HA1 Contaminated Harbour and River Sediment
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() Benthic ecological risk assessment – Balancing environmental and chemical stressors in an estuary.

Williams, L.1, Durda, J.2, Preziosi, D.2, Sparks, P.3, 1 Integral Consulting, Inc., Seattle, WA, USA2 Integral Consulting, Inc., Annapolis, MD, USA3 Integral Consulting, Inc., Olympia, WA, USA

ABSTRACT- Modern urbanized estuaries are challenged by multiple chemical and non-chemical stressors, all of which affect the structure and composition of benthic communities and influence ecological risk assessment and management decisions. Consequently, benthic ecological risk assessment in estuaries must rely on multiple lines of evidence to segregate chemical stressors from those attributable to other natural or anthropogenic factors. Greens Bayou, Texas is an example of a complex, urbanized estuary with multiple chemical and non-chemical stressors. Historical releases of DDT and its metabolites (DDTr) from a pesticide manufacturing facility have resulted in locally elevated concentrations of DDTr in sediments of the lower, tidally influenced bayou. Natural stressors include estuarine gradients in salinity, temperature, and dissolved oxygen. The lower bayou is also disturbed by channel maintenance and vessel traffic. A benthic ecological risk assessment was undertaken to assess the potential impacts of DDTr contaminated surface sediments on benthic communities in Greens Bayou. Lines of evidence that were used in the risk assessment were sediment chemistry, solid- and suspended-phase sediment toxicity, benthic community characteristics, conventional sediment and water quality, and qualitative indicators of physical disturbance. These lines of evidence were compared with reference conditions, including sediment quality benchmarks, background conditions, and a benthic community index for the Northern Gulf of Mexico. The ecological risk assessment shows localized elevated concentrations of DDTr, and a disturbed benthic community. However, benthic community disturbance appears to be related to estuarine gradients in salinity and possibly dissolved oxygen. Sediment toxicity was sporadic and was not related to any of the site chemicals. Collectively, the various lines of evidence indicate that site-related chemical impacts are unlikely and that other stressors dominate benthic community disturbance. These results underscore the benefit of multiple lines of evidence in providing ecological perspective for sound risk management decisions.

Key words: ecological risk assessement, sediments, benthic communities, environmental stressors

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