Determining degradation and restoration of benthic conditions for Great Lakes Areas of Concern

Abstract

“Degradation of benthos” is one of the most common beneficial use impairments identified in Great Lakes Areas of Concern (AOCs). Management of AOCs towards recovery from impairment can benefit from a consolidation of quantitative methods for describing benthic conditions, determining impairment and its probable cause, and detecting recovery that are linked to targets for restoring beneficial use. Benthic conditions are effectively characterized by multiple descriptors, such as physicochemical conditions of sediment, toxicity of sediment, benthic macroinvertebrate community structure, bioaccumulation of contaminants in benthic invertebrates, and substrate stability. Degradation is quantifiable in terms of the degree to which conditions in AOCs differ from reference conditions and exceed environmental quality criteria or other empirically derived benchmarks that are associated with adverse effects. Inferring causality of adverse effects by association with putative stressors is important for the development of management actions to promote restoration. Recovery of benthic conditions after elimination of exposure to the stressor(s) of concern can be identified as the reversal of degradation or, due to effects of interacting environmental factors, a restabilization at a state different from predisturbance conditions. It is recommended that delisting criteria, which define targets for restoration of the beneficial use, be based on the benthic descriptors and conditions used to identify degradation and recovery, with the recognition that the remedial action plan process allows the criteria to be modified to accommodate impacts from other nonmanaged stressors and additional nonecological considerations.