Spatially consistent but temporally divergent changes in nitrate and phosphorus loads and yields in Illinois watersheds, 1997–2022
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Abstract
Illinois contributes substantial nutrient loads to the Gulf of America, warranting watershed-scale assessment. This study estimated nitrate-nitrogen (nitrate-N) and total phosphorus (TP) loads and yields for 49 Illinois 8-digit hydrologic unit code (HUC8) watersheds draining to the Mississippi River Basin from 1997–2022, comparing recent (2018–2022) to baseline (1997–2011) conditions. Estimates included point and nonpoint source contributions, dissolved phosphorus, and water yields. During the recent period, nonpoint sources dominated nutrient export (82% nitrate-N, 78% TP), though point sources drove high yields in the Chicago area. Spatially, nonpoint source nutrient hotspots persisted with nitrate-N yields highest in east-central and northern Illinois and TP yields higher in southern and western Illinois. Temporally, statewide nitrate-N loads decreased 9%, while TP loads increased 27%. Nitrate-N yields increased in 22 HUC8s and decreased in 20, while TP yields increased in 32 HUC8s and decreased in 9. For both nutrients, baseline yields were negatively correlated with yield changes, indicating high-yielding watersheds tended toward larger decreases or smaller increases. Water yields increased 19% on average but were weakly correlated with nutrient yield changes (r = 0.23 and 0.20 for nitrate-N and TP). These results reveal spatially persistent yet temporally divergent nutrient export across Illinois, with contrasting nitrate-N and TP trajectories for nonpoint sources.
Suggested Citation
Kamrath, B.J., Murphy, J.C., Schafer, L.A., Podzorski, H.L., and McIsaac, G.F., 2026, Spatially consistent but temporally divergent changes in nitrate and phosphorus loads and yields in Illinois watersheds, 1997–2022: Journal of American Water Resources Association, v. 62, no. 2, e70114, 18 p., https://doi.org/10.1111/1752-1688.70114.
Study Area
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Spatially consistent but temporally divergent changes in nitrate and phosphorus loads and yields in Illinois watersheds, 1997–2022 |
| Series title | Journal of American Water Resources Association |
| DOI | 10.1111/1752-1688.70114 |
| Volume | 62 |
| Issue | 2 |
| Publication Date | April 22, 2026 |
| Year Published | 2026 |
| Language | English |
| Publisher | Journal of American Water Resources Association |
| Contributing office(s) | Central Midwest Water Science Center |
| Description | e70114, 18 p. |
| Country | United States |
| State | Illinois |