This data release supports "Diverging trends in nitrate and phosphorus loads and yields across Illinois watersheds, 1997–2022" (Kamrath and others, 2024) and the State of Illinois's Nutrient Loss Reduction Strategy (NLRS; IEPA and others, 2015). This data release contains estimates of incremental nitrate (NO3) and total phosphorus (TP) loads and yields for 49 watersheds in Illinois, defined using 8-digit hydrologic unit codes (HUC8; Jones and others, 2022). An "incremental" load or yield represents the load or yield attributable to each HUC8 watershed area determined by removing nested upstream drainage areas where present. For each HUC8 this data release also includes the proportion of the incremental load attributable to point and nonpoint sources, the proportion of the total phosphorus load attributable to dissolved and particulate phosphorus, and water yields. Data are provided as average annual values for three periods between 1997 and 2022: water years 1997–2011 (the baseline period used in the initial NLRS; IEPA and others, 2015), 2012–2017 (the period of previous update reported in the NLRS 2019 biennial report; IEPA and others, 2019), and 2018–2022 (the recent update). Data in "avg_loads_yields.csv" contains average annual loads (million pounds per year) and yields (pounds per acre per year) for each nutrient of interest, HUC8, and period. Data in "avg_water_yield.csv" contains average annual water yields (inches per year) for each HUC8 and period. Data in "avg_Pspecies.csv" contains the percentage of the TP loads attributable to dissolved and particulate phosphorus for each HUC8 and period. Supporting datasets include "site_list.csv," which contains the descriptions of each Illinois HUC8 and "site_calc_m23.csv," which contains the associated USGS and IEPA water quality sites used for HUC8-based computations IEPA, IDOA, and University of Illinois Extension, 2015, Illinois Nutrient Loss Reduction Strategy. Illinois Environmental Protection Agency and Illinois Department of Agriculture; Springfield, Illinois. University of Illinois Extension; Urbana, Illinois. IEPA, IDOA, and University of Illinois Extension, 2019, Illinois Nutrient Loss Reduction Strategy Biennial Report 2019: IISG19-RCE-RLA-071, accessed at https://epa.illinois.gov/content/dam/soi/en/web/epa/topics/water-quality/watershed-management/excess-nutrients/documents/nlrs-biennial-report-2019-final.pdf. Jones, K.A., Niknami, L.S., Buto, S.G., and Decker, D., 2022, Federal standards and procedures for the national Watershed Boundary Dataset (WBD) (5 ed.): U.S. Geological Survey Techniques and Methods 11-A3, 54 p., https://pubs.usgs.gov/tm/11/a3/. Kamarath and others, 2024 placeholder

This data release contains data in support of "Diverging trends in Nitrate and Phosphorus Loads and Yields Across Illinois Watersheds, 1997–2022" (Kamrath and others, 2025). It contains input and output data used to estimate total nitrate + nitrite, dissolved phosphorous and total phosphorous loads for sites in Illinois from water years 1974 to 2022. The input data includes "input-data_WQ.csv," which contains water quality data for nitrate + nitrite, dissolved phosphorous and total phosphorous. The water quality data comes from (1) the Water Quality Portal (WQP), (2) the Illinois Environmental Protection Agency (IEPA), and (3) the Environmental Protection Agency (EPA) STORET warehouse. The WQP includes the most complete record of U.S. Geological Survey and IEPA water quality samples. The most recent IEPA water quality samples, which are not yet in the WQP, were provided directly from IEPA. Legacy IEPA data that is housed via the EPA STORET warehouse was used to fill in any gaps in the data record. See the Entity and Attribute section of the metadata for details. The output data provides results calculated using the water-quality method Weighted Regressions on Time, Discharge, and Season (WRTDS) from the R package 'EGRET' (Exploration and Graphics for RivEr Trends, available from https://doi-usgs.github.io/EGRET/). The file "model-runs.csv" includes a list of all the models run using WRTDS with additional information for each run; for each run, WRTDS stationary and generalized flow normalization (SFN and GFN, respectively) were used along with the WRTDS Kalman (WRTDS-K) post processing. The results of each WRTDS run are saved in 'eList,' the native output format from 'EGRET,' in "eLists.zip." There are two eLists per run, one with SFN results and the other with GFN and WRTDS-K results. For more information on 'EGRET' and the WRTDS method see https://doi-usgs.github.io/EGRET/index.html. Additional output data includes estimated annual and monthly loads and concentrations of nitrate + nitrite, dissolved phosphorous and total phosphorous for all sites. The files are broken up by constituent, nitrate + nitrite (N) or phosphorous (P), and time frame, annual or monthly.

This data release contains data in support of "Diverging trends in Nitrate and Phosphorus Loads and Yields Across Illinois Watersheds, 1997–2022" (Kamrath and others, 2025). It contains input and output data used to estimate total nitrate + nitrite, dissolved phosphorous and total phosphorous loads for sites in Illinois from water years 1974 to 2022. The input data includes "input-data_WQ.csv," which contains water quality data for nitrate + nitrite, dissolved phosphorous and total phosphorous. The water quality data comes from (1) the Water Quality Portal (WQP), (2) the Illinois Environmental Protection Agency (IEPA), and (3) the Environmental Protection Agency (EPA) STORET warehouse. The WQP includes the most complete record of U.S. Geological Survey and IEPA water quality samples. The most recent IEPA water quality samples, which are not yet in the WQP, were provided directly from IEPA. Legacy IEPA data that is housed via the EPA STORET warehouse was used to fill in any gaps in the data record. See the Entity and Attribute section of the metadata for details. The output data provides results calculated using the water-quality method Weighted Regressions on Time, Discharge, and Season (WRTDS) from the R package 'EGRET' (Exploration and Graphics for RivEr Trends, available from https://doi-usgs.github.io/EGRET/). The file "model-runs.csv" includes a list of all the models run using WRTDS with additional information for each run; for each run, WRTDS stationary and generalized flow normalization (SFN and GFN, respectively) were used along with the WRTDS Kalman (WRTDS-K) post processing. The results of each WRTDS run are saved in 'eList,' the native output format from 'EGRET,' in "eLists.zip." There are two eLists per run, one with SFN results and the other with GFN and WRTDS-K results. For more information on 'EGRET' and the WRTDS method see https://doi-usgs.github.io/EGRET/index.html. Additional output data includes estimated annual and monthly loads and concentrations of nitrate + nitrite, dissolved phosphorous and total phosphorous for all sites. The files are broken up by constituent, nitrate + nitrite (N) or phosphorous (P), and time frame, annual or monthly.

The Illinois River receives nutrients from point and non-point runoff from upstream urban and agricultural areas. These excess nutrients could be contributing to harmful algal blooms in the Illinois River and its tributaries. Successfully mitigating the blooms requires an understanding of the underlying nutrient processes occurring in the river. Phosphorus is often the nutrient that limits phytoplankton growth and is a substantial concern in aquatic ecosystems because it can be stored long-term in the streambed sediment. Streambed sediment can act as a source or sink for phosphorus, and this dynamic is influenced by site conditions, including historic phosphorus loading and current stream water phosphorus concentrations. This study quantified streambed sediment phosphorus dynamics at 10 stream sites in the Illinois River Basin during the summer and fall of 2024.

This data release contains seasonal source-specific estimates of total nitrogen (TN) and total phosphorus (TP) loading to streams across the Illinois River basin (25,620 reaches) for 21 years from 2000 through 2020 using a dynamic SPARROW (Spatially Referenced Regressions on Watershed attributes) model. Input data including calibration loads, output predictions, model control files, and model source code are provided to fully reproduce results. The modeled period was from December 1999 through November 2020 in seasonal timesteps, or 84 periods, and the following seasonal definitions were applied: winter includes December, January, and February; spring includes March, April, and May; summer includes June, July, and August; and fall includes September, October, and November. See Schmadel and others (2024) for further details.

This data release contains seasonal source-specific estimates of total nitrogen (TN) and total phosphorus (TP) loading to streams across the Illinois River basin (25,620 reaches) for 21 years from 2000 through 2020 using a dynamic SPARROW (Spatially Referenced Regressions on Watershed attributes) model. Input data including calibration loads, output predictions, model control files, and model source code are provided to fully reproduce results. The modeled period was from December 1999 through November 2020 in seasonal timesteps, or 84 periods, and the following seasonal definitions were applied: winter includes December, January, and February; spring includes March, April, and May; summer includes June, July, and August; and fall includes September, October, and November. See Schmadel and others (2024) for further details.

Data on carbon and nutrient processing in key locations and over seasonal time scales can provide critical information about the concentrations and potential utilization rates of bioavailable constituents that are known to have a role in cyanobacteria harmful algal blooms (cyanoHABs). Laboratory experiments were performed to measure seasonal nutrient processing rates of carbon, nitrogen and phosphorus in river water and bottom sediments collected just upstream of the Next Generation Water Observing System (NGWOS) location at Starved Rock Lock and Dam USGS gaging station number 05553700 on the Illinois River. This site was chosen based on previous development of cyanoHABs. Sediments and unfiltered river water were collected during the spring (April), summer (August), and fall (November) of 2022 then shipped to Boulder, CO for laboratory experiments. River water alone and river water combined with < 2-millimeter sieved sediments were assessed under ambient nutrient conditions and nitrogen amended conditions to determine rates of production or consumption for the following processes: 1) aerobic carbon dioxide production, oxygen consumption, and aqueous nutrient transformations, and 2) anaerobic denitrification, carbon dioxide production, methanogenesis, and aqueous nutrient transformations. Modifications to certain experiments were made in November 2022 based on results from the April and August 2022 experiments and are noted in the metadata steps. Background sediment total carbon and nitrogen content, deionized water and potassium chloride extractable sediment nutrient concentrations, and river water nutrient concentrations were measured during each collection. Sequential extractions of the sieved sediment were performed using deionized water, sodium bicarbonate, sodium hydroxide, and hydrochloric acid to measure phosphorus content of the sediment during the various steps.

During water years 2016–2020, the U.S. Geological Survey, in cooperation with the Illinois Environmental Protection Agency, operated continuous monitoring stations on eight of the major rivers in Illinois to better quantify nutrient and sediment loadings from the State of Illinois to the Mississippi River. This data release presents estimates of daily nitrate, suspended sediment, and phosphorus concentrations and uncertainty over that period. The concentration estimates are based on a combination of discrete sampling data and surrogate regression (imputation). The data release comprises a single csv file containing daily timeseries of conentration and uncertainty for each monitoring station.

During water years 2016–2020, the U.S. Geological Survey, in cooperation with the Illinois Environmental Protection Agency, operated continuous monitoring stations on eight of the major rivers in Illinois to better quantify nutrient and sediment loadings from the State of Illinois to the Mississippi River. This data release presents estimates of daily nitrate, suspended sediment, and phosphorus concentrations and uncertainty over that period. The concentration estimates are based on a combination of discrete sampling data and surrogate regression (imputation). The data release comprises a single csv file containing daily timeseries of conentration and uncertainty for each monitoring station.

During water years 2016–2021 (a water year begins on October 1 and ends on September 30 and is designated by the year in which it ends), the U.S. Geological Survey (USGS), in cooperation with the Illinois Environmental Protection Agency (Illinois EPA), operated continuous monitoring stations on eight of the major rivers in Illinois to better quantify nutrient and sediment loadings from the State of Illinois to the Mississippi River. These eight rivers are the Illinois River, Rock River, Little Wabash River, Kaskaskia River, Vermilion River, Embarras River, Big Muddy River, and Green River. This data release presents estimates of daily nitrate, phosphorus, and suspended sediment concentrations and uncertainty over that period. The concentration estimates are based on a combination of discrete sampling and surrogate regression (imputation); see Hodson and others (2021) for details on the imputation model. The data release comprises a single comma-separated values (csv) file containing daily timeseries of concentration and uncertainty for each monitoring station. These data supersede Hodson and others (2021b), which was based on data through water year 2020. Reference cited: Hodson, T.O., Terrio, P.J., Peake, C.S., and Fazio, D.J., 2021a, Continuous Monitoring and Bayesian Estimation of Nutrient and Sediment Loads from Illinois Watersheds, for water years 2016–2020: U.S. Geological Survey Scientific Investigations Report 2021-5092, https://doi.org/3133/sir20215092. Hodson, T.O., Terrio, P.J., Peake, C.S., and Fazio, D.J., 2021b, Modeled nutrient and sediment concentrations from major rivers in Illinois based on continuous monitoring from October 1, 2015, through September 30, 2020: U.S. Geological Survey data release, https://doi.org/10.5066/P9MS8OIH.