Eutrophication And Phytoplankton Assemblages Of Reservoirs For Drinking Water Supply In Zhuhai

Middle and small sized reservoirs provide drinking water for Zhuhai city.Because of the limited watershed, natural precipitation can not meet the requirementof water supply, thus, water from downstream rivers is pumped into reservoirs ascomponsation. Due to the high loads of total phosphorus and nitrogen from thedownstream of Pearl River, the reservoirs are experiencing the process ofeutrophication. This thesis applied trophic state index and functional groups toexplore the eutrophication level and structures of phytoplankton community in thereservoirs. Key environmental factors shaping the structures of the phytoplanktonfunctional groups were discussed. The results showed that:1. All the18middle and small sized reservoirs in Zhuhai city were mesotrophicto eutrophic, The variation of eutrophication level between pumped storage reservoirsand normal reservoirs were not significant in2006. However, pumped reservoirsshowed significantly higher eutrophication level than that of normal reservoirs. Themain reason for the discrepancy in TSI level was water pumping.2. In January2013, functional groups:1b (large dinophytes),7b (small pennatediatoms), etc., dominated in the most normal reservoirs, reflecting the longer waterretention time and higher underwater light availability of normal reservoirs.Functional groups:5a (thin filamentose cyanobacterias),6a (large centric diatoms),3b(Eudorina sp. etc.), etc., dominated in most of the pumped storage reservoirs. Due tolow water level and water supply in the dry seasons, these reservoirs had highernutrient level and poor stability. In November2013, functional groups:1b,8a (largeunicellular desmidiaceae), etc., dominated in the most normal reservoirs. As theconsequence of large amount of inflow through pumping, the dominating functionalgroups in the pumped storage reservoirs were5b,6a,4(unicellular cyanobacterias).3. Data analysis showed that water supply (outflow) and total nitrogenconcentrations were the most important factors affecting phytoplankton community inall reservoirs January2013. In November2013, water pumping (inflow) and dissolved nitrogen concentrations were the most important factors affectingphytoplankton community. However, inflow and outflow were not directly effectedfactors for phytoplankton community. It was found that water retention time alsoplayed an important role in influencing phytoplankton community. Thus, byinfluencing the water retention time and nutrient level, pumping of inflow andoutflow water shape the phytoplankton community structure through changinghydrolic condition as well as nutrient concentration.