乌梁素海硝酸盐来源的季节性变化

乌梁素海是典型农业灌区退水型湖泊，其水生态环境保护对黄河流域生态保护具有重要意义.该研究通过开展乌梁素海流域农业排干和湖体硝酸盐的δ15N和δ18O分析，应用IsoSource同位素模型估算流域生产生活污水、土壤氮源、化肥和大气沉降的贡献率.结果表明:①湖区δ15N-NO₃-和δ18O-NO₃-值范围分别为-2.50‰~18.17‰和-12.02‰~45.09‰，其中夏秋两季δ15N-NO₃-值偏正，冬季偏负，且秋季δ18O-NO₃-值偏正.②春季湖水硝酸盐主要源于化肥和土壤氮源相关的农业活动，其贡献率为43.7%；夏季、秋季和冬季主要源于生产生活污水，贡献率分别为51.3%、38.8%和40.2%，其中夏季农业活动贡献率超过40%，大气沉降主要体现在秋季湖水中.研究显示:春季湖区硝酸盐来源主要集中于七排干和八排干的受水区域，以上区域应在春季着重加强农业面源污染控制；夏季和秋季湖区硝酸盐来源主要集中于五排干和七排干所处城乡区域，以上区域应强化城乡生活污水处理. 

Seasonal Variation of Nitrate Sources in Wuliangsuhai Lake

Lake Wuliangsuhai is a typical recession lake in agricultural irrigation area, which is of great significance to the ecological protection of the Yellow River Basin. Based on the analysis of δ15N and δ18O of nitrate in agricultural drainage and lacustrine water in the Wuliangsuhai Basin, the contribution of production and domestic sewage, soil nitrogen, chemical fertilizers and atmospheric deposition was estimated by using the IsoSource isotope model. The results showed that the range of δ15N-NO₃- and δ18O-NO₃- in the Lake area was from -2.50‰ to 18.17‰ and -12.02‰ to 45.09‰ respectively. The δ15N-NO₃- value was positive summer, negative in winter, the δ18O-NO₃- value was positive in autumn. The nitrate mainly came from agricultural activities related to chemical fertilizers and soil nitrogen in Lake Wuliangsuhai in spring, with a contribution rate of 43.7%. The nitrate mainly came from the production and domestic sewage in summer, autumn as well as winter, with the contribution rates of 51.3%, 38.8% and 40.2%, respectively. And the contribution rate of agricultural activities in summer was more than 40%, and the contribution of atmospheric precipitation was also important in autumn. The results also showed that the agricultural non-point source pollution control should be strengthened in the water receiving areas of the seventh and eighth drainage ditches in spring, since the nitrate in Lake Wuliangsuhai in spring mainly came from these ditches. The urban and rural domestic sewage treatment should be strengthened in the water receiving areas of the fifth and seventh drainage ditches in summer and autumn, because the nitrate in Lake Wuliangsuhai in spring mainly came from these ditches.