Seasonal variations in microbial parameters and trophic states in a large Chinese shallow lake (Lake Taihu)

During 2008-2009, a study was performed in two stations of the shallow Lake Taihu, to assess the response of microbial activities and biomass to environmental changes. The rates of microbial enzymatic activities (leucine aminopeptidase, LAP, beta-glucosidase, ?-GLU; alkaline phosphatase, AP) and heterotrophic prokaryotic production (HPP), and the amount of total prokaryotic biomass (PB) were estimated during two seasonal periods, together with the physical and chemical parameters. Variations in environmental and microbial parameters were more significant in seasonal scale than those in spatial one. All the microbial activities increased from autumn to spring, however only the GLU activity was statistically significant. HPP and PB did not undergo significant temporal changes throughout the study period. In spring, the decomposition data were not significantly related to the trophic parameters in spatial scale. Conversely, in autumn, high decomposition processes were associated to high production of new biomass (both phytoplanktonic and prokaryotic) at the station located in the eutrophic Meiliang Bay, showing a tight coupling between polymer degradation and monomer uptake and efficient incorporation of the carbon released by enzymatic hydrolysis into new biomass. Thus, it is suggested that distinct regulation pathways of microbial metabolism existed in different seasons in large shallow lakes.