The challenge of documenting water quality benefits of conservation practices: a review of USDA-ARSs conservation effects assessment project watershed studies

摘要

The Conservation Effects Assessment Project was established to quantify water quality benefits ofnconservation practices supported by the U.S. Department of Agriculture (USDA). In 2004, watershednassessment studies were begun in fourteen agricultural watersheds with varying cropping systems,nlandscapes, climate, and water quality concerns. This paper reviews USDA Agricultural ResearchnService ‘Benchmark’ watershed studies and the challenge of identifying water quality benefits innwatersheds. Study goals included modeling and field research to assess practices, and evaluation ofnpractice placement in watersheds. Not all goals were met within five years but important lessonsnwere learned. While practices improved water quality, problems persisted in larger watersheds. Thisndissociation between practice-focused and watershed-scale assessments occurred because:n(1) Conservation practices were not targeted at critical sources/pathways of contaminants;n(2) Sediment in streams originated more from channel and bank erosion than from soil erosion;n(3) Timing lags, historical legacies, and shifting climate combined to mask effects of practicenimplementation; and (4) Water quality management strategies addressed single contaminants withnlittle regard for trade-offs among contaminants. These lessons could help improve conservationnstrategies and set water quality goals with realistic timelines. Continued research on agricultural waternquality could better integrate modeling and monitoring capabilities, and address ecosystem services.