Physical and chemical stressors on algal, invertebrate, and fish communities in 14 Milwaukee area streams, 2004–2013

Abstract

In 2004, the U.S. Geological Survey (USGS) began sampling 14 wadable streams in urban or urbanizing watersheds near Milwaukee, Wisconsin (fig. 1). The overall goal of the study is to assess the health of the aquatic communities in the Milwaukee Metropolitan Sewerage District planning area to inform current and future watershed management. In addition to collection of biological data on aquatic communities, physical and chemical data were also collected to evaluate effects of potential environmental stressors on the aquatic communities. This fact sheet summarizes the primary results of the study from 2004 to 2013. Detailed information is described in Scudder Eikenberry and others (2020a), and all data are available in Scudder Eikenberry and others (2020b; https://doi.org/ 10.5066/ P9FWMODL). Evaluations of aquatic communities using multiple groups of organisms—algal, invertebrate, and fish assemblages—and multiple measures or “metrics” of the groups are needed to fully understand environmental tolerances of the communities to chemical and physical stressors related to urban development (Coles and others, 2012). Each assemblage and each species have different tolerances to environmental stressors, different ranges of mobility, and different life spans. Algae reproduce quickly, living from days to weeks, and can indicate short-term changes in their environment. Algae form the base of the food web in streams and contribute to the processing of nutrients such as nitrogen and phosphorus, with excess nutrients often reflected by high algal biovolumes. Invertebrates are good indicators of water quality because of their relatively longer lifespans of months to years in comparison to algae, and their mostly stationary nature when compared to predators like fish make them indicative of sitespecific conditions. Fish generally live longer than other aquatic organisms, so fish assemblages integrate longer time periods of exposure to pollutants and other stressors. Fish are more mobile than invertebrates, so fish may better reflect conditions within a larger area, such as a watershed. Use of all three assemblages helps provide a complete picture of the health of the aquatic community and the overall stream condition. Urban development can degrade streams physically and chemically through changes in characteristics such as streamflow, water quality, and habitat, which can in turn act as stressors on aquatic communities and adversely affect the overall ecological health of streams. Examples of stressors that can alter urban streams and aquatic communities in urban streams are increased runoff from impervious surfaces; straightening and armoring of natural streams; removal of trees and other vegetation along streams; and chemical inputs from sewage, road salt, and pesticides. Multiple lines of evidence, integrating key stressors and responses to them, are critical for understanding how different stressors adversely affect aquatic communities, which stressors are most important, and how the effects of those stressors may be lessened through watershed management actions. Long-term (10 years or more) monitoring of biological, physical, and chemical characteristics of streams provides a way to evaluate the effects of different stressors on aquatic communities.