Scaling Approaches to the Modelling of Water, Sediment and Nutrient Fluxes within Semi-Arid Landscapes, Jornada Basin, New Mexico

2007. Buch. 270 S. Softcover
Logos ISBN 978-3-8325-1754-0
Format (B x L): 14,5 x 21 cm
Overland flow generated by high-intensity rainstorms has been suggested as
having an important role in desertification, resulting in a significant vegetation change
from productive grassland to desert shrubland in the south-western part of the United
States. For the quantification of overland flow and associated nutrient and sediment
fluxes, there are significant scale issues involved that required resolution. To address
these issues, a fieldwork-integrated modelling approach was employed to enable the
quantification of water, sediment and nutrient fluxes within and between shrubland
and grassland associations in a semi-arid ecosystem, the Jornada Basin in the Chihuahuan
Desert, New Mexico. The aim of this thesis is the evaluation of scaling approaches
to the numerical modelling of these fluxes combined with the appropriate application
of scaling tools for model parameterisation. Special emphasis is placed on the
investigation of parameter and process scaling and the applicability of scaling tools to
interpolate and extrapolate field data, disaggregate remotely sensed data and aggregate
model parameters. Extensive field studies were carried out to acquire detailed understanding
of the spatial distribution of hydrological, soil- and nutrient-related model parameters
within black grama grassland and creosote, tarbush and mesquite shrublands.
The statistical and geostatistical analysis of the field data resulted in the development
of scaling techniques that enabled the spatially realistic reproduction of the small-scale
variability and connectivity features of model input parameters. Spatially distributed,
process-orientated models with a 2-m resolution were employed to enable an adequate
representation of model input parameters and an appropriate reproduction of overland
flow characteristics and sediment- and nutrient-transport processes. Based on these results,
the models were upscaled to a resolution of 10-m under specific evaluation of
process and parameter scaling issues. The upscaled model versions were then employed
for the flux quantification within and percentage change of fluxes between
shrubland and grassland associations. The modelling studies provided important insights
in the stability of grassland-shrubland boundaries as a function of nutrient depletion
and water-resource enrichment for the grassland by the action of overland flow. It
was hypothesised, that external forces such as overgrazing or climatic variations might
potentially disturb this stability, which consequently leads to the invasion of shrubs
into the grassland. The modelling results suggest that landscape linkages through the
redistribution of water and soil resources across vegetation-transitions zones at the
landscape scale play a significant role in desertification processes.
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