SEDIMENTATION RATES AND TRACE METAL INPUT HISTORY IN CHINCOTEAGUE LAGOON-MARSH SYSTEM DERIVED FROM PB-210 AND CS-137 CHRONOLOGY

Chincoteague Bay is a small coastal lagoon located on the Eastern Shores of Maryland and Virginia. This ecologically important lagoon-marsh system is habitat for diverse species, traps terrestrially-derived sediments, filtering run-off associated contaminants, and also protects the mainland from wave and tidal energy caused by storm events. Recent rapid population growth and increased tourism in Chincoteague Island is progressively altering this watershed and could prove detrimental to this natural ecosystem through increased sediment fluxes, and associated nutrient and trace metals leading to degraded water quality. This study uses six sediment cores from the lagoon and the marsh to analyze the probable impact of the modern land-use changes on the environmental evolution of this lagoon-marsh system.

The results show a notable increase in the average sediment accumulation rates since the mid 1930’s (top 15 cm) relative to deeper sediment layers. The Pb-210 and Cs-137 based sediment accumulation rates for the upper 15 cm ranged from 0.51 g/cm²/yr to 0.61 g/cm²/yr and the deeper layers (> 15 cm) from 0.06 g/cm²/yr to 0.14 g/cm²/yr. The recent increases in the number of storm events, coupled with increasing population rates and the associated land-use changes in Chincoteague, could be contributing to the modern increases in sediment fluxes to the lagoon. Sediment trace metal profiles of Al, As, Ba, Cd, Cu, Fe, Mn, Pb and Zn shows relatively low concentrations, but all cores have modern enrichments that are probably associated with increased sediment fluxes and anthropogenic related pollutants. Sediment trace metals also seem to be correlated to finer grain sizes as well as sediment diagenetic processes. Continued research and better management practices are needed in order to prevent sedimentation rates and trace metal contamination from increasing to detrimental levels.