Quantifying Geomorphic Controls on Time in Weathering Systems

AbstractThe time minerals spend in the weathering zone is crucial in determining soil biogeochemical cycles, solid state chemistry and soil texture. This length of time is closely related to erosion rates and can be modulated by sediment transport, mixing rates within the soil and the temporal evolution of erosion. Here we describe how time length can be approximated using geomorphic metrics and how topography reveals changing residence times of minerals within soils. We also show model simulations from a field site in California that can reproduce observed solid state geochemistry in the eroding portion of the landscape

Establishing the validity of the Personality Assessment Inventory drug and alcohol scales in a corrections sample

Abstract Although not originally designed for implementation in correctional settings, researchers and clinicians have begun to use the Personality Assessment Inventory (PAI) to assess offenders. A relatively small number of studies have made attempts to validate the alcohol and drug abuse scales of the PAI, and only a very few studies have validated those scales in nonclinical correctional samples. The current study examined evidence of convergent and discriminant validity for the substance abuse scales on the PAI in a large, nonclinical sample of offenders. The net sample for the current study consisted of 1,120 federal inmates. Both the drug abuse and alcohol scales showed good convergent validity through high correlations with relevant proximal and distal indicators of substance use across multiple measures from several data sources. Discriminant validity was established as neither scale showed any "erroneous" correlations after controlling for the other scale. Implications for future research and practice are discussed

Evolution of hillslope soils: The geomorphic theater and the geochemical play

How and how fast do hillslope soils form as the landscape’s morphology changes over time? Here results are shown from an ongoing study that simultaneously examines the morphologic and geochemical evolution of soil mantled hillslopes that have been exposed to distinctively different denudation history. In Northern Sierra Nevada, California, the authors are investigating a tributary basin to the Middle Fork Feather River. A major incision signal from the river is well marked in a knickpoint within the tributary basin which stretches from its mouth to the Feather River at an elevation of 700 m to the plateau at an elevation of 1500 m. Hillslopes are significantly steeper below the knickpoint. The area’s total denudation rates are currently being constrained using cosmogenic radio nuclides, but a previous study suggested an order of magnitude difference in total denudation rates below and above the knickpoint. When compared with topographic attributes calculated from LIDAR data, physical erosion rates can be modeled as a linear function of ridge top curvature. Surprisingly, over the wide range of total denudation rates, soil thicknesses do not vary significantly until a threshold point where soil mantled landscapes abruptly shift to bedrock dominated landscapes. Bioturbation by tree falls appear to buffer soil thickness over the wide range of physical soil erosion rates. From three hillslopes with different physical erosion rates, the concentrations of Zr, which were considered conserved during dissolution and leaching, were determined and used as a proxy for the degree of mass losses via chemical denudation. There is a general trend that colluvial soils along the hillslopes with lower physical erosion rates are enriched in fine size fractions, Zr, and pedogenic crystalline Fe oxides. Likewise, the saprolites show greater degrees of chemical denudation at the sites above the knickpoint, presumably because of the saprolites’ longer turnover time in the slowly eroding landscapes. In the two steep hillslopes below the knickpoint, no significant or systematic topgraphic trends were found for soil geochemistry. However, soils show increasing Zr enrichment in the downslope direction in the hillslope above the knickpoint, which suggests a critical denudation rate beyond which soils’ turnover time is too short to develop a geochemical catena. As detailed CRN-based soil production rates and catchment scale denudation rates are acquired, the data will be combined with a mass balance model to calculate the rates of chemical denudation and weathering in soils and saprolites along the denudation gradient

Impact of change in erosion rate and landscape steepness on hillslope and fluvial sediments grain size in the Feather River Basin (Sierra Nevada, California)

The characteristics of the sediment transported by rivers (e.g. sediment flux, grain size distribution – GSD) dictate whether rivers aggrade or erode their substrate. They also condition the architecture and properties of sedimentary successions in basins. In this study, we investigate the relationship between landscape steepness and the grain size of hillslope and fluvial sediments. The study area is located within the Feather River basin in northern California, and studied basins are underlain exclusively by tonalite lithology. Erosion rates in the study area vary over an order of magnitude, from > 250 mm ka<sub>−1</sub> in the Feather River canyon to < 15 mm ka<sub>−1</sub> on an adjacent low-relief plateau. We find that the coarseness of hillslope sediment increases with increasing hillslope steepness and erosion rates. We hypothesise that, in our soil samples, the measured 10-fold increase in D<sub>50</sub> and doubling of the amount of fragments larger than 1 mm when slope increases from 0.38 to 0.83 m m<sub>−1</sub> is due to a decrease in the residence time of rock fragments, causing particles to be exposed for shorter periods of time to processes that can reduce grain size. For slopes in excess of 0.7 m m<sub>−1</sub> , landslides and scree cones supply much coarser sediment to rivers, with D<sub>50</sub> and D<sub>84</sub> more than one order of magnitude larger than in soils. In the tributary basins of the Feather River, a prominent break in slope developed in response to the rapid incision of the Feather River. Downstream of the break in slope, fluvial sediment grain size increases, due to an increase in flow competence (mostly driven by channel steepening) as well as a change in sediment source and in sediment dynamics: on the plateau upstream of the break in slope, rivers transport easily mobilised fine-grained sediment derived exclusively from soils. Downstream of the break in slope, mass wasting processes supply a wide range of grain sizes that rivers entrain selectively, depending on the competence of their flow. Our results also suggest that, in this study site, hillslopes respond rapidly to an increase in the rate of base-level lowering compared to rivers

A social history of the alternative press in Kansas, 1875-1922

Typescript (photocopy).Digitized by Kansas Correctional Industrie

Contributions of floodplain stratigraphy and evolution to the spatial patterns of groundwater arsenic in Araihazar, Bangladesh

Extreme spatial heterogeneity has emerged as a salient characteristic of groundwater arsenic in many complex fluviodeltaic environments. Here we examine patterns of arsenic heterogeneity in the shallow (< 23 m) groundwaters of a well-studied floodplain setting in Araihazar, Bangladesh. Ninetyfive augers and 200 shallow wells sampled at spacings of 101−103 m in the 25 km2 area indicate that the concentration of arsenic in shallow groundwater largely varies with the grain size, thickness, and distribution of fine-grained ( < 63 µm) sediments that overlie buried aquifer sands. The overall pattern shows that lower arsenic concentrations are typically found where aquifer sands outcrop at or near the surface, whereas higher arsenic levels typically underlie, or are adjacent to thicker, fine-grained deposits. Furthermore, chronostratigraphic reconstructions of aquifer sediments indicate that sediment distribution, and consequently the patterning of dissolved arsenic, is readily explained in the context of local river history and flood-plain development within the past 1000 yr. An important implication is that complex patterns of groundwater arsenic in afflicted fluviodeltaic settings can be better understood through reconstructions of local aquifer history. This finding is especially relevant because the village and tube-well locations are closely linked with surface landforms such as former levees and bars. An additional and worrisome finding is that the artificial filling of villages to protect from flooding can mimic the natural fine-grained stratigraphy commonly associated with high concentrations of arsenic