典型富营养化城市河流——浙江温瑞塘河的浮游植物群落类型与季节变化

Seasonal variation of phytoplankton communities in Wenruitang River——A typical eutrophic urban river,Zhejiang Province

为评估温瑞塘河水环境状况及水华风险,于2015年每月15日7:00-18:00对其下游滞流河段进行高频监测分析,考察了水体叶绿素a浓度、浮游植物群落类型和光合活性等的季节变化及日变化情况,并分析了其与温度、营养盐等环境因子的关系.结果表明:温瑞塘河表层水体中的叶绿素a浓度表现为春季(3-5月)>夏季(6-8月)>秋季(9-11月)>冬季(12-2月),分别为39.98、37.62、21.59和10.74μg/L;4个季节的平均水温则是夏季>秋季>春季>冬季,分别为30.91、25.34、20.72和13.80℃.全年总氮浓度为5.33±0.81~9.40±1.25 mg/L,总磷浓度为0.32±0.18~0.95±0.25mg/L,营养程度属于超富营养.温瑞塘河的浮游植物群落类型为硅藻-绿藻型,全年以绿藻和硅藻种群为主,蓝藻种群只在春末夏初出现,并且所占比例很小.绿藻种群在夏季占绝对优势,而硅藻种群在冬季占优势.绿藻种群的相对丰度与水温呈正相关,而硅藻种群的相对丰度与水温呈负相关.水体的叶绿素a浓度与水温呈正相关,而与总氮、总磷浓度没有相关性.叶绿素a在不同季节呈现出不同的日变化模式,而浮游植物的有效光合量子产率在四季均呈现类似的日变化模式:都是先降后升,与晴天时的日照强度变化趋势相反.绿藻的有效光合量子产率高于硅藻,且除春季外皆存在显著差异.以上结果表明温瑞塘河具备发生各类水华的营养条件,但是由于蓝藻在全年所占的比例都很低,因此发生蓝藻水华的可能性很小;同时由于日照变化会对表层水体中叶绿素a浓度及浮游植物生理活动产生影响,因此在对小型湖泊或者水流滞缓的河道进行浮游植物群落结构调查时还应考虑时间和天气因素.

To evaluate the water quality and algal bloom occurrence in the eutrophic Wenruitang River,the eco-populations and photosynthetic activities of phytoplankton community in its surface water were investigated by high-frequency sampling during the day time in the middle of each month in 2015. The relationships between chlorophyll-a concentrations( Chl. a) and environmental factors such as water temperatures and nutrients were analyzed. It was found that the seasonal Chl. a were 39. 98,37. 62,21. 59 and 10. 74 μg/L with corresponding water temperatures 30. 91,25. 34,20. 72 and 13. 80℃ from spring to winter,respectively.The annual concentrations of total nitrogen( TN) ranged from 5. 33 ± 0. 81 to 9. 40 ± 1. 25 mg/L and those of total phosphorus( TP) ranged from 0. 32 ± 0. 18 to 0. 95 ± 0. 25 mg/L,belonged to a hypereutrophic level. The annual phytoplankton community in Wenruitang River was green-diatom algae type. Cyanobacteria were only found in the late spring and early summer and accountedfor a small percentage. The relative abundances of cyanobacteria were 11. 55% ± 7. 99% and 12. 70% ± 3. 48% in May and June. Green algae were dominant in summer,but diatoms( along with a few dinoflagellates) were prevalent in winter. The relative abundances of the green algae increased with water temperature while the diatoms decreased when water temperature risen. Total Chl. a was in a postive correlation with water temperature,while no obvious correlations with TN and TP. The Chl. a showed distinct seasonal and diurnal patterns. However,the effective quantum yields( ΔF/Fm) of both green algae and diatoms decreased at first and then increased in a day,contrary to the diurnal changed in solar irradiances. The results indicated that the hypereutrophic state of Wenruitang River was potential for algal blooms but the possibility of cyanobacterial bloom was very low still due to its negligible relative abundance in a full year. In view of effects of temperature and solar radiation on Chl. a and physiological activities of phytoplankton in the surface water of such hypereutrophic resting waters,the sampling time and weather should be considered during field sampling.