太湖上游圩区氮磷管理的减污效益分析

太湖水体富营养化的重要驱动之一是流域上游区域的氮磷流失。圩区作为太湖上游平原区域的主要地理单元，具有复杂的水文与氮磷流失过程。针对圩区科学氮磷识别与高效管控是太湖治理的关键。本研究以太湖上游平原圩区为研究对象，采用氮动态模型（Nitrogen Dynamic model for lowland Polder systems，NDP）和磷动态模型（Phosphorus Dynamic model for lowland Polder systems，PDP）模拟圩区氮磷流失的动态过程，并基于圩区氮磷流失机制进行管理情景定量模拟与氮磷减污效益分析。结果表明：1）圩区氮磷的年平均流失强度分别为40和1.75 kg/ha/yr，高于太湖流域的平均氮磷流失水平；2）当圩区外部水质控制为Ⅳ类时，氮磷流失强度分别为37.54和1.58 kg/ha/yr，圩区截流氮磷量分别增加4.9%和9.9%，高氮磷流失级别的圩区数量分别减少26.2%和63.8%；3）如将圩区内5%的水田转化为水体，氮磷流失强度分别为36.73和1.72 kg/ha/yr，圩区截流氮磷量分别增加6.6%和1.7%，高氮磷流失级别的圩区数量分别减少46.2%和22.5%；4）圩区氮磷的流失机制具有明显不同，圩外水质目标对于圩内磷的流失影响较大，圩内的水体和坑塘等对于氮滞留和净化更加有优势。

Pollution Reduction Benefit Analysis of Nitrogen and Phosphorus Management in Polders in Upper Reaches of Taihu Lake

One of the important drivers of eutrophication in Lake Taihu Basin is the loss of nitrogen (N) and phosphorus (P) in the upper reaches. As the main geographical unit of the lowland areas in the upper reaches of Lake Taihu Basin, polders have a complicated process of hydrology and N and P loss. Scientific identification and efficient control of N and P in polders are the key to the governance of Lake Taihu. In this study, the polders in the upper reaches of Lake Taihu were taken as the study area, and the dynamic process of N and P loss in polders were simulated using Nitrogen Dynamic model for lowland Polder systems (NDP) and Phosphorus Dynamic model for lowland Polder systems (PDP). Based on the mechanism of N and P loss in polders, the management scenarios were quantitatively simulated and the benefits of N and P pollution reduction were analyzed. The results show that: 1) The annual average loss intensity of N and P in the polders were 40 and 1.75 kg/ha/yr, respectively, which were higher than the average loss level of in Lake Taihu Basin; 2) When the water quality in the external rivers of polders was controlled as Grade IV, the loss intensity of N and P were 37.54 and 1.58 kg/ha/yr respectively, the amount of N and P intercepted in the polder increased by 4.9% and 9.9% respectively, and the number of polder with strong loss level decreased by 26.2% and 63.8% respectively; 3) If 5% paddy fields in polders were converted into water bodies, the loss intensities of N and P were 36.73 kg/ha/yr and 1.72 kg/yr, respectively, the amount of N and P intercepted in polders increased by 6.6% and 1.7% respectively, and the number of polders with strong loss levels decreased by 46.2% and 22.5% respectively; 4) The loss mechanism of N and P in the polders were obviously different. The water quality in the external rivers of polders had a strong influence on the loss of P in the polders, and the water bodies and ponds in the polders had a greater advantage for N retention and purification.