天津市北大港湿地沉积物氮磷分布特征及污染评价

北大港湿地是天津市最大的湿地自然保护区，是东亚——澳大利亚候鸟的重要迁徙中转站.了解北大港湿地水体和沉积物氮磷含量及分布特征，对探明湿地营养物质的污染状况，控制水体富营养化状态具有重要参考意义.本研究将北大港湿地自然保护区分为核心区、缓冲区、实验区3个区域，共采集65个点位表层水样和沉积物样，分析不同人为干扰条件下水和沉积物中主要营养物的空间分布特征，并运用单因子指数、综合污染指数和有机污染指数评价其污染程度.结果表明，北大港湿地表层水中总氮含量为1.33~18.8 mg·L^-1，有86%采样点位超过了V类水标准限值，但氨氮平均含量优于III类水标准限值.总磷浓度为0.030~2.32 mg·L^-1，38%采样点位超过了V类水标准限值.空间分布上，表层水氮磷含量从核心区到缓冲区、实验区总体呈现缓慢增长趋势.沉积物碳氮比含量为14~58，缓冲区、实验区沉积物有机质主要受到流域人类活动输入的影响.湿地沉积物总磷含量为417~886 mg·kg^-1，钙结合磷是沉积物总磷最主要形态，占总磷比例为60%~86%.单因子指数以及综合污染指数评价表明，北大港湿地表层沉积物总氮污染严重，整体呈现出重度污染状态，其中，尤其需要重视核心区北大港水库沉积物的总氮污染.

Distribution characteristics and pollution assessment of nitrogen and phosphorus in sediments from Beidagang Wetland in Tianjin City

Beidagang Wetland is the largest wetland nature reserve in Tianjin City, which is served as an important habit for the migratory shorebirds in the East Asian-Australasian flyway. Investigating the contents and distribution characteristics of nitrogen and phosphorus in water and sediments from Beidagang Wetland is of great significance to explore the nutrient status in this area. Here, both water and sediment samples from 65 sites were collected from three-sub areas, i.e., core, buffer and experimental zones, to analyze the spatial distribution characteristics of main nutrients under different intensities of anthropogenic activities. Moreover, single factor index, comprehensive pollution index and organic pollution index were used to evaluate the pollution degree of nutrients in sediments. Our results showed the levels of total nitrogen in surface water from Beidagang Wetland ranged from 1.33 to 18.8 mg·L^-1, and 86% of the sampling sites exceeded the limit of Class V of the Environmental Quality Standard for Surface Water in China (GB3838-2002). However, the average content of ammonia nitrogen was better than the limit of Class III. The ranges of total phosphorus in surface water were from 0.030 to 2.32 mg·L^-1, and 38% of the sampling sites exceeded the limit of Class V. In terms of spatial distribution, both of nitrogen and phosphorus increased significantly from the core zone to the buffer and experimental zones. The C/N ratio of sediments ranged from 14 to 58, which also indicated that the organic matter in sediments from the buffer and experimental zones was mainly affected by anthropogenic activities in the basin. The levels of total phosphorus in wetland sediments ranged from 417 to 886 mg·kg^-1. Calcium bound phosphorus was the main form in sediments, accounting for 60%~86% of total phosphorus. The single factor index and the comprehensive pollution index evaluation showed that the pollution of total nitrogen in sediments was in serious status. In particular, special attention should be paid to the east part of Beidagang Reservoir in the core zone.