Linking nitrate dynamics to water age in underground conduit flows in a karst catchment
Linking nitrate dynamics to water age in underground conduit flows in a karst catchment
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DOI：
10.1016/j.jhydrol.2020.125699
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发表时间：
2020-10
影响因子：
6.4
通讯作者：
Zhicai Zhang;Xi Chen;Siliang Li;F. Yue;Qinbo Cheng;Tao Peng;C. Soulsby
中科院分区：
文献类型：
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作者：
Zhicai Zhang;Xi Chen;Siliang Li;F. Yue;Qinbo Cheng;Tao Peng;C. Soulsby
尽管已有大量关于喀斯特流域硝酸盐迁移和转化的研究报道，但由于喀斯特关键带的独特结构和复杂的水文过程，在理解硝酸盐通量方面仍然存在许多挑战。水龄是水文功能的重要描述符，提供了对流域尺度上的水流路径和水源的洞察。这为更好地理解喀斯特流域硝酸盐动态的时空变化提供了潜在的机会。我们将地下管道流动的硝酸盐动态与水龄联系起来，该水龄是从中国西南部喀斯特集水区的稳健示踪辅助模型中提取的。研究结果表明，地下管道水流中硝酸盐的动态受岩溶汇水中硝酸盐供给与流道的耦合控制。小裂缝水的排水量贡献大，导致旱季地下管道水流中硝酸盐浓度低。这表明小裂缝可能是岩溶临界带反硝化脱硝的另一个重要“热点”。在输水限制和供水限制条件的切换下，雨季地下管道水流中硝酸盐浓度变化明显。虽然降雨开始时，通过大裂缝和天坑的快速入渗对地下管道流中的硝酸盐有很强的稀释作用，但在降雨期间，由于降雨对土壤硝酸盐的动员，更多的硝酸盐被排水带出了集水区。同时，当“老”水在高湿度条件下被降雨取代时，从集水区运输硝酸盐的能力可能会被激活。
Although numerous studies on nitrate transport and transformation in karst catchments have been reported, many challenges in understanding nitrate fluxes remain due to the unique architecture of karst critical zones and complex hydrological processes. Water age is an important descriptor of hydrological function providing insight to into flow paths and water sources at the catchment scale. This offers a potential opportunity to better understand the spatio-temporal variations in nitrate dynamics in karst catchments. We linked the nitrate dynamics of underground conduit flow to water age extracted from a robust tracer-aided model for a karst catchment in southwestern China. The results show that nitrate dynamics in underground conduit flow are controlled by the coupling of nitrate supply and of flow paths in the karst catchment. High contributions of drainage from small fractures water leads to low nitrate concentrations in underground conduit flow during the dry season. This reveals that the small fractures may be another important “hot spot” for denitrification leading to nitrate removal in the karst critical zone. The switching between transport limited and supply limited conditions cause the marked variations in nitrate concentration of underground conduit flow during wet season. Although rapid infiltration via large fractures and sinkholes have strong dilution effects on nitrate in underground conduit flow at beginning of rainfall, more nitrate was transported out of the catchment with drainage during rainfall events due to the mobilization of soil nitrate by rainfall. Meanwhile, the capacity to transport nitrate out of catchment can be potentially activated when the ‘old’ water is displaced by rainfall under high wetness condition.