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

目前对北极气候变化的预测估计平均气温每年升高2至4.5摄氏度。尽管二氧化碳和其他“温室”气体的排放和大气滞留量的增加被认为是这些升高的主要原因，但北极被认为是世界上存在净碳汇的地区之一，植物和陆地表面吸收的碳比排放的碳多。虽然这种汇在一定程度上改善了大气碳积累的影响，但水分可用性或温度的变化可能会改变该地区化学交换的动态。这个博士论文研究项目将研究北极化学交换的一个方面，特别是在瑞典北极地区Karkevagge的全球变化情景下，地球化学风化在控制土壤氮和磷可用性中的作用。该项目将利用现场数据收集和实验室模拟来开发一个模型，预测在变化的环境参数下氮和磷释放到环境中的速率。这项工作将建立在Karkevagge的初步野外工作基础上，调查化学风化的空间变异性。前人的研究表明，化学风化是该峡谷地貌系统的重要组成部分，化学风化模式具有空间差异性。风化速率和地表水溶质蚀变将通过结合现场风化测量与电子显微镜和水流化学测量来研究。地球化学模型将用于确定从电子显微探针计算的风化和测量的水化学之间的化学途径。有关土壤温度、矿物学、粒度和水通量的数据将用于进行实验室模拟实验，以调查人类引起的环境变化对向环境中释放氮和磷的潜在影响。这些模拟将用于理解这些参数对风化的控制。这些模拟可以用作预测自然系统风化速率的模型的一阶检验。然后将用现场数据验证这些模型。还将进行进一步的模拟，研究温度升高和pC02对风化速率的影响。然后，这些数据将被整合到一个综合模型中，预测地球化学风化作用下氮和磷向北极环境的释放。该模型将对人类引起的环境变化可能对该系统造成的变化作出预测。通过该项目调查的变化可能在改变北极生态系统的碳固存能力方面发挥作用。北极生态系统是全球气候模型中的主要未知因素之一，因为碳固存率在很大程度上是未知的。作为博士论文研究改进奖，该奖项还将提供支持，使有前途的学生建立一个强大的独立研究生涯。

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.