School of Environmental and Forest Sciences, University of Washington, Seattle, WA 98195-2100;
Center for Agricultural and Rural Development, Department of Economics, Iowa State University, Ames, IA 50011;
Proc Natl Acad Sci U S A. 2014 Dec 30;111(52):18530-5. doi: 10.1073/pnas.1405837111. Epub 2014 Dec 15.
A seasonally occurring summer hypoxic (low oxygen) zone in the northern Gulf of Mexico is the second largest in the world. Reductions in nutrients from agricultural cropland in its watershed are needed to reduce the hypoxic zone size to the national policy goal of 5,000 km(2) (as a 5-y running average) set by the national Gulf of Mexico Task Force's Action Plan. We develop an integrated assessment model linking the water quality effects of cropland conservation investment decisions on the more than 550 agricultural subwatersheds that deliver nutrients into the Gulf with a hypoxic zone model. We use this integrated assessment model to identify the most cost-effective subwatersheds to target for cropland conservation investments. We consider targeting of the location (which subwatersheds to treat) and the extent of conservation investment to undertake (how much cropland within a subwatershed to treat). We use process models to simulate the dynamics of the effects of cropland conservation investments on nutrient delivery to the Gulf and use an evolutionary algorithm to solve the optimization problem. Model results suggest that by targeting cropland conservation investments to the most cost-effective location and extent of coverage, the Action Plan goal of 5,000 km(2) can be achieved at a cost of $2.7 billion annually. A large set of cost-hypoxia tradeoffs is developed, ranging from the baseline to the nontargeted adoption of the most aggressive cropland conservation investments in all subwatersheds (estimated to reduce the hypoxic zone to less than 3,000 km(2) at a cost of $5.6 billion annually).
墨西哥湾北部的季节性夏季缺氧（低氧）区是世界上第二大缺氧区。需要减少流域内农田的营养物质，以将缺氧区面积缩小到国家海湾大任务部队行动计划设定的 5000 平方公里（5 年运行平均值）的国家政策目标。我们开发了一个综合评估模型，将农田保护投资决策对超过 550 个向海湾输送营养物质的农业子流域的水质影响与缺氧区模型联系起来。我们使用这个综合评估模型来确定最具成本效益的子流域，以进行农田保护投资。我们考虑针对位置（要处理的子流域）和保护投资的范围（要处理的子流域内的多少耕地）进行目标定位。我们使用过程模型来模拟农田保护投资对海湾营养物质输送的动态影响，并使用进化算法来解决优化问题。模型结果表明，通过将农田保护投资瞄准最具成本效益的位置和覆盖范围，可以以每年 27 亿美元的成本实现行动计划 5000 平方公里的目标。制定了大量成本-缺氧权衡方案，范围从基线到所有子流域中最激进的农田保护投资的非目标采用（估计每年以 56 亿美元的成本将缺氧区减少到小于 3000 平方公里）。
