Carbon sequestration in small-scale farming systems in semi-arid regions offers the possibility to increase local soil fertility, improve crop yields, enhance rural people's wellbeing, and strengthen the resilience of agricultural systems while reducing CO2 accumulation in the atmosphere and, thus, contributing to climate change mitigation. A variety of management practices and land use options have been proposed to increase carbon uptake and reduce system losses. So far, less attention has been paid to local smallholders, the ultimate agents of anticipated community carbon projects, and the complexity, diversity, and dynamics of their livelihoods in a highly variable and risk-prone environment. A hybrid research approach, combining biophysical, economic, cultural, and institutional analysis, was used to assess the potential for soil carbon sequestration in the Old Peanut Basin of Senegal. In situ soil and biomass measurements provided current carbon accounts. Historic carbon changes and future sequestration rates under various management practices were simulated with CENTURY, a biogeochemical model. The simulation results well represented general historic trends and carbon storage potential. However, they did not accurately reflect variable and flexible site-specific management strategies as farmers adapt to stress, shock, and crises over time. To account for these, distinct pathways of agricultural and environmental change were examined in Wolof and Serer villages and viable options for carbon sequestration were evaluated. Systems analysis was used to explore the various components that influence farmers' perceptions, choices, and decisions with respect to land management. Results showed that resource endowment and institutional and policy incentives determine which carbon sequestration activities might be most appropriate for different groups of farmers. Finally, a cost-benefit analysis and a cash-flow analysis (using STELLA) were performed to assess the financial profitability and economic feasibility of proposed management strategies. The study reveals large differences in these measures between farmers with low and high resource endowments. In most cases, local smallholders are not likely to have the investment capital necessary to implement the alternative management practices. A farmer-centered approach to carbon sequestration, as proposed by the study, can be used to more effectively address the needs and capacities of smallholders in dryland carbon offset programs.

The general objective of this research is to develop a methodology that will allow mapping and quantifying shrub encroachment with remote sensing. The multitemporal properties of the Moderate Resolution Imaging Spectroradiometer (MODIS) -250m, 16-day vegetation index products were combined with the hyperspectral and high spatial resolution (3.6m) computation of the Airborne Visible-Infrared Imaging Spectrometer (AVIRIS) to detect the dynamics of mesquite and grass/soil matrix at two sites of high (19.5%) and low (5.7%) mesquite cover in the Santa Rita Experimental Range (SRER). MODIS results showed separability between grassland and mesquite based on phenology. Mesquite landscapes had longer green peak starting in April through February, while the grassland only peaked during the monsoon season (July through October). AVIRIS revealed spectral separability, but high variation in the data implicated high heterogeneity in the landscape. Nonetheless, the methodology for larger data was developed in this study and combines ground, air and satellite data.

Air-water interface plays an important role in the transport of many contaminants in the vadose zone. It is also a limiting factor for many processes involve mass or energy transfer between air and water phases in vadose zone. In this research, the gas-phase partitioning tracer method was used to measure air-water interfacial area for eight porous media. The experimental results were used to investigate the influencing factors of the magnitude of air-water interfacial area and the relationship between the air-water interfacial area and water saturation, and capillary pressure. The porous media comprised a series of sands with narrow particle-size ranges, a sand with a wider particle-size distribution, a sandy soil, and a loamy sandy soil. The measurement range was extended to very low water contents in an attempt to determine upper limits for air-water interfacial areas. The measured values were compared to the normalized surface areas of the porous media. The results of the experiments showed that the magnitude of the air-water interfacial areas increased with decreasing water saturation, and approached that of the normalized surface areas. Generally, air-water interfacial areas were larger for media with larger specific surface areas. The change in air-water interfacial area with changing water saturation was less near saturated water contents and greater at smaller values. In addition, the change was greater for the poorly-sorted media than the well-sorted media. An empirical model was developed to describe the observed relationship between air-water interfacial area and water saturation. The coefficients of the model were found to correlate to the porous-medium uniformity coefficient. With this model and associated correlations, only bulk density, specific surface area, and uniformity coefficient are needed to estimate air-water interfacial area for a given water saturation. The model was shown to provide a reasonable description of a literature data set. Potential relationships between air-water interfacial area and capillary pressure under higher water-content conditions are investigated for unsaturated sandy porous media. A conceptual relationship between air-water interfacial area and capillary pressure is hypothesized, and is tested using air-water interfacial area data obtained from gas-phase tracer tests and saturation-pressure data obtained from water-drainage experiments. The results show that the magnitude of the air-water interfacial area increases with increasing capillary pressure, which corresponds to decreasing water content. (Abstract shortened by UMI.)

Concern for environmental management of our natural resources is most often focused on the human impacts upon these resources. Minor stresses on surface materials in sensitive desert landscapes can greatly increase the rate and character of erosion. The National Training Center, Ft. Irwin, located in the middle of the Mojave Desert, California, provides a study area of intense off-road vehicle (ORV) activity spanning a 50-year period. This study documents a case of concentrated ORV activity on sensitive desert environments, and the resulting environmental impacts. Geomorphic surfaces from two study sites within the Ft. Irwin area were mapped from 1:28,400 scale black and white aerial photographs taken in 1947. Surface disruption attributed to military activity was then mapped for the same areas from 1993, 1:12,000, black and white aerial photographs. Several field checks were conducted to verify this mapping. Images created from SPOT panchromatic and Landsat Thematic Mapper (TM) multispectral data acquired during the spring of 1987 and 1993 were analyzed to assess both the extent of disrupted surfaces and the surface geomorphology discernable from satellite data. Classified and merged images were then created from these data and demonstrate the capabilities of satellite data to aid in the delineation of disrupted geomorphic surfaces. Correlations were also established between highly disrupted surfaces and soil surface conditions on selected geomorphic surfaces. Disruption maps produced from the air photos indicate that the amount of disrupted surfaces within the study sites grew from a combined total of 1.3 km² in 1947 to 33.4 km² by 1993. A combination of 6 bands of Landsat TM data with a seventh band of SPOT panchromatic data yielded a product that delineated broad geomorphic surfaces that closely correlate with those mapped from the aerial photography. An error matrix between these two products resulted in an overall accuracy of 83.36% and a Kappa Index of Agreement of 77.28%. A 15-class unsupervised classification of the SPOT panchromatic data produced the representation of the extent and levels of disruption present in the study areas that closely matched field observations. Field sampling of soil strength and clay/silt percentages on disturbed and undisturbed surfaces reveals that these arid land surfaces react to intense ORV activity by becoming more compact and exhibiting higher percentages of clays and silts.

A three-year randomized field study was undertaken to evaluate the effects of prescribed burning and the intense rainfall events associated with the summer monsoon of southern Arizona, specifically examining the interchange between the plant, soil and surface hydrologic processes within a savanna. The effects of fire and rainfall treatments were evaluated by examining their specific effects on vegetation, arbuscular mycorrhizal fungi (AMF), soil structure, soil nutrient capital, surface runoff and sediment. In addition to the field study, two factorial greenhouse studies were completed in conjunction with the field study. The objectives of the greenhouse studies were: (1) to test the effects of prescribed fire and high intensity rainfall on AMF infectivity potential, and (2) to examine the effect of mycotrophy on the biomass production of native and introduced grasses grown in pasteurized and native soils. A third study examined the development of an empirical model to estimate sediment production from the field study's plots. The objectives of this third study were: (1) to develop the empirical model using two years of collected sediment, and (2) to compare model estimates with the commonly used Revised Universal Soil Loss Equation (RUSLE) model. The results of these studies indicate that a integrated mechanism exists between the plant community and biotic and physical soil processes, which when disturbed affect the hydrology of the watershed.

In order to better model the climate system, land-surface models are continuously being improved. Several studies using the Biosphere-Atmosphere Transfer Scheme (BATS) are presented. One study compares simulations with the new ten-layer soil model (TLSM) and the previous BATS soil model at global and regional scales. TLSM tends to have much higher bare soil evaporation than the previous soil model. Soil in regions with high precipitation became wetter, while soil in regions with less precipitation became much drier. Potential errors in TLSM included underpredicted runoff and high-latitude transpiration. Corrections for these errors were incorporated and tested at six points. Surface runoff is increased by extracting water from the upper three TLSM layers rather than only the top layer. Bare soil evaporation is limited to the water present in the surface soil layer. A diurnal temporal error in the downward longwave radiation forcing data did not appear to significantly affect simulated long-term or large-scale averages. However, the assumption of uniform hourly distribution of 6-hour total precipitation did impact the partitioning of precipitation into evaporation, transpiration and runoff. A new method for modeling vertical water flow in heterogeneous porous media using the water-content based form of Richards equation is described, then used with BATS/TLSM to simulate the boreal forest energy and water exchanges at a black spruce site, where a thick moss layer covers a peat/loam soil, and at an aspen site with a homogenous clay soil. The moss is treated as a type of porous media, so its unique hydraulic and thermal properties can be modeled directly. Simulated net radiation is very similar to that observed over the summer months at both sites, but latent heat is greatly overestimated and simulated sensible heat fluxes are not well correlated with the observations. Observed soil temperature profiles and soil water content profiles are well captured at the black spruce site, as is the ability of moss to keep the underlying soil layers moist and cool. Despite the successful modifications made to TLSM during this study, the overestimation of evaporation remains a problem that should be addressed before widespread use of this model occurs.

Accelerated soil erosion in Malawi, Southern Africa, increasingly threatens agricultural productivity, given current and projected population growth trends. Previous attempts to document soil erosion potential have had limited success, lacking appropriate information and diagnostic tools. This study utilized geomatics technologies and the latest available information from topography, soils, climate, vegetation, and land use of a watershed in southern Malawi. The Soil Loss Estimation Model for Southern Africa (SLEMSA), developed for conditions in Zimbabwe, was evaluated and used to create a soil erosion hazard map for the watershed under Malawi conditions. The SLEMSA sub-models of cover, soil loss, and topography were computed from energy interception, rainfall energy, and soil erodibility, and slope length and steepness, respectively. Geomatics technologies including remote sensing and Geographic Information Systems (GIS) provided the tools with which land cover/land use, a digital elevation model, and slope length and steepness were extracted and integrated with rainfall and soils spatial information. Geomatics technologies enable rapid update of the model as new and better data sets become available. Sensitivity analyses of the SLEMSA model revealed that rainfall energy and slope steepness have the greatest influence on soil erosion hazard estimates in this watershed. Energy interception was intermediate in sensitivity level, whereas slope length and soil erodibility ranked lowest. Energy interception and soil erodibility were shown by parameter behavior analysis to behave in a linear fashion with respect to soil erosion hazard, whereas rainfall energy, slope steepness, and slope length exhibit non-linear behavior. When SLEMSA input parameters and results were compared to alternative methods of soil erosion assessment, such as drainage density and drainage texture, the model provided more spatially explicit information using 30 meter grid cells. Results of this study indicate that more accurate soil erosion estimates can be made when: (1) higher resolution digital elevation models are used; (2) data from improved precipitation station network are available, and; (3) greater investment in rainfall energy research.

<p> The high cost and environmental risks associated with non-renewable energy sources has caused an increased interest in, and development of renewable biofuels. Switchgrass (<i>Panicum virgatum</i> L.), a warm season perennial grass, has been investigated as a source of biofuel feedstock due to its high biomass production on marginal soils, its tolerance of harsh growing conditions, and its ability to provide habitat for wildlife and soil conservation cover. West Virginia contains vast expanses of reclaimed surface mine lands and could potentially benefit from the production of switchgrass as a biofuel feedstock. Furthermore, switchgrass production could satisfy Surface Mining Reclamation and Control Act of 1977 (SMCRA) requirements for reclamation bond release to mine operators. Three separate studies will be discussed in this thesis to determine if switchgrass grown on reclaimed surface mines can produce yields similar to yields from stands grown under normal agronomic conditions and what common surface mining reclamation practices may be most appropriate for growing switchgrass. The first study examined yield production of three commercially-available, upland switchgrass varieties grown on two reclaimed surface mines in production years two, three and four. The Hampshire Hill mine site, which was reclaimed in the late 1990s using top soil and treated municipal sludge, averaged 5,800 kg (ha-yr)^-1 of switchgrass compared to 803 kg (ha-yr)^-1 at the Hobet 21 site which was reclaimed with crushed, unweathered rock over compacted overburden. Site and variety interacted with Cave-in-Rock as the top performer at the more fertile Hampshire Hill site and Shawnee produced the highest yields at Hobet 21 (7,853 kg ha^-1 and 1,086 kg ha^-1 averaged across years, respectively). Switchgrass yields increased from 2009 to 2010, but declined from 2010 to 2011. Switchgrass yields from farmlands in this region averaged about 15000 kg (ha-yr)^-1 in the research literature, so switchgrass grown on reclaimed lands appears to be about 50% lower. A second study to determine optimal nitrogen and mulch rates for switchgrass establishment began in June 2011 on two newly-reclaimed surface mines. Both sites were seeded at a rate of 11.2 kg pure live seed (PLS) ha^-1 of Cave-in-Rock on replicated treatments of 0, 33.6 and 67.0 kg N ha^-1, and high and low mulch rates of mulch applied as hydromulch. Switchgrass cover, frequency and yield improved with the addition of any amount of N fertilizer compared to no N application. There was no significant difference in yield associated with high and low levels of N. We also observed that yields were not affected by application of additional mulch. The final study compared a one- and two-harvest system in the fourth year of production at the Hampshire Hill and Hobet 21 sites. There was no increase in yield production utilizing a two-harvest system (2922 kg (ha-yr)^-1, averaged across site) compared to a one-harvest system (3029 kg (ha-yr)^-1). The data also showed that re-growth collected from July to October in the two-harvest system added negligible yield and that yield collected in July was comparable in one- and two-harvest systems.</p>

Three experiments focused on the contribution of rice productivity to methane emission were conducted in Texas flooded rice paddy soils during 1994-95 growing seasons. Measurements of methane emission from different rice paddy soils during 1991-92 growing seasons (Sass et al., 1994) and from ten different cultivars in 1993 growing season (Willis, 1995; Sass and Fisher, 1995) were cited to quantify the relationships of methane emission with soil, rice cultivar and grain yield. Under the similar soil sand content and agronomic management regime, total seasonal methane emission was positively correlated with rice grain yield and aboveground biomass at harvest. Linear relationships of daily methane emission with aboveground vegetative biomass and root biomass were also observed. On a carbon to carbon basis, the ratio of methane emission to rice net primary productivity was dependent on soil and rice variety, and increased with rice plant development. Models emphasized the contributions of rice plants to the processes of methane production, oxidation and emission and also the influence of environmental factors were developed to predict methane emission from flooded rice fields. Relative effects of soil texture, soil temperature and rice variety on methane production/emission were quantified by three dimensionless indices: soil index, temperature index and variety index, respectively. Model validation against observations from various regions of the world, including Italy, China, Indonesia, Philippines and USA demonstrated that methane emission can be predicted from rice growth and development, cultivar character, soil texture and temperature, and organic matter amendments. Of these, rice growth and development is a principal parameter governing the processes of methane production, oxidation and emission in irrigated rice paddies. Model estimates suggest that annual amount of methane emitted from Chinese rice fields ranges from 7.03 to 13.32 Tg CH$\sb4$ yr$\sp{-1}$ with an average value of 9.45 Tg CH$\sb4$ yr$\sp{-1}$ under permanent irrigation and the majority of methane was emitted in the region located at latitude between 25$\sp\circ$ and 32$\sp\circ$ N. Comparisons of estimated with the observed emissions show that the estimates were in general close to the measurements at most locations.

The sorption/desorption behavior in soil/water systems of $ sp{14}$C-radiolabeled naphthalene and nine of its nitrogen-substituted derivatives; quinoline, isoquinoline, quinoxaline, 1-aminonaphthalene, 2-aminonaphthalene, 1-amino-2-methylnaphthalene, 1-nitronaphthalene, 2-nitronaphthalene and 1-nitro-2-methylnaphthalene were investigated with respect to their physico-chemical properties and the type of interaction they form with soil organic and mineral matter. In turn, an investigation into the effect that sorption/desorption has on the bioavailability of these organic compounds and their mineralization kinetics was conducted. / The non-polar naphthalene, the slightly polar quinoxaline and the three nitronaphthalene compounds sorbed through hydrophobic interaction giving rise to linear sorption isotherms that are typical of partitioning processes in which organic matter functions as a partition medium. Amino-naphthalenes, being polar and slightly basic, adsorbed through cation exchange, hydrogen bonding and formed coordination complexes at soil organic and mineral matter surfaces. Quinoline and isoquinoline, due to their relatively high dipole moment, intercalated the interlamellar space of layered-soil minerals. However, quinoline did not exhibit a specific type of interaction in the interlamellar region, while isoquinoline molecules adsorbed specifically, probably through surface protonation or coordinate covalent bonding with metal ions, and produced micelles upon sorption between the basal planes of clay particles. The discrepancy between the sorption behavior of quinoline and that of isoquinoline is attributed, in part, to the stronger hygroscopic nature of the former compound, its lower acidity constant and to the asymmetric shape of its molecules. / The desorption behaviors of naphthalene and 1-nitro-2-methylnaphthalene, both yielding concave up desorption isotherms, show a readily reversible component that gradually gives way to an irreversible one. The -CH$ sb3$ group, in the case of 1-nitro-2-methylnaphthalene, reduced hysteresis which is attributed to an increase in the hydrophobicity of the molecule and the steric effect that the methyl substitution has on hydrogen bonding. Desorption of quinoline and isoquinoline followed a hysteresis loop (concave down desorption isotherm) such that reversibility increased with decreasing soluble concentrations in the aqueous phase. Amino-naphthalenes adsorbed irreversibly at soil surfaces which is suggestive of strong interaction forces resembling those of a chemical reaction. / The mineralization of all studied compounds gave rise to hyperbolic mineralization curves comprising two phases; an initial fast one followed by a second slow phase with gradually declining rates. / Quinoline maximum mineralization rates were first order with respect to soluble concentrations and the amounts of quinoline mineralized initially coincided with the soluble fraction. In contrast, the amounts of isoqoinoline mineralized during the fast phase exceeded its corresponding fractions in solution. Mineralization exhibited saturation-type kinetics (Michaelis-Menten type) which probably indicates that the biodegradation of isoquinoline was mediated by its sorption in the micellar form. / Finally, naphthalene maximum mineralization rates correlated linearly with total concentrations (soluble and sorbed) and the total amounts mineralized during the fast phase exceeded substantially the soluble fraction. (Abstract shortened by UMI.)