Contrasting the hydrologic response due to land cover and climate change in a mountain headwaters system

Land cover change due to drought and insect-induced tree mortality or altered vegetation succession is one of the many consequences of anthropogenic climate change. While the hydrologic response to land cover change and increases in temperature have been explored independently, few studies have compared these two impacts in a systematic manner. These changes are particularly important in snow-dominated, headwaters systems that provide streamflow for continental river systems. Here we study the hydrologic impacts of both vegetation change and climate warming along three transects in a mountain headwaters watershed using an integrated hydrologic model. Results show that while impacts due to warming generally outweigh those resulting from vegetation change, the inherent variability within the transects provides varying degrees of response. The combination of both vegetation change and warming results in greater changes to streamflow amount and timing than either impact individually, indicating a nonlinear response from these systems to multiple perturbations. The complexity of response underscores the need to integrate observational data and the challenge of deciphering hydrologic impacts from proxy studies

Fluid-driven metamorphism of the continental crust governed by nanoscale fluid flow

The transport of fluids through the Earth’s crust controls the redistribution of elements to form mineral and hydrocarbon deposits, the release and sequestration of greenhouse gases, and facilitates metamorphic reactions that influence lithospheric rheology. In permeable systems with a well-connected porosity, fluid transport is largely driven by fluid pressure gradients. In less permeable rocks, deformation may induce permeability by creating interconnected heterogeneities, but without these perturbations, mass transport is limited along grain boundaries or relies on transformation processes that self-generate transient fluid pathways. The latter can facilitate large-scale fluid and mass transport in nominally impermeable rocks without large-scale fluid transport pathways. Here, we show that pervasive, fluid-driven metamorphism of crustal igneous rocks is directly coupled to the production of nanoscale porosity. Using multi-dimensional nano-imaging and molecular dynamics simulations, we demonstrate that in feldspar, the most abundant mineral family in the Earth’s crust, electrokinetic transport through reaction-induced nanopores (<100 nm) can potentially be significant. This suggests that metamorphic fluid flow and fluid-mediated mineral transformation reactions can be considerably influenced by nanofluidic transport phenomena