Abstract In this study we investigated the impact of climate change on nutrient loading in the Cannonsville Reservoir watershed of the New York City (NYC) water supply system where management practices have reduced nutrient inputs in the last 25 years. A modified version of the SWAT hydrological and water quality model (SWAT-HS) that had been previously tested and verified for streamflow and phosphorus for this watershed was calibrated for nitrate to estimate contributions from point and nonpoint sources. Model simulations show that forests that occupy 64% of the watershed area contribute the greatest proportion of nitrate at 39%, while pastures that are in close proximity to streams and runoff generating areas contribute the greatest proportion of total nitrogen at 34%. Point sources contribute less than 5% of the annual nitrate load. Stream export accounts for only about 23% of the annual total N input to the watershed from anthropogenic sources, suggesting significant storage or loss from the landscape. We assumed stationary land use and management practices to assess the change in nutrient loading from baseline (2001–2010) to middle of the century (2051–2060) period due to a change in climate. Results indicated no change to moderate increase in the annual loading of dissolved forms of nutrients (N and P) whereas particulate forms of nutrients and sediment loadings are projected to increase due to an increase in the frequency and magnitude of large storm events. A seasonal shift in streamflow due to warmer winter temperatures, greater amounts of precipitation falling as rain, and earlier melting of snowpack may play an important role in controlling the seasonal pattern of nutrient loading. The methodology used in this study can be adapted in other watersheds to estimate the relative importance and partition contributions from various nonpoint sources to water quality, and to investigate the impacts of climate change.

中文翻译：

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气候变化对供水流域养分负荷的影响

摘要 在这项研究中，我们调查了气候变化对纽约市 (NYC) 供水系统 Cannonsville 水库流域养分负荷的影响，该系统的管理实践在过去 25 年中减少了养分输入。SWAT 水文和水质模型 (SWAT-HS) 的修改版本之前已针对该流域的径流和磷进行了测试和验证，并针对硝酸盐进行了校准，以估计点源和非点源的贡献。模型模拟表明，占流域面积 64% 的森林对硝酸盐的贡献比例最大，为 39%，而靠近溪流和径流产生区的牧场对总氮的贡献比例最大，为 34%。点源贡献不到每年硝酸盐负荷的 5%。河流出口仅占流域人为来源的年度总氮输入总量的 23% 左右，这表明景观存在显着的储存或损失。我们假设土地使用和管理实践是固定的，以评估由于气候变化导致的从基线（2001-2010）到本世纪中叶（2051-2060）期间养分负荷的变化。结果表明，溶解形式的养分（N 和 P）的年负荷没有变化到适度增加，而由于大风暴事件的频率和强度增加，预计颗粒形式的养分和沉积物负荷会增加。由于冬季温度升高而导致河流流量的季节性变化，更多的降水以降雨形式下降，积雪的较早融化可能在控制养分负荷的季节性模式方面发挥重要作用。本研究中使用的方法可适用于其他流域，以估计各种非点源对水质的相对重要性和分配贡献，并调查气候变化的影响。