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Water Quality in the Georgia-Florida Coastal Plain, Georgia and Florida, 1992-96

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MAJOR ISSUES AND FINDINGS
Trace Elements in Streambed Sediments

Trace element concentrations in streambed sediments are related to natural and human influences.

The trace elements antimony, arsenic, cadmium, chromium, copper, lead, mercury, nickel, silver, and zinc are included in the USEPA list of priority pollutants which may have adverse effects on aquatic life. Trace elements in streambed sediments are derived from a variety of sources. Natural sources include the weathering of soils and bedrock. Anthropogenic sources include atmospheric deposition, stormwater runoff, wastewater discharges, landfills, automobile exhaust, fertilizer, inorganic pesticides, and industrial emissions.

Long and Morgan (1991) developed criteria called "effects-range thresholds" for use in assessing the effects of differing concentrations of trace elements on aquatic organisms. They computed threshold concentrations for each element. When a trace element concentration exceeds the threshold, some aquatic organisms could be adversely affected.

One or more trace elements exceeded threshold concentrations in streambed sediments from most sites.

In the study area, the threshold concentration of one or more trace elements was exceeded at 83 percent of all sites. Lead, chromium, mercury, and zinc exceeded threshold concentrations most often. Lead concentrations exceeded thresholds at 57 percent of all sites. Concentrations of antimony, arsenic, and cadmium did not exceed threshold concentrations.

Bar chart: percentage of samples exceeding threshold concentrations

Streambed sediments from sites in urban basins exceeded threshold concentrations more frequently than those from other land uses.

Canoe photo (80,566 bytes)

The percentage of trace elements exceeding threshold concentrations in streambed sediments was related to land use. Threshold concentrations of lead, chromium, mercury and zinc were exceeded in at least 60 percent of sites in urban areas. Threshold concentrations were exceeded less frequently in mixed, agricultural, and forest-wetland areas, with the exception of lead. Lead exceeded the threshold concentration in more than 50 percent of the sites in all land-use categories.

Bar chart: percentage of samples exceeding thresholds, by land use

Chromium, lead, mercury, and zinc exceeded threshold concentrations most frequently in streambed sediment samples from urban basins.

The percentage of sites with lead and mercury exceeding threshold concentrations in forest-wetland basins is of concern because these basins are relatively pristine. The sources of these two elements in concentrations of concern could be due to (1) the natural weathering of bedrock and soils in the basin, (2) atmospheric deposition from the burning of fossil fuels, or (3) other previous activities in the basin.

U.S. Geological Survey Circular 1151

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Suggested citation:
Berndt, M.P., Hatzell, H.H., Crandall, C.A., Turtora, M., Pittman, J.R., and Oaksford, E.T., 1998, Water Quality in the Georgia-Florida Coastal Plain, Georgia and Florida, 1992-96: U.S. Geological Survey Circular 1151, on line at <URL: https://water.usgs.gov/pubs/circ1151>, updated April 14, 1998 .

This page is a subpage of <URL:http://water.usgs.gov/pubs/circ1151>
Email questions and comments to nawqa_gafl@usgs.gov

Last modified: April 14, 1998 10:45 am