Protecting water quality at catchment scales is complicated by the high spatiotemporal variability in water chemistry. Consequently, determining pollutant sources requires costly monitoring strategies to diagnose causes and guide management solutions. However, recent studies have shown that spatial patterns in water chemistry can be persistent at catchment scales, potentially allowing identification of pollution sources and sinks with just a few sampling campaigns. Here, we tested a new method to quantify spatial persistence (SP) of water chemistry patterns with data from synoptic samplings in 22 headwater subcatchments within a 375 km² catchment in western France (March 2018 to July 2019). This new method to quantify SP reduces dependence on long-term metrics such as flow-weighted concentrations, which are usually uncertain or unavailable. We applied the method to 16 ecologically relevant water quality parameters, including soluble reactive phosphorus, nitrate, and dissolved organic carbon. The results showed an average SP of 0.68 among parameters during the study period. For most parameters, SP was higher during the high-flow winter period but lower and more variable during the low-flow summer period. We found that the SP ultimately depended on the ratio between the temporal and spatial coefficients of variation (variance explained: 70%) rather than the temporal synchrony among subcatchments (variance explained: 4%). These results demonstrate that in these temperate catchments, synoptic sampling during the high-flow winter period allows efficient identification of source and sink subcatchments, while more frequent samplings are needed to characterize ecological conditions at low flow.

中文翻译：

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中尺度农业流域中不同流动条件下水化学模式的空间持久性

由于水化学的高时空变异性，在流域尺度保护水质变得复杂。因此，确定污染物来源需要昂贵的监测策略来诊断原因并指导管理解决方案。然而，最近的研究表明，水化学的空间模式可以在流域尺度上保持不变，只需几次采样活动就有可能识别污染源和汇。在这里，我们测试了一种新方法来量化水化学模式的空间持久性 (SP)，其数据来自 375 公里²内 22 个源头水流域的天气采样数据。法国西部的流域（2018 年 3 月至 2019 年 7 月）。这种量化 SP 的新方法减少了对流量加权浓度等长期指标的依赖，这些指标通常是不确定的或不可用的。我们将该方法应用于 16 个与生态相关的水质参数，包括可溶性活性磷、硝酸盐和溶解有机碳。结果显示，研究期间各参数的平均 SP 为 0.68。对于大多数参数，SP 在冬季高流量期间较高，但在夏季低流量期间较低且变化较大。我们发现 SP 最终取决于时空变异系数之间的比率（解释的方差：70%）而不是子汇水面积之间的时间同步性（解释的方差：4%）。这些结果表明，在这些温带集水区，