分层型水库暴雨潜流诱导内外源耦合铁锰污染

The coupled internal and external source pollution by storm-flow induced density stratification in Xi’an Jinpen reservoir

汛期暴雨径流入库过程含大量污染物的入流在水库水体密度分层的影响下,以层间流或底部潜流的形式进入库区,对水体、沉积物环境及污染物形态分布产生显著影响,并诱发了外源输汇入-内源加剧的耦合污染.本研究以西安金盆水库为例,对汛期暴雨径流潜流过程水质及沉积物进行了监测,探究潜流内外源耦合污染条件下的水质响应.结果表明:暴雨径流潜流过程,大量颗粒态污染物随径流潜入库区,潜流层浊度由15 NTU增加至274 NTU;铁、锰含量由0.19 mg·L^(-1)和0.03 mg·L^(-1)突增至4.93 mg·L^(-1)和0.17 mg·L^(-1),其中汇入后颗粒态铁锰占比分别为90.5%和96.7%.潜流入库过程同时对金盆水库水体热分层产生显著影响,其中表层水体由21.21℃降低至17.74℃,潜流层温度由9.99℃上升至13.36℃,等温层厚度由10 m降低至5 m,等温层以上水体温差由11.22℃降至4.38℃;潜流携带颗粒态污染物显著增强了底部水体厌氧环境.颗粒态污染物的沉降对表层沉积物污染分布产生显著影响,并加剧了还原性铁锰释放通量:表层沉积物中总铁总锰含量分别由15.25 g·kg^(-1)增长至21.09 g·kg^(-1)和0.94 g·kg^(-1)增长至0.97 g·kg^(-1).新形成的表层沉积物中可交换态占比由14.7%~23.0%升至21.6%~26.1%;表层沉积物中铁锰释放通量分别由0.170 mg·m^(-2)·d^(-1)和5.149 mg·m^(-2)·d^(-1)增长至0.889 mg·m^(-2)·d^(-1)和19.228 mg·m^(-2)·d^(-1).在内外源耦合污染条件下导致水质恶化迅速且持久,同时促进沉积物内源释放,增加水体二次污染风险,因此降低水中颗粒物浓度和提高底部溶解氧是汛期水质保障的关键措施.

density stratification in the deep reservoirs causes the inflow entering as the form of interflow and underflow,which significantly influences the benthic environment,and the distribution of pollutant in surface sediment,thereby leading to the coupled external and internal source pollution.This study monitored the water and sediment changes during rainstorm events in Xi'an Jinpen Reservoir.The results indicate that during heavy rainfall events,a considerable amount of particulate pollutants is transported into the reservoir through stormwater runoff,leading to an increase in turbidity levels in the subsurface layer from 15 NTU to 274 NTU.The concentration of iron and manganese surged from 0.19 mg·L^(-1)and 0.03 mg·L^(-1)to 4.93 mg·L^(-1)and 0.17 mg·L^(-1),respectively.Notably,after combining,particulate iron and manganese accounted for 90.5%and 96.7%of the total concentrations.At the same time,the submersible inflow process has a significant impact on the thermal stratification of the reservoir,in which the surface water decreased from 21.21℃to 18.01℃,the subsurface layer temperature increased from 9.99℃to 13.26℃,the isothermal layer thickness from 10 m to 5 m,and the temperature difference of the water above the isothermal layer from 11.22℃to 4.75℃.The Subcurrent carrying particulate pollutants significantly enhanced the anaerobic environment of the bottom water,leading to an increase in The proportion of exchangeable fraction in newly-formed surface sediments,from 14.7%to 23.0%to a range of 21.6%to 26.1%.Meanwhile,the fluxes of iron and manganese released from surface sediments increased from 0.170 mg·m^(-2)·d^(-1)and 5.149 mg·m^(-2)·d^(-1)to 0.889 mg·m^(-2)·d^(-1)and 19.228 mg·m^(-2)·d^(-1),respectively.Under the condition of coupled internal and external source pollution,these changes lead to rapid and prolonged water quality deterioration,and at the same time promotes the endogenous release of sediment and increases the risk of secondary pollution in water body.Therefore,reducing the concentration of particulate matter in water and improving the solution of the dissolved oxygen at the bottom are the key measures to ensure water quality in flood season.