Long-Term Water Quality Trends in the Lake Okeechobee Watershed, Florida

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.