Environmental Influences on Benthic Community Structure in a Great Lakes Embayment

Abstract

Biological and chemical measurements of sediment are useful parameters when establishing long-term assessment and monitoring tools for designated areas of concern (AOCs) in the Great Lakes. An intensified Environmental Monitoring and Assessment Program (EMAP) sampling grid in the St. Louis River estuary of western Lake Superior was used to assess the relationship between surficial sediment characteristics and benthic community structure. Ninety sites within two habitat classes (< 5.5 m and > 5.5 m depth) were randomly sampled. Sediment for chemical analysis was collected with a cylindrical drop core while benthic macroinvertebrate abundance and composition were determined from petite Ponar grab samples. Taxa richness was variable (1 to 25 taxa) among sites in the St. Louis River AOC. Oligochaeta were the most abundant taxa while Chironomidae larvae provided a majority of the taxa richness with 43 genera. Results from multivariate redundancy analysis (RDA) on 13 environmental parameters revealed that the majority of variation in benthic community structure was attributed to water depth and site distance from the headwaters. Although physical habitat alterations occur over large spatial scales and are more subtle than those conditions associated with chemically impacted sites, only a small portion of the variability in benthic community structure was explained by sediment chemistry variables. Variability in benthic community structure during this survey was best explained by physical habitat features and must first be quantified prior to understanding benthic response to contaminated sediments.