巢湖西部河口区沉积物氮磷分布特征与原位扩散通量估算

选取巢湖西部重污染入湖河口区,研究表层沉积物氮磷污染特征,并运用Fick定律估算沉积物-水界面氮磷原位扩散通量.结果表明:南淝河、派河、十五里河河口表层沉积物总氮平均含量达到2208.17 mg·kg~(-1),氮形态以有机氮为主,占比达到90%以上.表层沉积物总磷平均含量为704.59 mg·kg~(-1),其中铁铝结合磷、活性有机磷和钙镁结合磷分别占比27%、28%和18%.河口区水体氨氮浓度从上覆水到孔隙水中总体呈上升趋势,沉积物表层(0~5 cm)孔隙水中氨氮平均浓度为25.42 mg·L~(-1),是上覆水中的7倍.沉积物孔隙水中硝氮与正磷酸盐浓度在垂向上随深度的增加呈先上升后降低的趋势,在沉积物-水界面附近达到浓度最高值.3个河口沉积物孔隙水中氮磷营养盐均向上覆水扩散,其中氨氮扩散通量分别为25.87、74.85与18.08 mg·m~(-2)·d~(-1).硝氮与正磷酸盐扩散通量较低,范围分别在1.38~2.78和0.011~0.024 mg·m~(-2)·d~(-1)之间.总体上看,巢湖西部河流入湖河口区表层沉积物氮污染严重,且存在较高的氮磷营养盐释放风险,应是巢湖富营养化控制过程中重点关注的区域.

Distribution of nitrogen and phosphorus in sediments and estimation of the diffusion fluxes at river mouths of Western Chaohu Lake

River mouths of western Chaohu Lake were selected to study the characteristics of nitrogen and phosphorus pollution in the surface sediments, meanwhile the diffusion flux at the sediment-water interface was estimated by using Fick''s law. The results show that the average concentration of total nitrogen in surface sediments of Nanfei River, Shiwuli River and Paihe River mouths was 2208.17 mg·kg^-1, and the organic nitrogen was the major form of nitrogenous substances, accounting for more than 90% of TN. The average concentration of TP in surface sediments was 704.59 mg·kg^-1, among which NaOH-Pi, NaOH-Po and Ca-P account for 27%, 28% and 18% of TP, respectively. The concentration of ammonia in water shows an uptrend with the increasing depth at river mouths, and the average concentration of ammonia in the pore water was 25.42 mg·L^-1, which is seven times higher than that in the overlying water. Vertically, the content of nitrate nitrogen and orthophosphate in the pore water tends to increase until reaching to the maximum near the sediment-water interface and then decrease. The nitrogen and phosphorus in all the sediments at three river mouths release from pore water to overlying water, and the ammonia fluxes were 25.87, 74.85 and 18.08 mg·m^-2·d^-1, respectively. The fluxes of nitrate nitrogen and orthophosphate were lower, ranging from 1.38 to 2.78 and 0.011 to 0.024 mg·m^-2·d^-1, respectively. Overall, the results in this paper indicate a serious pollution status of nitrogen and a high risk of nutrients release in surface sediments at river mouths, which should pay more attention in eutrophication control of Chaohu Lake.