摘要
摘要:为控制流域氮素养分流失、改善流域水体环境，以亚热带典型农业小流域脱甲河为研究对象，对表层水体铵态氮（NH₄⁺-N）、硝态氮（NO₃^--N）浓度和水体硝态氮δ¹⁵N（δ¹⁵N-NO₃^-）、沉积物有机质δ¹⁵N（δ¹⁵N-Org）浓度进行了连续试验观测，分析氮素浓度及其稳定同位素值的时空特征，探讨影响氮素分布的环境因子及水体NO₃^-和沉积物有机质氮素的可能来源。结果表明：水体NO₃^--N浓度明显高于NH₄⁺-N，均值分别为1.62 mg·L^-1和0.90 mg·L^-1，并且分别在6月、8月及冬季较高；城镇区和农田区水体NH₄⁺-N浓度与其他类型区差异显著（P < 0.05），并且显著高于其他水体；NO₃^--N浓度在城镇区、农田区及山间林地区较高，水库区较低。支流NH₄⁺-N浓度高于干流，均表现为冬季 > 春季 > 夏季 > 秋季；干流、支流NO₃^--N浓度分别表现为冬季 > 夏季 > 秋季 > 春季、秋季 > 冬季 > 夏季 > 春季。源头和出口处水体均表现为NO₃^--N浓度高于NH₄⁺-N，源头处氮素浓度低于出口处。水体δ¹⁵N-NO₃^-及底泥δ¹⁵N-Org值分布范围分别为-19.87‰~8.11‰和-0.69‰~6.51‰，水体δ¹⁵N-NO₃^-最高值在Ⅲ级河段，最低值出现于Ⅳ级河段，各级河段间水体δ¹⁵N-NO₃^- 11月差异较小，而1、2月差异明显；河流底泥δ¹⁵N-Org最高值也位于Ⅲ级河段，而最低值则在Ⅰ级河段，Ⅲ、Ⅳ级河段δ¹⁵N-Org值随时间变化趋势较为一致，Ⅰ、Ⅱ级河段δ¹⁵N-Org最小值出现于1月。总之，脱甲河水体存在氮素污染现象且以外源输入为主，水体氮素来源主要为土壤有机质、人工合成肥料及陆源有机质，开展流域氮素分布及来源研究对认识流域尺度氮污染物的源解析具有一定科学意义。
关键词:脱甲河/
亚热带/
农业小流域/
氮污染/
氮同位素/
氮素来源
Abstract:The Tuojia River basin, a typical agricultural catchment in the subtropics, was investigated in this study to clarify the spatial and temporal distribution characteristics of nitrogen and the related stable isotopes in water system of the catchment. The environmental factors influencing nitrogen distribution and the sources of nitrate nitrogen and sediment organic matter nitrogen were also determined. The concentrations of NH₄⁺-N and NO₃^--N in surface water were analyzed in a continuous monitoring experiment. At the same time, the characteristics of δ¹⁵N-NO₃^- in water and of δ¹⁵N-Org in sediments were determined. Results showed that the concentration of NO₃^--N was significantly higher than that of NH₄⁺-N in the river, with respective mean values of 1.62 mg·L^-1 and 0.90 mg·L^-1. Higher values occurred in June, August and winter periods. NH₄⁺-N concentrations in urban and farmland regions were significantly different (P < 0.05) from other areas and obviously higher than that in other water bodies. The concentrations of NO₃^--N in urban, farmland and forest areas were higher than in other regions, with lower values in reservoir areas. The order of seasonal variations in NH₄⁺-N concentration in mainstream and tributary flows was winter > spring > summer > autumn, while that of NO₃^--N concentration was winter > summer > autumn > spring in mainstream, and autumn > winter > summer > spring in tributary flows. The concentrations of NO₃^--N of mainstream and tributary flows were high but similar, and NH₄⁺-N concentration in tributary flow was higher than that in mainstream flow. At source and estuary, NO₃^--N concentration was higher than NH₄⁺-N concentration. Also, nitrogen concentration of at source was lower than that in estuaries. The distributions of δ¹⁵N values (δ¹⁵N-NO₃^-) in the river and δ¹⁵N in sediment organic matters (δ¹⁵N-Org) were respectively -19.87‰ to 8.11‰ and -0.69‰ to 6.51‰. While the highest value of δ¹⁵N-NO₃^- was in the reach Ⅲ, the lowest was in the reach Ⅳ. The difference in δ¹⁵N-NO₃^- among different reaches was small in November, but was obvious in January and February. While the highest value of δ¹⁵N-Org in river sediment was also in the reach, the lowest was in the reach Ⅰ. The variation trend in δ¹⁵N-Org in the reach Ⅲ and reach Ⅳ was consistent with change in research time. However, the lowest δ¹⁵N-Org was in January in the reach Ⅰ and Ⅱ. The research indicated that there was nitrogen pollution in Tuojia River basin, and exogenous nitrogen was the priority in the region. The main environmental factors that influenced water pollution in the region included domestic sewage, industrial wastewater, farmland nitrogen and livestock/poultry waste. In addition, the sources of nitrogen in water bodies and sediments were mainly soil organic matter, synthetic fertilizers and terrestrial organic matter. The source of nitrogen in river systems was consistent with the identified environmental factors that caused nitrogen pollution. The study of the distributions and sources of nitrogen in the basin provided scientific basis for controlling nitrogen loss in the catchment, guiding agricultural production and improving water environment in the study area.
Key words:Tuojia River basin/
Subtropics/
Agricultural basin/
Nitrogen pollution/
Nitrogen isotope/
Nitrogen source



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