Inadequacy of best management practices for restoring eutrophic lakes in the United States: guidance for policy and practice

Abstract

The policy and practice of restoring eutrophic or phosphorus (P)-impaired lakes that relies heavily on watershed best management practices (BMPs) is mostly inadequate. This strategy has been prevalent in the United States for several decades, but there are few documented positive outcomes. To restore most eutrophic lakes requires external P reductions >80% in the United States. A review of BMP performance literature with respect to P removal indicates the maximum expected P removal under ideal conditions on a watershed-wide basis approaches 50%, however in practice reductions in P load may be <25%. The discrepancy between required P reductions and BMP performance explains the observed paucity of positive outcomes. BMPs may be sufficient in cases where watershed size is small (i.e., <10-times lake surface area) and external and internal P loading rates are modest, or where incremental water quality improvement rather than restoration is the management goal. Guidance for restoring eutrophic lakes is provided here. In cases where BMPs are inadequate as the sole restoration strategy, alternative or supplemental approaches are available. In many cases, effective P inactivation methods to mitigate internal P loading and to intercept dissolved P in inflowing waters are required to restore lakes. Engineering approaches or chemical treatment systems can feasibly, reliably, and effectively provide sufficient external or internal P load reductions.