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Carbon Dioxide Emissions from Exhumed Petrocalcic Horizons

^a Instituto Nacional de Investigaciones Forestales, Agricolas y Pacuarias, Calera, Zacatecas 98500, Mexico
^b Dep. of Plant and Environmental Science, New Mexico State Univ., Las Cruces, NM 88003
^c USDA-ARS, Jornada Experimental Range, Las Cruces, NM 88003
^d Univ. Statistics Center, New Mexico State Univ., Las Cruces, NM 88003

View larger version (115K): [in a new window]   Fig. 1. Location of study site and illustration of the three soil types. (A) Chihuahuan Desert and location of study site in New Mexico. (B) Locations of blocks and quadrats for the three soil types. The map units are of geomorphic units, including states of erosion (Monger et al., 2006). (C) Cross-section illustrating the three soil types evaluated for their CO2 emissions. (D) Example of a noneroded petrocalcic horizon soil (NEPHS) in the study area.

View larger version (65K): [in a new window]   Fig. 2. Soil CO2 emissions based on NaOH traps for the three sampling blocks. Soil temperature was taken at 10 cm at Jornada Long Term Ecological Research (LTER) weather station. Rainfall is the accumulated amounts between sampling dates (weekly from July to September and biweekly October to May). Soil temperature and rainfall share the same scale on the graph. Means with ** are different at = 0.05. Means with * are different at = 0.20. Arrows pointing up signify times when exhumed petrocalcic horizon soils (EPHS) is higher than at least one of the other two soil types. Arrows pointing down signify times when EPHS is lower than at least one of the other two soil types.

View larger version (69K): [in a new window]   Fig. 3. Soil CO2 emissions using soda lime traps for the three sampling blocks. Soil temperature and rainfall are the same as described in Fig. 2. Means with ** are different at = 0.05. Means with * are different at = 0.20. Arrows pointing up signify times when exhumed petrocalcic horizon soils (EPHS) is higher than at least one of the neighboring soils. Arrows pointing down signify times when EPHS is lower than at least one neighboring soil.

View larger version (28K): [in a new window]   Fig. 4. Fractionation values between 13C values of standards and 13C values of alkali traps. Reaction time for all alkali traps was 24 h except CDG6d which was 6 d.

View larger version (33K): [in a new window]   Fig. 5. Carbon isotopic values (13C) of CO2 emissions after correction using fractionation factors. Each point is the mean of n = 12 (i.e., four replications in each plot times three plots per soil type). Range of atmospheric CO2 from Clark and Fritz (1997). Range of C4 black grama and C3 mesquite, shown with black boxes, are from Connin et al. (1997a) and Monger (2003). Values for pedogenic carbonates shown in upper left of top figure are from the following areas in the Jornada Basin: (1) Stressor site; (2) Mayfield well; (3), (4), and (5) Liu (2002); (6) Connin et al. (1997a, 1997b). Open circles are Stage I pedogenic carbonates formed in coppice dunes.