Search

Bloom-forming cyanobacteria have been observed with increasing frequency in Poyang Lake, China since 2000. In the present study, we examined the mechanisms responsible for the horizontal distribution of these blooms in the main body of Poyang Lake. Specifically, we addressed the hypothesis that colonies of cyanobacteria are first generated in the Eastern Bay (EB, lentic region) and then advected offshore by large-scale horizontal transport processes, with the colonies subsequently found in Northern Poyang Lake (NPL, lotic region). The cyanobacteria biomass in the EB was significantly greater than that in NPL ( P < 0.0001), and negative correlations were observed between cyanobacteria biomass and nutrient concentrations in the EB. However, significant correlations were not observed between cyanobacteria biomass and nutrient concentrations in NPL. The peak abundance of cyanobacteria was first observed in the EB, with the cyanobacterial abundance peak in NPL lagging the EB peak by approximately 1 month. These results are all consistent with the cyanobacteria distribution hypothesis and show the potential for the accumulation of cyanobacteria in NPL that are normally considered unsuitable for in situ growth in EB. Variations of cyanobacteria biomass in eutrophic lakes, including Yangtze-connected (Poyang Lake and Dongting Lake) and Yangtze-isolated (Taihu) lakes, were monitored during summer (July-August), and eutrophic or even polytrophic conditions were not observed to support the development of cyanobacteria. Instead, a high rate of water flow with short retention times was the key factor preventing the accumulation of cyanobacteria in these eutrophic lakes. Therefore, the mean cyanobacteria biomass was significantly lower in the Yangtze-connected lakes (Poyang Lake, 1.01 mg l; Dongting Lake, 1.71 mg l) than in Taihu Lake at Meiliang Bay (13.54 mg l) or the mouth (3.45 mg l) ( P < 0.0001); however, the biomass more closely resembled Taihu Lake at the center (0.88 mg l). As expected, the cyanobacteria biomass was lower in the lakes with hydraulic connections to the Yangtze River compared with those isolated from the Yangtze River. This study revealed that hydrological parameters dominated the accumulation of cyanobacterial blooms in the Yangtze-connected eutrophic lakes in eastern China. [ABSTRACT FROM AUTHOR]

Arsenic species including arsenite, arsenate, and organic arsenic were measured in the porewaters collected from Poyang Lake, the largest freshwater lake of China. The vertical distributions of dissolved arsenic species and some diagenetic constituents [Fe(II), Mn(II), S(−II)] were also obtained in the same porewater samples in summer and winter. In sediments the concentration profiles of total As and As species bound to Fe-Mn oxyhydroxides and to organic matter were also determined along with the concentrations of Fe, Mn and S in different extractable fractions. Results indicate that, in the summer season, the concentrations of total dissolved As varying from 3.9 to 55.8μg/L in sediments were higher than those (5.3-15.7μg/L) measured in the winter season, while the concentrations of total As species in the solid phase varied between 10.97 and 25.32mg/kg and between 7.84 and 30.52mg/kg on a dry weight basis in summer and winter, respectively. Seasonal profiles of dissolved As suggest downward and upward diffusion, and the flux of dissolved As across the sediment-water interface (SWI) in summer and winter were estimated at 3.88mg/m2a and 0.79mg/m2a, respectively. Based on porewater profiles and sediment phase data, the main geochemical behavior of As was controlled by adsorption/desorption, precipitation and molecular diffusion. The solubility and migration of inorganic As are controlled by Fe-Mn oxyhydroxides in summer whereas they appear to be more likely controlled by both amorphous Fe-Mn oxyhydroxides and sulfides in winter. A better knowledge of the cycle of As in Poyang Lake is essential to a better management of its hydrology and for the environmental protection of biota in the lake. [ABSTRACT FROM AUTHOR]