Non-perennial Streams Through Space and Time

Abstract

The majority of river networks globally – from headwater streams to lowland alluvial rivers – cease to flow through space or time. These non-perennial rivers exhibit a range of wetting and drying patterns that influence and are ultimately influenced by water quantity, geomorphic processes, and vegetation dynamics. As the frequency and severity of disturbances such as drought increase, understanding the complex interactions between streamflow, morphology, and vegetation are crucial to predicting how non-perennial ecosystems will respond.  Here, we discuss the drivers of river corridor morphology and streamflow in non-perennial stream networks, with a particular focus on the influence of riparian vegetation dynamics and drought.

In the first talk, we discuss the drivers of river corridor complexity and geomorphic change in alluvial non-perennial streams. Geomorphic complexity or heterogeneity is thought to be driven by a dynamic balance between valley form, biotic factors, and inputs of water, sediment, and organic material. The importance of various drivers is compared across space by mapping geomorphic heterogeneity and potential influences across 30 field sites in the southwestern U.S., as well as through time, using numerical modeling to understand the influence of a single flash flood on river corridor morphology under vegetated and unvegetated scenarios. Results highlight the importance of river corridor width and riparian vegetation health on developing and maintaining the geomorphic template of alluvial non-perennial rivers.

In the next talk, we examine the influence of riparian vegetation on runoff generation and groundwater recharge in non-perennial streams. Ecohydrological interactions were investigated across drought and wet years using measurements of stream water level, riparian groundwater, soil moisture, sap flow, and vapor pressure deficit.  Cross-correlation analyses show that atmospheric losses associated with local sap flow and vapor pressure deficit are driving changes in soil moisture and streamflow, and that groundwater is more responsive to summer and fall precipitation events during drought years. Results emphasize the increasing role that warm season precipitation and vegetation dynamics will play in mediating runoff and recharge in mountain systems as riparian areas become more water limited.

Together, our talks stress the importance of ecohydraulic and ecogeomorphic processes in non-perennial streams, with implications for how drought and changing vegetation dynamics may influence topographic change and water quantity in the future.

Bio

Juli Scamardo is an Assistant Professor in the Watershed Sciences Department at Utah State University. She earned her BS in Environmental Science (Geoscience Concentration) at the University of Texas at Austin, and her MS and PhD from Colorado State University. Prior to moving to USU, Juli was a postdoctoral fellow at the University of Vermont with the Cooperative Institute for Research to Operations in Hydrology. Her research focuses on understanding how fluvial forms and processes influence and are influenced by disturbances, with a particular emphasis on variably inundated environments, including non-perennial streams and floodplains.