FLOW ALTERATION IMPACTS RIVER METABOLISM: CAPTURING VARIABILITY AT HABITAT AND REACH SCALES WITHIN A REGULATED TEMPERATE RIVER ECOSYSTEM

Flow alterations caused by the damming and diverting of rivers and streams have led to notable changes in geomorphology, community composition, and nutrient cycling within these ecosystems. We quantified the metabolic impacts of a water diversion on the reach scale and in individual hydrologic units (riffles and pools) on the Shasta River California USA. We evaluated the river above and below the diversion using chamber incubations to quantify differences across unit types and Bayesian modeling to estimate reach scale metabolism. The below diversion pool unit demonstrated significantly higher rates of respiration, gross primary production, and net primary production (mean change±SD, 0.16±0.01 O₂ g/m², 0.67±0.03 O₂ g/m², 0.04±0.03 O₂ g/m², respectively). The below diversion riffle unit was only significantly different in net primary production, which increased by 0.32±0.08O₂ g/m². When biomass-corrected metabolic rates were considered, only the riffle unit remained significantly increased by the diversion. Reach scale net ecosystem production below the diversion was 27% of ecosystem production above the diversion, indicating a potential increase in CO₂ flux out of the river. Our findings indicate that water diversions impact pool and riffle hydrological units differently and may significantly influence reach scale metabolism. Globally, there are many rivers affected by diversions and while our findings are limited to one river, we suggest future research should examine the role of water diversions and their effects on ecosystem metabolism and reach-level function.

Primary Presenter: Tara McKinnon, University of Nevada, Reno (taramckinnon@unr.edu)

Authors:

Tara McKinnon, University of Nevada, Reno  (taramckinnon@unr.edu)

Flavia Tromboni, Rheinland-Pfälzische Technische Universität Kaiserslautern-Landau (RPTU), Germany  (flavia.tromboni@gmail.com)

Suzanne Rhoades, McBain Associates, Arcata, California USA  (suzanne@mcbainassociates.com)

Simon Poulson, University of Nevada, Reno  (poulson@unr.edu)

Sudeep Chandra, University of Nevada, Reno  (sudeep@unr.edu)