Raindrop kinetic energy and sheet flow can disintegrate aggregates during interrill erosion, a process responsible for non point source pollution. Also, the dissolution process during aggregate wetting can affect interrill erosion. These factors can be responsible for changes in particle size distribution in the sediment, especially when different tillage systems are compared. The effect of soil tillage and management on soil properties is not uniform, which determine a wide range of runoff and sediment delivery rate. Variety in these rates can be associated with pore functions and their interactions with aggregate stability. One of the objectives of this study was to analyze the wetting behavior of soil aggregates from soils under conventional tillage compared with soils under no tillage. It was expected that the wetting rate is a function of pore system and that different tillage systems would affect the soil wetting behavior based on their impact on soil structure and shape. The second objective was to analyze the relationships among soil wetting rate, particle movement, organic carbon (OC) and iron release with the sediment produced via interrill erosion. A rainfall simulation experiment was performed in the field to determine the effect of low and fast soil wetting on total soil loss through high and low kinetic rainfall energy, sediment particle size distribution and OC loss. Two soils that differed in soil textural composition and that were under conventional and no tillage were investigated. Soil loss depended largely on soil characteristics and wetting rate. Particle size distribution of sediment was changed by treatment and the proportion of particles smaller than 0.053 mm increased over time, at any kinetic energy wetting level. Temporal OC and iron release were constant, which required a continuous source principally due to aggregate slaking. An empirical model was proposed to improve an interrill erosion equation by using a bond-dissolution mechanism that identified soil as a regulator of particle release.

This thesis explored the impacts of forest harvesting on gaseous elemental mercury emissions from forest soils in both field and laboratory studies, through novel use of enriched mercury isotope tracers. Forest floor Hg emissions, sourced from legacy deposition, increased proportionally to the vegetation quantity removed, with biomass harvesting most exacerbating emissions. Contemporary Hg deposition did not appear to be influenced by harvesting. Some of the tracer was rapidly lost to the atmosphere (~8%), but most was sequestered within the soil. Two regimes facilitating Hg emissions were observed in low-light conditions. Under extremely dry conditions deeper Hg sources (> 2cm depth) were as equally susceptible to emission as shallower sources. Following wetting to field capacity, emissions were elevated only from shallow sources, likely as a result of upward capillary transport. Impacts of vegetation removal and dry fluxes are previously uncharacterized and may constitute large additional sources to regional atmospheric Hg cycling.

This thesis explored the impacts of forest harvesting on gaseous elemental mercury emissions from forest soils in both field and laboratory studies, through novel use of enriched mercury isotope tracers. Forest floor Hg emissions, sourced from legacy deposition, increased proportionally to the vegetation quantity removed, with biomass harvesting most exacerbating emissions. Contemporary Hg deposition did not appear to be influenced by harvesting. Some of the tracer was rapidly lost to the atmosphere (~8%), but most was sequestered within the soil. Two regimes facilitating Hg emissions were observed in low-light conditions. Under extremely dry conditions deeper Hg sources (> 2cm depth) were as equally susceptible to emission as shallower sources. Following wetting to field capacity, emissions were elevated only from shallow sources, likely as a result of upward capillary transport. Impacts of vegetation removal and dry fluxes are previously uncharacterized and may constitute large additional sources to regional atmospheric Hg cycling.