杭州西湖北里湖沉积物氮磷内源静态释放的季节变化及通量估算

The seasonal variations of nitrogen and phosphorus release and its fluxes from the sediments of the Beili Lake in the Hangzhou West Lake

通过采集北里湖不同季节的柱状芯样,在实验室静态模拟沉积物氨氮(NH+4-N)和可溶解性磷酸盐(PO34--P)的释放,同时研究了沉积物间隙水中NH+4-N及PO34--P的垂直分布特征。结果表明,沉积物间隙水NH+4-N随深度的增加有上升的趋势,PO34--P随深度的增加呈先升后降的趋势。氮、磷营养盐在沉积物—水界面均存在浓度梯度,表明存在自间隙水向上覆水扩散的趋势。沉积物NH+4-N在春季、夏季、秋季、冬季的释放速率分别为0.074 mg·m-·2d-1、0.340 mg·m-·2d-1、0.087 mg·m-·2d-1、0.0004 mg·m-·2d-1,PO34--P的释放速率则分别为0.340 mg·m-·2d-1、0.518 mg.m-2.d-1、0.094 mg·m-·2d-1、-0.037 mg·m-·2d-1。不同采样点表现出明显的季节和空间差异性,释放速率表现为夏季>春季、秋季>冬季。根据静态模拟出的不同季节下内源氮、磷释放速率计算,全湖内源氮、磷营养盐的贡献分别为0.0037、0.0057 t/a。该研究可为北里湖富营养化及内源污染的治理提供基础数据。

Eutrophication is one of the most widespread environmental problems of inland waters, either because external loading has not been reduced sufficiently or because internal lake mechanisms. High internal loading of nitrogen （N） and phosphorus （P） from lake sediments is frequently reported as an important mechanism delaying lake recovery after a reduction of external loading. In this paper, the seasonal changes of ammonia nitrogen and phosphorus releasing rate from sediment were evaluated using intact sediment core simulation methods in the Beili Lake of the Hangzhou West Lake. Besides, vertical distribution characteristics of ammonia nitrogen and phosphors in the pore water were analyzed. The results showed that the concentration of ammonia nitrogen was expressed as the increasing trend with depth, while an increasing trend followed by decreasing was found for phosphorus. The difference in ammonia nitrogen and phosphorus concentration between pore water and overlying water can cause inner nitrogen and phosphorus nutrients releasing. The seasonal releasing rates from sediments were 0. 074 mg·m-2·d-1, 0. 340 mg·m-2·d-1, 0.087 mg·m-2·d-1 , 0.0004 mg·m-2·d-1 for ammonia nitrogen, and 0. 340 mg·m-2·d-1 , 0. 518 mg·m-2·d-1 , 0. 094 mg·m-2·d-1 , -0. 037 mg·m-2·d-1 for phosphorus, respectively. Seasonal and spatial variations of releasing rate were found from this study. The ammonia nitrogen and phosphorus releasing rate was higher in summer than in spring and autumn, but lowest in winter. The release fluxes of nitrogen and phosphorus across the sediment-water interface in different points were estimated using results from intact sediment core simulation methods. This difference is mainly focus on nitrogen and phosphorus releasing from the sediments in different environmental conditions including temperature, pH, dissolved oxygen （DO） and transparency. In summer, the temperature was the highest, the activity of bacterium was stronger than in other seasons. At the same time, the DO value decreased. The transparency was the lowest in summer, indicating the disturbance strength was the highest than other seasons. The results demonstrated the internal loading were 0. 0004 t, 0. 0025 t, 0. 0008 t, 0 t for ammonia nitrogen, and 0. 0015 t, 0. 0038 t, 0. 0009 t, -0. 0005 t for phosphorus, respectively. The conclusions indicated that the internal loading of N and P in the whole lake were estimated about 0. 0037 and 0. 0057 t/a, respectively. Therefore, nutrients from sediment made a contribution to lake eutrophication. The phosphorus was the limiting factor to the lake entrophication in Beili Lake, and the releasing of phosphorus was related to the forms. The active phosphorus including the dissolved phosphorus, Fe-bound P and Al-bound P, can release from sediment to overlying water easily. The proportion of active P was accounted 5.3% of TP in spring, and then decreased to 3.72% in summer. After that, the active P increased to 6. 16% and 6.73% in autumn and winter. The seasonal variation characteristics of active P were consitent with those of the phosphorus releasing. However, the simulation method used in this study didn＇t analyze the effect of environmental factors such as waves＇ disturbance and turbulence on nitrogen and phosphorus releasing rate, the results from simulation may be lower than the dynamic simulation value. Afterwards, the results from this study are important for the eutrophication control and ecological restoration in Beli Lake.