鄱阳湖浮游植物叶绿素a及营养盐浓度对水位波动的响应

鄱阳湖是长江中下游仅存的两个自然通江湖泊之一,其水情变化独特,与非通江湖泊显著不同.为探究水位波动对鄱阳湖水环境的影响及其浮游植物的响应特征,选取了鄱阳湖星子、都昌水域,于2011年9月至2012年11月对浮游植物叶绿素a(Chla)及其它相关水质指标进行每周一次的原位监测.结果表明,高Chla浓度出现在鄱阳湖高水位和高水温期,水位波动可加强鄱阳湖浮游植物Chla浓度的季节性变化效应,同时对浮游植物群落结构的改变也有一定的促进作用.回归趋势分析,Chla浓度与水温(P0.000 1)和透明度值(SD)(P0.000 1)显著正相关,与总氮(TN,P0.01)、溶解性氮(NO_x-N,P0.01;NH~+_4-N,P0.05)显著负相关,而SD值、总氮和溶解性氮浓度与鄱阳湖水位值显著相关(SD,P0.01;TN,P0.000 1;NO_x-N,P0.01;NH~+_4-N,P0.000 1).主成分分析(PCA)显示,不同水位期,鄱阳湖所表现出的水环境特征显著不同,低水位期,营养盐浓度,特别是氮营养盐浓度较高;而高水位期,鄱阳湖水温较高和SD值较高.总之,鄱阳湖的水位波动影响了湖区沉积物再悬浮和水体SD状况,加之高水位的稀释效应和人类活动,均直接影响了鄱阳湖营养盐状况以及Chla浓度.

Responses of Nutrients and Chlorophyll a to Water Level Fluctuations in Poyang Lake

As one of the few remaining lakes that are freely connected with the Yangtze River, Poyang Lake exhibits a unique aquatic ecology which is different from the disconnected lakes. In order to study the mechanism of limnological responses to water level fluctuations (WLFs), samples were collected weekly over 10 months from September 2011 to December 2012 in Xingzi and Duchang, and the effect of fluctuations in water level on nutrients and phytoplankton chlorophyll a (Chla) concentrations was investigated in Poyang Lake. Chla concentrations were strongly related to WLFs, with higher Chla concentrations in the higher water phase. The regression analysis indicated that Chla concentrations were significantly and positively correlated with water temperature (P<0.0001) and secchi depth (SD) (P<0.0001) but negatively correlated with total and inorganic nitrogen concentrations (TN,P<0.01; NO_x-N,P<0.01; NH₄⁺-N:P<0.05). SD and total and inorganic nitrogen concentrations were all significantly correlated with WLFs of Poyang Lake (SD,P<0.01; TN,P<0.0001; NO_x-N:P<0.01; NH₄⁺-N,P<0.0001). Two different water levels were identified in the lake by principal components analysis:the low water level with high nutrient values and the high water level with high water temperature, SD, and Chla values. These results supported the hypothesis that WLFs clearly exerted an overall impact on the growth of phytoplankton in Poyang Lake of the Yangtze River floodplain. WLFs affected the water transparency (expressed by SD), nutrients, and Chla concentrations of Poyang Lake, likely due to flush flood pulse, re-suspension of suspended matter, dilution effects, and human activities.