Impact of Grazing Management Strategies on Carbon Sequestration in a Semi-Arid Rangeland, USA

The effects of 12 years of grazing management strategies on carbon (C) distribution and sequestration were assessed on a semi-arid mixed-grass prairie in Wyoming, USA. Five grazing treatments were evaluated: non-grazed exclosures; continuous, season-long grazing at a light (22 steer-days ha-1) stocking rate; and, rotationally-deferred, short-duration rotation, and continuous, season-long grazing, all three at a heavy stocking rate (59 steer-days ha-1). Non-grazed exclosures exhibited a large buildup of dead plant material (72% of total aboveground plant matter) and forb biomass represented a large component (35%) of the plant community. Stocking rate, but not grazing strategy, changed plant community composition and decreased surface litter. Light grazing decreased forbs and increased cool-season mid-grasses, resulting in a highly diversified plant community and the highest total production of grasses. Heavy grazing increased warm-season grasses at the expense of the cool-season grasses, which decreased total forage production and opportunity for early season grazing. Compared to the exclosures, all grazing treatments resulted in significantly higher levels of C (6000-9000 kg ha-1) in the surface 15 cm of the soil. Higher levels of soil C with grazing are likely the result of faster litter decomposition and recycling, and redistribution of C within the 0-60 cm plant-soil system. Grazing at an appropriate stocking rate had beneficial effects on plant composition, forage production, and soil C sequestration. Without grazing, deterioration of the plant-soil system is indicated

Elevated CO\u3csub\u3e2\u3c/sub\u3e Enhances Productivity and the C/N Ratio of Grasses in the Colorado Shortgrass Steppe

Atmospheric CO2 concentrations have been increasing since the industrial revolution, and are projected to double within this century over today\u27s concentration of 360 µmol mol-1 . This study used six open-top chambers in the Colorado, USA shortgrass steppe to investigate how increasing CO2 will affect productivity and C and N status of indigenous perennial grasses and forbs. From March until October, chambers were placed on two plots in each of the three blocks. In each block, one chamber was assigned an ambient CO2 treatment (~360 µmol mol-1), the other an elevated CO2 treatment (~720 µmol mol-1). Each block also had an unchambered control plot. Growth under elevated CO2 increased above-ground phytomass an average 31% in 1997 and 47% in 1998, with no differences in relative growth responses of C3 and C4 grasses and forbs. Growth in chambers was greater than non-chambered control plots, presumably due to warmer temperatures in chambers and a longer growing season. Shoot N concentrations were reduced 21% and C/N ratios increased 23% in elevated compared to ambient chambers. Variation in aboveground phytomass due to year, CO2 and chamber effects correlated well to % shoot N and C/N ratios, although for both traits different regression lines were required for green plant material (harvested in July) and senescent plant material (harvested in October). Results suggest increased growth and reduced N concentrations in this mixed C3/C4 grassland in an elevated CO2 environment

Development of the Performance Confirmation Program at Yucca Mountain, Nevada

The Yucca Mountain Performance Confirmation program consists of tests, monitoring activities, experiments, and analyses to evaluate the adequacy of assumptions, data, and analyses that form the basis of the conceptual and numerical models of flow and transport associated with a proposed radioactive waste repository at Yucca Mountain, Nevada. The Performance Confirmation program uses an eight-stage risk-informed, performance-based approach. Selection of the Performance Confirmation activities (a parameter and a test method) for inclusion in the Performance Confirmation program was done using a risk-informed performance-based decision analysis. The result of this analysis and review was a Performance Confirmation base portfolio that consists of 20 activities. The 20 Performance Confirmation activities include geologic, hydrologic, and construction/engineering testing. Several of the activities were initiated during site characterization and are ongoing. Others activities will commence during construction and/or post emplacement and will continue until repository closure

Pneumatic testing in 45-degree-inclined boreholes in ash-flow tuff near Superior, Arizona

Matrix permeability values determined by single-hole pneumatic testing in nonfractured ash-flow tuff ranged from 5.1 to 20.3*10{sup -16} m{sup 2} (meters squared), depending on the gas-injection rate and analysis method used. Results from the single-hole tests showed several significant correlations between permeability and injection rate and between permeability and test order. Fracture permeability values determined by cross-hole pneumatic testing in fractured ash-flow tuff ranged from 0.81 to 3.49 x 10{sup -14} m{sup 2}, depending on injection rate and analysis method used. Results from the cross-hole tests monitor intervals showed no significant correlation between permeability and injection rate; however, results from the injection interval showed a significant correlation between injection rate and permeability. Porosity estimates from the cross-hole testing range from 0.8 to 2.0 percent. The maximum temperature change associated with the pneumatic testing was 1.2{degrees}C measured in the injection interval during cross-hole testing. The maximum temperature change in the guard and monitor intervals was 0.1{degrees}C. The maximum error introduced into the permeability values due to temperature fluctuations is approximately 4 percent. Data from temperature monitoring in the borehole indicated a positive correlation between the temperature decrease in the injection interval during recovery testing and the gas-injection rate. The thermocouple psychrometers indicated that water vapor was condensing in the boreholes during testing. The psychrometers in the guard and monitor intervals detected the drier injected gas as an increase in the dry bulb reading. The relative humidity in the test intervals was always higher than the upper measurement limit of the psychrometers. Although the installation of the packer system may have altered the water balance of the borehole, the gas-injection testing resulted in minimal or no changes in the borehole relative humidity

Air-injection testing in vertical boreholes in welded and nonwelded Tuff, Yucca Mountain, Nevada

Air-injection tests, by use of straddle packers, were done in four vertical boreholes (UE-25 UZ-No.16, USW SD-12, USW NRG-6, and USW NRG-7a) at Yucca Mountain, Nevada. The geologic units tested were the Tiva Canyon Tuff, nonwelded tuffs of the Paintbrush Group, Topopah Spring Tuff, and Calico Hills Formation. Air-injection permeability values of the Tiva Canyon Tuff ranged from 0.3 x 10{sup -12} to 54.0 x 10{sup -12} m{sup 2}(square meter). Air-injection permeability values of the Paintbrush nonwelded tuff ranged from 0.12 x 10{sup -12} to 3.0 x 10{sup -12} m{sup 2}. Air-injection permeability values of the Topopah Spring Tuff ranged from 0.02 x 10{sup -12} to 33.0 x 10{sup -12} m{sup 2}. The air-injection permeability value of the only Calico Hills Formation interval tested was 0.025 x 10{sup -12} m{sup 2}. The shallow test intervals of the Tiva Canyon Tuff had the highest air-injection permeability values. Variograms of the air-injection permeability values of the Topopah Spring Tuff show a hole effect; an initial increase in the variogram values is followed by a decrease. The hole effect is due to the decrease in permeability with depth identified in several geologic zones. The hole effect indicates some structural control of the permeability distribution, possibly associated with the deposition and cooling of the tuff. Analysis of variance indicates that the air-injection permeability values of borehole NRG-7a of the Topopah Spring Tuff are different from the other boreholes; this indicates areal variation in permeability

Carbon exchange rates in grazed and ungrazed pastures of Wyoming

The influence of cattle grazing on carbon cycling in the mixed grass prairie was investigated by measuring the CO(2) exchange rate in pastures with a 13 year history of heavy or light grazing and an ungrazed exclosure at the High Plains Grasslands Research Station near Cheyenne, Wyo. In 1995, 1996 and 1997 a closed system chamber, which covered 1 m(2) of ground, was used every 3 weeks from April to October to measure midday CO(2) exchange rate. Green vegetation index (similar to leaf area index), soil respiration rate, species composition, soil water content, soil temperature, and air temperature were also measured to relate to CO(2) exchange rates of the 3 grazing treatments. Treatment differences varied among years, but overall early season (mid April to mid June) CO(2) exchange rates in the grazed pastures were higher (up to 2.5 X) than in the exclosure. Higher early season CO(2) exchange rates were associated with earlier spring green-up in grazed pastures, measured as higher green vegetation index. As the growing season progressed, green vegetation index increased in all pastures, but more so in the ungrazed exclosure, resulting in occasionally higher (up to 2 X) CO(2) exchange rate compared with grazed pastures late in the season. Seasonal treatment differences were not associated with soil temperature, soil respiration rate, or air temperature, nor was there a substantial change in species composition due to grazing. We hypothesize that early spring green-up and higher early season CO(2) exchange rate in grazed pastures may be due to better light penetration and a warmer microclimate near the soil surface because of less litter and standing dead compared to the ungrazed pastures. When all the measurements were averaged over the entire season, there was no difference in CO(2) exchange rate between heavily grazed, lightly grazed and ungrazed pastures in this ecosystem.The Journal of Range Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform August 202

Decreased summer drought affects plant productivity and soil carbon dynamics in a Mediterranean woodland

Precipitation patterns are expected to change in the Mediterranean region within the next decades, with projected decreases in total rainfall and increases in extreme events. We manipulated precipitation patterns in a Mediterranean woodland, dominated by Arbutus unedo L., to study the effects of changing precipitation regimes on above-ground net primary production (ANPP) and soil C dynamics, specifically plant-derived C input to soil and soil respiration (SR). Experimental plots were exposed to either a 20 % reduction of throughfall or to water addition targeted at maintaining soil water content above a minimum of 10 % v/v. Treatments were compared to control plots which received ambient precipitation. Enhanced soil moisture during summer months highly stimulated annual stem primary production, litter fall, SR and net annual plant-derived C input to soil which on average increased by 130 %, 26 %, 58 % and 220 %, respectively, as compared to the control. In contrast, the 20 % reduction in throughfall (equivalent to 10 % reduction in precipitation) did not significantly change soil moisture at the site, and therefore did not significantly affect ANPP or SR. We conclude that minor changes (around 10 % reduction) in precipitation amount are not likely to significantly affect ANPP or soil C dynamics in Mediterranean woodlands. However, if summer rain increases, C cycling will significantly accelerate but soil C stocks are not likely to be changed in the short-term. More studies involving modelling of long-term C dynamics are needed to predict if the estimated increases in soil C input under wet conditions is going to be sustained and if labile C is being substituted to stable C, with a negative effect on long-term soil C stocks. \ua9 Author(s) 2011

Two years of carbon dioxide enrichment on the Shortgrass Steppe of Colorado

The SGS-LTER research site was established in 1980 by researchers at Colorado State University as part of a network of long-term research sites within the US LTER Network, supported by the National Science Foundation. Scientists within the Natural Resource Ecology Lab, Department of Forest and Rangeland Stewardship, Department of Soil and Crop Sciences, and Biology Department at CSU, California State Fullerton, USDA Agricultural Research Service, University of Northern Colorado, and the University of Wyoming, among others, have contributed to our understanding of the structure and functions of the shortgrass steppe and other diverse ecosystems across the network while maintaining a common mission and sharing expertise, data and infrastructure.Includes bibliographical references.This study assessed how doubling the CO2 concentration over present levels affects the growth and physiology of shortgrass steppe vegetation in eastern Colorado. In March, 1997, six open-top chambers (OTCs) were installed on native shortgrass steppe in NE Colorado, USA. Three grass species make up about 88% of the above-ground biomass of this ecosystem; Bouteloua gracilis (C4), Pascopyrum smithii (C3) and Stipa comata (C3). More than 20 other grass and forb species also occur here. CO2 was injected into three OTCs to raise the concentration to 720 ppm, approximately twice that in the three ambient chambers. Three non-chambered plots were established to evaluate chamber effects. The air temperature in the chambers averaged 2° C warmer than outside. During 1997 and 1998 significant chamber and CO2 effects were detected. Averaging over the two years, above-ground production in the ambient chambers was 22% greater than that in unchambered plots, probably due to warmer spring temperatures in the chambers. Production under elevated CO2 averaged 35% greater than that in ambient OTCs. Significant growth increases occurred for both C3 and C4 grasses and forbs in 1998. These CO2 -induced growth increases were primarily due to improved water status. Soil water content was often higher in elevated CO2 chambers. Leaf water potentials were generally higher in plants grown at elevated CO2 compared to ambient chambers. Leaf intercellular CO2 photosynthesis response curves indicated neither P. smithii nor B. gracilis leaves were saturated with CO2 at 360 ppm. Photosynthetic capacity of both species was reduced in plants grown at elevated CO2, although this response was much stronger in the the C3 species, P. smithii. Results suggest that future CO2 enrichment will lead to growth enhancements in both C3 and C4 grasses of the shortgrass steppe.This research was funded by USDA/ARS and funding received from the Terrestrial Ecology and Global Change Program (IBN-9524068)