HR: 08:40h
AN: B51A-03    [PDF]
TI: Scale Issues in Ecohydrological Processes in Grassland-Shrubland Transitions, Jornada, NM
AU: * Wainwright, J
EM: john.wainwright@kcl.ac.uk
AF: Environmental Monitoring and Modelling Research Group, Department of Geography, King's College London, Strand, London, WC2R 2LS United Kingdom
AU: Parsons, A J
EM: ajp16@le.ac.uk
AF: Department of Geography, Leicester University, University Road, Leicester, LE1 7RH United Kingdom
AU: Mueller, E N
EM: eva.mueller@kcl.ac.uk
AF: Environmental Monitoring and Modelling Research Group, Department of Geography, King's College London, Strand, London, WC2R 2LS United Kingdom
AU: Schlesinger, W H
EM: schlesin@duke.edu
AF: Nicholas School of the Environment and Earth Sciences, Duke University, A 237 Levine Science Research Center, Durham, NC 27708-0329 United States
AB: Rainfall-simulation experiments have proved invaluable in developing our understanding of ecohydrological processes relating to grassland-shrubland transitions in the American Southwest and elsewhere. Grassland communities are effective at buffering the runoff and erosional response, whereas shrublands accelerate runoff and erosion rates leading to local concentrations of resources. Further feedbacks occur in terms of nutrient redistribution both dissolved in overland flow and adsorbed onto transported sediment. Field experiments at the Jornada LTER site over the last ten years have evaluated these processes on undisturbed and grazed black grama grassland, and creosotebush and mesquite shrubland communities. More recently, investigations have been carried out to evaluate the behaviour of these systems at the landscape scale. Low-cost sampling designs have been used so that relatively large spatial samples can be collected. Currently, 96 of these samplers are in operation at Jornada, evaluating water, sediment and nutrient transfers in the interrill zone. A smaller number of samplers are used to characterize rill transfers of water and dissolved nutrients. The samplers are located along ecotones so that the spatial relationship of grassland-shrubland and shrubland-shrubland transitions can be evaluated. An interesting initial result of the use of these samplers is that they provide different relative patterns of fluxes from those that would be estimated using the plot-based studies. These results contribute to the growing body of evidence that the scaling properties of landscape-degradation processes in these environments are non-linear. Further instrumentation of watersheds is being carried out in order to evaluate these non-linearities at larger scales. At the same time, intensive spatial sampling of hydrological, sedimentary and nutrient characteristics of the surfaces of the different vegetation communities is being carried out. The rationale for this sampling is to be able to generate multi-scale databases that can be used to parameterize a range of models that investigate the transition processes and process interactions. These models work at a range of levels of abstraction, albeit all with a process base. Furthermore, the spatial measurements themselves give clues to the cause of the non-linearities in scaling and the processes that may generate them. This paper concludes by looking at the relative advantages and disadvantages of the different approaches that can be used to evaluate ecohydrological interactions.
DE: 1615 Biogeochemical processes (4805)
DE: 1625 Geomorphology and weathering (1824, 1886)
DE: 1655 Water cycles (1836)
DE: 1809 Desertification
DE: 1815 Erosion and sedimentation
SC: Biogeosciences [B]
MN: 2003 Fall Meeting