Peipoch, M., M. Daniels, and S. Ensign. 2025. Freshwater Science, early online access.
Permalink/DOI (Open access)
Abstract
Along the river continuum, phytoplankton biomass is differently supported by benthic algae responding to local factors that change over time and by planktonic algal growth responding to factors that change over an upstream distance. Understanding the patterns and factors influencing benthic and planktonic contributions to fluxes of suspended algae is critical for comprehending river phytoplankton composition and dynamics. We estimated the origin (planktonic or benthic) and fluxes of total suspended algae by analyzing chlorophyll a (Chl a) concentration–discharge (C–Q) relationships during storm events across 26 streams and rivers from the National Ecological Observatory Network database. We interpreted the responses of Chl a concentrations to high flows with commonly used C–Q metrics and environmental influences on algal growth and community composition across watersheds of different size, channel slope, and hydrologic regimes. We found evidence of rapid exhaustion of benthic algal supply in forested headwaters, more effective scour of benthic algae in snowmelt-driven flow regimes, relevant planktonic contributions in >5th-order flow-regulated rivers, and an apparent isometric scaling between benthic Chl a abundance and fluxes across multiple stream channel orders. In general, we conclude that there is ubiquitous dominance of benthic supply to suspended algal biomass in both streams and rivers. Chl a C–Q responses have the potential to provide valuable information on the origin, abundance, and mobility of river algae and to contribute to our understanding of fundamental discrepancies in how spatial and temporal changes in the location and abundance of river algae dictates riverine biodiversity and productivity.
