Doctoral Dissertation Research: Geochemical Weathering Controls on Soil Nitrogen and Phosphorus: Possible Implications of Global Change

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Current predictions of climate change in the Arctic estimate mean annual air temperature increases of between 2 and 4.5 degrees C. Although increases in the emission and atmospheric retention of carbon dioxide and other "greenhouse" gases are seen as the primary causes of these increases, the Arctic is one of the world's regions where a net carbon sink is thought to exist, with more carbon is absorbed by plants and the land surface than is emitted. While this sink somewhat ameliorates the impacts of atmospheric carbon accumulation, changes in moisture availability or temperature could alter the dynamics of chemical exchange in the region. This doctoral dissertation research project will examine one facet of chemical exchange in the Arctic, specifically the role of geochemical weathering in controlling the availability of soil nitrogen and phosphorus under a global change scenario in Karkevagge in the Swedish Arctic. This project will utilize both field data collection as well as laboratory simulations to develop a model that predicts the rates of nitrogen and phosphorus release into the environment under changing environmental parameters. This work will build on preliminary fieldwork in Karkevagge investigating the spatial variability of chemical weathering. Previous work has suggested that chemical weathering is an important component of the geomorphic system in this valley and that the patterns of chemical weathering vary spatially. Weathering rates and surface water solute alteration will be investigated by combining in situ weathering measurements made with electron microscopy and stream water chemical measurements. Geochemical models will be used to determine the chemical pathways between the weathering calculations from the electron microprobe and the measured water chemistry. Data on soil temperature, mineralogy, grain size, and water fluxes will be used to generate a laboratory simulation experiment for investigating the potential effects of human-induced environmental change on the release of nitrogen and phosphorus into the environment. These simulations will be used to understand the controls these parameters have on weathering. These simulations can be used as a first-order test of a model predicting weathering rates in natural systems. The models then will be validated with field data. Further simulations investigating the effects of increasing temperature and pC02 on weathering rates will also be undertaken. Data will then be combined into a synthetic model predicting the release of nitrogen and phosphorus into Arctic environments by geochemical weathering. This model will make predictions about the possible alterations to this system by human-induced environmental change. The changes investigated through this project may play a role in altering the carbon sequestration ability of Arctic ecosystems. Arctic ecosystems are one of the major unknowns in global climate models, because the rates of carbon sequestration are largely unknown. As a Doctoral Dissertation Research Improvement award, this award also will provide support to enable a promising student to establish a strong independent research career.