Booth Mary S, Campbell Chris
National Park Service, 4175 Geist Road, Fairbanks, Alaska 99709, USA.
Environ Sci Technol. 2007 Aug 1;41(15):5410-8. doi: 10.1021/es070179e.
Nitrogen derived from fertilizer runoff in the Mississippi River Basin (MRB) is acknowledged as a primary cause of hypoxia in the Gulf of Mexico. To identify the location and magnitude of nitrate runoff hotspots, and thus determine where increased conservation efforts may best improve water quality, we modeled the relationship between nitrogen inputs and spring nitrate loading in watersheds of the MRB. Fertilizer runoff was found to account for 59% of loading, atmospheric nitrate deposition for 17%, animal waste for 13%, and municipal waste for 11%. A nonlinear relationship between nitrate flux and fertilizer N inputs leads the model to identify a small but intensively cropped portion of the MRB as responsible for most agricultural nitrate runoff. Watersheds of the MRB with the highest rates of fertilizer runoff had the lowest amount of land enrolled in federal conservation programs. Our analysis suggests that scaling conservation effort in proportion to fertilizer use intensity could reduce agricultural nitrogen inputs to the Gulf of Mexico, and that the cost of doing so would be well within historic levels of federal funding for agriculture.
密西西比河流域（MRB）中肥料径流产生的氮被认为是墨西哥湾缺氧的主要原因。为了确定硝酸盐径流热点的位置和规模，从而确定加大保护力度在何处最能改善水质，我们对MRB流域氮输入与春季硝酸盐负荷之间的关系进行了建模。结果发现，肥料径流占负荷的59%，大气硝酸盐沉降占17%，动物粪便占13%，城市垃圾占11%。硝酸盐通量与肥料氮输入之间的非线性关系使该模型确定MRB中一个面积小但作物种植密集的区域是大多数农业硝酸盐径流的来源。肥料径流率最高的MRB流域参加联邦保护计划的土地面积最少。我们的分析表明，按照肥料使用强度按比例扩大保护力度可以减少进入墨西哥湾的农业氮输入量，而且这样做的成本完全在联邦农业资助的历史水平之内。
