Collaborative Research: Silicate Reaction Kinetics in a Major Groundwater Aquifer

0001080凡勃伦硅酸盐矿物的风化速率对地下水和地表水质量、养分有效性、全球碳循环及其对地质时期全球气候变化的影响具有重要控制作用。 然而，从流域和土壤剖面得出的风化速率比实验室测量的要慢。 理解这种巨大的差异仍然是现代地球化学中的一个基本问题，阻碍了我们定量地理解和预测表面活性剂过程和环境变化的能力。为了提供对差异的见解，我们建议在相对简单和良好的化学和水文约束的大型含水层系统中研究原位硅酸盐溶解和沉淀速率。 选定的现场是位于亚利桑那州北方的砂岩含水层，主要由纳瓦霍砂岩组成。 这一含水层中的地下水最佳停留时间约为35 000年。 由于饱和的水文环境和异常丰富的数据，首先从该含水层得出的动力学速率常数将比在流域和土壤剖面中受到更好的约束。 约翰霍普金斯的一种新的透射电子显微镜，具有0.12 nm成像和1 nm成分映射分辨率的能力，将提供风化长石微观结构和精细尺度化学变化的原子尺度信息。

0001080VeblenWeathering rates for silicate minerals exert important controls on groundwater and surface water quality, nutrient availability, and the global carbon cycling and its impact on global climatic changes over geological time. Yet, weathering rates derived from watersheds and soil profiles are several others of magnitude slower than laboratory measurements. Understanding this large discrepancy remains a fundamental problem in modern geochemistry, hampering our ability to understand and predict surficial processes and environmental changes quantitatively.To provide insights into discrepancy, we propose to study the in situ silicate dissolution and precipitation rates in large aquifer system with relatively simple and well-constrained chemistry and hydrology. The chosen field site is a sandstone aquifer, located in northern Arizona and mostly composed of the Navajo sandstone. Groundwater in this aquifer has an optimal residence time up to approximately 35,000 years. The kinetic rate constants derived from this aquifer first will be much better constrained than in watersheds and soil profiles because of the saturated hydrologic environment and unusually abundant data. A new transmission electron microscope at John Hopkins, with capabilities 0.12nm imaging and 1 nm compositional mapping resolution, will provide atomic scale information of microstructure and fine-scale chemical variations at weather feldspar.