High spatial resolution sensor-based surface water quality along 540 kilometers of the Illinois Waterway, 2022 and 2023

In support of the U.S. Geological Survey (USGS)-Next Generation Water Observing System (NGWOS) program, water quality data were collected in 2022-2023 in the Illinois River Basin—the third USGS Integrated Water Science (IWS) basin. These data were collected to document spatial heterogeneity in water quality across seasons and hydrologic conditions and to improve predictions of carbon and nutrient dynamics in the Illinois Waterway. Surface water quality was measured using a boat-mounted, continuous sampling platform known as the Fast Limnological Automated Measurements (FLAMe; https://doi.org/10.1021/es504773x). Water was continually pumped onboard a moving boat to a series of water quality sensors configured to capture data every second. Measurements were georeferenced and spatially corrected using established routines and can be used to produce maps of water quality where the boat traveled. Overall, 807,876-point measurements were collected across the Illinois River Basin. Additionally, sensor-based measurements are associated with 175 discrete water samples analyzed for additional chemical and biological attributes (https://doi.org/10.5066/P13V2HX6, https://doi.org/10.5066/P13XBWO7).

Ten onboard multiparameter instruments recording data from one or more sensors were used to collect up to 95 variables over the course of five sampling campaigns between May 2022 and July 2023. Onboard water quality sensors included a YSI EXO2 (temperature, specific conductivity, turbidity, pH, dissolved oxygen, fluorescent dissolved organic matter fluorescence, and total algal fluorescence), a Seabird SUNA V2 optical nitrate sensor (nitrate, absorbance), Turner C6P multi-fluorometer (turbidity, chromophoric dissolved organic matter, chlorophyll, optical brighteners, fluorescein, and refined fuels), a bbe fluoroprobe (green algae, blue green algae, diatoms, and cryptophytes), and a Los Gatos Research Ultraportable Greenhouse Gas Analyzer (dissolved carbon dioxide and methane). Additional instruments included two Garmin Global Poisitioning System (GPS) receivers (latitude, longitude, time), a Garmin depth sounder (water temperature and depth), and a Vaisala CS106 barometer (barometric pressure). All data were recorded continuously on a Campbell Scientific CR6 datalogger. System attributes (e.g., internal temperature, boat speed, wiper position, battery voltage) were also recorded to aid in data quality control.

Each 6- to 10-day campaign (May 2022, Aug 2022, Nov 2022, Mar/Apr 2023, and Jul 2023) started in Chicago, IL, including sampling of Lake Michigan, and progressed down the Illinois Waterway, ultimately reaching the Mississippi River near Alton, IL. During each campaign, the boat primarily traveled downriver through the main navigation channel. The boat also traveled laterally into the mouths of several major tributaries and into select backwater areas. On the final two campaigns in 2023, we expanded the transect to include the North Branch Chicago River, the Calumet-Saganashkee Channel, and the confluence with the Missouri River. The crew attempted to sample the same features on each campaign; however, the exact sample path varied based on weather and hydrologic conditions. Some tributaries and off-channel areas were unnavigable during low water, and thus were not sampled. Actual sampling locations loosely followed pre-determined routes, but they were adjusted based on weather, field observations, and communication with local guides.