Diagnosis of potential stressors adversely affecting benthic communities in New Bedford Harbor, MA (USA)

Diagnosing the causes of impaired ecosystems in the marine environment is critical for effective management action. When ecological impairment is based on toxicological or biological criteria (i.e., degraded benthic community composition or toxicity test results), managers are faced with the additional problem of diagnosing the cause of impairment before plans can be initiated to reduce the pollutant loading. We evaluated a number of diagnostic tools to determine their ability to identify pollutants in New Bedford Harbor (NBH), Massachusetts (USA), using a modified version of the US Environmental Protection Agency's (USEPA) stressor identification (SI) guidance. In this study, we linked chemical sources and toxic chemicals in the sediment with spatial concentration studies; we also linked toxic chemicals in the sediment with toxicity test results using toxicity identification and evaluation (TIE) studies. We used geographical information systems (GIS) maps to determine sources and to aid in determining spatially integrated inorganic nitrogen (SIIN). The SIIN values of reference and test estuaries were quantified and compared. Using this approach, we determined that toxic chemicals continue to be active stressors in NBH and that a moderate nutrient stress exists, but we were unable to link the nutrient stressor with a source. Also excess sedimentation was evaluated, but it does not appear to be an active stressor in this harbor. The research included an evaluation of the effectiveness of tools under development that may be used to evaluate stressors in water bodies. We found that the following tools were useful in diagnosing active stressors: toxicity tests, toxicity identification and evaluation (TIE) methods, comparison of grain size-normalized total organic carbon (TOC) ratios with reference sites, and comparison of SIIN with reference sites. This approach allowed us to successfully evaluate stressors in NBH retrospectively; however, a limitation in using retrospective data sets is that the approach may underestimate current or newly emerging stressors.