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.

Use of PFU protozoan community structural and functional characteristics in assessment of water quality in a large, highly polluted freshwater lake in China

Structural and functional parameters of protozoan communities colonizing on PFU (polyurethane foam unit) artificial substrate were assessed as indicators of water quality in the Chaohu Lake, a large, shallow and highly polluted freshwater lake in China. Protozoan communities were sampled 1, 3, 6, 9 and 14 days after exposure of PFU artificial substrate in the lake during October 2003. Four study stations with the different water quality gradient changes along the lake were distinguishable in terms of differences in the community's structural (species richness, individual abundance, etc.) and functional parameters (protozoan colonization rates on PFU). The concentrations of TP, TN, COD and BOD as the main chemical indicators of pollution at the four sampling sites were also obtained each year during 2002-2003 for comparison with biological parameters. The results showed that the species richness and PFU colonization rate decreased as pollution intensity increased and that the Margalef diversity index values calculated at four sampling sites also related to water quality. The three functional parameters based on the PFU colonization process, that is, S-eq, G and T-90%, were strongly related to the pollution status of the water. The number of protozoan species colonizing on PFU after exposure of 1 to 3 days was found to give a clear comparative indication of the water quality at the four sampling stations. The research provides further evidence that the protozoan community may be utilized effectively in the assessment of water quality and that the PFU method furnishes rapid, cost-effective and reliable information that may be useful for measuring responses to pollution stress in aquatic ecosystems.

The precocious Chinese mitten crab: Changes of gonad, survival rate, and life span in a freshwater lake

Changes of the gonad. survival rate, and life span of the precocious (i.e., sexually mature in their first October-November, at the age of 5 or 6 months) Chinese mitten crab (Eriocheir sinensis) were studied in a small, shallow, macrophytic, freshwater lake along the middle reaches of the Changjiang River, China. The gonosomatic index (GSI) reached peak during the next March when the female GSI was 12.32 +/- 1.75 SD% and the male GSI A as 4.24 +/- 0.19%. The sexual glands degraded from then on. In the first ten-day period of the following July, there was no complete ovum in the ovary. and the sperm became thin and lost adhesion. The population declined sharply from November to July, and the last one (a female) died in the middle of July, which indicated that the life span of the precocious crab was about 12 months (from larval hatching in June to death in July of next year). The survival curve might be expressed as Y = 1.09exp(-0.018x) (Y survival rate; x: days) for the precocious crabs stocked in experimental cages.

Seasonal variation in kinetic parameters of alkaline phosphatase activity in a shallow Chinese freshwater lake (Donghu Lake)

Seasonal variation of the kinetic parameters of total alkaline phosphatase activity (APA) was studied in a shallow Chinese freshwater lake (Donghu Lake). At the three experimental stations the values of V-max of APA were higher and the negative correlation between orthophosphate and the total APA specific activity (V-max/Chl.) was stronger during summer (from June to September) P depletion. At the same time, the values of Michaelis constant (K-m) of APA at the three stations decreased. Phytoplankton seem to compensate for their phosphorus deficiency not only by an increase in enzyme production but also by an improved ability to use low substrate concentrations. (C) 1997 Elsevier Science Ltd.

UV-sensitive P compounds: Release mechanism, seasonal fluctuation and inhibitory effects on alkaline phosphatase activity in a shallow Chinese freshwater lake (Donghu Lake)

Filtrable phosphorus compounds in a shallow Chinese freshwater lake (Donghu Lake) were fractionated by Sephadex G-25 gel-filtration chromatography. Some portions of those compounds released soluble reactive phosphorus upon irradiation with low dose ultraviolet light. Catalase and a hydroxyl radical scavenger (mannitol) markedly prevented photosensitive phosphorus release. The observed effects may be explained by the action of oxidizing reagents such as hydroxyl radicals, produced in photochemical reactions between UV irradiation and humic substances in the water. There was a strong seasonality in UV-sensitive P (UVSP) release. Michaels constants (K-m) of total alkaline phosphatase in the lake water showed a direct positive relation to UVSP. Plot of K-m against the UVSP/phosphomonoester ratio reveals a strong relationship between the two variables. These results suggest that in some situations UVSP may be a competitive inhibitor of alkaline phosphatase activity in the lake. The competitive inhibition of fractionated UVSP on alkaline phosphatase reagent (Sigma) apparently supports this hypothesis.

Isolation of a novel cyanophage infectious to the filamentous cyanobacterium Planktothrix agardhii (Cyanophyceae) from Lake Donghu, China

A previously unknown cyanophage, PaV-LD (Planktothrix agardhii Virus isolated from Lake Donghu), which causes lysis of the bloom-forming filamentous cyanobacterium P. agardhii, was isolated from Lake Donghu, Wuhan, China. PaV-LD only lysed P. agardhii strains isolated from Lake Donghu and not those isolated from other lakes. The PaV-LD particle has an icosahedral, non-tailed structure, ca. 70 to 85 nm (mean +/- SD = 76 +/- 6 nm) in diameter. PaV-LD was stable at freezing temperature, but lost its infectivity at temperatures >50 degrees C. Lysis of host cells was delayed about 3 d after the PaV-LD treatment with chloroform, and the virus was inactivated by exposure to low pH (<= 4). The latent period and burst size of the PaV-LD were estimated to be 48 to 72 h and about 340 infectious units per cell, respectively. The regrowth cultures of surviving host filaments were not lysed by the PaV-LD suspension. To our knowledge, this is the first isolation and cultivation of a virus infectious to the filamentous bloom-forming cyanobacterium Planktothrix from a freshwater lake.

Seasonal variation of virioplankton in a eutrophic shallow lake

Lake Donghu is a typical eutrophic freshwater lake in which high abundance of planktonic viruses was recently revealed. In this study, seasonal variation of planktonic viruses were observed at three different trophic sites, hypertrophic, eutrophic, and mesotrophic regions, and the correlation between their abundances and other aquatic environmental components, such as bacterioplankton, chlorophyll a, burst size, pH, dissolved oxygen, and temperature, was analyzed for the period of an year. Virioplankton abundance detected by transmission electron microscope (TEM) ranged from 5.48 x 10(8) to 2.04 x 10(9) ml(-1) in all the sites throughout the study, and the high abundances and seasonal variations of planktonic viruses were related to the trophic status at the sampled sites in Lake Donghu. Their annual mean abundances were, the highest at the hypertrophic site (1.23x10(9) ml(-1)), medium at the eutrophic site (1.19x10(9) ml(-1)), and the lowest at the mesotrophic site (1.02x10(9) ml(-1)). The VBR (virus-to-bacteria ratio) values were high, ranging from 49 to 56 on average at the three sampled sites. The data suggested that the high viral abundance and high VBR values might be associated with high density of phytoplankton including algae and cyanobacteria in this eutrophic shallow lake, and that planktonic viruses are important members of freshwater ecosystems.

The temporal and spatial distribution, composition and abundance of Protozoa in Chaohu Lake, China: Relationship with eutrophication

Systematic investigations into the temporal and spatial distribution, composition and abundance of protozoa in two regions with different trophic levels in Chaohu Lake, a large, shallow and highly eutrophic freshwater lake in China, were conducted during 2002-2003. A total of 114 species of protozoa, including phytomastigophorans, zoomastigophorans, amoebae and ciliates, were identified from 120 polyurethane foam unit (PFU) samples exposed at four stations and from various types of natural substrates. Of the 114 taxa, 36 core species were found on PFU substrates and 23 of these were found on natural ones. Protozoan abundance and chemical physical parameters at nine sampling stations, four in the western lake and five in the eastern part, indicate trophic gradient changes along the lake. Seasonal variations in the species composition of major groups at littoral PFU sampling stations illustrate the effect of a severe algal bloom on the protozoan community structure. Temporal and spatial distributions of individual abundance as functions of water temperature and trophic status were revealed. This study demonstrates again that the PFU artificial substrate method samples protozoan communities more effectively than routine natural substrate methods. (c) 2005 Elsevier GmbH. All rights reserved.

Variation in stable isotope signatures of seston and a zooplanktivorous fish in a eutrophic Chinese lake

Temporal and spatial changes in delta(13)C and delta(15)N of seston (mainly phytoplankton) and isotopic relationship between seston and the lake anchovy (Coilia ectenes) were studied in the large eutrophic freshwater Lake Chaohu in China. Much of the spatial and temporal variation in delta(13)C of lake anchovies was explained by variation in seston, indicating a strong link between pelagic primary production and higher order consumers. Because the lake is shallow, there were no significant differences in delta(13)C and delta(15)N of seston between surface and overlying waters. Spatially, the relatively high delta(13)C and delta(15)N of seston in the western part of the lake might be due to high levels of anthropogenically derived N and C introduced from the surrounding cities through sewage drainage systems. The trophic position of the lake anchovy in the food web of Lake Chaohu was estimated to be 2.9-4.1 (3.5 +/- 0.4), which agrees well with the previous stomach content analysis suggesting that the lake anchovy fed both on zooplankton and small planktivorous fishes.

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.

Temporal and spatial variations in kinetics of alkaline phosphatase in sediments of a shallow Chinese eutrophic lake (Lake Donghu)

Monthly sediment and interstitial water samples were collected in a shallow Chinese freshwater lake (Lake Donghu) from three areas to determine if alkaline phosphatase activity (APA) plays an important role in phosphorus cycling in sediment. The seasonal variability in the kinetics of APA and other relevant parameters were investigated from 1995-1996. The phosphatase hydrolyzable phosphorus (PHP) fluctuated seasonally in interstitial water, peaking in the spring. A synchronous pattern was observed in chlorophyll a contents in surface water in general. The orthophosphate (o-P) concentrations in the interstitial water increased during the spring. An expected negative relationship between PHP and V-max of APA is not evident in interstitial water. The most striking feature of the two variables is their co-occurring, which can be explained in terms of an induction mechanism. It is argued that phosphatase activity mainly contributes to the driving force of o-P regeneration from PHP in interstitial water, supporting the development of phytoplankton biomass in spring. The V-max values in sediment increased during the summer, in Conjunction with lower K-m values in interstitial water that suggest a higher affinity for the substrate. The accumulation of organic matter in the sediment could be traced back to the breakdown of the algal spring bloom, which may stimulate APA with higher kinetic efficiency, by a combination of the higher V-max in sediments plus lower K-m values in interstitial water, in Summer. In summary, a focus On phosphatase and its substrate in annual scale may provide a useful framework for the development of novel P cycling, possible explanations for the absence of a clear relationship between PHP and APA were PHP released from the sediment which induced APA, and the presence of kinetically higher APA both in sediment and interstitial water which permitted summer mineralization of organic matter derived from the spring bloom to occur. The study highlighted the need for distinguishing functionally distinct extracellular enzymes between the sediment and interstitial water of lakes. (C) 2002 Elsevier Science Ltd. All rights reserved.

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.

Vertical variations in kinetics of alkaline phosphatase and P species in sediments of a shallow Chinese eutrophic lake (Lake Donghu)

The vertical distribution of the variables relevant to P forms in sediments were studied in a shallow Chinese freshwater lake (Lake Donghu) in 1997, 1998, 1999 and 2000, to assess the contribution of enzyme to P availability in sediment cores. Sediment P was fractionationd into iron-bound P, calcium-bound P, acid soluble organic P (ASOP) and hot NaOH extractable residual organic P. The former two species made the largest contribution to the sediment P pool. All P species exhibited significantly higher concentrations in different depths at Station I, compared with those found at Station II, except for ASOP. Coupled with these lower ASOP concentrations, the V-max data of alkaline phosphatase, measured on the same samples, were significantly higher at station I. Taken together, ASOP were probably important in supplying the enzymatic substrate (Phosphatase Hydrolyzable Phosphorus, PHP) into interstitial water. Dissolved orthophosphate and PHP concentrations were highly heterogeneous , but peaked in subsurface, paralleled by higher V-max and lower K-m values of alkaline phosphatase, throughout the sediment core. Sediment in the eutrophic lake is not only enriched in available P (iron-bound P), or stores residual P, but also tends to release PHP, thereby inducing the production of alkaline phosphatase and releasing o-P into water column by enzymatic hydrolysis. The latter process may also occur in relatively deep sediment layers.

Effects of submerged macrophytes on kinetics of alkaline phosphatase in Lake Donghu - I. Unfiltered water and sediments

The impacts of submerged macrophytes on kinetics of alkaline phosphatase were studied in two 680 m(2) enclosures in a shallow Chinese freshwater lake (Donghu Lake) from April to October 1996, and two experimental pools (120 m(2)) built inland in 1998. The submerged macrophytes were Vallisneria sp, Potamogeton crispus. In the presence of macrophytes, the concentration of orthophosphate was significantly lower, coupled with the decreasing function of organic P hydrolysis, in terms of lower V-max and higher K-m values of aIkaline phosphatase in water, filtered and unfiltered (0.45 mu m); in the interstitial water, the V-max values of the enzyme in sediments were significantly lower, exhibited by a spatial and vertical profile. The results implied the key role of submerged macrophytes was the retention of P nutrients. (C) 2000 Elsevier Science Ltd. All rights reserved.