Calculation and analysis of total phosphorus pollution load based on mass balance in Lake Taihu since 2007

磷是太湖富营养化的关键性指标,为了解太湖总磷内、外源变化趋势及特征,从总磷污染负荷动态平衡角度分析太湖总磷主要来源与总磷浓度高位波动的原因,本研究基于2007年以来长时序水量水质监测资料和调查数据,开展了太湖进出各途径的总磷负荷质量平衡估算及分析。结果表明,2007—2020年入湖河道输入总磷负荷为1835~2799 t,占太湖总磷负荷的55%~73%,是外源输入最主要的途径;大气干湿沉降输入353~1380 t,占太湖总磷负荷量的12%~38%,是太湖总磷外源输入的第二大途径;太湖水体中总磷负荷量约占8%~15%。出湖河道输出总磷负荷量为516~906 t,占太湖总磷负荷量的13%~30%;水生动植物捕捞总磷负荷量为115~312 t,占太湖总磷负荷量的4%~12%,水厂输出占2%~3%左右;约41%~74%的总磷负荷量滞留于太湖湖体中,成为影响太湖总磷浓度的重要内源。同时,太湖地区气温升高、太湖水体流动速度加快一定程度上又加速了内源污染释放,使其成为总磷改善的限制性因素。;Phosphorus is the main indicator of eutrophication in Lake Taihu. In order to understand the trends and characteristics of the internal and external total phosphorus (TP) load in Lake Taihu, the main sources of TP in the lake and the reasons for the high fluctuation of TP concentration were analysed from the dynamic equilibrium of TP pollution load. The mass balance of TP load in different ways into and out of the lake was estimated and analysed based on a long series of water quality monitoring data. The results showed that the input TP load of rivers was about 1835-2799 t during 2007-2020 as the main source, accounting for 55%-73% of the TP load in Lake Taihu. The TP load transported by dry and wet deposition was 353-1380t, which accounted for about 12%-38% and was the second largest input pathway of TP load in Lake Taihu. Meanwhile, 8%-15% of the TP load was retained in the water of Lake Taihu. However, the TP discharged from the outlet river was about 516-906 t, accounting for about 13%-30% of the TP load in Lake Taihu; the TP removal by harvesting aquatic animals and plants was 115-312 t, accounting for 4%-12% of the TP load in Lake Taihu; and the percentage of TP output by drinking water extraction was about 2%-3%. Therefore, about 41%-74% of the TP load remained in the lake, which is an important endogenous factor influencing the epilimnetic TP concentration in Lake Taihu. In addition, the increase in temperature and water flow velocity in Lake Taihu had both accelerated the release of TP from sediment into water, resulting in sediment being one of the limiting factors for TP control.