Grantee Research Project Results
Patterns in Ecosystem Function Along an Intermittent Stream ContinuumEPA Grant Number: U916131
Title: Patterns in Ecosystem Function Along an Intermittent Stream Continuum
Investigators: Sponseller, Ryan A.
Institution: Arizona State University - Main Campus
EPA Project Officer: Cobbs-Green, Gladys M.
Project Period: January 1, 2003 through January 1, 2006
Project Amount: $108,343
RFA: STAR Graduate Fellowships (2003)
Research Category: Academic Fellowships , Aquatic Ecosystems , Fellowship - Aquatic Ecology and Ecosystems
Drainage networks are prominent features of arid landscapes, yet the importance of desert streams to patterns in ecological function is unknown. Water is routed across arid basins via a continuum of channels that drain subcatchments of increasingly greater area and constitute a gradient in stream intermittency. The objective of this research is to determine how hydrologic intermittency influences landscape patterns in: (1) aboveground primary productivity; (2) resource island development; (3) soil respiration; and (4) plant nutrient use efficiency (NUE) in streamside terraces.Approach:
This research focuses on Velvet Mesquite (Prosopis velutina) in five nested subcatchments that span six orders of magnitude in area and constitute a gradient in intermittency. Thus far, results show that Mesquite canopy volume and foliar 13C in riparian terraces vary as a function of catchment area (r2 = 0.95, p = 0.003; r2 = 0.97, p = 0.005, respectively). Both leaf-litter production and understory annual grass production increase across the landscape as a function of canopy volume. These results suggest that the routing of water through increasing larger and more perennial stream channels drives spatial patterns in aboveground productivity in Sonoran desert landscapes. The accumulation of organic matter (OM) in soils beneath Mesquite reflects these gradients in productivity, although flooding in the riparian zone of the largest streams reduces the accumulation of OM in surface soils. Total below-ground CO2 fluxes also vary among sites, ranging from approximately 195 g C m2 yr-1 in desert uplands to approximately 1,800 g C m2 y-1 in the riparian zone of the perennial stream—with values increasing as a function of Mesquite canopy volume (r2 = 0.88, p < 0.001). The range in respiration rates found across the landscape is equal in magnitude to that observed globally, with annual fluxes in riparian soils among the highest recorded.Supplemental Keywords:
fellowship, ecosystem function, intermittent stream continuum, streams, drainage networks, landscape patterns, soil, surface soil, riparian soil, soil respiration, plant nutrient use efficiency, NUE, Velvet Mesquite, Prosopis velutina, organic matter, OM.