Flooding of a Major Dry Waterway: Impacts of Flow Restoration on River-Carbon Composition and Fluxes in the Colorado River
Thomas S Bianchi1,2, Peter A Raymond3, David E Butman4, Rory Kates5, Karl W Flessa6, Hector Zamora6, Nicholas D Ward7 and Amy Brown2, (1)University of Florida, Department of Geological Sciences, Gainesville, FL, United States, (2)University of Florida, Geological Sciences, Ft Walton Beach, FL, United States, (3)Yale University, New Haven, CT, United States, (4)University of Washington Seattle Campus, Seattle, WA, United States, (5)University of Florida, Geological Sciences, Gainesville, FL, United States, (6)University of Arizona, Tucson, AZ, United States, (7)University of Florida, Geological Sciences, Ft Walton Beach, WA, United States
Abstract:
Coastal wetlands and marshes represent an important source of dissolved organic matter (DOM) to the coastal ocean that augments biogeochemical fluxes from inland waters. The abundance of dissolved greenhouse gasses (e.g. CO2 and CH4) in coastal regions is closely linked to DOM fluxes from rivers and wetlands along with biological, photochemical, and physical processes. Here we report for the first time, on the results of a unique sampling opportunity is the first of a hoped-for series of planned flow restorations (described in Minute 319), to gain a perspective on how the time interval of dry periods between flooding pulses affects carbon cycling (DOC, dissolved inorganic carbon [DIC], and particulate organic carbon [POC]) and greenhouse gas (CH4 and CO2) fluxes in the Colorado River basin. We also used chemical biomarkers (lignin phenols and amino acids), and isotopic analyses (δ13C and 14C) to determine how the age and sources of different stable and unstable carbon pools changed during the flooding event. DOC concentrations were generally higher during peak flooding at dry sites than at wet sites, ranging from 3.41 mg/L to 5.09 mg/L and 3.93 mg/L to 7.26 mg/L, respectively Well the age of the DOC in the source floodwaters above the dam was ca. 250 years old and the age of the DOC as the flood progressed reached about 1000 years old at downstream. So, in essence the age of the floodwater DOC increased in age to something very similar in age to OC in riverbed sediment. We posit that the old age is from aged dead and living microbial biomass, since we know that terrestrial plant material was solubilized (e.g. dissolved lignin) and mobilized from the soils into the river early in the flood stage. This also agreed with the notion that these dry sites had evidence of higher OC oxidation with higher CO2 concentrations, and δ13C-DOC values that were clearly from vascular plant sources (or microbial biomass that utilized vascular plant substrates). This suggests that these LOP moieties may remain intact in soil, during these dry phases and are flushed out during flooding periods. Finally, amino acid results corroborated the observations made with LOPs (e.g. increased Ad/Al ratios indicating a higher state of degradation) and provided another indication for a primarily bacterial OC source along with bulk C:N ratios.
