To study the impact of pollution sources on the eutrophication characteristic of reservoirs, three reservoirs (Shiyan, Dajingshan and Dashuiqiao) were sampled to measure the nutrients and planktons in 2000. The trophic state index of the three reservoirs indicated that the Shiyan reservoir is eutrophic, Dajingshan reservoir and Dashuiqiao reservoir are meso-eutrophic. The eutrophication of the three reservoirs was characterized with the pollution sources, especially, the reservoirs have different dynamics of trophic levels. Shiyan reservoir was principally polluted by municipal sewage. The nitrogen and phosphorous concentrations and plankton abundance in Shiyan reservoir are the highest of the reservoirs, and highly abundant Euglena Ehr. was observered in both flood season and dry season. Shiyan reservoir is heavily loaded with organic pollution. Dashuiqiao reservoir is mostly polluted through agricultural activity, the concentrations of PO4-P and TP in the flood season is much higher than in the dry season. The Cyanophyta's abundance is dominant in the flood season and the Bacillariophyta in the dry season. Dajingshan reservoir was polluted by industrial sewage mainly. In this reservoir there were distinct seasonal variations in TP concentration and zooplankton abundance, and the variations were controlled by pumping water from a river.
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