Long-term water quality trends after implementing best management practices in South Florida.

A mandatory best management practices (BMP) program was implemented in the Everglades Agricultural Area (EAA) farms basin-wide in 1995 as required by the Everglades Forever Act to reduce P loads in drainage water reaching the Everglades ecosystem. All farms in the EAA basin implement similar BMPs, and basin wide P load reductions have exceeded the 25% reduction required by law; however, differences remain in water quality between subbasins. Our objective was to determine long-term trends in P loads in discharge water in the EAA after implementing BMPs for 7 to10 yr and to explore reasons for differences in the performance of the subbasins. Two monitoring datasets were used, one from 10 research farms and the second from the EAA basin inflow and outflow locations. Mann-Kendall trend analysis was used to determine the degree of change in water quality trends. A decreasing trend in P loads was observed in general on sugarcane (Saccharum officinarum L.) farms, while mixed crop farms showed either decreasing or insignificant trends. The insignificant trends are probably related to management practices of mixed crop systems. Decreasing trends in P loads were observed in the outflow of the EAA basin, S5A, and S8 subbasins from 1992 to 2002. Inflow water from Lake Okeechobee had increasing P concentration from 1992 to 2006 with the highest trend in the east side of the lake. This analysis indicated there may be other factors impacting the success of BMPs in individual farms including cropping rotations and flooding of organic soils. Elevated P concentrations in Lake Okeechobee water used for irrigation may pose a future risk to degrade water quality on farms in the EAA, especially in the S5A subbasin.