The Florida experience: time for a revitalized and restructured Clean Lakes Program

Abstract

Canfield, DE Jr., Bachmann RW, Hoyer MV. 2023. The Florida experience: time for a revitalized and restructured Clean Lakes Program. Lake Reserv Manage. 39:191–212. Anthropogenic nonpoint source nutrient enrichment of lakes is a worldwide problem, but inputs from the watershed to Florida lakes may not be as severe as speculated. Long-term trends for total phosphorus (TP), total nitrogen (TN), chlorophyll (Chl), and Secchi disk transparency (SDT), enrichment surrogates, in 381 lakes monitored for 20–43 yr and having extensive management to none demonstrated improvements in trophic conditions following point source removals. Afterward, TP (R2 = 0.85), TN (R2 = 0.49), and Chl (R2 = 0.50) continued to decline significantly (P < 0.05) and SDT (R2 = 0.63) increased. For 99 state-designated “impaired” lakes, TP (R2 = 0.73), TN (R2 = 0.45), and Chl (R2 = 0.44) also declined and SDT (R2 = 0.69) increased. To consider natural background conditions, lakes were assigned to their ambient TP and TN zones. Geometric TP (93%) and TN (82%) zone averages for each lake after removal of point sources remained within each zone’s 95% confidence interval. Individual lake trend analyses documented that ∼80% showed no (most) or an improving trend for the trophic state variables. After correcting for “statistically meaningful” results or to remove false significances, <5% of the lakes had trophic state variable changes associated with eutrophication. If lakes are to be rehabilitated and/or protected to maintain designated uses, exclusive focus on watershed management of nonpoint source nutrients and associated regulatory actions should not be relied on to correct “impairments” in a timely manner. Management priorities should focus on actual causes of impairment and the most effective and efficient approaches for improvement.