The Microcystis Populations Spatial And Temporal Characteristics. Dianshan And Warning Significance,

Dianshan Lake is the largest freshwater lake in Shanghai suburbs and also one of the most important drinking water sources for Shanghai. The lake's water quality is of great importance to water safety. In the past twenty years, water quality of Dianshan Lake has deteriorated rapidly due to cultural eutrophication. The lake is mostly threatened by the presence and increase of harmful algal blooms (HABs) every year. One of the most dominant species is Microcystis sp. It's blooming causes loss of lake function for recreation, habitat and water supply. The need to control eutrophication and algal growth in Dianshan Lake has motivated several removal methods and experimental projects. Despite many attempts, elimination of blooms was not achieved. This is due to our lack of understanding of blooming trends, dominant species and Microcystis sp. distribution in the lake. Therefore, the aim of this paper is to study and understand the ecological characteristics of Microcystis sp. and its blooming status in Dianshan Lake. The research was carried out from Jan.2009 to Dec.2010, and the main results are as follows:1. New survey methods were developed based on the understanding of vertical transport and accumulation processes of Microcystis sp. These methods allowing comprehensive, quick and cost-effective whole-lake survey in large water bodies. Sampling methods were also improved for detecting Microcystis "during its recruitment and development phases. A grading standard was established to classify Microcystis blooming status in Dianshan Lake.2. A total of 8 species of Microcystis were identified in Dianshan Lake, including M.flos-aquae, M.ichthyoblabe, M.aeruginosa, M.psudofilamentos, M.wesenbergii, M.smithii, M.firma and M.aeruginosa. M.flos-aquae and M.ichthyoblabe were the dominant species that form blooms in most of the months while M. wesenbergii was dominant during August and September. M.firma and M.smithii were not seen forming dense bloom in Dianshan Lake.3.The study of temporal dynamics of Microcystis showed that the dormancy phase of Microcystis sp. in Dianshan Lake was between November and February, and recruitment phase was between March and June. Low concentrations of Microcystis sp. accumulated near the riverbank from April to June. Bloom was formed from July to early September. Starting in mid-September, the blooms began to dissipate. 4. Upper lakes were also affected by Microcystis blooms between June and August every year. The presence of Microcystis was only recorded in mid-August from the discharge of those connected rivers to Dianshan Lake. North and Northwest winds in August were found to explain this phenomenon.5.The spatial distribution of Microcystis blooming in Dianshan Lake was mainly affected by " JiShuiGang-LanLuGang" channel. Two separate incubation areas were found in the lake. Before August, Microcystis can be found along the river shoreline. In August, Microcystis blooms were not only found near the riverbank but also in the central part of the lake. The bloom was found to discharge through LanLuGang channel in mid-September. Tidal and wind direction are the main factors affecting discharging speed.