Changes in the benthic communities of Muskegon Lake, a Great Lakes Area of Concern

Abstract

Sediment contamination resulting from the direct discharge of industrial and municipal wastes contributed to the designation of Muskegon Lake (Michigan) as a Great Lakes Area of Concern. To assess the changes occurring in the sedient-dwelling invertebrate communities since wastewater diversion began in 1973, benthic samples were collected three times per year (spring, summer, fall) between 2004 and 2010 from six sites and compared to historic samples. The density and diversity of invertebrate populations were analyzed to: 1) identify spatial and temporal patterns in the community structure; 2) determine if community structure patterns were related to environmental variables; and 3) assess the recovery of Muskegon Lake's benthic community following wastewater diversion. Our results revealed that invertebrate community structure changed on both annual and spatial scales, while seasonal differences were shown to be modest between 2004 and 2010. The environmental variables with the greatest explanatory power included dissolved oxygen, pH, and depth. Overall, recovery of benthic invertebrate community structure was evident based on multiple lines of evidence, including increased densities of all major taxonomic groups and species diversity since wastewater diversion, decreases in both the oligochaete–chironomid ratio (0.92 in 1972; 0.69 in 2010) and the proportion of oligochaetes, and declining sediment metal concentration over time. However, comparisons of present-day and historic sampling sites must be viewed with caution because sampling locations and protocols varied among years. Significant changes in benthic invertebrate composition and water quality metrics since 1972 suggest improved environmental conditions and the continued recovery of Muskegon Lake from historic pollution.