The Effects Of Water Taking On Physical And Chemical Qualities And Distribution Of Plankton Communities At South Lake

Eutrophication has become one of the most important environmental pollution problemsof lakes and reservoirs in China .Water taking is one of the effective methods to cope with thelake eutrophication and improve the water quality.A project of water taking has been carried at South Lake of Changchun, Jilin ProvinceChina in 2005 in order to control the eutrophication. The physical-chemical characteristicsof water quality and the distribution of plankton communities have been investigated monthlyat 4 sample sites during the period from May to October 2005,. The objective of this paperaims to determine the effects of water taking on the water quality and distribution of planktoncommunities of the South Lake. The results were as follow:(1) The effects of water taking on suspended solids (SS) and Secchi disk depth (SD) ofsurface water were negligible, while the contents of dissolved oxygen (DO), pH value,chemical oxygen demand (CODcr) and total nitrogen (TN), ammonia nitrogen (NH4-N),total phosphorus (TP) decreased. Biological oxygen demand for five days (BOD5) increased.(2) After water taking, the species number of phytoplankton was 374, increasing by 62%with the comparison of pre-water taking period. The order of the quantities of the specieswere Chlorophyta > Bacillariophyta>Cyanophyta >Euglenophyta. The number ofChlorophyta and Cyanophyta did not changed, while that of Bacillariophyta decreased,Pyrrophrta and Chrysophyta increased. The average density of phytoplankton was 4.585×107ind/L;and Chlorophyll-a was 108.19μg/L.(3) Most dominant species of phytoplankton were α – ps and β – ps. The phytoplanktoncommunity was still chlorophyta-bacillariophyta-cyanophyta after water taking.(4) The species numbers of zooplankton were 126 in 2005, and most of the dominantspecies of phytoplankton were α – ps and β – ps. The zooplankton community was mainlyconsisted of protozoa, rotifer, cladocera and copepoda .The Margalef Index of zooplanktoncommunity increased from 1.96 to 5.99. The amount of zooplankton prior to and after watertaking averaged 3000 ind/L with litter change.(5) The TSIM value exceeds 53, which showed south lake is still in a eutrophication stateof water body.