Trends Analysis for Selected Water Quality Constituents in the Illinois Coastal Management Zone

Getahun, Elias; Zavelle, Atticus

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https://hdl.handle.net/2142/128753 Copy

Description

Title

Trends Analysis for Selected Water Quality Constituents in the Illinois Coastal Management Zone

Author(s)

• Getahun, Elias
• Zavelle, Atticus

Issue Date

2025-03-31

Keyword(s)

• Water Quality Trends
• ICoastalDB
• Illinois Coastal Management Zone

Date of Ingest

2025-06-11T14:18:57-05:00

Abstract

The Illinois Coastal Management Zone (ICMZ), managed by the Illinois Department of Natural Resources (IDNR), encompasses Lake Michigan’s shoreline, harbors, open waters, and adjacent landward areas within the Lake Michigan watershed. Covering approximately 1,500 square miles of lakeward territory and 110 square miles of landward zones, the ICMZ faces challenges from urban development, engineered drainage systems, and invasive species. The Illinois Coastal Management Program (ICMP) prioritizes restoring aquatic habitats, improving stormwater management, and reducing pollution to meet Clean Water Act (CWA) objectives. This report updates the Illinois Coastal Zone Water Quality Database (ICoastalDB), a centralized repository of water quality data, and analyzes trends for 14 constituents critical to assessing water quality status and the efficacy of management strategies. An extensive exploratory data analysis (EDA) of water quality data from 314 monitoring sites (84 inland and 230 Lake Michigan assessment units) over a 25-year period (1998–2022) revealed significant variability in data availability and trends. Water quality parameters selected by the project advisory group—total phosphorus, chloride, fecal coliforms, dissolved oxygen, and nitrogen species—mostly aligned with those parameters in Illinois’ 303(d) List of impaired waters in the ICMZ. Derived parameters, such as total nitrogen and organic/inorganic nitrogen, provided additional insights into nutrient dynamics. Key sites with robust data suitability for trend analysis included grab sample locations like North Shore Channel at Touhy Ave (NS9) and Little Calumet River at Indiana Ave (LC4), as well as automatic sampling sites such as North Shore Channel at Church St (NS4) and South Fork South Branch Chicago River at 36th St (BC1). These sites consistently provide reliable data across multiple timeframes, enabling comprehensive trend assessments. Based on data suitability analyses, 1,532 annual and seasonal trend evaluations were completed across three periods (5-, 10-, and 25-year) for selected water quality constituents. Total phosphorus trends showed stability in recent 5-year periods, while mixed decreases and increases were observed over 10- and 25-year spans. Seasonal analyses indicated winter declines but variability in spring, summer, and fall, suggesting seasonal factors like runoff and temperature may have influenced phosphorus loading. Long-term improvements in phosphorus levels appear to be plateauing, highlighting the need for targeted interventions. Recent (5-year) chloride trends in the ICMZ show localized increases, notably at Grand Calumet River (GC1). Long-term (25-year) trends generally indicate rising chloride levels, though some sites, like GC1, exhibited decreases in certain seasons. Seasonal analyses revealed varied trends: winter and spring were mostly stable with isolated increases, while summer showed both significant recent increases and long-term decreases. Overall, chloride levels demonstrated complex, site-specific changes over time, highlighting the need for targeted management strategies. Long-term rising trends could be attributed to the growing impact of road salt application for de-icing. The different forms of nitrogen constituents displayed complex dynamics. Nitrate plus nitrite (NNN) trends were highly variable annually and seasonally, with no consistent improvement. Total Ammonia Nitrogen (TAN) stabilized or declined at most sites but increased at Grand Calumet River at Burnham Ave (GC1), signaling localized pollution. Total Kjeldahl Nitrogen (TKN) generally declined over longer periods but saw recent upticks at GC1. Inorganic (TIN) and Total Nitrogen (TN) trends diverged, with increases at Little Calumet River at Halsted St (LC6) and GC1 contrasting with declines at South Fork South Branch Chicago River at Archer Ave (BC2). Analysis of fecal coliform levels revealed complex trends, with long-term data generally indicating decreases, while shorter-term (5- and 10-year) trends showed more variability. The Chicago River Main Stem at Wells Street (CR8) consistently exhibited an increasing trend across multiple timeframes and seasons, suggesting a persistent contamination source, while the Little Calumet River at Halsted Street (LC6) also demonstrated recent increases. Seasonal variations showed minimal winter trends, with spring, summer, and fall generally exhibiting decreasing levels, but CR8 remained an exception. Dissolved oxygen (DO) data revealed a positive trend, with both annual and seasonal analyses indicating increases, particularly over longer timeframes. While some sites exhibited stable levels, most showed significant improvements. However, the Chicago River at Michigan Ave. (CR4) demonstrated a concerning decrease in minimum DO over the recent 5 years. The overall positive trend towards higher DO signifies enhanced water quality, crucial for supporting aquatic life, although localized variations and specific problem areas like CR4 necessitate continued monitoring and targeted interventions. Specific conductance trends presented a mixed picture, with short-term increases, such as at Little Calumet River at Halsted St. (LC5), and decreases, such as at Little Calumet River at C&W Indiana Harbor Belt RR (LC2). However, longer-term trends generally indicated stability, with some sites, like North Branch Chicago River at Division St. (NB11), showing a shift from increasing to decreasing conductance. Over the 25-year period, North Branch Chicago River at Addison St. (NB6) displayed increasing seasonal trends except in winter. The overall trend suggests localized variations in salinity and dissolved ion concentrations, requiring site-specific monitoring to understand the underlying causes. The ICMZ’s water quality trends reflect complex interactions between natural processes and anthropogenic impacts. Total phosphorus and chloride remain critical concerns, with seasonal and long-term trends underscoring the need for adaptive management strategies. Nitrogen dynamics vary widely, with sites like GC1 and LC6 signaling localized pollution hotspots requiring targeted nutrient management. Fecal coliform variability highlights seasonal influences, while dissolved oxygen improvements validate ongoing restoration efforts but necessitate sustained monitoring. The specific conductance trends may indicate the need to address road salt use and urban runoff. These findings collectively stress the importance of integrating data-driven insights into policy and management to address persistent impairments. To enhance water quality monitoring and management in the ICMZ, sustained monitoring at key sites—such as NB6, BC1, and LC5—is critical. Expanding automatic monitoring networks will provide real-time data for parameters like dissolved oxygen and specific conductance. Targeted strategies should prioritize reducing road salt applications, implementing nutrient management plans at nitrogen hotspots, and strengthening stormwater controls to mitigate fecal coliform and phosphorus loads. Data integration efforts, including regular updates to the ICoastalDB and the use of machine learning models, will improve trend predictions and allow identification of pollution sources. Finally, leveraging these findings to refine the 303(d) List and Total Maximum Daily Loads (TMDLs) will ensure compliance with CWA goals and enhance the ecological resilience of the ICMZ. This report provides exploratory data analysis and trend evaluations for selected water quality constituents, informing decision-making towards better management of aquatic ecosystems in the ICMZ. By addressing persistent impairments through targeted interventions and adaptive management, stakeholders can enhance the resilience of coastal waters, ensuring their ecological and recreational value. Sustained collaboration across agencies, coupled with strategic investments in monitoring and technology, will be essential to achieving long-term water quality goals and preserving the health of waterbodies in the ICMZ.

Publisher

Illinois State Water Survey

Series/Report Name or Number

ISWS Contract Report 2025-01

Type of Resource

text

Genre of Resource

report

Language

eng

DOI

https://doi.org/10.13012/B2IDB-7799136_V2

Sponsor(s)/Grant Number(s)

llinois Department of Natural Resources - Grant Code D5013

Copyright and License Information

© 2025 University of Illinois Board of Trustees. All rights reserved. For permissions information, contact the Illinois State Water Survey.

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