Several soil chronosequences were studied in southern California to determine the relative impacts of time and climatic change on soil genesis. Studying soil development in climatic regimes that vary from the moist, xeric climate of the coastal basins and Transverse Ranges to the hot, arid climate of the interior deserts of southern California provide data useful for evaluation of the impact of climatic change as well as time on pedogenesis. Seven distinctive stages of soil development are recognized in the study area. The first three occur in Holocene soils, and the last four are associated with late to mid-Pleistocene geomorphic surfaces. A distinct pattern of secondary soil mineral authigenesis is observed in increasingly older soils. The rapid formation of vermiculite and iron oxyhydroxides in xeric climates is attributed to rapid alteration of unstable Fe-bearing aluminosilicates. Continuous weathering of abundant feldspars results in a predominance of neogenetic kaolinite in mid-Pleistocene soils. Slightly acidic to mildly alkaline soil pH, rapid hydrolysis, and availablity of organic complexes result in formation of significant amounts of metastable ferrihydrite in young Holocene and late Pleistocene soils. Ferrihydrite dehydration and crystal aggregation result in hematite formation and increasingly lower Fe(,2)O(,3)o:Fe(,2)O(,3)d ratios. Arid climatic regimes are conductive to minimal chemical weathering. Clay/iron oxhydroxide regression analyses and mass balance calculations show that much of the silicate clay and secondary carbonate have been derived from external sources rather than by chemical weathering. Clay mineral authigenesis is characterized primarily by conversion of montmorillonite to palygorskite. A compartmental model developed in this study accurately predicts calcic horizon development under Holocene soil water balance characteristics. Results of model predictions indicate that the distribution of carbonate observed in latest Pleistocene soils is related to past changes in climate. In addition, mass balance calculations suggest that large decreases in chemical reaction rates in soils due to soil temperature decreases may well be offset by increases in the magnitude of weathering. However, the results of this study indicate that calcium carbonate provides the most sensitive index of past climates when compared to other indices and that temporal change in climate has significantly influenced soil development in southern California.

Globally, the forestry sector is the second largest contributor of greenhouse gases, and sustainable forest management is a major target of international environmental policy. However, there is the assumption underlying many policy recommendations that an increase in above-ground carbon stocks correspond to long term increases in ecosystem carbon stocks, the majority of which is stored in soils. We analyzed soil carbon and nitrogen dynamics in forest soils that had undergone twenty years of organic inputs manipulations as part of the Detritus Input and Removal Treatment (DIRT) network. There was no statistically significant effect of the rate of litter or root inputs on the carbon or nitrogen in bulk soil, on respiration rates of soil in laboratory incubations, on the non-hydrolyzed fraction of soil organic matter, or on any organic matter associated with any density. However, there is evidence for positive priming due to increased litter inputs; doubling the rate of litter inputs decreased C and N contents of bulk soil and decreased respiration rates of soil. Furthermore, there is evidence that roots influence soil organic matter dynamics more strongly than above-ground inputs. Both of these results trends match data from other DIRT sites, and are supported by the literature. / Graduation date: 2012

Thesis (Ph. D.)--University of Oregon, 2008. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 128-156). Also available online in Scholars' Bank; and in ProQuest, free to University of Oregon users.

Land-atmosphere interaction includes complex feedbacks among radiative, hydrological, and ecological processes, and the understanding of it is hindered by many factors such as the heterogeneity of land surface properties, the chaotic nature of the atmosphere, and the lack of observational data. In this study, several different methods are used to investigate the land-atmosphere interaction processes and their relationship with climate variability. Firstly, a simple one-dimensional model is developed to simulate the dominant soil-vegetation-atmosphere interaction processes in the warm climate. Although the physical processes are described coarsely, the model can be more easily used to find some relationships which may be drown out or distorted by noise. The influence of land on climate variability mainly lies in it memory, which is greatly related with the atmospheric forcing, so this model is used to investigate the influence of different forcing strengths on land-atmosphere interaction and its difference at different land covers. The findings from the simple model can provide guidance for other studies. The second part of the study compares a lagged soil moisture-precipitation (S-P) correlation (soil moisture in current day and precipitation in future 30 days) in three atmospheric reanalysis products (ERA-40, NCEP/DOE reanalysis-2, and North American Regional Reanalysis (NARR)), Global Soil Wetness Project Phase 2 (GSWP-2) data, and NCAR CAM3 simulations. Different datasets and model simulations come to a similar negative-dominant S-P correlation pattern. This is different from the traditional view that the soil moisture should have positive influence on future precipitation. Further analysis shows that this correlation pattern is not caused by the soil moisture feedback but due to the combined effect of the precipitation oscillation and the memory of soil moisture. Theoretical analysis confirms the above results and finds that the precipitation time series with the strongest oscillation at 32-60 day period is most likely to induce a significantly negative S-P correlation, and regions with longer soil water retention time are more likely to have a significantly negative S-P correlation. This study illustrates that a lagged correlation does not always indicate a causal relation.

Thesis (MScAgric)--Stellenbosch University, 1932. / No Abstract Available