Judson Harvey Jay Choi Sarah M. Stackpoole Jennifer L. Graham Jennifer C. Murphy Noah M. Schmadel 2024 <div class="article-section__content en main"><p>Measurement of planktonic chlorophyll-<i>a</i>—a proxy for algal biomass—in rivers may represent local production or algae transported from upstream, confounding understanding of algal bloom development in flowing waters. We modeled 3&nbsp;years of chlorophyll-<i>a</i><span>&nbsp;</span>transport through a 394-km portion of the Illinois River and found that although algal biomass is longitudinally widespread, most net production occurs at river control points in the upper reaches (up to 3.7&nbsp;Mg chlorophyll-<i>a</i>&nbsp;y⁻¹&nbsp;km⁻¹). Up to 69% of the algal biomass in the upper river was a result of within-reach production, with the remainder recruited from headwaters and tributaries. High chlorophyll-<i>a</i><span>&nbsp;</span>measured farther downstream was largely because of transport from source-area control points, with substantial net losses of algal biomass occurring in the lower river. Modeling the often-overlooked river transport component is necessary to characterize where, when, and why planktonic algae grow and predict how far and fast they move downstream.</p></div> application/pdf 10.1029/2023GL105137 en American Geophysical Union River control points for algal productivity revealed by transport analysis article