Research On Spatial Distribution Characteristics Of Chlorophyll A And Its Influence Factors In Songhua Lake

Songhua Lake, the biggest artificial lake in the northeast area and the oversize lake in our country, is a large-scale water conservancy that is used for controlling flood, generating electricity, irrigation, shipping, fishery, voyage and so on. Chlorophyll a is an important means and index for researching and evaluating eutrophication. The paper studied the spatial distribution characteristics of chlorophyll a and its influence factors in Songhua Lake by indoor experiment and field investigation from June to October, 2006. The influence factors included TP, phytoplankton, water temperature, dissolved oxygen and turbidity. The results showed that:①The concentration of chlorophyll a decreased from upstream to downstream in Songhua Lake. The concentration of Huifahekou was maximal and this instance proved that the Huifa River was primary source of nitrogen and phosphorus. The change of chlorophyll a concentration at Dafengman was small. The concentration of chlorophyll a at Shashihu was less than upstream and more than downstream. As a whole, the concentration at Xiaohuangdi was less than Huashulinzi and this proved that Huifa River was primary source of polluter and Lafa River and Jiao River was lesser. At the time, the concentration in June and September was bigger and October was smaller.②The vertical distribution of chlorophyll a has only a maximum. The maximum appeared at from 2 to 4m. The concentration of surface layer was higher than bottom. The concentration and the trend of vertical distribution of Dafengman, Shashihu and Xiaohuangdi were similar and curves overlapped each other almost.③Songhua Lake was mesotrophic lake as a whole but part was eutrophic. Eutrophication mainly appeared at Huifahekou. Songhua Lake was phosphorus limitation.The relationship between TP and chlorophyll a was: Log10(chl.a)= 1.350 + 2.318 Log10(TP)(R=0.947,n=5,p=0.015)。④The effect of water temperature, dissolved oxygen and turbidity to chlorophyll a were different. The descend in June and ascend in October affected chlorophyll a at a certain extend. The water temperature at surface layer and chlorophyll a was strong correlative. The thermocline affected chlorophyll a at deep water. The dissolved oxygen and chlorophyll a was little correlative. The turbidity and chlorophyll a was the strongest correlative in Songhua Lake. The positive strong relativity appeared at 5 sampling points in June and August. Relativity appeared at define depth at Dafengman, Shashihu and Huifahekou in vertical distribution and Xiaohuangdi and Huashulinzi not.