Hydrodynamic Controls on Primary Producer Communities in Spring‐Fed Rivers

Abstract

Abstract In many spring‐fed rivers, benthic macroalgae and periphytic algae are increasing and, in some cases, replacing rooted vascular plants, which are critical to ecosystem function. While most research has focused on the role of nutrients in driving this change, in‐channel hydrodynamics also control vascular plant and algal abundances and their interactions. Understanding relationships between hydrology and primary producers is essential for developing ecologically relevant flow regulations. We investigated the relationship between flow velocity and primary producer abundance in spring‐fed rivers using observational data from 16 springs to determine critical velocity thresholds for periphyton, macroalgae, and vascular plants. We also used flow suppression experiments to quantify periphyton growth rates and test for hysteretic behavior. Results suggest a critical velocity of 0.22 m/s (95% CI: 0.13–0.28 m/s) for periphyton but no specific thresholds for macroalgae or vascular plants. Experimental and theoretical results supported these findings and suggest periphyton establishment is not hysteretic.