Areas of Concern: Benthos Toxicity at Wisconsin's AOCs

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USGS is assessing sediment toxicity at Wisconsin's Sheboygan River and Milwaukee Estuary areas of concern (AOCs) on Lake Michigan. The study will assess if sediment toxicity from polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), selected metals, ammonia, or low dissolved oxygen is present at either acutely toxic or chronically toxic concentrations. Sediment toxicity tests are being conducted with amphipods and midges. This study helps address concerns regarding sediment toxicity, and it will inform management decisions regarding the Beneficial Use Impairment (BUI) for Degraded Benthos, which must be removed prior to delisting the AOCs.

Sampling on river for benthos toxicity in the WI area of concern

Sampling on river for benthos toxicity in the WI area of concern

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All four of Wisconsin's Areas of Concern (AOCs) along Lake Michigan have the "Degradation of Benthos" Beneficial Use Impairment (BUI) designation, although little historical data is available to compare conditions at the time of listing to current conditions. This BUI is one of the most widespread BUIs in the United States, and benthic invertebrate (benthos) communities at some AOCs may never be brought back to a pre-disturbance state. The BUI is most often related to sediment contamination, but, water chemistry, substrate type, inadequate food supply, and river flows may also be important. Current data related to toxicity of the sediments at these four AOCs is not available and the USGS is uniquely poised to provide this data in a regional context and build upon benthos community studies that it has been doing in these sites. The need is presently greatest at two of these AOCs: Sheboygan River and Milwaukee Estuary.

The USGS collected sediment at two AOCs along the Lake Michigan shoreline (Sheboygan River and Milwaukee Estuary) and two less-degraded study areas (Manitowoc River and Root River) that are not AOCs and determined sediment toxicity and contaminant concentrations. Also, to help guide habitat restoration planning by the Wisconsin Department of Natural Resources (WDNR), USGS evaluated sediment at the Kewaunee River and at Oak Creek for the same toxicity and chemical tests. For each sediment sample concentrations of PCBs, PAHs, selected simultaneously-extracted metals, total metals, acid-volatile sulfide, organic carbon, and grain size were measured. Sediment toxicity was then determined by exposing amphipods and midges to the samples.

Midge toxicity showed low severity in both AOC and non-AOC samples, whereas amphipod toxicity was more severe. Amphipod survival and reproduction endpoints had strong associations with concentrations of total PAHs and simultaneously-extracted metals in sediments. Trends in sediment contaminants (organics, metals) corresponded to severity of amphipod toxicity. Biological metrics for benthos sampled in 2014 at a subset of sites correlated with metrics for toxicity and chemistry of sediment collected in 2016.

The Wisconsin Department of Natural Resources anticipates using results of this study as input to their BUI removal decisions for the Sheboygan River and for evaluating potential remediation activities at the other sampled locations.

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Wisconsin Department of Natural Resources