José Ledesma’s paper on shifts in the Dominant Source Layer (DSL) under a future climate is now published in Journal of Hydrology.
The DSL is the riparian zone (RZ) depth layer that contributes most of the water and solute fluxes to streams. Specifically, the DSL concept can be used to explain timing and amount of terrestrial solutes transferred from RZs to headwater streams. Understanding the behavior of the DSL is key to predicting water quality responses to a changing climate. José and colleagues investigated the potential impact of future climate changes on the long-term position of the DSL in a subhumid Mediterranean headwater catchment. They used PERSiST to simulate reference (1981–2000) and future (2081–2100) stream runoff. Possible future conditions were simulated using synthetic temperature, precipitation, and inter-event length scenarios to project possible effects of changes in temperature, rainfall amount, and rainfall event frequency and intensity. Simulated stream runoff was then used to estimate RZ groundwater levels and DSL position. Their simulations suggested that future changes in temperature and precipitation will have similar effects on long-term DSL position. Nearly all scenarios projected drier conditions with less runoff and a deeper DSL. Shallow organic-rich layers in the RZ will likely only be hydrologically activated during sporadic, large rainfall episodes predicted for the most extreme inter-event length scenarios. In the future, terrestrial organic matter inputs to streams will decrease, likely reducing catchment organic matter exports and stream dissolved organic carbon concentrations.