Summary of Major Issues and Findings

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Nutrients in Ground Water and Streams

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Nitrate concentrations (as nitrogen) exceeded the U.S. Environmental Protection Agency (USEPA) drinking-water standard of 10 milli-grams per liter (mg/L) in more than 20 percent of ground-water samples from surficial aquifers in agricultural areas (page 6). In the 23 ground-water samples from the row-crop agricultural area in the upper Suwannee River Basin, 33 percent exceeded the drinking-water standard. These samples were from aquifers that overlie the Upper Floridan aquifer, the major source of drinking water for the study area.

Nitrate concentrations in streams did not exceed drinking-water standards or guidelines, but were higher in streams draining basins with agricultural and mixed land uses (pages 7-9). Phosphorus concentrations in nearly 30 percent of stream samples were greater than 0.1 mg/L, the USEPA guideline for the prevention of nuisance algal growth.

Ground-Water/Surface-Water Interactions

Nitrate concentrations (as nitrogen) in the lower Suwannee River are affected by a cycle of water exchange between the river and the adjoining aquifer (pages 10-11). During low flow in the river, ground water containing nitrate enters the river, increasing river nitrate concentrations. During high flow river water enters the aquifer, resulting in a decrease in nitrate concentrations. As the exchange cycle reverses, ground water flows into the river.

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Pesticides in Ground Water and Streams

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Photo by D.N. Skofronick, Fla.

Of 85 pesticides and degradation products analyzed, 21 were detected in ground water and 32 were detected in streams (pages 12-14). Pesticide concentrations did not exceed any USEPA drinking-water standards, but criteria for protection of aquatic life were exceeded in some streams. The most frequently detected pesticides in ground water and streams were three herbicides--atrazine, metolachlor, and prometon. No insecticides were detected in ground water. The kinds and frequency of pesticides detected differed in agricultural and urban areas.

Volatile Organic Compounds (VOCs) and Radon in Ground Water

Eleven different volatile organic compounds (VOCs) were detected in ground water, with one VOC usually detected in each sample (page 15). Most concentrations were less than 1 microgram per liter (µg/L). VOCs were detected in ground water in all land-use areas; however, samples from wells in urban and agricultural areas contained VOCs more often than samples from rangeland and forest areas.

Radon concentrations in ground water were among the highest in the Nation and are related to the minerals naturally present in aquifer sediments (pages 15, 20). Elevated radon concentrations were present in the Upper Floridan aquifer in central Florida, the primary drinking-water aquifer for that area.

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Organic Compounds and Trace Elements in Streambed Sediments

Concentrations of organochlorine pesticides in 22 percent of streambed-sediment samples exceeded aquatic-life criteria (page 16). Most exceedances were for chlordane and DDT and their degradation products, which were also the organochlorine pesticides most frequently detected in streambed sediments. Semivolatile organic compounds (SVOCs) were detected in nearly all streambed sediments. Polychlorinated biphenyls (PCBs) detected were at only one site (in an urban basin) at a concentration below the aquatic-life criterion.

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