Identification of human-induced perturbations in Daya Bay, China: Evidence from plankton size structure

Plankton size structures were investigated based on estimated individual biovolumes at six typical stations of Daya Bay in the summer (August 2010) and winter (January 2011). The biomass size distribution (BSD) and the number size spectra (NSS) of plankton were established to analyze plankton size structures from taxonomic and ataxonomic perspectives, respectively. In Daya Bay, the phytoplankton individual biovolume was in the range of 64–496,757 µm3, and the zooplankton individual biovolume was in the range of 1.15×106–5.23×1011 µm3. The average biomasses of phytoplankton and zooplankton were 1.60 mg L−1 and 1.19 mg L−1 in the summer, and .42 mg L−1 and .35 mg L−1 in the winter, respectively. The ranges of the NSS slope were −1.94 to −.75, −2.60 to −.69, and −2.11 to −1.64 for phytoplankton, zooplankton, and total plankton, respectively. The ranges of the NSS intercepts were 13.17 to 23.97, −3.19 to 38.88, and 20.14 to 27.86 for phytoplankton, zooplankton, and total plankton, respectively. Our results indicate that the thermal water discharge from nuclear power plants, aquaculture and riverine nutrients significantly influenced the BSD and NSS patterns of plankton in Daya Bay. Moreover, the influence of aquaculture was more significant in the summer, and the influence of thermal water discharge was more significant in the winter. In general, a steeper NSS slope usually suggested more human-induced perturbations. The NSS parameters well reflected the horizontal variations of the environmental characteristics between these stations.