暴雨径流对新安江入库总磷负荷量的影响

Effect of Rainstorm Runoff on Total Phosphorus Load in Xin’anjiang

为定量揭示暴雨径流对大型水库外源总磷(TP)负荷量的影响,构建新安江模型,结合TP浓度高频在线监测数据,计算千岛湖主要入库河流新安江街口断面逐日TP负荷量,并在此基础上划分暴雨径流携带TP负荷量对新安江TP年总入库负荷量的贡献.结果表明:①近60年来,千岛湖流域年暴雨雨量占年降雨总量的28.1%,平均暴雨频次为6.2次/a,年暴雨雨量和频次均在0.001显著性水平上呈上升趋势;②基于逐日流量模拟和高频水质监测数据计算的入库TP负荷量为基于逐月常规监测数据计算结果的2.9倍;③典型年(2020年5月1日—2021年4月30日)通过街口断面进入千岛湖的径流量和TP负荷量分别为96×10^(8) m^(3)和1506 t,其中由暴雨产生的径流量和TP负荷量占比分别为47.9%和69.4%.研究显示,暴雨事件对水库外源磷负荷的贡献较大,暴雨径流携带高浓度磷的汇入对水库水质和生态系统健康构成较大威胁,采用高频监测网络与水文数值模型高效融合的方法,能有效提升水库TP外源负荷量的计算精度,可为加强认识水库磷污染过程、保障水库水质安全提供科技支撑.

The Xin’anjiang model was used to quantify the impact of rainstorm-induced runoff on the external load of total phosphorus(TP)in the Qiandaohu Reservoir Basin.The daily TP load of Xin’anjiang,which is the largest inflow of Qiandaohu Reservoir,was calculated using high-frequency monitoring data of TP concentration and the hydrological model outputs.The contribution of TP load carried by rainstorm-induced runoff to annual total TP load in the Xin’anjiang is quantified.The results showed that:(1)The Xin’anjiang model performed well in the runoff simulation of the Qiandaohu Reservoir Basin.In the past 60 years,the annual rainstorm rainfall in the Qiandaohu Reservoir Basin accounted for 28.1%of the total annual rainfall.The rainstorm frequency was 6.2 times/a.The trends in annual rainstorm rainfall and the rainstorm frequency dramatically increased at the significance level of 0.001.(2)The external TP load calculated by using the Xin’anjiang model outputs of daily runoff as well as high-frequency monitoring TP concentration was 2.9 times monthly manual monitoring values.(3)During May 1,2020 to April 30,2021,the inflow of the Xin’anjiang was 96×10^(8) m^(3),of which the inflow generated by rainstorm accounted for 47.9%of the total inflow.The TP load entering Qiandaohu Reservoir through Jiekou Section was 1506 t,and TP load generated by rainstorm accounted for 69.4%of the total TP load.The results indicate that rainstorm events contributed greatly to the external load of TP of Qiandaohu Reservoir.Correspondingly,the external load of TP carried by rainstorm runoff posed a great threat to the lake water quality and ecosystem health.The combination of high-frequency monitoring and hydrological models can effectively improve the calculation accuracy of TP load.It can also provide scientific and technological support for improving the understanding of the phosphorus pollution process in lakes.The water quality safety of the lakes can be better guaranteed.