Land Resources and Environmental Sciences Thesis Defense

John Sugden, M.S. Candidate in Land Resources and Environmental Sciences, will defend his thesis, titled "Caveat emptor: Accounting for the influence of two parent materials on soils in Hyalite Canyon, Montana" at 3:00 p.m. in 134 ABB.

John is advised by Dr. Tony Hartshorn.

Abstract

Existing mass balance approaches have only recently begun to quantify soil chemical weathering referenced to two parent materials.  Chemical weathering rates control the delivery of geologically derived nutrients like potassium and phosphorus and play an important role in the carbon cycle.  Differences in immobile elemental chemistry between soil horizons and several parent materials were used to select second parent materials (loess or colluvium as exogenous materials), aside from underlying rock, that best fit each horizon composing five soils on different lithologies in Hyalite Canyon, Montana.  These differences were also used to determine the relative influence of both parent materials on each soil horizon.  A conventional mass balance approach quantified total and elemental chemical weathering for each parent material.  The relative influences of each selected parent, as informed by immobile elements, were used to scale and combine mass fluxes.  Findings suggest that soils on sandstone and limestone have more than 50% loess influence at all depths, while shale has less than 50% loess influence at all depths.  Soils on gneiss and basaltic andesite have a majority loess influence in surface horizons and a majority rock influence at depth.  Total mass losses in all soils are reduced by accounting for loess with the largest mass loss reductions occurring in soil on limestone.  Total, sodium, potassium, and phosphorus mass losses are greatest in soil on sandstone.  Soil textures, as ultimately determined by underlying rock, create five depositional settings that bar the entry of new exogenous materials, incorporate exogenous materials, or readily incorporate and leach exogenous materials from the soil profile.

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