Advances in soil genesis and morphology and their impact on the water cycle

Abstract

Broad-scale approaches to soil genesis and morphology and their impact on the water cycle are critically important to address widespread ecosystem service challenges in the future especially given increasing climatic and land-use pressures on soils. Thus, the general aim of this dissertation was to quantify pedogenic development and examine the impact of soil properties and soil-climate interactions on the water cycle at continental, basin, and ecoregion scales. I utilized continental-scale data to develop and evaluate horizon and profile development indices based primarily on relative horizon properties instead of parent material information. These indices—which reflect generalizable pedogenic processes—are valid proxies of soil development applicable at large geographic scales and may aid in numerous broad-scale applications including pedogenic modeling, use in pedotransfer functions, identification of anomalies, and estimation of surface soil ages, and have the potential to address the impact of climate and land-use changes on pedogenesis. Combined effects of near-surface soil organic carbon (SOC) and ped roundness were used to explain systematic differences in long-term water balance (as represented within the Budyko framework) at a continental scale and explore potentially important feedbacks to climate. Evidence presented across basins of the conterminous US point to the need to include soil structural information in Earth system models. Effective porosity (EP) determined from continental and ecoregion-stratified data show that surface and subsurface macroporosity is strongly influenced by the fraction of clay complexed with SOC. The relationship between EP and this fraction could serve as a framework for understanding soil macropore sensitivity to additions of SOC and its incorporation into hydrologic and Earth system models has the potential to more effectively predict land use- and climate-induced changes to soil hydraulic properties and alterations to water cycling across scales. These findings, associated implications, and future research directions are explored.