NITRATE TRENDS IN SELECTED SECOND MAGNITUDE SPRINGS OF FLORIDA

Florida’s more than 700 springs are natural treasures which provide recreation and enjoyment to millions of people each year. Over the past 55 years, the Florida Geological Survey (FGS) has periodically sampled and analyzed water from selected springs across the state. As part of the Florida Springs Initiative, the FGS has recently sampled spring water from Florida’s 33 first magnitude springs and published the newly acquired data in comparison to historic data in order to document changes in water quality over time. The FGS documented increasing trends in nitrate levels in the first magnitude springs when compared to historic nitrate levels.

Following the sampling effort of the first magnitude springs, the FGS sampled selected second magnitude springs. Data from second magnitude springs were analyzed using the Mann-Kendall and the Wilcoxon Signed-Ranks tests. Both tests are nonparametric. The first was used to check for a monotonic trend over time for nitrate from an individual spring. The second was used to compare nitrate data from all sampled second magnitude springs during any time step (e.g. 2002) to a previous step (e.g. 1985). As with the first-magnitude springs, nitrate trends similar to those seen in the first magnitude springs were observed.

The documenting of increasing nitrate levels in Florida’s springs by the FGS, and other state and federal agencies has prompted research efforts aimed at pinpointing nitrate sources. The Florida Primary Drinking Water standard for nitrate is currently 10 mg/l. However, concentrations of as little as 1mg/l of nitrate have caused significant alteration in the ecology of some springs and spring runs. Currently, the Florida Springs Initiative is funding further research into nitrate trends and sources and is working to develop best management practices for springsheds that have been impacted by elevated nitrates.