Seasonal succession patterns of plankton in eutrophic rivers on plains

The typical annual circulation of phytoplankton in eutrophic rivers has been documented. However, there is still a conspicuous lack of consistency in subsequent reports. On the basis of an overall investigation of 15 eutrophic rivers on the Lower Yangze-Huai River Plain, the seasonal successions of phytoplankton according to morpho-functional groups (MFGs) were clustered. The results indicated fundamental agreement with the classic paradigm, but differences were found and tended to converge to at least three regular patterns. They were characterized respectively by: (1) winter peaks of large diatoms and a summer peak of cyanobacteria colonies, different zooplankton dominating alternately; (2) only a summer peak of blue-green filaments, rotifers dominating all year round; and (3) composite peaks of filamentous cyanobacteria, centric diatoms and small flagellates, extremely low zooplankton density. All were potentially driven by anthropogenic influences through significantly changing water environments. Pattern 1 often developed in rivers with slow flow controlled by physicochemical factors, which was attributed to high levels of water retention. Pattern 2 often developed in rivers with massive suspended sediment controlled by hydrological features, which was attributed to massive shipping. Pattern 3 often developed in rivers with significant levels of organic pollutants controlled by dissolved oxygen, which were attributed to the agricultural load and over-industrialization. As a successful application of MFGs, we suggest that this type of morpho-functional approach for phytoplankton performed better in statistical analysis targeted to general ecological laws than to local details about just one specific water body, though this approach still needs to be improved.