Abstract

This Florida Geological Survey/U.S. Department of Interior Minerals Management Service Cooperative study provides baseline data for major and trace metal concentrations in the Steinhatchee River Estuary. The study provides a benchmark for comparison of future metal concentration measurements.

The Steinhatchee River Estuary is a small, relatively pristine bay located on the Florida Big Bend coastline. Sedimentary accretion rates within the estuarine system vary from 1.41 to 4.13 mm/yr and are consistent with rates determined for other estuaries in the Gulf of Mexico system. In this study, 79 samples were collected from 66 locations representing four sedimentary lithofacies, including quartz sands, organic-rich sands, clay-rich organics, and oyster bioherms. All samples were analyzed for major and trace metal content, texture, total organic matter, and clay mineralogy.

Normalization of element concentrations assumes a linear relationship between either geochemical or sedimentological characteristics and the element of interest. Granulometric normalization of metal concentration against total weight percent fines (<62.5 μm) was evaluated. Geochemical methods tested include normalization against reference elements (aluminum, iron, and carbon) and normalization against sediment organic matter content.

The best correlations were found when trace metals were normalized with respect to aluminum. Data normalization indicated that nearly all metal concentrations were within 95% confidence limits of the expected value. In general, the metal levels observed in the estuary indicate little significant contamination from anthropogenic sources. Exceptions included lead levels that appeared to be significantly elevated in a few samples taken in the organic-rich sand facies of the salt marsh. Mercury values were also elevated with respect to the expected trends in three locations. Potassium and phosphorus may be slightly elevated in several of the marsh facies samples. Possible explanations include nutrient loading from nearby communities and application of these elements in fertilizer to reduce moisture stress to pine seedlings within the watershed.