Sediment quality of North Carolina estuaries: an integrative assessment of sediment contamination, toxicity, and condition of benthic fauna

Sediment quality of North Carolina estuaries was evaluated using synoptic data on sediment chemistry, toxicity, and macroinfaunal community structure from 175 subtidal stations sampled during the summers of 1994–1997. The study area included Currituck, Albemarle, and Pamlico Sounds; estuarine portions of major rivers (e.g., Chowan, Roanoke, Tar-Pamlico, Neuse, New, Cape Fear); and numerous smaller tributaries and coastal embayments between the Virginia and South Carolina borders. A probabilistic sampling design permitted statistical estimation of the spatial extent of degraded versus non-degraded condition across these estuaries. Over half (54 ± 7%) of the surveyed area had high sediment quality characterized by healthy benthic assemblages and low levels of sediment contamination and toxicity. The remaining 46% showed evidence of significant stress in one or more of the above sediment-quality-triad components. While this is a sizable area, portions of it (27 ± 6%) were represented by sites with no connection between presence of stressors and adverse biological responses. Only 19% of the total area showed evidence of an impaired benthos coupled to significant pollution exposure (high sediment contamination, toxicity, or both). Impaired benthic condition was more closely linked to sediment contamination than to low dissolved oxygen (based on instantaneous oxygen measurements). The most pervasive contaminants were the metals arsenic, mercury, chromium, and nickel; the pesticides lindane, dieldrin, DDT, and DDT derivatives; and total PCBs. Degraded condition in all three components of the sediment quality triad co-occurred in <10% of the study area, suggesting that strong contaminant-induced effects on the benthos are limited to a small (yet ecologically significant) percentage of total estuarine area. The spatial extent of sediment contamination and toxicity was much less in these estuaries in comparison to other U.S. coastal regions where similar studies have been performed.