Agricultural fertilizer use is widely acknowledged to be a leading cause of water pollution. Yet, no national estimates exist on the effect of fertilizer application on concentrations of agricultural pollutants in US watersheds. This paper employs a watershed‐level panel data on nitrogen and phosphorus pollution readings to examine the impact of fertilizer use on US water quality over a fifty‐five‐year time period from 1951 to 2005. Findings show that a 10% increase in the use of nitrogen and phosphorus fertilizers leads to a 1.52% increase in the concentration of nitrogen and a 1.37% increase in the concentration of phosphorus across watersheds. Results also indicate that there exists heterogeneity in nutrient pollution elasticity estimates across eighteen US water resource regions, ranging from 0.082 to 0.733 in the case of nitrogen and from 0.036 to 0.475 in the case of phosphorus. Combining our results with prior hydrology‐based studies, we find that a 100% increase in the use of nitrogen fertilizers in the Lower Mississippi water resource region expands the size of the hypoxic zone in the Gulf of Mexico by roughly 3,389 square miles, equivalent to about two‐fifths of the estimated size of the dead zone in the Gulf of Mexico.

中文翻译：

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来自农业的环境外部性：来自美国水质的证据

农业肥料的使用被广泛认为是造成水污染的主要原因。然而，没有关于施肥对美国流域农业污染物浓度影响的国家估计。本文使用关于氮和磷污染读数的流域级面板数据来检查从 1951 年到 2005 年的 55 年间化肥使用对美国水质的影响。结果表明，化肥使用量增加了 10%施氮磷肥导致流域氮浓度增加 1.52%，磷浓度增加 1.37%。结果还表明，美国 18 个水资源区域的养分污染弹性估计存在异质性，在氮的情况下从 0.082 到 0.733 和从 0 不等。在磷的情况下为 036 至 0.475。将我们的结果与之前基于水文学的研究相结合，我们发现在下密西西比州水资源地区，氮肥使用量增加 100% 会使墨西哥湾缺氧区的面积扩大约 3,389 平方英里，相当于大约是墨西哥湾死亡区估计面积的五分之二。