AWRI Environmental Chemistry
Manistee Lake, MI
A preliminary investigation of the nature and extent of sediment contamination in Manistee Lake was performed. The investigation utilized the sediment quality triad approach with integrated assessments of chemistry, toxicity, and benthic macroinvertebrates. Diverse populations of benthic macroinvertebrates and limited evidence of anthropogenic chemical contamination were found in the control locations near the Manistee and Little Manistee Rivers (upper northeast and lower southeast sections of the lake). The remainder of Manistee Lake was characterized by depauperate benthic communities and sediments impacted by the influx of contaminated groundwater and the presence of oils and polycyclic aromatic hydrocarbons (PAH). The influx of contaminated groundwater and brines from surface discharge were evident by the presence of chemical stratification in the lower hypolimnion. A layer (approximately 5') of water with high specific conductance was present at the bottom of the lake in July 1998. High levels of chloride were also found in the sediments. Areas of intense brine intrusion were found one mile north of the Martin Marietta facility where abandon brine wells and transmission pipelines were located across the lake from Hardy Salt. The chloride levels in the remaining stations suggested a more diffuse venting of contaminated groundwater and the formation of a density gradient in the sediments. Chloride concentrations increased with sediment depth. Sediment oil contamination and the detection of elevated levels of PAH compounds indicated extensive hydrocarbon pollution was still present in Manistee Lake. The levels reported for oils were similar to the amounts found in 1975. Of the 12 sites investigated in areas of anthropogenic impact, 10 locations exceeded the Probable Effect Concentrations (PECs) for individual PAH compounds. The highest level of PAH compounds was near Morton Chemical (M-13: 29.4 mg/kg) and the highest level of oil was found near Manistee Drop Forge (M-6: 26,000 mg/kg). Elevated levels of metals were found at all stations however concentrations were below the PEC guidelines. Resin acids were found to be distributed throughout Manistee Lake. The highest levels were found in the 20''-40'' core section downstream from the old PCA outfall. The distribution of resin acids in the surficial sediments also supported the hypothesis of a diffuse venting of groundwater from the PCA site. Resin acids were not detected in the fish samples collected. The diffuse nature of the groundwater influx, the presence chemical stratification during the summer, and the high levels of oil contamination in the sediments create conditions that limit the exposure of fish populations to these chemicals.
Sediment toxicity to amphipods and midges was observed at M-6 and M-13. These stations had the highest levels of hydrocarbon oils and PAH compounds. Amphipod toxicity was measured at five additional sites, all containing levels of individual PAH compounds exceeding PEC concentrations. A variety of statistical techniques were employed to examine the difference between the control population and locations impacted by the PCA groundwater plume and the salt brine companies. The results showed a clear difference between diversity and trophic status with respect to the controls and the impacted sites. ANOVA results confirmed that the impacted populations were less diverse and dominated by pollution tolerant organisms. The ANOVA 2 results also suggested that the brine-impacted sites as a group, have benthic macroinvertebrate populations with a lower trophic status than benthos collected in the area influenced by the PCA/Martin Marietta groundwater plume.
Page last modified January 21, 2010