Riparian Ecohydrology: The Role of Lateral Moisture Transport in Supporting Hydraulic Redistribution at a Semiarid Site

Lateral moisture transport between a river and the surrounding corridor alters the ecohydrologic dynamics in riparian zones. Especially it regulates the availability of belowground moisture throughout a soil matrix that is coupled with nutrient transport, plant survival under extreme climate conditions, and the coexistence of deep-rooted and shallow-rooted vegetation species. Based on a 3D ecohydrological simulation and field measurements, we examine how lateral moisture transport from/to a river impacts the moisture gradient over a soil matrix and hydraulic redistributiona transport of moisture from wet to dry soil layers through rootsthat is linked to how the coexisting trees and grasses survive through an extended dry period in a semiarid woodland site in Tucson, Arizona. At the site, only trees have access to deep groundwater, which is tightly coupled with the fluctuation of river level. Our hypothesis is that lateral moisture supply from river buffers drought for trees, and also indirectly support shallow-rooted grasses by moisture that is hydraulically redistributed via tree roots. Lateral flow from/to a river and hydraulic redistribution will promote more facilitative relationships between coexisting trees and grasses. This modeling study highlights the roles of vertical moisture transport via roots and lateral flow to and from the river on the riparian ecohydrologic dynamics and the interaction between deep-rooted and shallow-rooted vegetation species.