Rainfall driven nitrate transport in agricultural karst surface river system: Insight from high resolution hydrochemistry and nitrate isotopes
Rainfall driven nitrate transport in agricultural karst surface river system: Insight from high resolution hydrochemistry and nitrate isotopes
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DOI：
10.1016/j.agee.2019.106787
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发表时间：
2020-04
期刊：
影响因子：
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通讯作者：
Zhong-Jun Wang;Si‐Liang Li;F. Yue;Caiqing Qin;Sarah J. Buckerfield;Jie Zeng
中科院分区：
文献类型：
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作者：
Zhong-Jun Wang;Si‐Liang Li;F. Yue;Caiqing Qin;Sarah J. Buckerfield;Jie Zeng
与降雨事件相关的高排放导致养分快速运输到岩溶地形的排水系统。研究了西南地区典型喀斯特混合土地利用小流域降雨过程中硝态氮的动态变化和迁移机制。高频率（每小时）水采样，放电和水化学传感器数据在15分钟的时间间隔，从喀斯特农业地表河收集超过四个降雨事件，跨越40天的雨季开始。结果表明，在雨季的第一次降雨事件中，在长期干旱期之后，观察到高[NH 4 +-N]（高达3.12 mg L−1）和[PO 43 −- P]（高达1037 μg L−1）。[NO3−-N]的增加也发生在与早期事件流相关的高排放期间，但最高的[NO3−-N]浓度（高达14.9 mg L−1）在最高排放事件期间的季节后期观察到。双硝酸盐同位素的所有最小值都是在高放电条件下发现的，并通过事件时间序列增加。这表明氮在雨季开始前在集水区积累，并被早期降雨事件冲入排水系统。[NO3−-N]、δ 15 N和δ 18 O-NO3 −值分析表明，降雨前后硝酸盐同位素值较高是由于反硝化作用，而不是同化作用。根据源解析结果，降雨过程中硝酸盐的主要来源为化肥、土壤有机氮、粪便和污水，且随排放量的不同而不同。土壤有机氮中硝态氮所占比例较高，说明岩溶区暴雨过程中峰丛和低地农田的土壤流失应引起重视。
High discharge associated with rainfall events causes rapid transport of nutrients to drainage systems in karst terrain. The objective of this study was to understand nitrate dynamics and transport mechanisms during rainfall events in a typical mixed land-use karst catchment in Southwest China. High frequency (hourly) water sampling, discharge and hydrochemistry sensor data at a 15-minute interval were collected from a karst agricultural surface river over four rainfall events, spanning 40 days at the commencement of the wet season. The results showed that high [NH4+–N] (up to 3.12 mg L−1) and [PO43−– P] (up to 1037 μg L−1) were observed in the first rainfall event of the wet season, after a long preceding dry period. Increased [NO3−–N] also occurred during the high discharge associated with early event flows, but the highest [NO3−–N] concentrations (up to 14.9 mg L−1) were observed later in the season during the highest discharge events. All minima for dual nitrate isotopes were found during high discharge conditions and increased through the event time series. This indicates that nitrogen accumulated in the catchment prior to the commencement of the wet season and was flushed by the early rainfall events into the drainage system. Analysis of [NO3−–N],δ15N andδ18O-NO3−values indicate that denitrification, not assimilation, resulted in the high nitrate isotope values before and after rainfall events. According to source apportionment, chemical fertilizer, soil organic nitrogen, and manure and sewage, which varied with discharge, were the main sources of nitrate during rainfall events. The high proportion of nitrate from soil organic nitrogen suggested that soil loss from peak clusters and lowland farmland during heavy rainfall events should be paid more attention in karst area.