Evaluating methods for assessing sediment quality in a Great Lakes embayment

A probability-based, sediment quality assessment was conducted during 1995 in the lower St. Louis River Area of Concern, located in western Lake Superior. A regional application of the intensified sampling grid developed for the United States Environmental Protection Agency's Environmental Monitoring and Assessment Program was used to randomly select 90 sites for measuring the following sediment quality indicators: sediment chemistry, physical parameters, sediment toxicity, and benthic macroinvertebrate community structure. Screening methods were used to assess sediment chemistry and sediment toxicity at all sites, whereas more conventional metrics were used at a subset of sites. In addition, sediment quality data were collected from 20 a priori training sites, 10 in low impact areas and 10 in high impact areas. Mean probable effect concentration quotients were calculated for sediment chemistry variables at each site. As the range of mean probable effect concentration quotients values increased, the incidence of sediment toxicity increased. Benthic data from the training sites were used to establish standard criteria for developing two benthic integrity indices based on multimetric analysis and discriminant function analysis. Based on the training site results, the discriminant function analysis categorized the macroinvertebrate community at all random sites as 45 percent low impact and 55 percent high impact. A multimetric approach categorized 55 percent of the random sites as low impact and 36 percent as high impact. Due to the overlap of 95 percent confidence intervals, the multimetric approach also placed 9 percent of the random sites into an indeterminate category. The incidence of high impact sites appears to be primarily due to physical habitat characteristics. This finding was supported by the sediment quality triad assessment of 52 random sites that indicated alteration of the benthic community at 71 percent of sites was probably not due to chemical contamination.

Keywords:

• benthic macroinvertebrates
• Lake Superior
• toxicity tests
• chemistry
• multimetric index
• discriminant function analysis

Acknowledgments

We wish to thank the many participants of this study. Harold Wiegner, Scot Beebe, Patti King, Carol Hubbard, and Jerry Flom, all of the Minnesota Pollution Control Agency (MPCA), provided field sampling assistance and conducted the 10 d sediment toxicity tests. James Beaumaster (MPCA) provided graphical support. Field assistance and benthic sample processing was conducted by Jacque Alexander, John Juaire, Barb Peichel, Maartje Thjssen, and Aaron Undeland at the University of Minnesota Duluth (UMD) Natural Resources Research Institute (NRRI), Duluth, MN. In addition, Sherry Bertelsen, Tim Corry, Jill Scharold, and Jo Thompson, USEPA Duluth, MN, assisted in processing benthic samples. Sediment chemistry analyses were conducted by John Ameel, Rich Axler, Sarah Kohlbry, Keith Lodge, Irene Moser, and Greg Peterson at the Analytical Chemistry Laboratory and Trace Organic Laboratory at UMD-NRRI. Microtox^® analyses were conducted by Greg Peterson and Chris Owen at UMD-NRRI. Particle size analyses were done by Keith Lodge at UMD-NRRI. This research was largely supported by Cooperative Agreement CR823497 between the MPCA and US EPA and Grant Contract Number 47002 between the MPCA and UMD-NRRI. This research was partially supported by the Minnesota Sea Grant College Program (MSGCP), and this paper is journal No. JR 505 of the MSGCP. This paper is journal No. 368 of the Center for Water and the Environment of the NRRI. The views expressed herein are those of the authors and do not necessarily reflect the views of the MPCA, UMD-NRRI, Minnesota Sea Grant, or the USEPA.

Notes

^a (−) = mean PEC-Q < 0.6; (+) = mean PEC-Q ≥ 0.6.

^b (−) = non-toxic response in both 10-d sediment toxicity tests; (+) = toxic response in either 10-d sediment toxicity test.

^c low impact or indeterminate benthic community based on both benthic classification procedures (i.e., multimetric and DFA); high impact benthic community designated by either the multimetric or DFA category.

^d Based on contingency table given in Crane et al. (2000).

^e Based on Chapman (1992).

^f PAH compounds were not analyzed in sediment samples collected from sites 44 (Hog Island Inlet) and 102 (USS Superfund site). This represents a data gap in the determination of mean PEC-Qs for these high impact training sites.

^a EC50 as percent dry sediment; toxic response (shown in bold) defined as EC50 < 0.5 (± 0.05)%.

^b Percent light reduction relative to control; toxic response (shown in bold) defined as > 20 (± 0.5)%.

^c Control failure (i.e., 78% survival); therefore, the toxicity test failed quality assurance requirements.

^d Mean survival significantly less than control survival at p = 0.05.