The Impact of Best Management Practices on Water Nutrients Levels in the United States

Best Management Practices (BMPs) are often designed to restore the water quality of impaired waterbodies. They are expensive to install and maintain and often have limited post-installation analysis. There is a gap in our knowledge of the long-term real-world efficiency of such systems as their dynamics are complex and poorly understood, and we have very limited data about these systems. We looked at water quality changes pre- and post-BMP implementation from sites around the US to better understand the impacts of BMPs on the nitrogen (N) and phosphorus (P) concentrations in the waterbodies. Water quality data was obtained from 72 waterbodies across the United States using the National Water Quality Monitoring Council’s Water Quality Portal. This data was analyzed for trends using the Kaplan-Meier method, exceedance probability, and lag time analysis. Out of the seventy-two (72) watershed locations, twenty-two (22) did not have enough data for analysis. Of these fifty (50) remaining watersheds locations one hundred eighty-four (184) monitoring sites were analyzed. Only sixty-nine (69) of these monitoring sites were found to have enough data for analysis. Forty-eight (48) sites saw improvement in nutrient levels, where overall post-implementation exceedance probability for critical thresholds (defined as 1 mg/l for N and 0.1 mg/l for P) decreased. Twenty-one (21) sites did not see improvement, where post-implementation exceedance probabilities did not show any reduction; in some cases, it showed an increase. Even among the efficient sites, where improvement was found, significant variation was observed in changes in exceedance probability with time, with many sites not demonstrating an expected uniform decreasing trend. It was also found that 56 out of the 72 water bodies had some biological indicator present, these included dissolved oxygen concentrations, benthic macroinvertebrate populations, fish communities/aquatic life, bacteria, and index scores. However, data gaps were detrimental to conclusively assessing BMPs with biological indicators. It was determined that sparse biological indicators data were not indicative of BMP success. These observations highlight the importance of designing a monitoring strategy that can capture these unexpected trends and allow a better understanding of BMPs. Along with better monitoring strategies, consistent and frequent monitoring is needed. Therefore, the effectiveness of best management practices was inconclusive due to a lack of available data on many sites.