conditions in determining the structure and seasonal dynamics of zooplankton species assemblages. A total of 52 zooplankton species were recorded and rotifers dominated the community structure qualitatively as well as quantitatively. The genus Brachionus comprised a significant component of zooplankton community with B. plicatilis as the most dominant species. The other common taxa were B. quadridentatus, B. angularis, Lecane grandis, L. thalera, L. punctata, Mesocyclops sp., and Alona rectangula. Multivariate data analysis techniques, Canonical Correspondence Analysis (CCA) along with Monte Carlo Permutation Tests were used to determine the minimum number of environmental factors that could explain statistically significant (P < 0.05) proportions of variation in the species data. The significant variables selected by CCA were NH₃–N followed by percent saturation of DO, COD, SS, BOD, NO₂–N, rainfall, silicates, and PO₄–P. The results indicate that the seasonal succession patterns of the zooplankton species were largely controlled by physicochemical factors related directly or indirectly to the process of eutrophication, whereas hyposaline conditions in the lake determined the characteristic species composition. Guest Editors: J. John & B. Timms Salt Lake Research: Biodiversity and Conservation—Selected papers from the 9th Conference of the International Society for Salt Lake Research     

The effect of fertilization on the below-ground diversity and community composition of ectomycorrhizal fungi associated with western hemlock (Tsuga heterophylla)

Fertilization typically reduces ectomycorrhizal diversity shortly after its application but less is known about its longer-term influence on fungal species. Long-term effects are important in forests where fertilizer is rarely applied. We compared fungal species composition in western hemlock control plots with plots last fertilized 7 years ago with nitrogen (N) or nitrogen plus phosphorus (N + P). The N + P fertilization had a significant lingering effect, increasing the tree size and foliar P content of the western hemlocks. From ectomycorrhizal roots of 24-year-old trees from northern Vancouver Island, Canada, we identified fungi from 12 samples per treatment, by amplifying, cloning, and sequencing fungal ribosomal DNA fragments, placing sequences with 97% or more identity in the same operational taxonomic unit (OTU). Diversity was high across treatments; we detected 77 fungal OTUs, 52 from ectomycorrhizal genera, among 922 clone sequences. The five most frequent OTUs were similar in abundance across treatments. Only 19 OTUs matched any of the 197 previously reported ectomycorrhizal species of western hemlock. Species composition but not diversity in nitrogen plus phosphorus plots differed significantly from control or nitrogen plots. Two Cortinarius OTUs were indicator species for nitrogen plus phosphorus plots and presence of Cortinarius cinnamomeus was correlated with control or nitrogen plots. After 7 years, fertilization history had made no detectable difference in ectomycorrhizal fungal diversity, but long-lasting changes in environment resulting from fertilization had a lingering effect on fungal ectomycorrhizal species composition. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

A comparison of the fatty acid composition of Gammarus lacustris and its food sources from a freshwater reservoir, Bugach, and the saline Lake Shira in Siberia, Russia

We studied fatty acid (FA) composition in samples from bodies and intestinal contents of the littoral amphipod Gammarus lacustris Sars, from the Bugach freshwater reservoir. Simultaneously, samples of seston and bottom sediments were also collected from the reservoir during early August. There were no differences in FA composition of gut contents, seston and sediments of pebbly bottom. Seston was the main food source of Gammarus but some FAs Gammarus got from sediments. The FA composition of G. lacustris and seston from the Bugach freshwater reservoir were compared with those of the animals from the saltwater Lake Shira (Siberia). While FA composition of the two Gammarus populations differed significantly, those of seston were practically similar: the composition of long-chain unsaturated fatty acids, 20:53, 22:63 and 20:46, were significantly higher in animals from saline Shira Lake, whereas 16:1 and 16:0 were higher in the freshwater populations of amphipods from the Bugach freshwater reservoir. Taking into account the relevant literature data, we hypothesise that this difference in C16 acid might be a distinguishing characteristic of FA composition of freshwater and saltwater crustaceans.     

Effects of nutrient (N,P, C) enrichment upon the littoral diatom community of an oligotrophic high-mountain lake

The effects of nutrient additions upon the epilithic diatom communities and the algal standing crop were investigated in the oligotrophic, softwater Lake Piccolo Naret, situated in the Swiss alps. Nutrient-diffusing flower pot substrates were filled with either N (0.15 mol NaNO₃), P (0.015 mol Na₂HPO₄) or C (0.15 mol NaHCO₃) or combinations of them. Twenty-five pots representing eight treatments were placed into the lake in July 1991 and sampled after 42 days of exposure.On the surfaces of all pots containing P we measured higher algal biomasses as on the control pots. The chlorophyll-a maximum of 12.9 µg cm^{– 2} was obtained on NPC pots (0.47 µg cm^{– 2} on control pots). On pots with P, NP or NPC supply high amounts of green algae were detected, also reflected in an increased chl-b/chl-c ratio related to the controls which showed algal communities dominated by diatoms.The diatom communities on the control pots as well as on the pots with N, P and NP had a structure similar to the epilithic community in Lake Piccolo Naret (dominance identity > 58 %). However, the community structures of the diatoms from pots with C addition (C, NC, PC and NPC) differed considerably. This is discussed in view of the cell densities of dominant diatom species. For further comparisons the results of two additional high-mountain lakes are used. By means of a cluster analysis it could be shown that epilithic diatom communities were considerably influenced by C addition, while N and P supply were of minor importance.     

Effects of egg composition and prey density on the larval growth and survival of lake whitefish (Coregonus clupeaformis Mitchill)

Eggs were collected from two stocks of lake whitefish, Coregonus clupeaformis , in Lakes Michigan and Huron to assess the effect of egg composition and prey density on larval growth and survival. Egg composition parameters including wet weight (mg egg⁻¹), dry weight (mg egg⁻¹), percent water, total caloric content (cal egg⁻¹), caloric density (cal egg⁻¹), percent lipid content, and total lipidcontent (mg egg⁻¹) were measured. Fish hatched from six parental females in each stock were fed one of four rations (0, 18, 24, 50 brine shrimp larva⁻¹ day⁻¹) after yolk sac absorption. Length at hatch, endogenous growth, exogenous growth, and survival were measured during a 42-day laboratory experiment. Length at hatch of larvae was positively related to egg caloric content ( r ²=0.780). Endogenous growth for lake whitefish larvae was positively related to percent lipid content ( r ²=0.896) and total egg lipid content ( r ²=0.876) of parental females. Exogenous growth and survival of larval lake whitefish was positively related to prey availability. Larval fish growth was accurately modelled ( r ²=0.973) as a function of prey abundance using a threshold-corrected hyperbolic equation. These results indicate that both egg composition and prey availability have the potential to influence the growth and survival dynamics of larval lake whitefish significantly.     

Spatial variability in the abundance and composition of the free-living bacterioplankton community in the pelagic zone of Lake Bourget (France)

Spatial variations in the abundance and diversity of the free-living bacterioplankton community of a large Alpine lake, Lake Bourget (France), were investigated in the pelagic zone by means of two two-dimensional samplings taken in 2003. Lake-water samples were collected in winter during water mixing, and in early summer during stratification. The population abundance in each sample was determined by flow cytometry. Denaturing gradient gel electrophoresis of PCR-amplified 16S rRNA gene fragments from organisms measuring less than 2 mum was used to assess eubacterioplankton community composition. In winter, no obvious differences were observed in either the abundance or the diversity of the bacterial community, on either the horizontal or the vertical scales. The only influence detected was that of river water input, but this was at a very minor scale relative to the surface area of the lake. In early summer, changes were found in the community composition on the vertical scale related to the thermal stratification of the water column. There were also marked differences on the horizontal scale at 15 m depth due to internal waves. The implications of these findings for sampling strategies are very important from the perspective of comparative studies of free-living bacterial community diversity and functioning in large and deep lakes.     

Species richness, diversity and biomass production of desert annuals in an ungrazed Rhanterium epapposum community over three growth seasons in Kuwait

Two blocks, each consisting of twelve 0.25 m²permanent plots, were established in a community dominated by desert annuals inan area of Kuwait protected from grazing, and community attributes wereinvestigated over three growth seasons. A linear relationship was found betweenestimated desert annual cover and biomass production. Species frequency wasassessed by the number of 100 cm² subplots occupied byaspecies in a block (block incidence). Over the three seasons,vegetation features varied considerably. The first season (spring 1997) wascharacterised by very sparse vegetation cover, low vegetation block incidence(sum of individual block incidences of each species present in a block) and lowspecies richness. The second season (spring 1998) had high vegetation cover,relatively low vegetation block incidence, but high species richness. In thethird season (spring 2000), vegetation cover was very sparse (as in 1997), butboth blocks had the highest vegetation block incidence of the three years andspecies richness was moderately high, although individual plants were verysmall. The growth period was much shorter in the very productive andspecies-rich 1998 season than in 2000. Fluctuations in biomass and speciesincidence coincided with pronounced variation in key meteorological variables,in particular the onset of the first rains, the amount of rainfall during thegrowing season and its temporal distribution. Species composition, however,appears mainly to be determined by the amount and possibly the timing of thefirst rainfalls of the season to trigger germination. There was little evidenceto suggest that particularly favourable or unfavourable microsites existed inplots for more than one vegetation period, either for individual species or fordiversity in general. Despite substantial between-season fluctuations inincidence, the relative abundances of the more frequent species to each otherremained broadly similar over the three seasons, with Plantagoboissieri being the predominant species and accounting for thelargest proportion of biomass.     

Faunal trophic interaction in an oligotrophic-dystrophic lake (Shirakoma-ike, Japan)

 The trophic interaction in the pelagic food web of oligotrophic-dystrophic Lake Shirakoma-ike was investigated by a stable isotope technique. Carbon and nitrogen isotope analyses revealed the trophic interaction among Piona carnea (a water mite), Chaoborus sp. (a phantom midge), Daphnia longispina (a cladoceran), and Acanthodiaptomus pacificus (a calanoida copepoda). The δ¹³C values for estimating the relative contributions of D. longispina and A. pacificus to carnivores were used, and they were also used for the constraint of the trophic enrichment factor of δ¹⁵N. Both Chaoborus sp. and P. carnea were suggested to consume D. longispina and A. pacificus at almost the same ratio (1 : 1). However, both carnivores preferred A. pacificus to D. longispina, because D. longispina was much more abundant in the lake than A. pacificus. Omnivory of P. carnea was also analyzed by the mixing model. Received: February 28, 2002 / Accepted: July 10, 2002 Present address: Hydrospheric Atmospheric Research Center, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan Tel. +81-52-789-3434; Fax +81-52-789-3436 e-mail: lee@ihas.nagoya-u.ac.jp Present address: Research Institute for Humanity and Nauture, Kyoto, Japan Acknowledgments We would like to thank Professor Kikuo Kato for providing useful comments and colleagues in the Laboratory of Biogeochemical Data Analysis, Nagoya University, for their support with the sample collection. We are in debt to Dr. R. Coucett for the kind suggestion on the trophic enrichment factors for blood-sucking insects. We also thank the members of the Suwa Hydrobiological Station, Shinshu University, who kindly allowed us to use facilities for sampling in Lake Shirakoma-ike. The zooplankton samples were partly provided by Mr. Masataka Yoshida. Correspondence to:J.-Y. Lee     

Composition,density and feeding of crustacean zooplankton community in a shallow,temperate lake (Lake Balaton,Hungary)

Composition density and filtering rates of crustacean zooplankton were studied in the open water and among the macrophytes of the oligo-mesotrophic part of Lake Balaton from 1981 to 1983. From the individual filtering rates of the different populations and the densities community grazing rates were derived.Copepoda made up 79–90% of crustacean plankton community in the open lake and 95–97% of it in littoral zone. Among them the nauplii dominated. At the end of summer 1982, when Anabaenopsis was in bloom, the filter-feeding species (Eudiaptomus, Daphnia) practically disappeared, being replaced by cyclopoids. Daphnia had the highest filtering rates followed by those of Eudiaptomus and Diaphanosoma. Among copepods, the filtering rates in decreasing order were: ovigerous > all adults > copepodites > nauplii. > . The filtering rates of the different species varied both seasonally as well as from year to year. In 1983, when the concentration of organic seston decreased, filtering rate increased compared with those in the earlier years. During the water bloom in 1982, the rates decreased by 70% on the average.The community grazing rate was very low (3% per day) in the open lake and among macrophytes, both in 1981 and 1982; also the share of crustacean zooplankton in grazing was very low. In 1983, together with the improving of water quality, the community grazing rate increased 4-fold. In 1981 and 1983 the rates were influenced by water temperature but in 1982 by seston concentration.     

Agricultural land use and black fly (Diptera,Simuliidae) species richness and species assemblages in tropical streams,Northeastern Thailand

Habitat degradation through agricultural land use is the major factor threatening lotic ecosystems. Although black flies are major components of these ecosystems, the impact of agricultural land use on species diversity and species assemblages has been largely ignored in tropical streams of the Oriental region. The objectives of this study are to examine patterns of species distribution and species richness and to compare black fly species richness and species assemblages in forest and agricultural streams in Thailand. A total of 143 collections were made from 70 stream sites between June 2007 and May 2008. Whereas 19 black fly species found in these collections were all found in forest sites, only 13 species were found in agricultural sites. High species richness was associated with larger, faster, and cooler streams with larger streambed particles and the presence of riparian trees. Logistic regression analyses revealed that stream size, velocity, and riparian vegetation are among the most important factors determining patterns of spatial distribution. The results are largely consistent with studies in other zoogeographic regions, suggesting the existence of general rules for black fly species distributions. Comparisons of the physicochemical conditions between forest and agricultural streams indicated that streams in agricultural areas are warmer, with higher conductivity and fewer riparian trees. Species richness was significantly higher in forest than in agricultural streams (t = 3.61, P < 0.001). Streams in forest areas were predominantly occupied by S. siamense (73%) but other species were also found at a relatively high frequency (>20%) of the sampling sites. In contrast, streams in agricultural areas were predominantly occupied by S. aureohirtum (>80%) among the sole black fly species at 27% of the sites. The results indicate that agricultural land use has a significantly detrimental impact on black fly diversity and species assemblages. Handling editor: D. Dudgeon     

Impact of river management history on the community structure,species composition and nutrient status in the Rhine alluvial hardwood forest

The present-day Rhine alluvial hardwood forest (Querco-Ulmetum minoris, Issler 24) in the upper Rhine valley (France/Germany) is comprised of three vegetation units, one still flooded by calm waters (F) and the two others unflooded, one for 30 years (UF30) (after the river canalisation) and the other for about 130 years (UF130) (after river straightening and embankment work in the middle nineteenth century). In the three stands, species composition, structure and diversity of vegetation and nutrient content of mature leaf, leaf litter and soil have been studied. Fungi (Macromycetae) were only studied in two stands (F and UF130). The intensity of nutrient recycling was exemplified by comparing the chemical composition of rainwater, flood, throughfall, mature leaf, leaf litter, soil and groundwater in two of these stands (F and UF30).The elimination of floods has caused a change in floristic composition, tree density and plant diversity. Tree density was higher in the two unflooded stands and was related to a large increase in sapling (< 6 cm dbh) density more than to a change of stem (> 6 cm dbh) density. Sapling density increased 2 times and three times in the UF30 and the UF130 respectively, whereas the stem density increased only 12% in the first stand and decreased 29% in the second one. The saprophytic macromycete communities have been supplemented with mycorrhizal species. Leaf litter production was slightly greater in the flooded (4.44 T ha^-1 yr^-1) than in the two unflooded stands ( 3.72 T ha^-1 yr^-1). Foliar N level is twice as high in the flooded stands in spite of an opposite soil status. P level decreased in soil and leaves with the duration of isolation and was at the same level in the groundwater in two stands (F and UF30). K, Mg and Ca contents of green leaf and leaf litter were high due to the geochemistry of the Rhine substrate (calcareous gravels and pebbles) and similar in all the stands studied, even though there are large inputs of these three elements by floods. Moreover we showed that the groundwater chemistry reflected the variations of nutrient inputs and thus could be a good indicator of the functioning of an alluvial ecosystem and of its change as a result of human activities. The restoration of floods in hardwood forest contributes to the preservation of alluvial vegetational structure and composition, the stimulation of biological processes and a better plant mineral nutrition and water supply.     

Changes in the Georgian Bay fish community,with special reference to lake trout (Salvelinus namaycush) rehabilitation

We describe and explain some of the changes in the fish community as reflected by the catches of the commercial fishery, and evaluate the efforts to restore the trout (Salvelinus spp.) in Georgian Bay. The changes in the fish community were caused in part by excessive fishing for lake trout (S. namaycush), lake whitefish (Coregonus clupeaformis) and deepwater ciscoes (Coregonus spp.), and the introduction of new species such as sea lamprey (Petromyzon marinus), alewife (Alosa pseudoharengus), rainbow smelt (Osmerus mordax) and salmonids (Oncorhynchus spp.). The most striking changes were the near extinction of the lake trout, reductions in lake herring (Coregonus artedii), deepwater ciscoes and lake whitefish, and the increase in abundance of smelt and alewife. In an effort to replace the loss of yield from the cold-water habitat, a fast growing and early maturing hybrid trout (splake [S. namaycush × S. fontinalis]) and its backcross to lake trout were selectively bred for stocking in Georgian Bay. Splake did poorly because of low survival immediately after planting. The survival of backcross after planting was better, but adult mortality was still high. Adult survival of backcross improved considerably after restrictions were placed on the commercial fishery in 1984. The first naturally produced backcross larvae were collected in 1985.     

Covariation between zooplankton community composition and cyanobacterial community dynamics in Lake Blaarmeersen (Belgium)

The cyanobacterial community composition in the mesotrophic Lake Blaarmeersen was determined by denaturing gradient gel electrophoresis (DGGE) of PCR-amplified 16S rRNA gene fragments during two consecutive years to assess the importance of different classes of explanatory variables (bottom-up and top-down factors, physical variables and phytoplankton) in cyanobacterial community dynamics. The most dominant cyanobacteria in Lake Blaarmeersen were Synechococcus (three genotypes), Limnothrix redekei and Anabaena/Aphanizomenon. Analyses of Similarity revealed that the cyanobacterial community in Lake Blaarmeersen differed significantly between the growing season and the winter season as well as between the epilimnion and hypolimnion during the stratified periods. Mantel tests revealed significant correlations between the DGGE data and bottom-up factors, physical variables, the phytoplankton community composition and, interestingly, the zooplankton community composition. In general, the zooplankton community composition (especially the cladoceran community) was more important in structuring the cyanobacterial community than the total zooplankton biomass. This study shows that grazing zooplankton communities can have a relatively strong impact on the cyanobacterial community dynamics and that this impact can be equally important as bottom-up processes regulated by nutrient concentrations and/or physical variables.