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ARS Home » Pacific West Area » Tucson, Arizona » SWRC » Research » Publications at this Location » Publication #331648

Research Project: Ecohydrological Processes, Scale, Climate Variability, and Watershed Management

Location: Southwest Watershed Research Center

Title: Subterranean ventilation of allochthonous CO2 governs net CO2 exchange in a semiarid Mediterranean grassland

Author
item LOPEZ-BALLESTEROS, A. - Universidad De Granada
item SERRANO-ORTIZ, P. - Universidad De Granada
item KOWALSKI, A. - Universidad De Granada
item SANCHEZ-CAÑETE, E.P. - Universidad De Granada
item Scott, Russell - Russ
item DOMINGO, F. - Consejo Superior De Investigaciones Cientificas (CSIC)

Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/26/2016
Publication Date: 1/3/2017
Citation: Lopez-Ballesteros, A., Serrano-Ortiz, P., Kowalski, A., Sanchez-Cañete, E., Scott, R.L., Domingo, F. 2017. Subterranean ventilation of allochthonous CO2 governs net CO2 exchange in a semiarid Mediterranean grassland. Agricultural and Forest Meteorology. 234-235:115-126. doi: 10.1016/j.agrformet.2016.12.021.

Interpretive Summary: Recent research has shown that semiarid regions play an important role in the global carbon cycle. However, detailed site investigations and experiments are still necessary in order to fully understand how particular semiarid sites behave and to determine the main factors currently affecting their carbon balance. Here, we explore how biological and abiotic processes contribute to an ecosystem’s net carbon dioxide (CO2) exchange with the atmosphere by examining six years of measurements made over a semiarid grassland in southeast Spain. Results point to the dominant importance of CO2 releases from the soil that occur especially during the summer drought periods when it is windy. Extremely large annual net CO2 releases were found over the whole study period. Since this occurred mostly during the dry seasons, it was not likely to be caused by biological activity. The potential origins of the released CO2 could be geological or from CO2 that was produced elsewhere and transported underground to below the site. This study exposes how belowground abiotic processes can complicate the interpretation of the ecosystem carbon cycling.

Technical Abstract: Recent research highlights the important role of (semi-) arid ecosystems in the global carbon (C) cycle. However, detailed process based investigations are still necessary in order to fully understand how drylands behave and to determine the main factors currently affecting their C balance with the aim of predicting how climate change will affect their structure and functions. Here, we explore the potential biological and abiotic processes that may compose net CO2 exchange in a semiarid grassland in southeast Spain by means of eddy covariance measurements registered over six hydrological years (2009-2015). Results point out the great importance of subterranean ventilation, an advective transport process causing net CO2 release, especially during drought periods and under high-turbulence conditions. Accordingly, extreme CO2 release, far exceeding that found in the literature, was measured over the whole study period (2009-2015) averaging 230 g C m-2 year-1; this occurred mostly during the dry season and was very unlikely to correspond to concurrent biological activity and variations of in situ organic C pools. Underground CO2 concentrations corroborate this finding. In this regard, the potential origins of the released CO2 could be geological degassing and/or subterranean translocation of CO2 in both gaseous and aqueous phases. However, future research is needed in order to understand how CO2 transport and production processes interact and modulate drylands’ terrestrial C balance. Overall, the present study exposes how subterranean ventilation and hydrogeochemistry can complicate the interpretation of the terrestrial C cycle.