There is a pressing need to understand the consequences of human activities, such as land transformations, on watershed ecosystem services. This is a challenging task because different indicators of water quality and yield are expected to vary in their responsiveness to large versus local-scale heterogeneity in land use and land cover (LUC). Here we rely on water quality data collected between 1977 and 2000 from dozens of gauge stations in Puerto Rico together with precipitation data and land cover maps to (1) quantify impacts of spatial heterogeneity in LUC on several water quality indicators; (2) determine the spatial scale at which this heterogeneity influences water quality; and (3) examine how antecedent precipitation modulates these impacts. Our models explained 30–58% of observed variance in water quality metrics. Temporal variation in antecedent precipitation and changes in LUC between measurements periods rather than spatial variation in LUC accounted for the majority of variation in water quality. Urbanization and pasture development generally degraded water quality while agriculture and secondary forest re-growth had mixed impacts. The spatial scale over which LUC influenced water quality differed across indicators. Turbidity and dissolved oxygen (DO) responded to LUC in large-scale watersheds, in-stream nitrogen concentrations to LUC in riparian buffers of large watersheds, and fecal matter content and in-stream phosphorus concentration to LUC at the sub-watershed scale. Stream discharge modulated impacts of LUC on water quality for most of the metrics. Our findings highlight the importance of considering multiple spatial scales for understanding the impacts of human activities on watershed ecosystem services.

中文翻译：

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土地利用对热带景观水质的影响：多尺度分析

迫切需要了解人类活动（如土地改造）对流域生态系统服务的影响。这是一项具有挑战性的任务，因为预计不同的水质和产量指标对土地利用和土地覆盖 (LUC) 的大尺度与局部尺度异质性的响应会有所不同。在这里，我们依赖于 1977 年至 2000 年间从波多黎各数十个测量站收集的水质数据以及降水数据和土地覆盖图，以 (1) 量化 LUC 中空间异质性对若干水质指标的影响；(2) 确定这种异质性影响水质的空间尺度；(3) 检查前期降水如何调节这些影响。我们的模型解释了水质指标中观察到的 30-58% 的差异。前期降水的时间变化和测量周期之间 LUC 的变化而不是 LUC 的空间变化是造成水质变化的主要因素。城市化和牧场开发普遍降低了水质，而农业和次生林再生长则产生了混合影响。LUC 影响水质的空间尺度因指标而异。浊度和溶解氧 (DO) 对大规模流域中的 LUC 有响应，流域内氮浓度对大流域河岸缓冲液中的 LUC 有响应，粪便物质含量和流中磷浓度对子流域尺度的 LUC 有响应。对于大多数指标，河流排放调节 LUC 对水质的影响。