Effects Of Ecological Purification Simulation Experiment In Water Sources On Phytoplankton Community Structure

Safe drinking water sources is an important factor in the harmony and development of social economy and the people’s health and stablility.Providing safe drinking water is the one among the four major water problems that the word is facing.The key to ensure the safety of drinking water is to protect the drinking water sources.And the growth of phytoplankton in the drinking water resources is one of the important factors that threat to water quality stability.Intuitively,it can be supposed that a large input of allochthonous phytoplankton may change the composition of phytoplankton communities in lakes.According to the function of the reservoir,the reseach sets up four experimental scheme to study the effect of water quality purification.The shape,area distribution and the water depth of the reservoir are simulated in each scheme.From August 2014 to June 2015,the phytoplankton samples were collected quarterly.And when the hydraulic retention time is 2d,3d,5d and 7d,we collect the samples in each quarter and in the reseach,the total of 18 samples were investigated.By comparing the changes in different experimental schemes phytoplankton community structure to analyze the effects of the planting density of aquatic macrophytes and the ecological floating bed and the subsidence area and the hydraulic retention time on the phytoplankton community structure.It provides the basic date for the prevention of eutrophication and the design and construction of the water resources.The main results as follows:1. Be raised the subsidence area,increased the water transparency and the biomass of phytoplankton.The results showed that Phytoplankton biomass range are respectively 1.90*106~7.14*106,3.89*106~2.41*107/L and 3.01*106~1.58*107/L, the variation range of transparency are 11~15cm,46~89cm and 40~67cm in the source of water, A basin and B basin.2. Planting density of aquatic higher plants had an effect on growth of phytoplankton. The biomass of phytoplankton in water with denser aquatic higher plants was far below those in water with sparse aquatic higher plants when the hydraulic retention time was more than 5 days. In spring and autumn, The higher the density of aquatic higher plants was, the lower the biomass of phytoplankton was. But in summer, both the biomass of phytoplankton in test pool with high density(50%) and test pool with low density(30%) was low, and showed no difference. At any season and under any HRT, the biomass of Cyanophyta remained exceedingly low when the density of aquatic higher plants was high.3. Ecological floating bed had an effect on the growth of phytoplankton. when the hydraulic retention time was 3 days, ecological floating bed showed strong competitiveness, the biomass of phytoplankton was lower in the water with ecological floating bed. In the water with ecological floating bed, the biomass of phytoplankton remained exceedingly low in spring, summer and autumn. In the water with no ecological floating bed, the biomass of phytoplankton in spring and autumn were extremely high(over 10 million/L), but it was very low in summer. The biomass of Cyanophyta in the water with ecological floating bed remained exceedingly low.4. Planting density of aquatic macrophytes, ecological floating bed and subsidence area have a little effect on phytoplankton species and dominant species.And phytoplankton species in diferent experimental schemes has changed from 81 to 93, dominant species all are Chlamydomonas sp., Chroomonas acuta, Cryptomonas erosa, Cyclotella sp., and Melosira granulata.5. By comparing the phytoplankton biomass and chlorophyll a in different hydraulic retention time(HRT=2d, 3d, 5d and 7d),found that,overall,they will increase when hydraulic retention time become longer.And phytoplankton biomass and chlorophyll a are relatively low if we keep hydraulic retention time within 5 days.However,when the hydraulic retention time equal to 7 days, phytoplankton twill grow rapidly and it’s biomass will increase highly,even more than 15 million/L that is the threshold of blooms outbreak,and chlorophyll a also more than 10 ug/L that is eutrophication threshold.Therefore, the best hydraulic retention time is to keep within 5 days,which can effectively prevent water from damaging by phytoplankton blooms.6. The species and biomass of the phytoplankton in diferent experimental schemes obvious seasonal change,and it’s higher in the spring and winter,it’s lower in the summer and fall.