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Soils are a critical resource for supporting ecosystems, agricultural systems, and human wellbeing. However, these same soils have been degraded by human activities throughout human history. Despite the rapid development of global models that include dynamic changes in land use and land cover (LULC) and biogeochemical processes to assess climate and hydrological impacts, soil properties are often assumed to be spatially or temporally constant. These assumptions can affect the results of model projections, impact assessments and underestimate the human impact on Earth systems. This study reveals the physical impacts of human-altered soil conditions on the global water balance through a meta-analysis study and soil degradation modeling. We link major global LULCs to four hydrologic soil groups: sandy (sand, sandy loam, and loamy sand), loamy (loam, silty loam, and silt)), clayey soils (clay, sandy clay, clay loam, silty clay, and silty clay loam), and sandy clay loam) from 850 to 2015 AD, and identified loamy and clayey soils as the preferred soils for most human land uses. Humans selectively use those soils for intensive agriculture and pasture activities, while grazing occurs on sandier soils. To simulate the impact of human activities on soils, several soil change models were built for soil organic carbon (SOC) content, soil texture (sand, silt, and clay), and soil bulk density from meta-analyses of site observations. The models were applied globally based on the LULC and soil relations, global environmental and soil conditions, and LULC distributions. Pedotransfer functions were applied to estimate soil water-holding capacity using those soil properties, then a Thornthwaite-type water balance model was used to assess the impacts of soil degradation on the global water balance. Results show that under a high-intensity LULC scenario (conventional tillage on croplands and heavy grazing), SOC decreases by 363 Pg and water deficit increases 78 km3 globally. The impacts on SOC and deficit are reduced to 213 Pg and 51 km3, respectively, when reducing land-use intensity by substituting animal ploughing/no-till and light grazing for conventional tillage and heavy grazing. Impacts from other LULC types are identical for these two LULC scenarios. Development of this history between LULC and soil properties allows for improved simulation of human impacts on global water, energy, and biogeochemical cycles. The results of the water balance simulations demonstrate how different soils representations in models can significantly alter the estimates of global evapotranspiration, water deficit, and surplus. This study contributes to developing a better understanding of the processes by which human-induced soil degradation impacts climate/hydrological models and providing a mechanism to better assess the impacts of humans on the Earth system. The outcome will also complement numerous ongoing global studies that evaluate the impacts of climate change on water resources and society. / Graduate / 2023-08-09

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Carbon accreditation of forest development projects is essential for sequestering atmospheric CO2 under the provisions of the Kyoto Protocol. The carbon sequestration potential of surface coal-mined lands is not well known. The purpose of this work was to determine how to measure carbon sequestration and estimate the additional amount that could be sequestered using different reforestation methods compared to the common practice of establishing grasslands. I developed a thermal oxidation technique for differentiating sequestered soil carbon from inorganic and fossilized carbon found at high levels in mine soils along with a geospatial and statistical protocol for carbon monitoring and accounting. I used existing tree, litter, and soil carbon data for 14 mined and 8 adjacent, non-mined forests in the Midwestern and Eastern coal regions to determine, and model sequestered carbon across the spectrum of site index and stand age in pine, mixed, and hardwood forest stands. Finally, I developed the framework of a decision support system consisting of the first iteration of a dynamic model to predict carbon sequestration for a 60-year period for three forest types (white pine, hybrid poplar, and native hardwoods) at three levels of management intensity: low (weed control), medium (weed control and tillage) and high (weed control, tillage, and fertilization). On average, the highest amount of ecosystem carbon on mined land was sequestered by pine stands (148 Mg ha-1), followed by hardwood (130 Mg ha-1) and mixed stands (118 Mg ha-1). Non-mined hardwood stands contained 210 Mg C ha-1, which was about 62% higher than the average of all mined stands. After 60 years, the net carbon in ecosystem components, wood products, and landfills ranged from 20 to 235 Mg ha-1 among all scenarios. The highest net amount of carbon was estimated under mixed hardwood vegetation established by the highest intensity treatment. Under this scenario, a surface-mined land of average site quality would sequester net carbon stock at 235 Mg C ha-1, at a rate of 3.9 Mg C ha-1 yr-1, which was 100% greater than a grassland scenario. Reforestation is a logical choice for mined land reclamation if carbon sequestration is a management objective. / Ph. D.