乌梁素海氮污染及其空间分布格局

Nitrogen pollution and spatial distribution pattern of Wuliangsuhai Lake

针对草型富营养化湖泊乌梁索海富营养化日趋严重和湿地面积逐渐萎缩的现实，本文系统地研究了TN、NH4^＋-N、NO2^-—N和Org—N在上覆水与沉积物中的分布规律。结果表明，上覆水中TN含量平均为1．78mg／L，且无机氮污染以NH4^＋-N为主，占无机氮总量的69％以上；表层沉积物中氮素的水平分布格局均体现出西高东低的经向分异特征并主要以OrgN的形式存在；表层沉积物中TN对底栖生物已经具有一定的生态毒性效应并正甫最低级向严重级过渡；氮素在乌梁素海沉积剖面上均表现出随深度增加而含量递减的规律，表层0～10cm的TN平均含量达到1．28g／kg，分别为10～22cm和22-40cm的1.6和1．9倍，揭示了乌梁素海富营养化进程加速始于20世纪90年代。

Wuliangsuhai Lake is one of the representative inland freshwater lakes in grassland area in China. Recently, the lake is shrinking and eutrophication has become serious. This paper interpreted the spatial distribution patterns of total nitrogen （TN）, ammonium nitrogen （NH4^＋ N）, nitrate nitrogen （NO3^-N） and organic nitrogen （Org-N） in surface water and sediment cores systematically. The results revealed that the average content of TN was 1.78mg/L and the main inorganic nitrogen pollutant was NH4^＋-N which accounted for more than 69% of the inorganic nitrogen in surface water;spatial distribution pattern of nitrogen in surface sediment indicated that the nitrogen content in the west of the lake was higher than in the east and the main species of nitrogen was Org-N which was more than 95% of TN. Furthermore based on the Sediment Quality Estimation Guide which was enacted in terms of ecological toxic effects by Department of Environment and Energy of Ontario Province, Canada, 1992, the content of TN in surface sediment has certain ecological toxic effects which are more serious; the content of nitrogen decreased with depth and the eutrophication process existed in three periods which revealed that the acceleration of the eutrophication process dated back to the 1990s. The content, speciation distribution and spatial distribution pattern of TN in Wuliangsuhai Lake＇s surface water and sediment cores indicated that its pollution was characterized by exogenous and endogenous poilu tion. The exogenous pollution was mainly the drainage water from farmland and industrial wastewater,which accounted for 50% and 35% of the TN load respectively, pouring into the lake through the main drainage canals, the eighth and the ninth drainage canal. And under certain conditions, the endogenous load could release nitrogen into surface water and make it the main pollution source. Besides the exogenous and the endogenous pollution, the intense evaporation, which accelerated the eutrophication process of Wuliangsuhai Lake, was also a key factor which caused nitrogen accumulation in the surface and modern sediments.