Satellite derived Chlorophyll-a of the Ohio and Illinois Rivers (CHOIR)

Chlorophyll-a is a vital water quality measurement used as a proxy for algal biomass in freshwater systems. However, limited field data in rivers, particularly within the Ohio River Basin located in the central United States, has impeded understanding of how river algae is changing over time and where it most impacts water quality. We built a 38-year (1984 – 2022) dataset of satellite derived chlorophyll-a that enables, for the first time, quantification of long-term trends and spatially explicit downstream patterns in chlorophyll-a in rivers. We trained and validated a machine learning model based on matchups between field observations and satellite overpasses that estimates chlorophyll-a across rivers and reservoirs in the Ohio and Illinois basins using Landsat 5-9. The Chlorophyll-a of the Ohio and Illinois Rivers database (CHOIR) includes observations over 6,116 river reaches linked to the National Hydrography Database(NHD) from 1984-2022 generating 3,211,825 observations to date. CHOIR has broad practical and research applications for algal monitoring and river ecology for purposes such as source water protection, assessment of past blooms, and provides a workflow that can be applied to other river basins.