Collaborative Research: Silicate Reactions Kinetics in a Major Groundwater Aquifer

0003816硅酸盐矿物的风化速率对地下水和地表水的质量、养分的可用性、全球碳循环及其在地质时期对全球气候变化的影响起着重要的控制作用。然而，从流域和土壤剖面得出的风化速度比实验室测量的慢了几个数量级。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，阻碍了我们定量了解和预测地表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约束的化学和水文学的大型含水层系统中研究现场硅酸盐溶解和沉淀速率。选定的场地是一个砂岩含水层，位于亚利桑那州北部，主要由纳瓦霍砂岩组成。地下水在该含水层的最佳停留时间长达约35,000年。由于饱和的水文环境和异常丰富的数据，首先从该含水层获得的动力学速率常数将比在流域和土壤剖面中得到的约束要好得多。约翰霍普金斯大学的一种新的透射式电子显微镜，具有0.12 nm的成像能力和1 nm的成分测绘分辨率，将提供气象长石的微观结构和精细尺度化学变化的原子尺度信息。

0003816 ZhuWeathering 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.