The impact of planktivorous fishes on microcystin concentrations in Meiliang Bay, Lake Taihu, China

In an eight-month enclosure experiment in Meiliang Bay of Lake Taihu, a shallow subtropical lake in China, silver carp (Hypophthalmichthys molitrix) and bighead carp (Aristichthys nobilis) collectively reduced cyanobacterial biomass. Microcystin concentration was six times higher in the 0.35 km(2) control enclosure (without fish) than in two similar-sized enclosures that had been stocked with both carp species. Furthermore, toxic Microcystis spp. increased microcystin production when exposed to silver carp and bighead carp.

Population genetic structure of Carchesium polypinum (Ciliophora : Peritrichia) in four chinese lakes inferred from ISSR fingerprinting: High diversity but low differentiation

Although the peritrichous ciliate Carchesium polypinum is common in freshwater, its population genetic structure is largely unknown. We used inter-simple sequence repeat (ISSR) fingerprinting to analyze the genetic structure of 48 different isolates of the species from four lakes in Wuhan, central China. Using eight polymorphic primers, 81 discernible DNA fragments were detected, among which 76 (93.83%) were polymorphic, indicating high genetic diversity at the isolate level. Further, Nei's gene diversity (h) and Shannon's Information index (I) between the different isolates both revealed a remarkable genetic diversity, higher than previously indicated by their morphology. At the same time, substantial gene flow was found. So the main factors responsible for the high level of diversity within populations are probably due to conjugation (sexual reproduction) and wide distribution of swarmers. Analysis of molecular variance (AMOVA) showed that there was low genetic differentiation among the four populations probably due to common ancestry and flooding events. The cluster analysis and principal component analysis (PCA) suggested that genotypes isolated from the same lake displayed a higher genetic similarity than those from different lakes. Both analyses separated C. polypinum isolates into subgroups according to the geographical locations. However, there is only a weak positive correlation between the genetic distance and geographical distance, suggesting a minor effect of geographical distance on the distribution of genetic diversity between populations of C. polypinum at the local level. In conclusion, our studies clearly demonstrated that a single morphospecies may harbor high levels of genetic diversity, and that the degree of resolution offered by morphology as a marker for measuring distribution patterns of genetically distinct entities is too low.

Genetic diversity of common carp from two largest Chinese lakes and the Yangtze River revealed by microsatellite markers

Six polymorphic microsatellites (eight loci) were used to study the genetic diversity and population structure of common carp from Dongting Lake (DTC), Poyang Lake (PYC), and the Yangtze River (YZC) in China. The gene diversity was high among populations with values close to 1. The number of alleles per locus ranged from 2 to 11, and the average number of alleles among 3 populations ranged from 6.5 to 7.9. The mean observed (H (O)) and expected (H (E)) heterozygosity ranged from 0.4888 to 0.5162 and from 0.7679 to 0.7708, respectively. Significant deviations from Hardy-Weinberg Equilibrium expectation were found at majority of the loci and in all three populations in which heterozygote deficits were apparent. The analysis of molecular variance (AMOVA) indicated that the percent of variance among populations and within populations were 3.03 and 96.97, respectively. The Fst values between populations indicated that there were significant genetic differentiations for the common carp populations from the Yangtze River and two largest Chinese freshwater lakes. The factors that may result in genetic divergence and significant reduction of the observed heterozygosity were discussed.

Contributions of phosphatase and microbial activity to internal phosphorus loading and their relation to lake eutrophication

Phosphatase may accelerate the process of lake eutrophication through improving phosphorus bioavailability. This mechanism was studied in three Chinese eutrophic shallow lakes (Lake Taihu, Lake Longyang,and Lake Lianhua). Phosphatase activity was related to the concentration of soluble reactive phosphorus (SRP) and chlorophyll a. Stability of dissolved phosphatase in reverse micelles may be attributed to molecular size, conformation and active residues of the enzyme. At the site with Microcystis bloomed in Lake Taihu, dissolved phosphatase activity was higher and more stable in micelles, SRP concentrations were lower in interstitial water, the contents of different forms of phosphorus and the amounts of aerobic bacteria were lower while respiration efficiency was higher in sediments. Phosphobacteria, both inorganic and organic and other microorganisms were abundant in surface water but rare in sediments. Therefore, internal phosphorus may substantially flux into water column by enzymatic hydrolysis and anaerobic release, together with mobility of bacteria, thereby initiating the bloom. In short, biological mechanism may act in concert with physical and chemical factors to drive the internal phosphorus release and accelerate lake eutrophication.

Optimization of an effective extraction procedure for the analysis of microcystins in soils and lake sediments

Microcystin analysis in sediments and soils is considered very difficult due to low recovery for extraction. This is the primary limiting factor for understanding the fate of toxins in the interface between water and sediment in both the aquatic ecosystem as well as in soils. In the present study, a wide range of extraction solvents were evaluated over a wide range of pH, extraction approaches and equilibration time to optimize an effective extraction procedure for the analysis of microcystins in soils and lake sediments. The number of extractions required and acids in extraction solutions were also studied. In this procedure, EDTA-sodium pyrophosphate solution was selected as an extraction solvent based on the adsorption mechanism study. The optimized procedure proved to be highly efficient and achieved over 90% recovery. Finally, the developed procedure was applied to field soil and sediment sample collected from Chinese lakes during bloom seasons and microcystins were determined in six of ten samples. (c) 2005 Elsevier Ltd. All rights reserved.

Stocking models of Chinese mitten crab (Eriocheir japonica sinensis) in Yangtze lakes

The fanning of Chinese mitten crab, a quality aquatic product in China and neighbouring Asian countries, has been developing rapidly in China since last decade. It reached a total yield of 3.4 X 10(5) tonnes in 2002. Due to the successive over-stocking year after year, many lakes in the mid-lower Yangtze Basin, the main farming area, are under deterioration, leading to a reduction of crab yield and quality, and, subsequently, a loss of fanning profits. Aiming at a normal development of crab culture and the sustainable use of lakes, an annual investigation dealing with lake environmental factors in relation to stocked crab populations was carried out at 20 farms in 4 lakes. The results show that the submersed macrophyte biomass (B-Mac) is the key factor affecting annual crab yield (CY). Using the ratio of Secchi depth to mean depth (Z(SD)/Z(M)), an easily measured parameter closely correlated to BMac, as driving variable, 10 regression models of maximal crab yields were generated (r(2) ranging 0.49-0.81). Based on the theory of MSY (Maximum Sustainable Yield), in combination with body-weight (BW) and recapture rate (RR) of adult crabs, a general optimal stocking model was eventually formulated. All models are simple and easy to operate. Comments on their applications and prospects are given in brief. (c) 2006 Elsevier B.V. All rights reserved.

Detection of extracellular phosphatases in natural spring phytoplankton of a shallow eutrophic lake (Donghu, China)

The species-specific production of extracellular phosphatases in phytoplankton of a subtropical polymictic take was investigated from March to May 2004. Phosphatase activity was detected directly at the site of enzyme action using the enzyme-labelled fluorescence (ELF) technique. Size fractionation of bulk phosphatase activity (PA), concentrations of soluble reactive phosphorus (SRP), chlorophyll a, and phytoplankton composition were determined in parallel. Phosphatase-positive cells were present in every phytoplankton sample; labelled cells were detected in 33 algal taxa, including many chlorophytes, dinoflagellates and some diatoms, but never among cyanobacteria. We recorded an unusual dinoflagellate bloom (Peridiniopsis sp.), of which similar to 25% of the cells were phosphatase-positive. Several populations were partly phosphatase-positive whenever present, while some other species never showed any activity. The production of extracellular phosphatases was not primarily regulated by ambient P concentrations; algae produced these enzymes even if SRP concentrations were high. Moreover, heterotrophic nanoflagellates most probably contributed to the pool of particle-bound PA in some samples.

Molecular phylogenetics of Gymnocypris (Teleostei : Cyprinidae) in Lake Qinghai and adjacent drainages

149 complete mitochondrial DNA (mtDNA) cytochrome b (Cyt b) genes (1140 bp) of Gymnocypris przewalskii, Gymnocypris eckloni and Gymnocyptis scolistomus from the Lake Qinghai, Yellow River and Qaidam Basin were sequenced and analyzed. Consistent dendrogram indicated that the samples collected from the same species do not constitute a separate monophyletic group and all the samples were grouped into three highly divergent lineages (A, B and C). Among them, Lineage A contained all samples of G. przewalskii from the Lake Qinghai and partial samples of the G. eckloni from the Yellow River. Lineage B contained the remaining samples of G. eckloni from the Yellow River. Lineage C was composed of a monophyletic group by G. eckloni from the Qaidam Basin. Analysis of molecular variance (AMOVA) indicated that most of genetic variations were detected within these three mtDNA lineages (93.12%), suggesting that there are three different lineages of Gymnocypris in this region. Our Cyt b sequence data showed that G. przewalskii was not a polytypic species, and G. scolistomus was neither an independent species nor a subspecies of G. eckloni. The divergent mtDNA lineages of G. eckloni from the Yellow River suggested that gene flow between the different populations was restricted to a certain extent by several gorges on the upper reach of the Yellow River. Lineage B of G. eckloni might be the genetic effect from the ancestor which was incorporated with the endemic schizothoracine fishes when the headward erosion of the Yellow River reached to its current headwaters of late. The G. eckloni from Basin Qaidam was a monophyletic group (lineage C) and F-st values within G. eckloni from the Yellow River were higher than 0.98, suggesting that the gene flow has been interrupted for a long time and the G. eckloni from Basin Qaidam might have been evolved into different species by ecology segregation. The correlation between the rakers number of Gymnocypris and population genetic variation was not significant. All Gymnocypris populations exhibited a low nucleotide diversity (pi = 0.00096-0.00485). Therefore the Gymnocyptis populations from Basin Qaidam could have experienced severe bottleneck effect in history. Our result suggested Gym-nocypris populations of Basin Qaidam should give a high priority in conservation programs.

Negative effects of Microcystis blooms on the crustacean plankton in an enclosure experiment in the subtropical China

Effects of Microcystis blooms on the crustacean plankton were studied using enclosure experiments during July-September, 2000. Eight enclosures were set in the hypereutrophic Donghu Lake. Different nutrient concentrations through additional nutrient and sediment in enclosures were expected to result in different abundance of Micropystis. From July to early August, the phytoplankton community was dominated by Chlorophyta, Cryptophyta, Bacillariophyta and Cyanophyta other than Microcystis aeruginosa. M. aeruginosa showed a rapid increase during early August in all enclosures and predominated. Crustacean plankton was dominated by the herbivorous Moina micrura, Diaphanosoma brachyurum and Ceriodaphnia cornuta, and the predaceous Mesocyclops sp. and Thermocyclops taihokuensis. During the pre-bloom period, the dynamics of M. micrura population appeared to be mainly affected by the predaceous cyclopoids. With the development of Microcystis blooms, such interaction between M. micrura and cyclopoids seemed weakened, especially when the Microcystis biomass was high. But there was no apparent influence on the interaction between Leptodora kindti and its zooplanktonic prey. The density of two cyclopoids decreased with the enhancement of Microcystis. The density decline of M. micrura was caused by both predation and inhibition by Micropystis. The low food availability of other edible phytoplankton during the blooms led to low densities of both C. cornuta and D. brachyurum by late August. It appears that dense Microcystis blooms exert strong negative effects on the herbivorous cladocerans and the predaceous cyclopoids.

Attenuation of photosynthetically available radiation by chlorophyll, chromophoric dissolved organic matter, and tripton in lake Donghu, China

The attenuation coefficient of photosynthetically available radiation [K-d(PAR)] and three water quality parameters [chlorophyll a (chl a)], chromophoric dissolved organic matter (CDOM) and tripton] were measured at three stations in shallow, subtropical Lake Donghu from April 2003 to March 2004. The multiple regression equation of K-d(PAR) versus chl a, CDOM, and tripton was: K-d(PAR) = 0.44 + 0.019 chl a + 1.88 CDOM + 0.016 tripton, which revealed the relative contributions of the three parameters to K-d(PAR). The effects of water and CDOM on K-d(PAR) were of minor importance (19-26%), while chl a and tripton were the two greatest contributors, accounting collectively for 74-81%.

Differing estrogen activities in the organic phase of air particulate matter collected during sunny and foggy weather in a Chinese city detected by a recombinant yeast bioassay

Total air suspended particles (PM 100) collected from an urban location near a traffic line in Wuhan, China, were examined for estrogen using a recombinant yeast bioassay. Wuhan, located at the central part of China, is the fourth biggest city in China with 7 million populations. Today, Wuhan has developed into the biggest city and the largest traveling center of central China, becoming one of the important bases of industry, education and research. Wuhan is right at the confluent point of Yangzi River, the third longest river in the world, and its largest distributary Hanjiang, with mountains and more than 100 takes in downtown area. Therefore, by its unique landscape, Wuhan has formed clear four seasons with relatively long winter and summer and short spring and autumn. Foggy weather usually happen in early spring. The yeast line used in this assay stably expresses human estrogen receptor-alpha. Weak but clear estrogenic activities were detected in the organic phase of crude extracts of air particle materials (APM) in both sunny and foggy weather by 0.19-0.79 mug E2/gPM(100) which were statistically significantly elevated relative to the blank control responding from 20% to 50% of the maximum E2 response, and the estrogenic activity was much higher in foggy weather than in sunny weather. The estrogenic activities in the sub-fractions from chromatographic separation of APM sampled in foggy days were also determined. The results indicated that the responses of the fractions were obviously higher than the crude extracts. Since there is no other large pollution source nearby, the estrogenic material was most likely from vehicle emissions, house heating sources and oil fumes of house cooking. The GC/MS analysis of the PM100 collected under foggy weather showed that there were many phenol derivatives, oxy-PAHs and resin acids which have been reported as environmental estrogens. These results of the analysis of estrogenic potency in sunny and foggy weather in a subtropical city of China indicate that further studies are required to investigate the actual risks for the associated health and atmospheric system. (C) 2004 Elsevier Ltd. All rights reserved.

The picophytoplankton in three Chinese lakes of different trophic status and its relationship to fish populations

A year-round comparison was made of the picophytoplankton populations in three lakes of different trophic status (oligotrophic, mesotrophic, and hypereutrophic), as well as in experimental enclosures stocked with various densities of fish. Picophytoplankton abundance was significantly different between the hypereutrophic lake and the oligotrophic lake (P<0.018) and between the hypereutrophic lake and the mesotrophic lake (P<0.021), whereas the difference between the mesotrophic and oligotrophic lakes was not significant (P<0.745). The effect of total nitrogen:total phosphorus ratio on the abundance of picophytoplankton was demonstrated in the oligotrophic lake, but such effect did not manifest itself in the other lakes or in the experimental enclosures. The average annual picophytoplankton population sizes in the three lakes in 1995-1998 were correlated with estimated fish abundance (r=0.824, n=9, P=0.006). The results of enclosure experiments demonstrated that the abundance of picophytoplankton increased with the stocking density of fish (r=0.619, n=8, P=0.100).

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.

Measurement of estrogen activity in two Chinese lakes

Estrogenic activities of samples from two Chinese lakes, Ya-Er Lake and Donghu Lake, were measured by in vitro recombinant yeast assay and found in both lakes polluted with industrial and domestic wastewater. In methanol extracts of lake water samples the estrogen-like activity was higher than in toluene extracts. These results have been inverted for solid samples. Furthermore, the EC50 value of the water samples was close to the original concentration in the lake.

Kinetics of alkaline phosphatase in lake sediment associated with cage culture of Oreochromis niloticus

Variations in kinetics of alkaline phosphatase occurring in different sites of sediment associated with cage culture of Oreochromis niloticus in a shallow Chinese freshwater lake (Lake Donghu) were described. In addition, the kinetic parameters of each 2.5-cm stratum in the sediment from the surface down to 37.5 cm were analyzed. Horizontally, the V-max values of alkaline phosphatase in surface sediments increased markedly at sites immediately under and adjacent to the cage that would be subjected to the deposition of fish feces. Peak V-max values in the top 5 cm of the sediment under the cage were also observed relative to their deeper control. After a treatment where the fish feces were added over 12 days, the sediment in deeper layer exhibited a significantly higher V-max value, thereby corroborating the relationship between V-max values of alkaline phosphatase and fish feces in sediments. The fish feces exhibited a remarkable alkaline phosphatase activity (APA). Thus, it is indeed a source of the enzyme. Effects of the fish feces were dose- and time-dependent. The V-max values in sediments were always stimulated, but the K-m values showed much more variability. (C) 2001 Elsevier Science B.V. All rights reserved.