Click on “Download PDF” for the PDF version or on the title for the HTML version.

If you are not an ASABE member or if your employer has not arranged for access to the full-text, Click here for options.

Best Management Practices (BMPs) are commonly used to address water quality concerns from nonpoint source activities. BMPs must be effective and must be implemented at a high rate to reduce impacts to acceptable levels at a watershed scale, but there is controversy about how to represent BMP effectiveness. The most common way is by calculating a percent reduction in pollutant load, but some criticize this as potentially misleading. Here we argue that percent reduction is a legitimate method to describe effectiveness, but it is only one of many ways. Other approaches include attainment of water quality or habitat standards and goals, biological response, and even economic efficiency. Perhaps the three biggest challenges for assessing BMPs directed at nonpoint source activities are defining appropriate water quality expectations (how much is enough), determining what site conditions limit BMP effectiveness, and determining appropriate spatial and temporal scales for assessment. Ongoing efforts to develop effective and realistic numeric nutrient criteria and contemporary forest watershed studies, both using monitoring of multiple responses provide examples of how weight-of-evidence approaches may be the most useful way to judge BMP effectiveness.