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Influence of run of river dams on floodplain sediments and carbon dynamics

Pearson, Adam J., Pizzuto, James E., Vargas, Rodrigo
Geoderma 2016 v.272 pp. 51-63
carbon, carbon dioxide, carbon sequestration, ecosystems, floodplains, hydrology, methane, methane production, models, rivers, sediments, streams, temperature
Quantifying the biophysical impacts of management on river and stream ecosystems is an important issue that requires understanding of ecological, hydrological and geomorphological processes. We conducted a year-long ecogeomorphological experiment to determine sedimentation and carbon cycling differences between run-of-river (ROR) dams in a 200year old impounded floodplain and a floodplain that was formerly impounded >65years ago. Our study shows that ROR dams do not necessarily enhance floodplain sedimentation or carbon storage, but promote brief periods of sediment CH4 flux (up to 2.91nmolCH4m⁻²s⁻¹) to the atmosphere. Removal of a ROR dam may result in channel widening, and removal by lateral transport (i.e., erosion) of nearly 14 MgC per floodplain. We did not find significant differences in mean sediment CO2 fluxes or temperature sensitivity (Q10=2.1±0.4) of CO2 efflux among floodplains. All floodplains were likely an annual net source of sediment CO2 flux (annual mean of 2.12±0.974μmolCO2m⁻²s⁻¹) to the atmosphere, and a sink for atmospheric CH4 (annual mean of −0.221±0.163nmolCH4m⁻²s⁻¹). We provide a conceptual model on the management consequences on ROR dam structures for floodplain sedimentation/erosion, and sediment carbon cycling.