ABSTRACT

Changes in the water quality of stream ecosystems in an urban area may manifest in conspicuous ways, such as in murky or smelly streamwater, or in less conspicuous ways, such as fewer native or pollution-sensitive organisms. In 2004, and again in 2007, the U.S. Geological Survey sampled stream organisms—algae, invertebrates, and fish—in 14 Milwaukee area streams to assess water quality as part of the ongoing Milwaukee Metropolitan Sewerage District (MMSD) Corridor Study. In addition, passive-sampling devices (SPMDs, “semipermeable membrane devices”) were deployed at a subset of sites in order to evaluate the potential exposure of stream organisms to certain toxic chemicals. Results of the 2007 sampling effort are the focus of this report. Results of sampling from 2007 are compared with results from 2004.

The water quality of sampled streams was assessed by evaluating biological-assemblage data, metrics computed from assemblage data, and an aggregate bioassessment ranking method that combined data for algae, invertebrates, and fish. These data contain information about the abundance (number) of different species in each group of stream organisms and the balance between species that can or cannot tolerate polluted or disturbed conditions. In 2007, the highest numbers of algal, invertebrate, and fish species were found at the Milwaukee River at Milwaukee, the largest sampled site. Algal results indicated water quality concerns at 10 of the 14 sampled sites due to the occurrence of nuisance algae or low percentages of pollution-sensitive algae. When compared to 2004, total algal biovolume was higher in 2007 at 12 of 14 sites, due mostly to more nuisance green algae from unknown causes. Results of several metrics, including the Hilsenhoff Biotic Index (HBI-10), suggest that invertebrate assemblages in the Little Menomonee River, Underwood Creek, and Honey Creek were poorer quality in 2007 compared to 2004. Six sites received “very poor” quality ratings for fish in 2007, mostly because inadequate numbers of fish were collected at five sites to allow computation of an Index of Biotic Integrity (IBI); this resulted in three additional sites receiving “very poor” ratings compared to 2004. Some signs of potential improvement in the fish assemblage were evident at Lincoln Creek, possibly reflecting delayed effects of the restoration of stream habitat, completed in 2002; however, algae and invertebrates did not show signs of improvement.

Aggregate bioassessment rankings across all groups of organisms for 2004 and 2007 indicated that water quality at the two Milwaukee River main stem sites (at Milwaukee and near Cedarburg), Jewel Creek, and the Menomonee River at Menomonee Falls was the least-degraded among all sampled sites. Rankings for Oak Creek and Little Menomonee suggested water quality was worse in 2007 compared to 2004 and placed these two sites together with Kinnickinnic River and Underwood Creek, two concrete-line sites, indicating the most-degraded water quality among all sampled sites. The aggregate ranking for Lincoln Creek in 2007 would have placed it in the most-degraded category but for the positive influence of the fish ranking when compared to poor algal and invertebrate rankings. Potential toxicity due to certain manmade chemicals, such as polycyclic aromatic hydrocarbons (PAHs), was found at all six sites where SPMDs were deployed. As was found in 2004, the highest potential toxicity in 2007 was observed at Lincoln Creek where chemical screening in 2007 also showed the highest total PAHs of all six sites; however, potential toxicity at Little Menomonee River, Honey Creek, and Kinnickinnic River was relatively high compared to Milwaukee River near Cedarburg. Although toxicity and chemical results in 2007 did not agree with aggregate rankings for Lincoln Creek because of fish, nor for Honey Creek, the results did agree with aggregate rankings at four of the six sites. In addition to toxicological and chemical influences, the more urbanized sites have high percentages of impervious surface area, resulting in frequent high stream flows that can adversely affect algal, invertebrate, and fish assemblages. Assessments of the ecological status of different groups of organisms and of potential chemical and physical stressors to organisms are important tools in evaluating streamwater quality.

First posted October 28, 2010

Revised February 4, 2014