气象因素对封闭浅水湖泊浮游藻类生长和分布影响

Effects of Meteorological Factors on Growth and Distribution of Phytoplankton in an Enclosed Shallow Lake

为探究主要气象因素对浮游藻类单因素和综合影响特征,选择典型封闭水体中心湖,研究了2008-2011年气温、风和降雨对浮游藻类生长和分布的影响,选取春末和夏季藻类生长期的典型降雨事件,通过逐日密集观测,探讨气象因素对浮游藻类的影响规律。结果表明,气温显著影响藻类的生物量和季节变化,风是藻类生物量空间分布差异的主要原因,降雨是重要的辅助因素。当气温大于15℃时,强风力扰动和频繁降雨均能直接或间接抑制藻类生长。当气温大于20℃以后,风及其引起的水力扰动成为藻类生长的主要影响因子。弱风条件下,气温基本在30℃左右,经过强降雨刺激后,Chl-a浓度突然升高,最大值接近120μg/L,短时暴雨会造成水体营养盐浓度成倍增加,有效地刺激了藻类生长,而长时间的降雨主要通过稀释效应和水下光强降低抑制藻类生长增殖;在连续大风天气条件下,日均风速大于3.1 m/s时,较大强度的风浪扰动会造成藻类生物量显著下降,7.0 m/s左右的风速后可使Chl-a浓度下降50%。对于类似封闭/半封闭人工水体而言,在营养负荷一定的情况下,尤其是夏季高温时,应根据气象因子的动态变化采取适宜的措施,改善水力条件,可防止藻类水华暴发。

An enclosed,simple water ecosystem with little point source pollution provides a unique opportunity to study freshwater eutrophication mechanisms.Zhongxinhu Lake is an enclosed artificial lake located in Chongming Island of Shanghai,with a total water surface area of 52 000 m^2.In this study,we explored the individual and combined effects of primary meteorological factors(wind,rainfall and temperature)on the growth and distribution of the phytoplankton community in Zhongxinhu Lake,based on data collected from 2008 to 2011.The algal growth periods following typical rainfall events in late spring(April 25-May 20)and summer(August 10-26)of 2010 were selected for detailed analysis.The concentration of chlorophyll-a(Chl-a)was monitored daily and the influence of meteorological factors on planktonic algae was analyzed.Primary meteorological factors,including wind velocity and direction,were obtained from the websites of the Shanghai Meteorological Administration and Chongming Meteorological Administration.Phytoplankton biomass and seasonal variation were significantly affected by temperature.Wind was the primary factor affecting spatial distribution and rainfall was an important mediating factor.Low levels of phytoplankton biomass in the northern section of the lake correlated closely with prevailing winds from the southeast.Phytoplankton grew slowly when the temperature was below 15℃.At above 15℃,strong wind and frequent rainfall inhibited phytoplankton growth.When the temperature was above 20℃,wind driven water turbulence inhibited growth.After short,heavy rainfalls in warm water(near 30℃)and gentle winds,the concentration of Chl-a increased dramatically(maximum value 120μg/L).However,algal growth was inhibited during extended rainfall events.Heavy,short-term rainfall events carry large nutrient loads into the water,stimulating phytoplankton growth,while continuous rainfall dilutes nutrients and decreases light intensity.Water turbulence induced by constant strong wind(wind speed>3.1 m/s)significantly decreased Chl-a.A decrease of 50%in blue-green algae biomass was observed after a strong wind(~7.0 m/s).These findings indicate that hydrodynamic conditions can be adjusted to reduce the risk of algae bloom in semi-closed or closed water bodies when the nutrient load is relatively stable,particularly during the summer.