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ABSTRACT: Long-Term Sampling of Selected Heavy Metals Concentrations in the Bottom Sediments of Imperial River and Spring Creek, Lee County, Southwestern Florida

MITCHELL-TAPPING, HUGH J. and ALETA M. MITCHELL-TAPPING

Heavy metal concentrations are important in terms of their potential toxic effects and as a signal for the presence of other types of pollution. However, heavy metals pollution has four major interpretive problems: (1) determining residual long-term geologic chemical reactions, (2) distinguishing those components attributable to natural causes from those attributable to man's activities, (3) determining whether anthropogenically-enriched sediments are likely to cause adverse affects, and (4) determining if the pollution is permanent (long-term) or is an isolated event (short-term). Among the toxic heavy metals found in stormwater, lead, copper and zinc appear to be the most abundant and frequently detected. As stormwater runoff is of major importance in southwestern Florida, this study has examined copper, lead, zinc and iron concentrations, quarterly from 1981 to 1995, from sites along Spring Creek and Imperial River. The results have given insight into the relationship of metal concentration to changes in sediment grain-size and content during both wet and dry seasons, and also to long-term pollution assessments. For example, a very high copper concentration was detected in silt and clay-sized particles at an Imperial River marina site. The same site was sampled the following year at the end of the wet season. The analysis indicated that sediment size had increased and copper concentration had returned to the lower natural background values of previous years. The high copper concentration was subsequently determined to be due to antifouling and preservatives of newly installed wooden mooring posts and that the wet season stormwater runoff had flushed many of the clay-sized particles from the marina sediments.

AAPG Search and Discovery Article #90941©1997 GCAGS 47th Annual Meeting, New Orleans, Louisiana