淀山湖氮磷营养物20年变化及其藻类增长响应

20-year variations of nutrients (N and P) and their impacts on algal growth in Lake Dianshan, China

从淀山湖20年的监测数据和AGP试验结果入手,结合20年的遥感影像资料,分析淀山湖氮磷营养物的长期变化规律及其对藻类演替和增长的影响.从1985年第一次大规模藻类水华暴发,经过15年的营养物积累,在1999-2000年之间,淀山湖由中度富营养化湖泊逐渐转化为重度富营养化湖泊,1999年之后淀山湖水体氮磷营养物大量聚集,叶绿素a水平迅速提高,分别以1999年前的2.25倍、6.67倍和3.40倍的速率上升,其中以磷的上升速率为最快;透明度则以平均每年递减5cm的速度下降.藻类群落转化为以绿藻和蓝藻为主,藻类水华的频率为1999年前的2-3倍.当水体TN浓度超过3.5mg/L时,AGP试验不再有任何显著性反应.2002年的现场试验和藻类水华频次与高浓度TN出现概率的相关分析表明,夏秋季当水体TN浓度在3.5mg/L时,可以引起藻类大量增长;高浓度TN出现概率越高,藻类水华的次数越多.研究证明淀山湖已经具备暴发大规模、大面积蓝藻水华的条件,水体TN浓度超过临界值(>3.5mg/L)的频次越多,淀山湖爆发蓝藻水华的可能性越大.

Data of 20 year monitoring of water quality, algal bioassay, and remote sensing information were analyzed to determine the long-term effect of nutrients （N and P） on algal growth. Since the first algal bloom in 1985 and the accumulation of nutrient, Lake Dianshan has become hyper-euthophicated. The concentrations of TN, TP and Chlorophyll have rapidly increased since 1999, and their annual rates were 2.25, 6.67 and 3.40 times respectively higher than that of the past 15 years, among which phosphorus was the highest. The transparency decreased 5cm annually. Algal community has been transited to green-bluegreen algae dominated since 1999, the frequency of algal bloom occurrence were 2-3 times of before. When concentration of TN in water column was higher than 3.5mg/L, AGP test did not have any positive response at any significant levels. In situ experiment in 2002 and regression analysis of frequencies between algal bloom and higher concentration of TN found that during the period of summer, autumn, algal growth could be increased when TN was around 3.5mg/L： the higher TN concentration, the more frequency algal bloom. The evidence showed that Lake Dianshan was of high risk of harmful bluegreen algal bloom.