The rotifer assemblage in a shallow, eutrophic Chinese lake and its relationships with cyanobacterial blooms and crustacean zooplankton

Rotifer assemblage in the subtropical eutrophic Lake Chaohu was investigated monthly from September 2002 to August 2003. Forty-nine species belonging to 18 genera and 14 families were recorded. The highest densities of rotifer were observed during summer when there were heavy cyanobacterial blooms. There was a significant positive correlation between total rotifer density and the biomass of cyanobacteria. However, no correlations were found between the densities of rotifer and crustacean zooplankton, possibly owing to the paucity of large-bodied planktonic crustaceans. It is likely that the occurrence of cyanobacterial blooms not only caused the shift of dominant crustacean zooplankton from large species to smaller ones but also weakened the negative interaction between crustaceans and rotifers.

Tissue distributions and seasonal dynamics of the hepatotoxic microcystins-LR and -RR in a freshwater snail (Bellamya aeruginosa) from a large shallow, eutrophic lake of the subtropical China

Tissue distributions and seasonal dynamics of the hepatotoxic microcystins-LR and -RR in a freshwater snail (Bellamya aeruginosa) were studied monthly in a large shallow, eutrophic lake of the subtropical China during June-November, 2003. Microcystins (MCs) were quantitatively determined by High-Performance Liquid Chromatography (HPLC) with a qualitative analysis by a Finnigan LC-MS system. On the average of the study period, hepatopancreas was the highest in MC contents (mean 4.14 and range 1.06-7.42 mug g(-1) DW), followed by digestive tracts (mean 1.69 and range 0.8-4.54 mug g(-1) DW) and gonad (mean 0.715 and range 0-2.62 mug g(-1) DW), whereas foot was the least (mean 0.01 and range 0-0.06 mug g(-1) DW). There was a positive correlation in MC contents between digestive tracts and hepatopancreas. A constantly higher MC content in hepatopancreas than in digestive tracts indicates a substantial bioaccumulation of MCs in the hepatopancreas of the snail. The average ratio of MC-LR/MC-RR showed a steady increase from digestive tracts (0.44) to hepatopancreas (0.63) and to gonad (0.96), suggesting that MC-LR was more resistant to degradation in the snail. Since most MCs were present in the hepatopancreas, digestive tracts and gonad with only a very small amount in the edible foot, the risk to human health may not be significant if these toxic parts are removed prior to snail consumption. However, the possible transference of toxins along food chains should not be a negligible concern. (C) 2004 Elsevier Ltd. All rights reserved.

Modeling of cyanobacterial blooms in hypereutrophic Lake Dianchi, China

Compared with other approaches for modeling and predicting, artificial neural networks are more effective in describing complex and non-linear systems. The occurrence of cyanobacterial blooms has been a continuous and serious problem over the past decades in hypereutrophic Lake Dianchi. Yet, the main factor(s) initiating these blooms remain(s) unclear. During 2001-2002 at 40 sampling sites in Lake Dianchi, physicochemical parameters possibly relating to the blooms were measured. Parameters directly or indirectly relating to the cyanobacterial blooms were used as driving factors in a back-propagation network to model the concentration of chlorophyll a. According to sensitivity analysis, chemical oxygen demand was identified as a very significant environmental factor for algal growth in Lake Dianchi.

Diel variation of methane fluxes in summer in a eutrophic subtropical lake in China

The summer diel variation of methane (CH4) flux was investigated in a eutrophic, subtropical lake in China. The CH4 concentration was always supersaturated, and the emission rate ranged from 0.24 to 45.51 mg m(-2) h(-1). The diel variations of CH4 flux in June and August showed a single peak in early afternoon and a minimum in the morning, while the pattern varied irregularly in May. There was a moderate relationship between water and sediment temperature and CH4 emission rate in some months.

Discharges and sediments as sources of extracellular alkaline phosphatase in a shallow Chinese eutrophic lake

Total alkaline phosphatase activity (APA) and soluble reactive phosphorus (SRP) concentrations were measured in municipal wastewater, and a shallow Chinese freshwater lake receiving it. Activities of Dissolved alkaline phosphatase ( ADAP) in overlying and interstitial water were also analyzed monthly at three sites for several years. The lake was enriched with SRP and alkaline phosphatase by discharge of the wastewater, indicating that the inclusion of APA for estimating water pollution was reasonable. Annual data showed that APA in coarser fraction was significantly higher at the site receiving more wastewaters, both in surface and overlying water, suggesting that resuspension of enzyme most likely occurred in the basin heavily discharged. ADAP was an order of magnitude higher in the wastewater than those in lake waters, and was generally higher in interstitial water, a feature more striking at the site receiving more discharges. Besides, it was irrespectively inhibited by Na2WO4, L-cysteine and EDTA-Na, but stimulated by Cu2+, Zn2+, CTAB and Triton X-100 in interstitial, overlying and surface waters. This similarity of responding patterns to the stressors indicated an analogy between dissolved alkaline phosphatase in water column and that in interstitial water, supporting the hypothesis that the polluted sediments act as source of dissolved alkaline phosphatase in eutrophic lakes.

Distribution of the meiofaunal community in a eutrophic shallow lake of China

In a Chinese eutrophic shallow lake, the spatial, temporal and vertical distributions of meiofauna in different lake zones along a eutrophic gradient were analyzed. The spatial distribution of meiofauna among sampling stations changed with nutrient levels. Nematoda were most abundant at the majority of sampling stations comprising 70.6 - 93.2 % meiofaunal abundance except for a hypereutrophic station. The seasonal patterns in abundance of nematodes, oligochaetes, rotifers, chironomids and different nematode feeding groups differed among stations, which revealed that the temporal variations of these meiofaunal groups and the nematode feeding groups may vary with different nutrient loadings. The vertical distributions of meiofaunal groups, nematode species, and nematode trophic groups in the upper and lower sediment layers were similar, suggesting a consistent vertical distribution pattern across different trophic conditions. Nematode species richness, Shannon-Wiener species diversity index, trophic diversity and Maturity Index were significantly correlated with nutrient levels (total phosphorus and nitrogen in lake water and total phosphorus in sediment). Our results suggest the importance of nematode community analyses in the assessment of freshwater eutrophication.

Variation of microcystins in a lake for water supply

A site investigation was conducted to correlate the relationships between microcystins (MC) concentration and algal growth in Dianchi Lake in China. Laboratory experiments were undertaken to test the effects of sediment adsorption, photoirradiation and biodegradation on microcystins removal. Bioaccumulation of microcystins was also determined using silver carp fish. It was observed that MC concentrations varied in accordance with algae growth in Dianchi Lake. The results obtained in the laboratory demonstrated that the removal of MC with fresh sediments was less than 10%, photoirradiation removed more than 75% MC within two hours, and the biodegradation needed much longer time to produce substantial degradation of MC. The results suggest that bioaccumulation of microcystins in fish was not significant in Dianchi Lake.

Application and validation of a new biotic index using data from several water systems

Protozoans of Lake Donghu were collected from five stations using the PFU method. The sampling was conducted for one year and two times a month. The aim of this research was to test the applicability of a new protozoa biotic index, species pollution value (SPV) and community pollution value (CPV), established by the authors using data from the River Hanjiang. Each station's CPV was calculated from the SPV and the correlation analysis between the CPV and the comprehensive chemical index of stations I, II, III showed a significant correlation between them. The pollution status of the five stations was correctly evaluated by the CPV. These results suggested that the biotic index could be applied in water systems other than the River Hanjiang. The SPV of some protozoa species in Lake Donghu, not observed in the River Hanjiang were established. In order to further test the applicability of the biotic index, protozoan and chemistry data from the Rivers Torrente Stirone and Parma of Italy were used. The results showed that the CPV for the two rivers had a close relationship with the chemical water quality, which indicated that the biotic index could be applied in other parts of the world for the monitoring and estimating of water quality. Since the results of testing and verifying the biotic index in some other water systems in China were also satisfactory, this indicated that the biotic index has an extensive suitability for freshwater ecosystems. As long as more than 50% of the species in a sample have a SPV, the CPV calculated from the SPV is reliable for monitoring and evaluating water quality.

Silver carp, Hypophthalmichthys molitrix, in the Poyang Lake belong to the Ganjiang River population rather than the Changjiang River population

The Poyang Lake is the largest lake and the main nursery area in the middle basin of the Changjiang (Yangtze) River. We compared molecular genetic markers of silver carp among populations of the Changjiang River, the Ganjiang River and the Poyang Lake using the ND5/6 region of mtDNA. Analysis of restriction fragment length polymorphisms (RFLPs) of this region revealed distinct variation between the Ganjiang River and the Changjiang River populations. The Poyang Lake is linked with the Ganjiang River and the Changjiang River. Shared RFLP fragments between the Ganjiang River population and the Poyang Lake population are as high as 61.4%. The value is 47.74% between the populations of the Changjiang River and that of the Poyang Lake. Frequencies of bands peculiar to the Ganjiang River population are the same as in the Poyang Lake population. We conclude that the Poyang Lake silver carp population consists mainly of the Ganjiang River population. The water level of the Poyang Lake outlet, which is higher than that of the Changjiang River in the silver carp spawning season, supports this conclusion.

Food habits of two-year-old Chinese mitten crab (Eriocheir sinensis) stocked in Lake Bao'an, China

Gastric mills of 362 specimens of two-year-old Chinese mitten crab (Eriocheir sinensis), which contained recognizable food items, from Lake Bao'an, China were examined. The food items were macrophytes, algae, arthropods, oligochaetes, fish, protozoa, rotifers, gastropods, and detritus, and the percent frequencies of occurrence (FO) for these items were 87.3%, 82.0%, 48.2%, 28.2%, 28.7%, 0.3%, 0.6%, 0.3% and 88.7%, respectively. Unidentified animal tissue was often observed and had a FO of 46.1%. In total, FO of plants (macrophytes + algae) was 87.7% and of animals was 89.8%. However, 5.8% of the gastric mills contained only animals, 5.3% had only macrophytes, and 0.3% contained only algae. There was no significant difference (p>0.05) in food habits between male and female crabs. The ratio of cell number of macrophytes to algae was about 156:1.

The low TN : TP ratio, a cause or a result of Microcystis blooms?

An enclosure experiment in the shallow, subtropical Lake Donghu, China, was performed in the summer of 2001 to examine the effect of TN:TP (total phosphorus) ratios and P-reduction on the occurrence of Microcysitis blooms. The treatments were performed with enough amounts of N but with different amounts of P in the water column and sediment. Microcystis blooms occurred in the enclosures either with an initial TN:TP <29 or TN:TP >29 where the nutrients (N, P) were high enough. Microcysitis blooms never occurred in the treatments with low P concentration in spite of the presence of sufficient N. The P-rich sediments served as an important source for the P supply in the water column, and such a process was activated greatly by the outburst of Microcystis blooms which pumped up selectively P from the sediments and thus decreased the TN:TP ratios. Therefore, the low TN:TP ratio is not a cause but rather a result of Microcystis blooms. (C) 2002 Elsevier Science Ltd. All rights reserved.