Revisiting the total maximum daily load total phosphorus goal in Lake Okeechobee
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PRIMARY RESEARCH PAPER
Revisiting the total maximum daily load total phosphorus goal in Lake Okeechobee Zachary A. Siders
. Karl E. Havens
Received: 31 May 2020 / Revised: 28 August 2020 / Accepted: 5 September 2020 Ó Springer Nature Switzerland AG 2020
Abstract In 2000, a total maximum daily load (TMDL) total phosphorus (TP) goal of 40 lg/L was established for Lake Okeechobee, Florida. The goal was selected to reduce the ‘‘imbalance to flora and fauna’’ caused by excessive phosphorus loading in the lake. We recalculate the TMDL TP goal using a water quality data series of TP and chlorophyll-a concentrations from 1986 to 2018 for the original 30 in-lake stations plus an additional 29 stations. Using the crosstabulation approach used to generate the original TMDL TP goal, we determined a new goal of 42 lg/L, nominally different from the original. We also reevaluate the goal’s ability to maintain an implicit goal of 11.5% bloom frequency. We conclude
substantial changes in the frequency and scope of the water quality sampling scheme prevent a determination on the effectiveness of the TMDL TP goal. The implementation, however, appears to have failed as the median TP concentration has increased by 93 lg/L to 133 lg/L and bloom frequency, after correcting for the declining sampling frequency, has increased from 1986 to 2018. An increased sampling frequency of TP and chlorophyll-a sampling is needed, or else tracking responses of chlorophyll-a to future TP reductions will be virtually impossible. Keywords Algal blooms Eutrophic Sampling frequency Chlorophyll-a Time series
Handling editor: Alex Elliott
Introduction Karl E. Havens—Deceased.
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10750-020-04406-8) contains supplementary material, which is available to authorized users. Z. A. Siders (&) K. E. Havens Fisheries and Aquatic Sciences Program, School of Forest Resources and Conservation, University of Florida IFAS, 7922 NW 71st St, Gainesville, FL 32653, USA e-mail: [email protected] K. E. Havens Florida Sea Grant College Program, University of Florida, Gainesville, FL, USA
The setting of total maximum daily loads (TMDLs) for pollutants affecting impaired waters of the United States is required under section 303(d) of the Clean Water Act. The State of Florida identified Lake Okeechobee as an ecosystem impaired by excessive phosphorus inputs in 1998 and a total phosphorus TMDL was established and approved by the Florida Department of Environmental Protection in 2000 (FDEP 2000). Since the year 2000, the lake has seen an increase in extreme weather events (Havens et al., 2016), increasing but highly variable mean total
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Hydrobiologia
phosphorus concentrations, and little reduction in phytoplanktonic bloom events. Given the contrast inlake conditions before and after setting the phosphorus TMDL, it is prudent to revisit the setting of TMDL goal for Lake Okeechobee and evaluate the performance of the current
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