The Priliminary Study On The Spatial And Temporal Distribution And The Causes Of Algae Bloom In Chaohu Lake

In order to identify the main factors that influencing of alga blooming in Chaohu Lake,Situ observation and constructed enclosure simulation experiment were conducted for one year.Algae distribution in Chaohu Lake and Variation of dominant species was investigated.the inflow rivers are clustered and the pollution levels are classified by statistical methods and the correlation between algal biomass and the river nutrients input loads are derived.Inorganic nitrogen fluxes at water-sediment interface was analyzed, seasonal occurrence characteristics of the free nitrogen , the exchangeable nitrogen , the acid hydrolysable nitrogen and the residual nitrogen in the surface sediment of Chaohu Lake were studied by sequential extraction methods. Quantitative research on alga blooming process was conducted and horizontal transference and vertical hybrid effects of blooming alga caused by wind waves in Chaohu Lake were also observed.The results indicates that:(1) cyanobacteria algae dominated in bloom algae all the year round in Chaohu Lake, but different dominant species appeared in different seasons. Anabaena dominanted in spring with microcystis as subdominant specie; Microcystis dominated through the whole summer and autumn. The algae biomass in surface sediments had a tendency to gradually decrease from January to early summer, and minimum appeared between June and July ,while it increased through mid-summer and autumn, maximum appeared in winter. Multiple stepwise regression showed that temperature was the most significant factor which impacted the variation of algae biomass in Chaohu Lake.(2) the inflow rivers could be classified into three types, namely urban pollution rivers, clear aquatic flow rivers, and water quality stable rivers. The input load of CODMn,NH₄⁺-N,TN,TP from urban pollution rivers to the whole lake are 41.29%,89.49%,72.27% and 60.14% to all inflow rivers Respectively. Organic pollution is the main pollution resource of inflow rivers by factor analysis. The pollution rank of nine inflow rivers are as follows: Nanfei river>Shiwuli river>Paihe river>Shuangqiao river>Zhegao river>Yuxi river>Baishishan river>Zhaohe river>Hangbu river. The algal biomass and the NH₄⁺-N, TN, TP inputs of inflow rivers are positively correlated, while the TN inputs could increase the algal biomass more significantly.(3) Chaohu Lake could be divided into severe polluted area, moderately polluted area, and mildly polluted area from the west to the east. The Chla and DTN are the directive factors for the significantly spatial differentiation of water environment. The pollution classification sequence of monitoring sites was Nanfei river inlake area> Shiwuli river inlake area> Tangxi river inlake area> West lake center area> Paihe river inlake area> Hangbu river inlake area> Zhongmiao area> Zhaohe river inlake area> East lake center area> Ship factory> Zhonghan town area. The classification sequence of monthly average water environment quality was August> June> September > April> May> July> October> January> March> December> November> February. The screened relatively important environmental factors to algal biomass vary with seasons. The TP, TN, temperature, NO₃^--N and NH₄⁺-N are closely related to algal biomass all the year round.(4) NH₄⁺-N decreased as the algal bloom intensity increased, while dissolved total nitrogen increased apparently after algal bloom, NO₃^--N decreased only during serious algal bloom period in overlying water. NO₃^--N and NH₄⁺-N were the main part of nitrogen before algal bloom (in April and May) and then DON was the main part after that. In pore water, NH₄⁺-N was the main part of nitrogen which increased as temperature rised. Dissolved organic nitrogen decreased first and then increased. Fluxes calculation results suggested that the sediment was the source of NH₄⁺-N which dissolved from pore water to overlying water, NH₄⁺-N fluxes were ranged from 13.06 mg/(m2·d)～32.94 mg/(m2·d) in west semi lake, and were ranged from 13.06 mg/(m2·d)～32.94 mg/(m2·d)in east semi lake; The sediment was the pool of NO₃^- -N before algal bloom period, but was the source of NO₃^--N which increased nitrate concentrations in overlying water after that.(5) The concentrations of FN and EN was lower in summer and higher in autumn and winter; HN had a higher level in the winter and a lower level in spring and summer; While RN varied little; The TN concentrations had a lower level in summer and higher level in autumn and winter; the seasonal order of mineralizable nitrogen (MN) content was winter> spring> autumn> summer. The nitrogen forms playing a major role on available nitrogen had a disparity in difference seasons, which was the amino acid nitrogen (AAN) in spring, EN in summer and autumn, FN in winter.(6) sufficient nutrient sources played a crucial role in algal blooming process. Sediment supplied nutrients and seeds for this process as the resource of nutrients and algae seeds. Hybrid caused by wind waves accelerated alga multiplication and alga sedimentation and suspension on water-sediment interface. When wind speed was less than 3m·s-1alga clusters drifted on water surface with speed which was exponential dependent on wind velocity with dependent coefficient equaling 0.9052. When wind speed was larger than 3m·s-1, alga mixed up-down together and sunk into lake water. Leading wind directions dominate the distributions of alga blooms. During the test period alga biomass on surface water in leeward wind is 8.8 times as that on upper drift.