内外源共同作用对太湖营养盐贡献量研究

本文根据环太湖25条主要入湖河流的监测结果对入湖水量及污染物输入量进行分析,计算了不同季节外源对太湖营养物质的贡献量。分别于春、夏、秋、冬4个季节对太湖梅梁湾水体开展5次野外试验,利用沉积物捕获器收集沉积物,采用Gansith公式法计算沉积物的再悬浮通量,并建立其与风速的关系;对代表不同风浪作用下的太湖悬浮物进行7次静沉降试验,计算悬浮物的静沉降通量,并建立其与风速关系。以3.7m/s为界对底泥悬浮沉降过程进行分解和概化,并利用近10年的风速资料估算太湖年均内源释放量。计算结果表明,全年外源负荷和内源释放对太湖营养盐的贡献总量COD为24.23万t、总氮为3.80万t、总磷为2 045.20t,其中内源所占比例分别为20.47%,20.44%和13.47%外源、内源对太湖的贡献量在不同季节有较大差异,夏季贡献量最大,春季次之。风浪作用下的COD、TN释放量只相当于外源输入量的25.7%,而TP释放量仅相当于外源输入量的15.6%。外源输入量对营养盐的贡献占据相当高的比重,太湖河道入湖污染负荷的增加是太湖水质恶化的根本原因。

Contribution of combined action of exogenous source and internal load on water nutrient in Taihu Lake

The input amount of water and pollutant to the Taihu Lake from 25 rivers around the lake were monitored and the contributions of exogenous source on water nutrient in different seasons were evaluated. In the same period, five times in situtest on water quality at Meiliang Bay of the Lake in different seasons were carried out and the sediment settling flux and re suspended flux were calculated according to the observation data by using the Gansith formula. The relationship between the re suspended flux of sediment matter and wind speed were established. Furthermore, experiments for investigating the hydrostatic settling behavior of suspended matter affected by wind were conducted in laboratory. The hydrostatic settling flux of suspended matter were calculated and the relationship between flux and wind speed was established. On the basis of these studies, the suspension sedimentation process was decomposed and generalized according to the critical wind speed, 3.7m/s. Consequently, the annual average released amount of internal load can be estimated using the wind data. The result indicates that the total annual contributions of exogenous source load and internal load on water nutrient include 24.23×10.5 t COD, 3.80×10.5 t TN and 0.20×10.5 t TP, among them the portions of internal load are 20.47%, 20.44% and 13.47% respectively. The contribution in summer is the maximum. It is concluded that the exogenous source plays the important role affecting the water quality of the lake and the increase of input pollution is the main cause resulted in the deterioration of water quality in lake.