Periphyton and ecosystem metabolism as indicators of river ecosystem response to environmental flow restoration in a flow-reduced river

Tracking river ecosystem responses to river flow restoration is a necessary and important step for adaptive management of environmental flow. In this study, we used a unique experimental scheme to investigate the responses of water quality, periphyton, and river metabolism to a new environmental flow in a flow-reduced river in Japan. After implementing the new environmental flow, water quality improved. Periphyton biomass increased substantially in terms of both chlorophyll a and ash-free dry mass. However, the new flow also promoted the growth of filamentous species that could deteriorate the river environment. River metabolism was determined by continual measurement of the diel oxygen concentration. Gross primary production and ecosystem respiration both increased after the increase in environmental flow. These results indicate that the periphyton and metabolism can potentially be used as indicators for monitoring river ecosystem response to increased minimum environmental flow.