High spatial resolution water quality data using the Fast Limnological Automated Measurements sensor platform in the Upper Mississippi River Basin pools 10-24 in 2024-2025

In support of the U.S. Army Corps of Engineers Long Term Resource Monitoring Mississippi River program, water quality data were collected in 2024 and 2025 in the Upper Mississippi River Basin. Data were collected in 2024 to document spatial heterogeneity in water quality across seasons and hydrologic conditions with a focus on understanding patterns in chlorophyll. Additional data were collected in 2025 as part of a project to document spatial patterns in turbidity in lower pool 13 prior to implementation of a Habitat Rehabilitation and Enhancement Project (HREP). 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, 582,368-point measurements were collected across the Upper Mississippi River Basin in pools 10-24 (available in file: FLAMe_data.csv). Additionally, sensor-based measurements are associated with 196 discrete water samples collected in 2024 (available in file: FLAMe_samples.csv) and analyzed for additional chemical and biological attributes (https://doi.org/10.5066/P13YXDFR).

Ten onboard multiparameter instruments recording data from one or more sensors were used to collect up to 95 variables over the course of four sampling campaigns between May-September 2024 in pools 10-24 and two sampling campaigns in April and July 2025 in pool 13. 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), 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 Positioning 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. Details on data attributes including descriptions, units, and sources are included in the file: FLAMe_data_dictionary.csv.

Each 5-day campaign in 2024 (May, June, and August) started in pool 19, followed by pools 20-21, 18, 13, and 10. During each campaign, the boat primarily traveled downriver through the main navigation channel in pools 19-21 and upriver in pools 18, 13, and 10. The boat also traveled laterally into the mouths of several major tributaries and into approximately six backwater transects per pool. In September 2024, a 13-day campaign started in pool 10 and traveled consecutive pools downriver to pool 24. The boat and crew sampled the same backwater transects in pools 10, 13, and 18-21. In pools 11-12, 14-17, and 22-24, approximately 2-3 backwater transects were sampled. Some tributaries and off-channel areas were unnavigable during low water and thus were not sampled in all trips. Additionally, motor issues prevented sampling of half of pool 13 and most of pool 10 during the May campaign. In 2025, just lower pool 13 was sampled once in April and once in July. The area surveyed in 2025 was similar to transects surveyed during all campaigns in 2024, providing six timepoints for the area proposed for HREP implementation and an adjacent “reference” area that is similar geomorphologically but will not have an HREP constructed. See file: FLAMe_map.png for transect paths organized by campaign.