Under the threat of global warming it is vital to determine the impact that future changes in climate may have on the environment and to what extent any adverse effects can be mitigated. In this research an assessment was carried out on the impact that climate trends may have on soil erosion and contaminant transport in India and examined the potential for top soil management practices to improve or maintain soil quality. Historical rainfall data from 50-135 years and extreme temperature data for 103 years were analysed and long term trends were assessed for various aspects of Indian climates using suitable statistical techniques. Results indicated that intra-region variability for extreme monsoon seasonal rainfall is large and mostly exhibited a negative tendency leading to increasing frequency and magnitude of monsoon rainfall deficit and decreasing frequency and magnitude of monsoon rainfall excess everywhere in India except in the peninsular Indian region. This is further exacerbated by increased and more variable extreme temperatures. Intra-region rainfall variability in India is linked to the pacific Southern Oscillation, where the associations of monsoon drought and El-Niño Southern Oscillation (ENSO) in the regions near to coast are greatest. 50-years high resolution daily gridded rainfall data was analysed to set up certain indices for the extreme daily rainfalls to assess their changes for the six gridded regions of Kerala, the extreme south western state of India where monsoon rainfall initiates every year. This was also done for two study sites, namely Bhoj wetland area of west central India and Sukinda chromite mining site of central north east India. Significant decrease was found in monsoon and spring rainfall extremes and increase in winter and autumn rainfall extremes in Kerala that would affect the tendency of change in seasonal total rainfall as well. Decrease in monsoon rainfall in Kerala also indicate that monsoon rainfall is decreasing in India as a whole, increased occurrence of floods is expected in winter and autumn seasons, together with water scarcity are expected to be felt both in spring and monsoon seasons with a delaying monsoon onset in Kerala. Soil erosion studies were conducted for two northern most gridded regions of Kerala as an extended work of the related MPhil study, and contaminant transport with eroded sediments was looked at for the Bhoj and Sukinda sites using RUSLE2 model software and other suitable numerical methods. It was found that soil erosion depended on a complex interaction of climate, soil properties, topography, and cover management. An assessment on extreme climate patterns for Bhoj and Sukinda showed an increasing tendency of seasonal and annual rainfall extremes and temperatures leading to an increasing pattern of soil erosion at both the sites. However, a certain consensus was difficult to reach because of the complex interaction of climate and soil carbon that is a very important deciding factor for soil erosion potential. Vegetative cover and plant residue was found providing essential soil nutrients, enhancing soil properties and retarding rainfall impact on bare top soil leading to reduction of soil erosion. Therefore, a soil erosion and contaminant transport prevention plan should take care of the top soil such that it is not kept bare especially when rainfall intensity is high in a given year. This work as a whole has highlighted the importance of regional climatological analysis with the large scale spatial averages especially at local decision making level, which is very useful for the broad scenarios such as climatological and ecological risk management.

Anthropogenic disturbances are increasing in arid lands, as are expectations to successfully minimize impacts to natural resources and reclaim sites to publicly acceptable levels. This research explores the effectiveness of reclamation practices on a 60 mile natural gas pipeline constructed in September of 2014 that spans from west of Tucson to the border of Mexico. First, a controlled field experiment was conducted to assess the effects of seeding, grazing, and trampling (vehicular, cattle, and human foot traffic) on the reclaimed pipeline Right-Of-Way (ROW). Vegetation establishment (native plant cover; undesirable plant cover; species richness; herbaceous biomass), soil movement, and plant functional group community development was compared among the treatments. Reclaimed ROW areas left to recover without seeding resulted in similar vegetation cover, species, and community composition as undisturbed desert areas, although the presence of undesirable species was greater. The combined impacts of grazing and trampling resulted in reduced vegetation establishment and increased soil erosion. Second, the impacts of the pipeline construction on ephemeral wash channels were analyzed in terms of channel morphology and riparian vegetation changes. Channel cross section dimensions were measured upstream of the ROW, downstream of the ROW, and within the ROW before and after the 2015 Monsoon season to evaluate impacts on channel morphology and erosion processes. High resolution aerial imagery taken before and after pipeline construction was used to evaluate changes in riparian vegetation cover. Reduced herbaceous vegetation cover downstream of the ROW was detected, which may have been the result of increased channel scour within the ROW and increased sediment deposition downstream of the ROW. This research improves our understanding of and may aid in selection of appropriate reclamation practices.

Soil erosion is a major problem confronting land and water resources in many parts of the world and the spatial extent should be assessed and continually monitored. The combination of existing erosion models and remote sensing techniques within a Geographical Information System framework is commonly utilized for erosion risk assessment. In most countries, however, especially in developing countries such as South Africa, there is still an absence of standardized methodological frameworks that deliver comparable results across large areas as a baseline for regional scale monitoring. Assessment at the regional scale is often problematic due to spatial variability of the factors controlling erosion and the lack of input and validation data. Due to limitations of scale at which techniques can be applied and processes assessed, this study implemented a multi-process and multi-scale approach to support establishment of a methodological framework for South African conditions. The approach includes assessment of (i) sheet-rill erosion at a national scale based on the principles and components defined in the (Revised) Universal Soil Loss Equation, (ii) gully erosion in a large catchment located in the Eastern Cape Province by integrating eleven important factors into a GIS, and (iii) sediment migration for a research catchment near Wartburg in KwaZulu-Natal by means of the Soil and Water Assessment Tool. Case Study i illustrates that 20% (26 million ha) of South African land is classified as having a moderate to severe actual erosion risk (emphasizing sheet-rill erosion) and describes the challenges to be overcome in assessment at this scale. Case Study ii identifies severe gully erosion affecting an area of approximately 5 273 ha in the large catchment (Tsitsa valley) of the Eastern Cape Province and highlights gully factors likely to emerge as dominant between continuous gullies and discontinuous gullies. Case Study iii illustrates that a cabbage plot in the upper reaches of a research catchment near Wartburg is a significant sediment source, but is counterbalanced by sinks (river channel and farm dams) downstream. Model assumptions affecting outputs in the context of connectivity between sources and sinks are described. The factor-based nature of this multi-process and -scale approach allowed scrutiny of the role of the main factors in contributing to erosion risk. A combination of poor vegetation cover and susceptible parent material-soil associations are confirmed as the overriding factors in South Africa, and not topography and rainfall as frequently determined in the USA and Europe. A methodological framework with three hierarchical levels is then presented for South Africa. The framework illustrates the most feasible erosion assessment techniques and input datasets for which sufficient spatial information exists, and emphasizes simplicity required for application at a regional scale with proper incorporation of the most important factors. The framework is not interpreted as a single assessment technique but rather as an approach that guides the selection of appropriate techniques and datasets according to the complexity of the erosion processes and scale dependency. It is useful in determining the relative impact of different land use and management scenarios, as well as for comparative purposes under possible future climate change scenarios. / Thesis (PhD)--University of Pretoria, 2012. / Geography, Geoinformatics and Meteorology / unrestricted

This study investigates gully erosion on an east Tennessee hillslope in a humid subtropical climate. The study area is deeply gullied in Ultisols (Acrisol, according to the World Reference Base for Soil), with thirty years of undisturbed erosional history with no efforts to correct or halt the erosion. The objectives are (1) to examine how different gully morphologies (channel, sidewall, and interfluve) behave in response to precipitation-driven erosion, and (2) to identify an appropriate temporal scale at which precipitation-driven erosion can be measured to improve soil loss prediction. Precipitation parameters (total accumulation, duration, average intensity, maximum intensity) extracted from data collected at an on-site weather station were statistically correlated with erosion data. Erosion data were collected from erosion pins installed in four gully systems at 78 locations spanning three different morphological settings: interfluves, channels, and sidewalls. Kruskal-Wallis non-parametric tests and Mann-Whitney U-tests indicated that different morphological settings within the gully system responded differently to precipitation (p<0.00). For channels and sidewalls, regression models relating erosion and precipitation parameters retained antecedent precipitation and precipitation accumulation or duration (R2=0.50, p<0.00 for channels, R2=0.28, p<0.00 for sidewalls) but precipitation intensity variables were not retained in the models. For interfluves, less than 20% of variability in erosion data could be explained by precipitation parameters. Precipitation duration and accumulation (including antecedent precipitation accumulation) were more important than precipitation intensity in initiating and propagating erosion in this geomorphic and climatic setting, but other factors including mass wasting and eolian erosion are likely contributors to erosion. High correlation coefficients between aggregate precipitation parameters and erosion indicate that a suitable temporal scale to relate precipitation to soil erosion is the synoptic time-scale. This scale captures natural precipitation cycles and corresponding measurable soil erosion.

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Soil erosion undermines agricultural productivity, limiting the lifespan of civilizations. For agriculture to be sustainable, soil erosion rates must be low enough to maintain fertile soil, as was present in many agricultural landscapes prior to the initiation of farming. However, there have been few measurements of long-term pre-agricultural erosion rates in major agricultural landscapes. We quantified geological erosion rates in the Midwestern U.S., one of the world’s most productive agricultural areas. We sampled soil profiles from 14 native prairies and measured concentrations of the cosmogenic nuclide 10Be and chemically immobile elements to calculate physical erosion rates. We used the erosion rates and measurements of topographic curvature to estimate a pre- agricultural topographic diffusion coefficient. We find pre-agricultural erosion rates of 0.0001–0.1 mm yr-1 and a site-averaged diffusion coefficient of 0.005 m2 yr-1. The pre- agricultural erosion rates and diffusion coefficient we measured are both orders of magnitude lower than anthropogenic values previously measured in adjacent agricultural fields. The pre-agricultural erosion rates are one to four orders of magnitude lower than the 1 mm yr-1 soil loss tolerance value assigned to these locations by the U.S. Department of Agriculture. Hence, as currently defined, tolerable soil loss will lead to unsustainable erosion of Midwestern soils. However, quantifying natural erosion rates via cosmogenic nuclides provides a means for more robustly defining rates of tolerable soil loss and developing management guidelines that promote soil sustainability.

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