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ARS Home » Plains Area » Mandan, North Dakota » Northern Great Plains Research Laboratory » Research » Publications at this Location » Publication #142530
Title: SIX YEARS OF CO2 FLUX MEASUREMENTS FOR A MODERATELY GRAZED MIXED-GRASS PRAIRIE.

Author
item Frank, Albert

Submitted to: Environment Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/2/2003
Publication Date: 12/4/2003
Citation: FRANK, A.B. SIX YEARS OF CO2 FLUX MEASUREMENTS FOR A MODERATELY GRAZED MIXED-GRASS PRAIRIE. ENVIRONMENT MANAGEMENT. Published online 4 December 2003.

Interpretive Summary: Agriculture is increasingly taking on the role of mitigating carbon dioxide emissions into the atmosphere. The large area in the US occupied by temperate grasslands make it important to determine their strength as a carbon sink. The Bowen ratio/energy balance technique was used to measure annual carbon dioxide fluxes over a six year period from 1996 to 2001 for a moderately grazed mixed-grass prairie at Mandan, ND. Maximum daily CO2 fluxes generally coincided with periods of maximum LAI and above-ground green biomass. Over the six years of study the prairie was a sink for carbon dioxide from 5 May to 3 October. The prairie lost carbon dioxide to the atmosphere for the remainder of the year. Annual CO2 fluxes averaged. Fluxes varied widely over years ranging from a low of 13 g CO2 m-2 yr-1 in 1998 to a high of 247 g CO2 m-2 yr-1 in 2001 and averaged 108 g CO2 m-2 yr-1. The total flux over all 6 years was 646 g CO2 m-2 or 176 g CO2-C m-2. These results indicate that the strength of this grazed prairie grassland sink for atmospheric carbon dioxide is about 30 g CO2-C m-2 y-1 which is quite small, but considering that the site was grazed and still remains a sink for carbon is significant.

Technical Abstract: The large area occupied by temperate grassland ecosystems makes it important to determine their strength as a carbon sink. The Bowen ratio/energy balance (BREB) technique was used to determine CO2 fluxes over a moderately grazed mixed-grass prairie at Mandan, ND over a six year period from 1996 to 2001. Above-ground biomass and leaf area index (LAI) were measured about every 21 days throughout the growing period. Root biomass was determined to 1.1 m depth in mid-July each year. Peak above-ground biomass typically occurred between mid-July to early-August and ranged from 782 kg ha-1 in 1998 to 2173 kg ha-1 in 1999. Maximum LAI ranged from 0.4 in 1998 to 0.9 in 1999. Root biomass ranged from 11.8 Mg ha-1 in 1997 to 17.4 Mg ha-1 in 1996. Maximum daily CO2 fluxes generally coincided with periods of maximum LAI and above-ground green biomass. The average time period for CO2 uptake was 5 May to 3 October. Annual CO2 fluxes ranged from a low of 13 g CO2 m-2 in 1998 to a high of 247 g CO2 m-2 in 2001, nearly a 20 fold difference, and averaged 108 g CO2 m-2. The cumulative annual flux over all 6 years was 646 g CO2 m-2 or 176 g CO2-C m-2. These results indicate that the strength of the carbon sink for this moderately grazed prairie site is about 30 g CO2-C m-2 y-1 which is quite small, but considering that the site was grazed and still remains a sink for carbon is significant.