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Florida Lake Management Society Annual Conference, Naples, Florida, June 4 – 7, 2007

SOURCES OF NITRATE IN THE WEKIVA RIVER BASIN

W. A. Tucker, S. A. Rizzo, and N.M. Goodwin MACTEC Engineering and Consulting, Inc. Newberry, FL R. A. Mattson St. Johns River Water Management District Palatka, FL

Central Florida’s Wekiva River is a springfed system of regional, state and national

significance. Several of the Basin’s seven 2nd magnitude springs have impaired water quality due to nitrate contamination. The Basin, including its springshed, encompasses 415,000 acres within four counties (Lake, Orange, Seminole, and Marion).

Land Use in the Wekiva Basin

Forest, open land 52%

Residential 21%

Sources of nitrate include fertilizer use, sewage (sewered systems and septic tanks) and atmospheric deposition. Inputs (e.g., fertilizer applied) from these sources were estimated. Transport mechanisms to waters of the Basin were defined, and nitrate loadings to surface water and groundwater were estimated.

Golf course, rec 2%

Agriculture 18%

Transportation 2%

Commercial, Industrial, Institutional 5%

UF/IFAS Extension Service recommendations were the primary source of fertilizer application rates, unless published evidence indicated that actual application rates differed from Extension recommendations. Acreage in various land uses were determined using ArcGIS™ from the St. Johns River Water Management District (SJRWMD) 2004 land use data. Florida Department of Environmental Protection permits were used to identify wastewater facilities discharging nitrate, and compliance monitoring data from 2004 through 2006 were used to estimate effluent loads. Septic tank information provided by FDOH was used to estimate the number of septic tanks in the basin.

Loadings to groundwater were estimated using ArcGIS™ by multiplying representative

groundwater concentrations for each land use by groundwater recharge rates used in SJRWMD’s E. Central Florida groundwater model. Representative groundwater concentrations for each land use were based on field scale monitoring studies from sites in Florida, if available, or studies from similar land uses elsewhere. Field scale monitoring studies were not identified that could be used to estimate groundwater concentrations in residential areas, and residential land use is a large and growing portion of the Wekiva Basin. Stormwater loadings were estimated by application of the Watershed Management Model (WMM) developed for the Wekiva Study Area

Stormwater Master Plan.

Session 8B – Page 3

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