Nature’s Kidneys: The Role of Wetland Reserve Easements in Restoring Water Quality
Journal of the Association of Environmental and Resource Economists · 2026 · Nicole Karwowski、Marin Elisabeth Skidmore
中文摘要
美国已投入数十亿美元用于治理农业非点源污染。湿地通过过滤地表径流中的沉积物和过量养分,提供了一种事后(ex post)的自然解决方案。量化湿地储备计划(Wetland Reserve Program, WRP)与农业保护地役权计划(Agricultural Conservation Easement Program, ACEP)中湿地地役权对水质的影响,对于非点源污染治理资金的最优配置至关重要。我们因果识别了新修复的湿地是否能降低密西西比河流域子流域层面的氮、磷负荷。结果表明,湿地地役权降低了当地子流域及下游的氨氮和总凯氏氮浓度。修复之后当地磷含量随即出现的短期上升可能反映了土壤扰动。尽管湿地对当地磷水平没有统计显著的长期影响,但在下游观察到了磷含量的下降。我们估计,联邦对自然基础设施的这一投资降低了当地水系统的处理成本。
Abstract
Billions of dollars have been dedicated to mitigating nonpoint source pollution from US agriculture. Wetlands provide an ex post natural solution by filtering sediments and excess nutrients from the landscape. Quantifying the impact of wetland easements in the Wetland Reserve Program (WRP) and Agricultural Conservation Easement Program (ACEP) on water quality is critical for optimal fund allocation for nonpoint source pollution abatement. We causally identify whether newly restored wetlands reduce nitrogen and phosphorus loads at the subwatershed level in the Mississippi River Basin. Results show that wetland easements reduce ammonia and total Kjeldahl nitrogen concentrations in the local subwatershed as well as downstream. A short-term increase in local phosphorus immediately following restoration likely reflects soil disturbance. While wetlands have no significant long-term impact on local phosphorus levels, downstream reductions are observed. We estimate that this federal investment in natural infrastructure leads to lower treatment costs for local water systems.