Stressors Analysis

Monitoring and analysis provides insight into the highest priority stressors affecting stream health in order to identify projects or initiatives with the greatest potential to attain stream use goals.    

Integrated Prioritization System (IPS) for Northeastern Illinois

The Northeastern Illinois Integrated Prioritization System (IPS) provides the framework within which high resolution monitoring data and assessment results are organized, analyzed, and merged to better support Clean Water Act (CWA)[1] management programs in meeting their goals and objectives and guiding a wide array of water quality related decision-making. It was developed to better inform the actions of watershed groups in Northeastern Illinois by identifying patterns and thresholds of stressors that affect aquatic life condition based on comprehensive analyses of a regional database comprised of high resolution biological, habitat, chemical/physical, and land use parameters and indicators.

The data was generated by the systematic watershed monitoring conducted by the DuPage River Salt Creek Workgroup (DRSCW) since 2006, the Lower DuPage River Watershed Coalition (LDRWC) since 2012, the Des Plaines River Watershed Workgroup (DRWW) since 2016, and the North Branch Chicago River Watershed Workgroup (NBWW) since 2018 that has been focused on determining the status of Illinois aquatic life designated uses and determining the causes (agents) and sources (origins) of impairments and threats. Suitable data from Illinois EPA and Illinois DNR was also used to supplement these more spatially intensive datasets. The limits of application include small headwater streams, wadeable streams, and small rivers up to 350 mi.2 in drainage area. The thresholds and analyses are not suitable for application outside of these stream and river sizes.

In 2010 the DRSCW engaged the Midwest Biodiversity Institute (MBI) to develop the IPS.  In 2019, the DRSCW and other watershed partners elected to update the IPS model.  The updated version drew on a larger regional dataset consisting of paired biological, chemical, and physical data.   It was used to derive tiered stressor thresholds for 87 stressors from a total dataset of 139 water column parameters, 144 sediment parameters, 16 habitat variables, and 39 land use variables each of which were paired with the biological data at the site level across a total of 640 sites in the NE Illinois IPS study area.

The updated version offers a number of improvements over the original:

  • Expansion from 120 to 640 sites including sites from the IEPAs basin monitoring program and from DRSCW reference sites (sites sampled outside the DRSCW area to supplement the data set).
  •  Better temporal depth of data at the original sites. The original was based on one assessment year’s data per site; the updated version had three.
  • The updated IPS covers a larger and more heterogeneous geographical area. The original suffered from being based only in the DRSCW watersheds which, due to their high level of physical and chemical modifications, support a truncated list of fish species and macroinvertebrate taxa.   The additional sites, especially the accumulation of data from reference sites and those supplied by IEPA, allowed a number of better performing sites to enter the database.  This in turn allowed the stressor response relationships to be more fully developed for good and excellent categories of aquatic communities.
  • The newer approach of first identifying stressor-sensitive species and taxa and then linking these species or taxa back to the Illinois General Aquatic Life Use benchmarks (for fish and macroinvertebrates) and five narrative classes of condition, provides a more sensitive method of deriving stressor benchmarks.
  • Statistical Tools and software applications have continued to improve since 2012 and with that the ability to manipulate large databases.

[1] Federal Water Pollution Control Act, Public Law 92-500 (33 U.S.C. 1251 et seq.) as amended via PL 107-303, Nov. 2002.

The full report of the updated 2023 analysis is linked below:

IPS 2010 Original Report

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The mission of the DRSCW is to bring together a diverse coalition of stakeholders to work together to preserve and enhance water quality and stream resource quality in the East Branch DuPage River, West Branch DuPage River, Salt Creek, and their tributaries.

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