Size-related shifts in reliance on benthic and pelagic food webs by lake anchovy

This paper reports large variations in stable carbon and nitrogen isotope ratios of lake anchovy (Coilia ectenes taihuensis) from Lake Chaohu, China. The lake anchovy exhibited a significant C-13- and N-15- enrichment in relation to increasing fish length, and the isotopic compositions of small lake anchovy (<= 130 mm) were significantly more enriched than those of large lake anchovy (> 130 mm). The significant differences in the isotopic compositions of small and large lake anchovy suggested that their assimilated diets differed over a period of time and reflected the size-related diet shift of this fish. Bellamya aeruginosa and Corbicula fluminea were used to establish the baseline carbon signal of benthic and pelagic food webs, and these data were used to parameterize a 2-source mixing model to estimate in consumers the contribution of carbon derived from benthic versus pelagic food webs. Mixing models showed that small lake anchovy derived only 37% of their carbon from benthic food web, indicating increased reliance on pelagic prey, whereas benthic prey contributed 71% of large lake anchovy diet, suggesting greater use of benthic sources. These data indicate that there was a change in lake anchovy feeding strategy related to their size, suggesting a role in dynamic coupling between pelagic and benthic food chains. The trophic position of small lake anchovy averaged 3.0, indicating a zooplankton-based diet, compared with 3.6 in large lake anchovy, indicative of an increase in piscivorous diet. Overlap in the isotopic compositions of small and large lake anchovy probably indicated that these fish occasionally shared common diets, as suggested by stomach content studies, and/or resulted from the differences in the rate of isotopic turnover depending on differences in growth rate and metabolic turnover between small and large anchovy during diet shift from pelagic to benthic food webs. This study presents the contributions of benthic and pelagic food webs supporting lake anchovy and indicates that the intraspecific isotopic dynamic should be considered when applying stable isotope analyses to infer trophic interactions in aquatic ecosystems.

Macrozoobenthic community of Poyang Lake, the largest freshwater lake of China, in the Yangtze floodplain

Poyang Lake (Poyang Hu) is located at the junction of the middle and lower reaches of the Yangtze (Changjiang) River, covering an area of 3283 km(2). As one of the few lakes that are still freely connected with the river, it plays an important role in the maintenance of the unique biota of the Yangtze floodplain ecosystem. To promote the conservation of Poyang Lake, an investigation of the macrobenthos in the lake itself and adjoining Yangtze mainstream was conducted in 1997-1999. Altogether 58 benthic taxa, including, 22 annelids, 8 mollusks, 26 arthropods, and 2 miscellaneous animals, were identified from quantitative samples. The benthic fauna shows a high diversity and a marine affinity. The standing crops of benthos in the lake were much higher than those in the river, being 659 individuals/m(2) and 187.3g/m(2) (wet mass) in the main lake, and 549 individuals/m(2) and 116.6 g/m(2) in the lake outlet, but only 129 individuals/m(2) and 0.4g/m(2) in the river. The dominant roup in the lake was Mollusca, comprising 63.4% of the total in density and 99.5% in biomass. An analysis of the functional feeding structure indicated that collector-filterers and scrapers were predominant in the lake, up to 42.2% and 24.7% in density and 70.2% and 29.2% in biomass, respectively, while shredders and collector-gatherers were relatively common in the river. The present study was restricted to the northern outlet and the northeast part of Poyang Lake. A scrutiny is required for the remaining areas.

Food composition and dietary overlap of macroinvertebrates in a shallow eutrophic lake in China: spatial and temporal variations

The present study was conducted in Lake Donghu, a suburban eutrophic lake arising from the middle reaches of the Yangtze River, China. Food composition of 32 taxa of zoobenthos was analyzed from 1251 gut samples. Macroinvertebrate primary consumers ingested mainly detritus, sand grains and diatoms. The predators primarily preyed on rotifers, crustaceans, oligochaetes and chironomid larvae. The dietary overlap was relatively high among collector taxa but low among other macroinvertebrates. Food composition and dietary overlap of macroinvertebrates changed considerably, both spatially and temporally. Food web structure differed between inshore and offshore regions of Lake Donghu. The inshore web was relatively complex and dynamic whereas the offshore web was simple and stable. Taxon-specific changes of diet seem to have little effect on the benthic food web structure in offshore waters of a eutrophic lake.

Changes in the life history of Abbottina fivularis in Lake Fuxian

After invading Lake Fuxian, China, Abbottina rivularis showed marked changes in its life history traits, including alterations in annuli formation, extension to the length of the breeding season, and an increase in fecundity and growth rate. The results are explained in the context of the enemy release hypothesis. (c) 2007 The Authors. Journal compilation (c) 2007 The Fisheries Society of the British Isles.

Studies on temporal and spatial variations of phytoplankton in Lake Chaohu

Temporal and spatial variations of the phytoplankton assemblage in Lake Chaohu, a large shallow eutrophic lake in China, were studied from September 2002 to August 2003. A total of 191 phytoplankton species was identified, among which Chlorophytes (101) ranked the first, followed by Cyanophytes (46) and Bacillariophytes (28). On average over the entire lake, the maximum total algal biomass appeared in June (19.70 mg/L) with a minimum (5.05 mg/ L) in November. In terms of annual mean biomass, cyanobacteria contributed 45.43% to total algal biomass, followed by Chlorophytes (27.14%), and Bacillariophytes (20.6%). When nitrate (NO3-N) and ammonium (NH4-N) concentrations dropped in spring, fixing-nitrogen cyanobacterium (Anabaena) developed quickly and ranked the first in terms of biomass in summer. It is likely that dominance of zooplanktivorous fish and small crustacean zooplankton favored the development of the inedible filamentous or colony forming cyanobacteria. The persistent dominance of cyanobacteria throughout all seasons may indicate a new tendency of the response of phytoplankton to eutrophication in Lake Chaohu.

In situ studies on the distribution patterns and dynamics of microcystins in a biomanipulation fish - bighead carp (Aristichthys nobilis)

The distribution and dynamics of microcystins in various organs of the phytoplanktivorous bighead carp were studied monthly in Lake Taihu, which is dominated by toxic cyanobacteria. There was a good agreement between LC-MS and HPLC-UV determinations. Average recoveries of spiked fish samples were 63% for MC-RR and 71% for MC-LR. The highest MC contents in intestine, liver, kidney and spleen were 85.67, 2.83, 1.70 and 1.57 mu g g(-1) DW, respectively. MCs were much higher in mid-gut walls (1.22 mu g g(-1) DW) than in hind- and fore-gut walls (0.31 and 0.18 mu g g(-1) DW, respectively), suggesting the importance of mid-gut wall as major site for MC absorption. A cysteine conjugate of MC-LR was detected frequently in kidney. Among the muscle samples analyzed, 25% were above the provisional tolerable daily intake level by WHO. Bighead is strongly resistant to microcystins and can be used as biomanipulation fish to counteract cyanotoxin contamination in eutrophic waters. (c) 2006 Elsevier Ltd. All rights reserved.

Development of the microbial communities in Lake Donghu in relation to water quality

There is increasing recognition that protozoa is very useful in monitoring and evaluating water ecological healthy and quality. In order to study the relationship between structure and function of protozoan communities and water qualities, six sampling stations were set on Lake Donghu, a hypereutrophic subtropical Chinese lake. Microbial communities and protists sampling from the six stations was conducted by PFU (Polyurethane foam unit) method. Species number (S), diversity index (DI), percentage of phytomastigophra, community pollution value (CPV), community similarity and heterophy index (HI) were mensurated. The measured indicators of water quality included total phosphorus (TP), dissolved oxygen (DO), Chemical oxygen demand (COD), NH4 (+), NO2 (-) and NO3-. Every month water samples from stations I, II, III, IV were chemically analyzed for a whole year, Among the chemically analyzed stations, station I was the most heavily polluted, station II was the next, stations III and IV had similar pollution degrees. The variable tendencies of COD, TP, NH3, NO2-, NO3-, and DO during the year was approximately coincident among the six stations. Analysis from the community parameters showed that the pollution of station 0 was much more serious than others, and station V was the most slight. Of the community parameters, CPV and HI were sensitive in reflecting the variables of the water quality. Community similarity index was also sensitive in dividing water qualities and the water quality status of different stations could be correctly classified by the cluster analysis. DI could reflect the tendency of water quality gradient, species number and percentage of Phytomastigophora was not obvious in indicating the water quality gradient.

Environmental mechanism of change in cyanobacterial species composition in the northeastern part of Lake Dianchi (China)

Environmental mechanism of change in cyanobacterial species composition in the northeastern part of Lake Dianchi (also called Macun Bay and Haidong Bay) was studied using canonical correlation analysis (CCA), but also bottom-up control and top-down control were fully discussed. Results from CCA suggest: (1) the abundance and dominance of Microcystis aeruginosa in Macun Bay and Haidong Bay are influenced by total phosphorus (TP), nitrate (NO3--N), nitrite (NO2--N), dissolved oxygen (DO) and water temperature (WT); (2) water temperature has a positive correlation with the abundance of M. aeruginosa and it also has negative correlations with the abundances of Anabaena flos-aquae and Aphanizomenonon flos-aquae; and (3) abundances of both Anabaena flos-aquae and Aphanizomenon flos-aquae have positive correlations with ammonia-N (NH4+-N). Furthermore, cyanobacterial species composition has no significant correlations with light and size-fractioned iron in this study. Grazers, cyanophages and viruses were able to control cyanobacterial blooms and change the composition of cyanobacterial species. Though we studied physical and chemical factors intensely enough, we still are not able to predict the change in the composition of cyanobacterial blooms, because of plankton system in a chaotic behavior.

Community structure of small fishes in a shallow macrophytic lake (Niushan Lake) along the middle reach of the Yangtze River, China

This study describes the current status of the small fish community in Niushan Lake in China, and examines the spatial and seasonal variations of the community in relation to key environmental factors. Based on macrophyte cover conditions, the lake was divided into three major habitat types: (1) Potamogeton maackianus habitat, (2) Potamogeton maackianus and Myriophyllum spicatum habitat, and (3) uncovered or less-covered habitat. Fish were sampled quantitatively in the three habitat types by block nets seasonally from September 2002 to August 2003. A total of 10 469 individuals from 27 fish species were caught, among which 20 species were considered as small fishes. Rhodeus ocellatus, Paracheilognathus imberbis, Pseudorasbora parva, Micropercops swinhonis and Cultrichthys erythropterus were recognized as dominant small fishes according to their abundance and occurrence. It was noted that (1) small fishes predominated the total number of fish species in the lake, which reflected to some degree the size diminution phenomenon of fish resources; (2) many small fishes had plant detritus as their food item, which was consistent with the abundance of macrophyte detritus in the lake and implied the importance of detritus in supporting small fish secondary production. Canonical correspondence analysis suggested that the spatial distributions of most small fishes were associated with complex macrophyte cover conditions. Macrophyte biomass was positively correlated with species richness, diversity index and the catch per unit of effort (CPUE) of the fish community. Water depth had no significant effects on species diversity and distribution of the small fishes. Correspondence analysis revealed a higher occurrence of the small fishes and higher abundance of individuals in summer and autumn. Seasonal length-frequency distributions of several species indicated that more larval and juvenile individuals appeared in spring and summer. This study provides some baseline information which will be essential to long-term monitoring of small fish communities in the Yangtze lakes.

Effects of seasonal succession and water pollution on the protozoan community structure in an eutrophic lake

The purpose of the research is to study the seasonal succession of protozoa community and the effect of water quality on the protozoa community to characterize biochemical processes occurring at a eutrophic Lake Donghu, a large shallow lake in Wuhan City, China. Samples of protozoa communities were obtained monthly at three stations by PFU (polyurethane foam unit) method over a year. Synchronously, water samples also were taken from the stations for the water chemical quality analysis. Six major variables were examined in a principal component analysis (PCA), which indicate the fast changes of water quality in this station I and less within-year variation and a comparatively stable water quality in stations II and III. The community data were analyzed using multivariate techniques, and we show that clusters are rather mixed and poorly separated, suggesting that the community structure is changing gradually, giving a slight merging of clusters form the summer to the autumn and the autumn to the winter. Canonical correspondence analysis (CCA) was used to infer the relationship between water quality variables and phytoplankton community structure, which changed substantially over the survey period. From the analysis of cluster and CCA, coupled by community pollution value (CPV), it is concluded that the key factors driving the change in protozoa community composition in Lake Donghu was water qualities rather than seasons. (c) 2006 Elsevier Ltd. All rights reserved.

The change of gaseous carbon fluxes following the switch of dominant producers from macrophytes to algae in a shallow subtropical lake of China

Successions of lake ecosystems from clear-water, macrophyte-rich conditions into turbid states with abundant phytoplankton have taken place in many shallow lakes in China. However, little is know about the change of carbon fluxes in lakes during such processes. We conducted a case study in Lake Biandantang to investigate the change of carbon fluxes during such a regime shift. Dissolved aquatic carbon and gaseous carbon (methane (CH4) and carbon dioxide (CO2)) across air-water interface in three sites with different vegetation covers and compositions were studied and compared. CH4 emissions from three sites were 0.62 +/- 0.36, 0.70 +/- 0.36, and 1.31 +/- 0.57 mg m(-2) h(-1), respectively. Correlation analysis showed that macrophytes, rather than phytoplankton, directly positively affected CH4 emission. CO2 fluxes of three sites in Lake Biandantang were significantly different, and the average values were 77.8 +/- 20.4, 52.2 +/- 14.1 and 3.6 +/- 26.8 mg m(-2) h(-1), respectively. There were an evident trend that the larger macrophyte biomass, the lower CO2 emissions. Correlation analysis showed that in different sites, dominant plant controlled CO2 flux across air-water interface. In a year cycle, the percents of gaseous carbon release from lake accounting for net primary production were significantly different (from 39.3% to 2.8%), indicating that with the decline of macrophytes and regime shift, the lake will be a larger carbon source to the atmosphere. (c) 2006 Elsevier Ltd. All rights reserved.

Estimation of the natural purification rate of a eutrophic lake after pollutant removal

Pollution resulting from increased human activities is threatening Lake Donghu, its effects being characterized by serious eutrophication. A steady increase of phosphorus loading is the most important factor of the lake eutrophication. Pollution external control projects are being implemented and will be accomplished before the year 2010. In order to predict the restoration rate by the lake's self-purification after the projects of external control, a model of predicting the removal rate of total phosphorus (TP) from lake water is developed, and a brief method of estimating the release and export rate of sediment phosphorus is suggested. Results show that, on the premise of external loading fully controlled. The restoration needs about 55 years or more. Obviously, the great P pool in the sediment will be a limiting factor of preventing the improvement of water quality after the external loading is under control. Based on the estimation we conclude that after the external control projects before 2010, in order to restore the lake in a few years, although highly cost, the first step must be the sediment dredging to remove internal loading. The second step is diverting water of River Changjiang into the lake to accelerate the improvement of lake water. Otherwise, removal of pollutant sources will become meaningless. (c) 2006 Elsevier B.V. All rights reserved.

Microfabries of lacustrine sediments to pollutant adsorption from a polluted Eutrophic lake, the Yangtze delta region

Two types of microfabrics relating to pollutant adsorption were studied in the scanning electronic microscope (SEM) in a polluted, eutrophic lake, the Yangtze delta region. Agglutinational texture or the aggregates of small particles are composed of clay minerals and fine organic fragments among the silty grains and the coatings with a thickness about 1 mu m were on the surfaces of the silty grains in the sediments. The chemical constituents of the aggregates and the coatings are K, Na, Ca, Mg, Si, Al, O, Fe, Ti, C, N and P determined in X-ray energy spectrometry connected with the SEM. In some cases, Pb was detected in the aggregates in the top sediment. It is suggested that nutrients and metals are adsorbed to the aggregates, which were formed by electrostatic attraction of physicochemical floes. The coatings on the surface of quartz grains were formed by the interaction of dissociated Al, Si, Fe, etc from silicates with dissolved N, P and C nutrients in interstitial water, which was aroused by human pollution to the lake in recent two decades.

Sedimentary records of water environment in lake Chaohu in the Yangtze delta region, China

Three lacustrine core samples were collected from Chaohu lake in December 2002 in the Yangtze delta region. The grain sizes were analyzed using a Laser Analyzer to obtain grain-size parameters. Sediment geochronology was determined in radioisotopes Cs-137 and the average sedimentary rates are 0.29cm.a(-1), 0.35 cm.a(-1) and 0.24cm-a(-1) in Cores C 1, C2 and C3, respectively. The grain-size parameters of the deposits vary regularly with the fluctuation of hydrodynamics. From 1950s to the beginning of 20th century, coarse-grained sediment was deposited, suggesting strong hydraulic conditions and high water-level periods with much precipitation; from the start of 20(th) century to latter half of 18(th) century, fine-grained sediment was deposited, indicating that weak hydraulic conditions and low water-level periods with less precipitation; before the first half of 18(th) century, coarse-grained sediment was deposited, suggesting great velocity of flow and high water-level periods of more precipitation.