Satellite‐Derived Chlorophyll‐a of the Ohio and Illinois Rivers (CHOIR)

Abstract

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 our understanding of how river algae change over time and where it most impacts water quality. We built a 38‐year (1984–2022) data set 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 tested 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 (CHOIR) database includes observations over 6,116 river reaches linked to the National Hydrography Database (NHD) from 1984 to 2022, generating 3,211,825 observations to date. CHOIR has broad practical and research applications for algal monitoring and river ecology, such as source water protection and the assessment of past blooms, and provides a workflow that can be applied to other river basins.