The Impact of Riparian Vegetation on Spatial and Temporal Hyporheic Zone Fluctuations

Abstract:

In semi-arid climates, intermittent headwater streams play a vital role in supplying water to drier downstream ecosystems. Along these important stream corridors, mixing between groundwater and surface water can occur in the hyporheic zone (HZ), the area underneath and adjacent to the stream, reaching into the riparian area. The HZ in the riparian area helps establish habitat for vegetation by providing easily accessible soil water for plant consumption. The spatial extent of the HZ is known to change seasonally due to fluctuations in discharge and water uptake by vegetation, but its location in space and time is largely unknown. Our research aims to identify the impact of riparian vegetation on the changes in the HZ in both space and time in a small headwater catchment in the Laramie Mountains in southeast Wyoming. We are monitoring the bidirectionality of flow in the HZ along six stream reaches, four with willows, two without appreciable riparian vegetation, using a suite of nested soil moisture probes and piezometers while also monitoring the variability of stream flow throughout the runoff season. Meteorological variables for evapotranspiration via Bowen Ratio Energy Balance are recorded at a nearby tower. Along with the hydrologic data, we are using a vadose zone hydrologic model, coupled with detailed vegetation characteristics of each plot to model the ecohydrologic processes in the HZ. We present results from the first full year of the study, comparing willow and non-willow plots and how they respond at high and low flow.