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United States Department of Agriculture

Agricultural Research Service

Title: Carbon Dioxide Fluxes in a Southern Mixed Grass Prairie

Authors
item Sims, Phillip
item BRADFORD, JAMES

Submitted to: Agriculture Forest Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 11, 2001
Publication Date: July 20, 2001

Interpretive Summary: Atmospheric CO2 concentrations have increased because of changes in land use and burning of fossil fuels. Specifically, our objective was to compare the CO2 flux patterns, and their potential to sequester C, of a grass dominated and a sand sagebrush dominated Southern Plains mixed-grass prairie (latitude 36ø36' N, longitude 99ø35' W, elevation 2,061 ft). CO2 flux, calculated at 20-minute intervals, were measured from mid-February t early May through mid to late December in 1995, 1996, and 1997 on both sites using Bowen ratio/energy balance instrumentation. Plant measurements included aboveground and belowground biomass, leaf area, and canopy height. Net downward CO2 fluxes, i.e., carbon dioxide uptake, over the measurement period averaged 3,601 and 178 lb/acre for the grass and sagebrush dominated sites, respectively. Estimated annual net CO2 fluxes were 2,290 and 205 lb/acre/year, or about 918 and 53 lb C/acre/year sequestered on the grass and sagebrush dominated sites, respectively. Average annual and seasonal CO2 fluxes for the grass-dominated prairie site were greater (14 and 6 lb/acre/day) than the carbon flux on the sagebrush site (0.09 and 0.53 lb/acre/day). Water-use, measured as evapotranspiration (ET), for the two treatments was similar, averaging about 0.09 inches/day on both sites. This study indicates that these Southern Plains mixed-grass prairie communities have the potential to sequester C. Similar sites in lower ecological status would have an even better opportunity to sequester C in response to improved management. These and related data will be useful as land owners and managers develop and market carbon credits on these types of resources.

Technical Abstract: Atmospheric CO2 concentrations have increased because of changes in land use and burning of fossil fuels. Grasslands, along with other temperate and arid rangeland resources, comprise over 50% of the world's land area. The role these ecosystems play in the global C budget has not been adequately documented. The objective of this study was to determine the relationship of vegetation structure to the CO2 fluxes for a grass and a sagebrush dominated Southern Plains mixed-grass prairie (latitude 36ø36' N, longitude 99ø35' W, elevation 630 m). The CO2 flux and evapotranspiration (ET), calculated at 20-minute intervals, were measured from mid-February to early May through mid-December in 1995, 1996, and 1997 on both sites using Bowen ratio/energy balance instrumentation. Plant measurements included above ground and belowground biomass, leaf area, and canopy height. Net downward CO2 fluxes over the measurement period averaged 404 and 20 g m-2 for the grass and sagebrush dominated sites, respectively. Estimated annual net CO2 fluxes into these systems were 257 and 23 g/m2/yr, respectively, or about 103 and 6 g C sequestered, for the grass and sagebrush dominated sites, respectively. Average annual and seasonal CO2 fluxes for the grass-dominated prairie site were greater (1.54 and 0.70 g/ m2/d) than the carbon flux on the sagebrush site (0.01 and 0.06 g/m-2/d), respectively. ET measured over the sampling period averaged 564 and 515 mm for the grass and sagebrush dominated mixed-grass prairie sites, respectively. The daily ET rates for the two treatments were similar, averaging 2.28 and 2.30 mm d-1. This study indicates that these Southern Plains mixed-grass prairie communities have the potential to sequester C especially if they are in low ecological status and respond to improved management.

Last Modified: 8/19/2014
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