Field Characterization of Potential Reference Sediments in the Gulf of Mexico: Chemical and Biological Quality

Abstract

Baseline information on the chemical and biological quality of sediments is provided for six coastal locations in the northern Gulf of Mexico, which were considered possible candidates for regional reference areas. Chemical quality, toxicity and benthic community composition were determined for sediments collected three times from each of 12 sites during an approximate one-year period. Potential contaminants in the usually sand-dominated sediments exceeded individual threshold effects level guidelines proposed for Florida coastal areas in approximately 31% of the samples collected from 8 of 12 sites. No probable effects level guidelines were exceeded. Acute toxicity occurred in 16% or less of the sediment samples and no significant chronic toxicity was observed to the infaunal amphipod, Leptocheirus plumulosus. Approximately, 11% and 17% of the sediments were classified as poor or marginal, based on low benthic taxa abundance and diversity index values, respectively. Sediment quality at many sites was less degraded than that for nearby coastal areas receiving point and non-point source contaminants, which suggests their suitability to serve as reference sediments although further confirmation is recommended. In a broader context, the results of this survey reflect the complexity in field verification of reference conditions for near-coastal sediments. This is attributable largely to the natural variability in their physical, biological, and chemical characteristics and to the lack of biocriteria for benthic macro and meiofauna.