Long-term regional nutrient contributions and in-lake water quality trends for Lake Okeechobee

Abstract Faridmarandi S, Khare YP, Naja GM. 2020. Long-term regional nutrient contributions and in-lake water quality trends for Lake Okeechobee. Lake Reserv Manage. XX:XXX–XXX. A long-term dataset was used to investigate the historical regional changes in Lake Okeechobee water quality from water year 1974 to 2018. During this period, the total phosphorus (TP) load from the northern region to the lake remained statistically stable while the in-lake TP concentrations showed a statistically significant increasing trend, despite decades of state plans to restore this ecosystem. During the investigated period of record, the inflow TP flow weighted mean concentration from the southern region had a slightly higher value of 0.191 mg/L (when compared to the northern region) with a statistically significant increasing trend. The average annual total nitrogen unit area inflow loading (678.6 kg/km2) and flow weighted mean concentration (4.35 mg/L) into Lake Okeechobee from the southern region had the highest levels when compared to other regions. Lake Okeechobee TP sedimentation rate showed a statistically significant decreasing trend indicating a reduction in the capacity of the lake sediments to assimilate phosphorus. Results showed that the lake sediments may become a continuous source of phosphorus in water year 2035. Sustained and long-term efforts on the scale of decades will be required for restoring the lake using a multipronged approach consisting of mainly the implementation of nutrient/fertilizer best management practices and the construction of ∼200 km2 of constructed wetlands for a total project cost of US$4.26 billion. Unless a proven cost-effective technology is developed to tackle the legacy TP problem in the lake sediments, a prioritization of state resources is required while focusing on Lake Okeechobee watershed.