MMSD Watercourse Corridor Study: Ecological Assessments and Trends

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Changes in streams that result from urban development such as loss of stream habitat, inadequate or flashy streamflow, and degraded water quality can adversely affect communities of aquatic organisms. MMSD Watercourse Corridor Study ecological assessments evaluate water quality over time by pairing community assessments of aquatic organisms with chemical assessments using passive samplers.

During the current 5-year study period for Phase V (2016-2020) of the Milwaukee Metropolitan Sewerage District (MMSD) Watercourse Corridor Study, the following four topics are being addressed by one or more USGS subprojects:

1.    Ecological Assessments and Trends
       a.    Ecological Assessments and Trends at 15 Core Stream Sites
       b.    Bioavailable PCBs and PAHs at 15 Core Stream Sites
2.    Geomorphology and Sediment Studies Related to Stream and Estuary Rehabilitation
3.    Contaminants in Water and Sediment
4.    Continuous Real-Time Streamflow

This webpage focuses on topic 1. Ecological Assessments and Trends.


Ecological data, together with physical and chemical data, are complementary means of assessing water quality. Changes in streams that result from urban development such as loss of stream habitat, inadequate or flashy streamflow, and degraded water quality can adversely affect communities of aquatic organisms. Ecological assessments of these communities can provide a view of water quality that is integrated across physical and chemical characteristics and through time. For additional assessment of the effects of contaminants on organisms, biological tissues are sometimes analyzed; however, the constraints of finding sufficient numbers of the same species and size/age of organisms across multiple sites often preclude use of this technique. Instead, passive chemical samplers can be deployed in a stream for about a month. These samplers are used to estimate concentrations of biologically available contaminants (polychlorinated biphenyls [PCBs], polycyclic aromatic hydrocarbons [PAHs], organochlorine pesticides, and other anthropogenic chemicals) in the water that can passively enter tissues of aquatic organisms. USGS ecological assessments that are part of the Watercourse Corridor Study evaluate water quality by pairing community assessments of aquatic organisms with chemical assessments using passive samplers.


1a. Ecological Assessments and Trends at 15 Core Stream Sites

Ecological assessments most often include community assessments, evaluations of the type and number of organisms (e.g., algae, invertebrates, and fish) present, and their physical and chemical preferences or tolerances.  Different groups of aquatic organisms respond to changes in water quality in different ways and over different lengths of time, emphasizing the need for assessments that include more than one group of organisms. Direct cause and effect relationships between environmental stressors and aquatic community changes are seldom possible in non-laboratory settings. However, studies that use multiple lines of evidence, including adequate characterization of a wide variety of possible stressors and detailed (species level) community data over multiple dates and locations, can succeed in characterization of the primary stressors mostly likely affecting aquatic communities. Such assessments at long term monitoring sites provide the strongest evidence of stressor effects and trends (the direction of change: positive or negative).


The USGS is providing ecological assessments of the integrity of aquatic communities at 15 core stream sites, noting any changes since prior phases of work, and evaluating possible environmental stressors on the communities. 


Data collected as part of this subproject includes the distribution and abundance of aquatic organisms (algae, invertebrates, and fish) and data on stream habitat, streamflow, and selected water quality at 15 core stream sites. At each site, sampling is done along a stream reach, a set length of stream (for our ecological studies, a reach is about 150 to 300 meters in length, depending on the size of the stream).  In 2016, a new site was added to the 14 original core sites that USGS has monitored every three years since 2004. Sampling is done during the same period/season as in previous phases of work (late summer-early fall). At each sampled site, the species of organisms, their abundance and distribution, as well as pollution tolerances and other environmental preferences of the organisms will be used to compute metrics for assessment of water quality and aquatic communities. Biological methods are based on methods used by the USGS National Water-Quality Assessment (NAWQA) Program (Moulton and others, 2002; Scudder Eikenberry and others, 2010). Various aspects of stream habitatare measured based on NAWQA methods (Fitzpatrick and others, 1998). All but two sites have USGS gages that provide continuous measures of stream flow.  Water-quality measurements are made at the time of sampling for water temperature, pH, and conductance. In 2016, dissolved oxygen was monitored continuously from May through October with deployed probes at 15 core stream sites, including 10 sites that were not already monitored by MMSD. Available data for potential physical and chemical stressors are being examined in relation to aquatic communities at the sites, including additional water-quality data collected at regular intervals by MMSD monitoring studies. In addition to ecological sampling at all sites every three years, aquatic communities were sampled at a subset of three sites in 2017 and 2018 to provide information about annual differences in the communities. This effort will help define annual variability that is not being captured by the 3-year interval sampling, providing insight into the significance of long-term changes in aquatic communities at sites, and enable more complete assessments of the 15 core stream sites.

1b. Bioavailable PCBs and PAHs at 15 Core Stream Sites


In 2016, passive sampling devices (for example, Semipermeable Membrane Devices [SPMDs] and Polar Organic Chemical Integrative Samplers [POCIS]) were deployed at 15 core stream sites to estimate waterborne concentrations of biologically available synthetic organic contaminants that can passively enter tissues of aquatic organisms. Organic chemicals pass through the membranes of SPMDs and into the solution they contain, similar to how these chemicals would pass through the gills of a fish and accumulate in the fish’s fatty tissues. Results from SPMDs provide time-weighted average concentrations of hydrophobic synthetic organic compounds, such as PCBs, PAHs, and organochlorine pesticides. POCIS samplers provide data on many hydrophilic organic contaminants such as pesticides, endocrine disruptors, prescription and over-the-counter drugs, steroids, hormones, antibiotics, and personal care products. After a one month in-stream deployment, the solutions were extracted from passive samplers and were tested for toxicity and concentrations of selected chemicals.

Passive samplers can provide better estimates of these waterborne contaminants than simple water grab samples because chemicals accumulated in passive samplers are integrated over the 4-week deployment period. Concentrations of these chemicals in one-time grab samples of water can be below or near the lower limit of detection in laboratory analyses, even though they can accumulate to levels of concern in aquatic biota. Use and analyses of passive samplers are also cheaper than tissue analyses of fish in streams and alleviates difficulties with obtaining adequate tissues of a common fish species across all sites.


Passive sampler techniques using SPMD and POCIS passive samplers were used to yield time-integrated measures of a broad suite of potentially toxic chemicals to aquatic organisms at the 15 core stream sites. Data from analyses of passive sampler extracts post-deployment will be compared to aquatic community data at the sites as well as to appropriate chemical and physical data to gain insight regarding the nature and significance of these chemical stressors on the aquatic communities.


Passive sampling devices will be deployed at each of the 15 core stream sites for a period of about one month following USGS methods (Alvarez and others, 2008). Analyses of the extracts from SPMD samplers included screening tests for toxicity: Results from the cytochrome P450 test indicate the presence of chemicals such as dioxins, PCBs, and PAHs; Fluoroscan test indicates the presence of chemicals such as PAHs. Analyses of the extracts from POCIS samplers included the YES (Yeast Estrogen Screen) test for response to the presence of endocrine-disrupting chemicals, and chemical analyses of common pharmaceuticals and pesticides. Additional analysis of SPMD extracts for concentrations of selected organic chemicals provided a time-integrated concentration of the bioavailable fraction of these chemicals in the water column at sites. SPMDs were previously deployed at a subset of six stream sites during earlier phases of the Corridor Study, and comparisons will be made to these results, other chemical data, and aquatic community assessments at sites.