巢湖十五里河沉积物磷平衡浓度对外源碳的响应及释放风险

2017年7月至2018年5月,在巢湖十五里河干流的城乡梯度方向,按照每两个月采样1次的频率,采集5个点位的表层沉积物样,分析沉积物磷形态,解析磷平衡浓度及对外源碳(乙酸钠)的响应,并对沉积物磷释放风险进行评估.结果表明,十五里河水体磷素污染严重,沉积物总磷含量平均为915. 04～1 205. 31 mg·kg~(-1),且沿城乡梯度方向缓慢下降,而生物有效性磷含量则保持稳定;外源碳降低了沉积物EPC_0值(下降约29%),也改变了各采样点EPC_0值大小排序;上覆水SRP浓度高于EPC_0值所占比例为66. 7%,而且磷吸附解吸平衡饱和度EPC_(sat)-20%所占比例约60. 0%,表明十五里河沉积物以磷吸附占优势,即沉积物总体上处于磷"汇"状态;外源碳的输入使得EPC_(sat)-20%所占比例由60. 0%上升为73. 3%,降低了沉积物磷释放风险水平.

Effects of Exogenous Carbon Addition on Equilibrium Phosphate Concentration and Risk of Phosphorus Release from Sediments in the Shiwuli River, Chaohu Lake Basin

Five surface sediment samples were collected every two months from the Shiwuli River along an urban-rural gradient, Chaohu Lake Basin, from July 2017 to May 2018. Sediment phosphorus fractions were investigated, and equilibrium phosphate concentration (EPC₀) and its response to exogenous carbon (sodium acetate) addition were explored. Moreover, the risk of phosphorus release from sediment into water column was also evaluated. Results show that the Shiwuli River was seriously polluted by phosphorus. The average values of total phosphorus content in sediments ranged from 915.04 to 1205.31 mg·kg^-1, and it decreased slowly along the urban-rural gradient, while the bio-available phosphorus content remained stable. Exogenous carbon addition not only reduced the EPC₀ values of sediments (about 29%), but changed the order of EPC₀ values among the five sampling sites as well. In general, the ratio of overlying water SRP (soluble reactive phosphorus) concentration to EPC₀ value was 66.7%, and phosphorus adsorption-desorption equilibrium saturation EPC_sat<-20% accounted for about 60.0%, indicating that the surface sediments in the Shiwuli River were dominated by phosphorus adsorption, namely, keeping the phosphorus "sink" state. The inputs of exogenous carbon addition increased the proportion of EPC_sat<-20% from 60.0% to 73.3%, which lowered the risk of phosphorus release from sediments.