| Abstract: | ABSTRACT: Nitrate levels in the Ocklawaha River Basin in north central Florida were reviewed over a 50‐year period. Data were obtained from the literature, U.S. Environmental Protection Agency (USEPA) STOrage and RETrieval (STORET), and U.S. Geological Survey (USGS) databases. The study objective was to determine whether nitrate concentrations are increasing and if so, whether this increase is linked to land use changes. Increasing nitrate levels were seen at 5 of the 14 stations, while other stations showed no trend or a decreasing trend. Median nitrate concentrations in the Ocklawaha River increased from 0.07 mg‐N/L to 0.78 mg‐N/L at sites downstream from the Silver River. Throughout the Rodman Reservoir, median nitrate concentrations decreased from 0.48 mg‐N/L to 0.01 mg‐N/L and increased to 0.04 mg‐N/L after the Kirkpatrick Dam. Flow and concentration relationships were correlated for five stations. At four of the five stations nitrate concentrations decreased in response to increasing flow, likely the result of dilution with nitrate poor water. Changes in land use over a 20‐ year period (1970 to 1990) also were monitored. Sources of nitrate have been linked by isotopic analysis to organic and inorganic fertilizers, which appear to be related to increased urbanization and an increase in lawns that require nutrient fertilization. |
