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Great Lakes Monitoring

Sediment Indicators
Sediment Quality Assessment 

R/V Mudpuppy analyzing contaminant sedimentsThis article describes one method of tracking levels of contaminants present in Great Lakes sediments and analyzing contamination trends over time using sediment quality guidelines (SQGs). SQGs were developed to predict contaminant concentration levels that are associated with the absence or occurrence of adverse biological impacts (i.e. toxicity to benthic organisms). In this study, thirteen sediment data sets from eleven Great Lakes sites are compared to the sediment quality guidelines in an effort to determine the relative level of contamination in the first and second sediment layers. The sites included in the study are Clinton River, Duluth Harbor, Fox River, Grand River, Maumee River, Muskegon Lake, Olcott Harbor, Oswego River, Sheboygan River, Trenton Channel, and White Lake.  Five common sediment contaminants (including three BNS priority pollutants) were chosen for this comparison: mercury, total polychlorinated biphenyls (PCBs), total polycyclic aromatic hydrocarbons (PAHs), chromium, and lead. 

The Great Lakes National Program Office, GLNPO, sediment program is active throughout the Great Lakes basin in performing sediment assessments, supporting sediment-based mass balance modeling efforts, promoting sediment clean-up activities, and participating in the development of Great Lakes sediment policy.  In order to promote these objectives, GLNPO provides funding, technical support, and a sampling vessel for various sediment projects throughout the Great Lakes basin.  GLNPO’s sediment program has collected a multitude of chemical data sets from these assessment efforts demonstrating the extent of sediment contamination within the Great Lakes.  

The following figure provides a visual representation of the chemical data for both the first and second sediment layers. The figure displays the proportion of sediment data from the first and second layers that fall into four ranges of contaminant severity: from little or no contamination, to severe levels of contamination.

 

As shown in the pie charts for each of the five contaminants, the contamination always appears to be higher in the top (surficial) layer than in the second layer of sediment.  These results are interesting since, in the last few decades, water quality and environmental standards have become more stringent throughout the United States.  Therefore, we would expect to find that the surficial sediments were becoming less contaminated as environmental controls reduced the inputs of contaminants into the Great Lakes basin.  However, it appears that the surficial sediments are actually more contaminated than deeper sediments, possibly due to migration of historical contamination from upstream source areas.

Before the present study, it was often assumed that levels of contamination present in the surficial layer of Great Lakes sediments were decreasing due to natural recovery, the process of natural sedimentation and natural bio-degradation to reduce the impacts of sediment contamination on water quality and the ecosystem.  Natural recovery assumes that natural processes can act independently over time in order to reduce the hazards associated with contamination by cleaner material covering over the non-contaminated, older material.  The results of this study seem to call into question some of the underlying assumptions regarding natural recovery. Further monitoring of these sediments will help to establish a pattern of increasing or decreasing contamination in the upper sediment layers. It will also help to determine if remediation efforts are necessary and feasible.

Acknowledgements

The development of freshwater SQGs are more fully described in Persaud et al. (1992), Smith et al. (1996), and MacDonald et al. (2000).

 



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