Knowledge Bank

Eutrophication threatens water quality, aquatic ecosystems, human health, and recreation. In freshwater systems like Lake Erie, phosphorus (P) is commonly the limiting nutrient. Thus, international efforts are underway to reduce P loads by 40% across the Lake Erie basin. Targeting best management practices (BMPs) may accelerate progress towards this goal by addressing fields responsible for disproportionately greater P loads. Models have been effective at demonstrating the value of targeted management but have neglected to incorporate soil test P (STP) data representing legacy-P field contributions. The objective of this study was to quantify the benefits and elucidate the uncertainty of targeting a BMP (P-filters) to legacy-P fields as opposed to a random placement approach. A field-scale Soil and Water Assessment Tool model of the Maumee River watershed was updated to include a representative distribution of STP concentrations observed across the region. Our analysis considered the total dissolved reactive P (DRP) losses from "agronomic-P" fields (< 100 ppm Mehlich3-P) and "legacy-P" fields (≥ 100 ppm Mehlich3-P). Equivalent acreages were randomly selected to estimate the P-filter load reductions for a targeted approach versus a non-targeted approach. A Monte Carlo simulation was applied to elucidate the uncertainty of each approach at incremental amounts of adoption (10-100%). Further, different rates of P reduction were assumed for the P-filters (39.7-41.7% reduction). Legacy-P fields were, on average, responsible for greater DRP concentrations (0.241mg/L) compared to agronomic fields (0.107 mg/L). Assuming P-filter adoption across equivalent areas, a targeted approach yielded 2-fold greater P load reductions compared to a random placement approach (7.4% vs. 3.5%). This analysis will be used to support the development of a government supported program that will target BMPs to legacy-P fields across Ohio.