T249 From Pores to Mountains, and Minutes to Millennia (Posters): Session Dedicated to the Contributions of Rob Bowman, Fred Phillips, and John Wilson

Tuesday, 27 September 2016
9:00 AM - 6:30 PM
Exhibit Hall E/F

RELATIVE CARBON FLUXES FROM SOIL, DEEP VADOSE ZONE AND GROUNDWATER TO ATMOSPHERE AND RIVER OF A SEMI-ARID FLOODPLAIN IN COLORADO

Paper number: T249-6
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

Understanding of terrestrial carbon cycling relies primarily on studies of topsoils that are typically shallower than 0.3 m and seldom deeper than 1 m. Much less is known about carbon fluxes through deeper strata where about half of the Earth’s terrestrial carbon inventory resides. This is especially true in semi-arid and arid regions, which represent about 40% of the Earth’s land surface. Unique field instrumentation was installed within a semi-arid floodplain of the Colorado River to understand carbon inventories and carbon and water fluxes. Measurements were made over a 2 year period along a transect extending laterally for 250 m and vertically for 7 m through the unsaturated zone into the underlying aquifer. Year-round vadose zone pore-water sampling revealed the existence of a high dissolved organic carbon (DOC) influx from the rhizosphere infiltrating into the deeper vadose zone. The field and associated laboratory derived seasonal- and depth-resolved CO2 fluxes and respiration rates combined with vadose zone and groundwater flow rates led to the important discoveries that 1) about 30% of the CO2 emitted from the land surface is originating from depths below 1 m and above the water table, although the current global scale land models (CLM/ALM) show practically no CO2 emission from below 1 m depth. 2) The CO2 efflux to the atmosphere accounts for ~85% of the total floodplain carbon export, with only ~15% of the total carbon as DIC (the characteristics of the semi-arid climate) and < 1% of total DOC export to the aquifer and river, despite being along the river. To our knowledge, these analyses of a novel dataset are the first to quantify the relative contributions to carbon exports from different subsurface compartments into the atmosphere and river at a semi-arid floodplain. While studies of carbon cycling in other semi-arid region floodplains are needed, a similar hierarchy for magnitudes of carbon exports is expected in other semi-arid flood plains because of efficient OC utilization in soils and the deep vadose zone, and relatively low flow rates and DOC concentrations in groundwater.

Geological Society of America Abstracts with Programs. Vol. 48, No. 7

doi: 10.1130/abs/2016AM-287166

© Copyright 2016 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.