Land use interacts with changes in catchment hydrology to generate chronic nitrate pollution in karst waters and strong seasonality in excess nitrate export
Land use interacts with changes in catchment hydrology to generate chronic nitrate pollution in karst waters and strong seasonality in excess nitrate export
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DOI：
10.1016/j.scitotenv.2019.134062
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发表时间：
2019-12
影响因子：
9.8
通讯作者：
F. Yue;S. Waldron;Si‐Liang Li;Zhong-Jun Wang;Jie Zeng;Sen Xu;Zhichuan Zhang;D. Oliver
中科院分区：
文献类型：
--
作者：
F. Yue;S. Waldron;Si‐Liang Li;Zhong-Jun Wang;Jie Zeng;Sen Xu;Zhichuan Zhang;D. Oliver
岩溶系统中的农田会污染水道，受污染的沃茨会迅速流到并穿过地下。了解硝酸盐在高透射岩溶临界区（从土壤到含水层）内的移动速度受到低分辨率数据的限制。为了了解硝酸盐的行为及其控制，我们在五个地点部署了传感器技术，以自动生成中国西南部一个农业喀斯特流域的排放和NO3−-N（主要含氮成分）的高分辨率时间序列。[NO3−-N]时间序列显示出快速响应，在五个站点中，[NO3−-N]的浓度从0.72 mg/L到16.3 mg/L不等。然而，NO3−-N的响应在每个站点的幅度是不同的降雨事件（雨季）和旱季。最高的平均[NO3−-N]和归一化的年度河流输出发生在一个发达的岩溶含水层系统的源头流域。NO3--N输出的季节性变化发生在响应源的可用性，最显着的流域与山谷农业：在雨季高达94%的硝酸盐在两个月内从源头流域输出，但在更大的流域规模，在6个月的雨季，只有61%的总出口发生。在较大的集水区尺度上，由于岩溶含水层网络的缓冲作用，[NO3−-N]较低。从时间序列中，我们观察到很少减少[NO3−-N]的排放量减少，在旱季，表明岩溶含水层的硝酸盐通过缓慢的流动途径长期污染。
Agricultural land in karst systems can pollute water courses, with polluted waters travelling quickly to and through the sub-surface. Understanding how rapidly nitrate moves within the highly-transmissive karst critical zone (from soils to aquifers) is limited by low resolution data. To understand nitrate behavior and its controls, we deployed sensor technology at five sites to generate autonomously high-resolution time series of discharge and NO3−–N, which is the major nitrogenous component, in a farmed karst catchment in Southwestern China. The [NO3−–N] time series exhibited rapid response to rainfall-induced increases in discharge and a large magnitude in [NO3−–N], from 0.72 to 16.3 mg/L across five sites. However, the magnitude of NO3−–N response at each site was varied during rainfall events (wet season) and dry season. The highest mean [NO3−–N] and normalized annual fluvial export occurred in a headwater catchment with a developed karst aquifer system. Seasonal variation in NO3−–N export occurred in response to source availability, most notable in catchments with valley agriculture: in the wet season up to 94% of nitrate was exported from the headwater catchments within two months, but at the larger catchment scale, over the 6 month wet season, only 61% of total export occurred. At the larger catchment scale, [NO3−–N] were lower due to buffering by the karstic aquifer network. From the time series we observe little decrease in [NO3−–N] as discharge decreases in the dry season, indicating the karst aquifers are chronically-polluted with nitrate through slow flow pathways.