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Abstract
A Seasonal Kendall Tau test was used to determine statistical significance of mean monthly total phosphorus (TP) and total nitrogen (TN) concentration trends during the time period of 1991–2007, by station and basin at 35 long-term water quality monitoring stations located within the northern Lake Okeechobee watershed. One drainage basin (S-154) had a significant decreasing trend for mean monthly TP concentrations during the analysis period. A significant increase in TN concentrations was detected for four basins during this same time period. The S-154 basin which had the significant decreasing trend for TP also had the highest percentage of implemented Best Management Practices (BMPs) and the most rigorous types of nutrient control projects. These findings emphasize the need for continued implementation of intensive P management strategies. The increasing trend in TN for this watershed signals the need for added focus on reductions of TN in future nutrient source control projects and BMPs.
ACKNOWLEDGMENTS
The authors thank David Unsell, Paul McCormick, Tom James, Steffany Gornak, Temperince Morgan, Christopher King, Cheol Mo, Brad Jones, and the three anonymous reviewers for their valuable comments and suggestions on an early version of this paper. Appreciation also goes to Denise Watts, Greg Kennedy, John Folks, and Jim Laing for the information regarding biosolids applications.