Comprehensive assessment of macroinvertebrate community condition and sediment toxicity in the Eighteenmile Creek Area of Concern, New York, 2021

The degradation of benthic communities (benthos) is one of four remaining beneficial use impairments (BUIs) in the Eighteenmile Creek Area of Concern (AOC), located on the south shore of Lake Ontario in New York. The historical rationale for listing this BUI as impaired relied heavily on inferred or expected impact to benthic communities based on elevated contaminant concentrations in bed sediments from past industrial and municipal discharges, hazardous-waste disposal, and pesticide usage. Previous assessments of macroinvertebrate community condition in the AOC have produced inconclusive results, and it remains unclear if contaminated sediments are impairing benthic communities. In 2021, a comprehensive assessment of macroinvertebrate community condition and sediment toxicity was conducted at eight sites in the AOC and six sites in a reference area on Oak Orchard Creek to determine if the removal criteria for this BUI have been met or if additional remedial measures are needed. The New York multi-metric index of biological integrity classified the mean community condition across AOC sites as slightly impacted, and 10-day toxicity tests with Chironomus dilutus and Hyalella azteca found no evidence of toxicity in AOC sediments. Equivalence testing indicated that community condition, and survival and growth of both test species, were not inferior in the AOC relative to the reference area. The weight of evidence from this study and other relevant datasets indicate that sediment contamination is not causing measurable impairment to benthic communities in the Eighteenmile Creek AOC.