Ecohydrologic controls on groundwater-surface water interactions along a non-perennial mountain stream
Abstract
With projected changes in precipitation amount and timing, as well as increased temperatures driving higher evaporative demand, the water balance of mountain headwater catchments is changing. In catchments drained by non-perennial streams, changes to the water balance are poised to affect the timing and length of drydown. Several studies have investigated the influence of soils, geology, and runoff generation processes on drying patterns; however, we still have a limited understanding of how atmospheric losses, particularly losses associated with near-stream plant water use, impact stream drying. This study aims to provide a process-based approach to quantify the ecohydrology of a non-perennial, riparian mountain headwater system. Our extensive monitoring of groundwater dynamics across a range of flow conditions, paired with riparian plant water use measurements shows a strong coupling of groundwater, surface water, and riparian sap flux. Across three focal transects, the correlation between sap flow and stream water level strengthens during drydown, with the strongest correlation occurring at the wettest site. This correlation corresponds to daily fluctuations in not only water levels but also diel differences in the channel water balance, with more streamflow losses occurring during the day than at night. Further, both vertical and lateral head gradients across the hillslope-riparian-stream transition reveal more variability in the driest site, and increasingly losing head gradients in the wetter stream sites. These preliminary results support a conceptual model of stream drying that integrates vertical losses from plant transpiration as an active control on stream drying. A better understanding of near-stream plant water use and groundwater dynamics in these highly variable systems will inform more sustainable riparian restoration methods, improve flow forecasts for communities reliant on mountain streamflow, and offer insight into how the hydrology and ecology of non-perennial streams will respond to changing climatic conditions.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFM.H46F..08N