南四湖出湖口沉积物-水界面中营养盐分布特征分析及释放风险评估

Distribution Characteristic Analysis and Releasing Risk Assessment of Nutrients in Sediment-Water Interface at Outlet of the Nansi Lake

为了解决南四湖出湖口沉积物-水界面中磷酸盐、氨氮和硝态氮等营养盐释放风险控制缺乏科学依据的问题,利用薄膜扩散梯度技术、高分辨率孔隙水采样技术分析南四湖出湖口沉积物-水界面中营养盐浓度的垂直剖面分布特征,并根据有效态磷、有效态氨氮和有效态硝态氮的浓度,计算三者的净扩散通量,评估三者的释放风险。结果表明:非泄洪期南四湖出湖口上覆水中的溶解态磷浓度低于孔隙水中的,表明沉积物孔隙水中的溶解态磷可能会因浓度梯度的存在而向上覆水中扩散;根据连续分级提取法,钙结合态磷是南四湖出湖口沉积物中磷元素的主要赋存形态,表层沉积物中的不稳定磷元素含量高于深层沉积物中的;有效态磷与有效态铁呈显著正相关,说明南四湖出湖口沉积物-水界面中有效态磷的释放受铁氧化物还原释放影响;有效态磷、有效态氨氮和有效态硝态氮的净扩散通量分别为17.58、1.16、-40.72 ng/(cm^(2)·d),说明有效态磷和有效态氨氮有从沉积物向上覆水中释放的潜在风险。

In order to solve the problem of lack of scientific basis for controlling the risk of nutrient release such as pho-sphate,ammonia nitrogen(NH_(4)^(+)-N)and nitrate nitrogen(NO_(3)^(-)-N)in sediment-water interface at outlet of the Nansi Lake,China,the vertical profile distribution characteristics and release risks of nutrients in sediment-water interface of outlet of the Nansi Lake were analyzed using diffusion gradients in thin-films and high-resolution dialysis technique.Based on the concentrations of labile phosphorus(DGT-P),labile NH+4-N and labile NO_(3)^(-)-N,the net diffusion fluxes of the thr ee were calculated and the release risks of the three were assessed.The results show that the concentration of soluble phosphate in overlying water at the outlet of the Nansi Lake is lower than that in pore water,indicating that soluble pho-sphate in sediment may diffuse upward to overlying water due to the concentration gradient.Based on sequential extract methods,calcium-bound phosphorus is the main occurrence form of phosphorus in the sediments at the outlet of the Nansi Lake,and the content of unstable phosphorus in the surface sediments is higher than that in the deep sediments.DGT-P is positively correlated with labile iron,indicating that the release of DGT-P from the sediment-water interface at the outlet of the Nansi Lake is affected by the reduction of iron oxides.The net diffusion fluxes of DGT-P,labile NH_(4)^(+)-N and labile NO_(3)^(-)-N at the outlet of Nansi Lake are 17.58,1.16,-40.72 ng/(cm^(2)·d),respectively,indicating that DGT-P and l abile NH_(4)^(+)-N at the outlet of Nansi Lake are released from sediments to the overlying water and have potential release risks.