Physical heterogeneity in the subsurface creates preferential flowpaths that have the potential to impact mineral dissolution rates. Previous studies using numerical simulations have found that physical heterogeneity can reduce the mineral dissolution rate by an order of magnitude relative to homogeneous simulations. These findings indicate that the long-studied difference between laboratory dissolution rates, and field dissolution rates could be the result of processes caused by heterogeneity in the subsurface, specifically variable fluid flowpaths controlling the approach to fluid saturation. In this study, we investigate the behavior of mineral dissolution rates in heterogeneous fractured rock domains through time. Domains containing albite and non-reactive quartz evolve through 1 million years as rainwater percolates through the system and allows for albite dissolution and secondary mineral precipitation. Fracture density and orientation vary in the domains to determine the importance of fracture topology on mineral dissolution rates. In addition, the volumetric flow rate through each domain is systematically varied to determine the impact of changing flow conditions relative to reaction rates.

Temporal analysis of the simulation results indicates that domain-averaged dissolution rates decrease with time, similarly to what has been observed in field systems and long-term laboratory experiments. Spatial analysis of the mineral dissolution rates throughout the simulations, indicates that fractures remain reaction limited through most of the simulation, while the matrix is transport limited. Since most of the domain consists of matrix, the domain is transport limited as a whole. However, speciation of the flux-weighted fluid leaving the domain indicates that the fluid is undersaturated with respect to albite, potentially leading to an interpretation that dissolution within the domain is not transport limited. The direct comparison of the spatial distribution of rates and the integrated flux signal appears contradictory, however, this approach reveals that the transport-limited signal that persists through most of the domain is diluted by the higher volume of water that leaves the system through fast-flowing fracture pathways compared to the mass of solutes diffusing out of disconnected portions of the domain. This parsing of the domain into transport-limited regions and kinetic-limited regions, induced by physical heterogeneity, has the potential to further explain the differences between laboratory dissolution rates and field dissolution rates. It is possible that mineral weathering is dominated by transport-limited conditions in many field systems with disconnected fluid pathways where reaction rates are slow due to a buildup of solutes, despite integrated signals in streams indicating far-from equilibrium conditions for dissolution reactions of primary minerals.

地下的物理异质性产生了可能影响矿物溶解速率的优先流动路径。先前使用数值模拟的研究发现，相对于均质模拟，物理异质性可以将矿物溶解速率降低一个数量级。这些发现表明，长期研究的实验室溶解速率和现场溶解速率之间的差异可能是由地下非均质性引起的过程的结果，特别是控制流体饱和度方法的可变流体流动路径。在这项研究中，我们调查了非均质裂隙岩石域中矿物溶解速率随时间的变化。含有钠长石和非反应性石英的区域随着雨水渗入系统而演变了 100 万年，并允许钠长石溶解和次生矿物沉淀。各域中的裂缝密度和方向各不相同，以确定裂缝拓扑对矿物溶解速率的重要性。此外，系统地改变通过每个域的体积流速，以确定相对于反应速率变化的流动条件的影响。

模拟结果的时间分析表明，域平均溶解速率随着时间的推移而降低，类似于在现场系统和长期实验室实验中观察到的情况。整个模拟过程中矿物溶解速率的空间分析表明，在大多数模拟过程中，裂缝仍然是反应受限的，而基质是输运受限的。由于大部分域由矩阵组成，因此域作为一个整体受到传输限制。然而，离开域的流量加权流体的形态表明流体相对于钠长石是不饱和的，这可能导致域内溶解不受输运限制的解释。然而，速率空间分布和积分通量信号的直接比较似乎是矛盾的，这种方法表明，与从域的不连接部分扩散出的溶质质量相比，通过快速流动的断裂路径离开系统的水量更大，从而稀释了通过大部分域持续存在的传输受限信号。这种由物理异质性引起的域解析为传输受限区域和动力学受限区域，有可能进一步解释实验室溶解速率和现场溶解速率之间的差异。在许多流体通路不连接的现场系统中，矿物风化可能受输运限制条件的支配，其中由于溶质的积累，反应速率很慢，尽管流中的综合信号表明原生矿物的溶解反应远非平衡条件.