ISTOPore Seminar by Jennifer Druhan

Abstract

In upland environments, roots commonly extend deep below soil into partially saturated bedrock. This Bedrock Vadose Zone (BVZ) has been shown to store and circulate water, host organic carbon respiration and serve as a critical source of rock-derived nutrients. However, the extent to which deep roots influence chemical weathering rates remains poorly understood. Here, we report 4 years of depth-resolved major ion chemistry over a 16-m thick BVZ hosting a deep rhizosphere in a catchment subject to a Mediterranean climate. Contrary to prior inferences, we show that water resides for a sufficiently long time in the BVZ to weather silicate minerals. CO2(g) produced at depth in association with deeply rooted trees is a major contributor to this mineral alteration, indicating that this ecosystem enhances the breakdown of rock in the BVZ. These data allow development and validation of a reactive transport model (RTM), which we use to link the internal weathering dynamics of the watershed to stream concentration-discharge relationships guided by the stable isotope ratios of lithium.