| Scale issues are present in all forms of spatial analysis and have been identified as one of the most ubiquitous and fundamental aspects of spatial research. Scale provides the required link between what is being studied and the observation. The core of the problem is the nature of scale dependency and scale-linkage.; The objectives of the study were to conceptualize, characterize and interpret scale effects in an environmental policy analysis study. These were accomplished by developing a conceptual framework revealing the role of scale within modeling processes typical of the development of nutrient Total Maximum Daily Loads (TMDL.) This was interpreted in review of EPA's BASINS model. Methods focused upon measurement scale effects based upon the results of extensive field and modeling studies (using the SWAT model) in the upper Bosque River watershed in central Texas.; In order to examine the effects of measurement scale upon the established equations used in SWAT this study looked at the results of using re-scaled GIS data sets upon environmental modeling. The model used a single rainfall event with GIS-based data for soils, elevation and land use. The processes that were modeled include runoff, peak discharge, sediment yield and mineral/organic sediment loading.; The results of analysis show decreasing heterogeneity with increasing resolution determined by the weak influence of elevation and the dominant influence of land use categories. While the predictive relationship between land use and elevation was weak (r2 < .25), the relationship between r2 values for land use/elevation regression and resolution had a predictive relationship of r2 = .66. Re-scaling had a strong influence upon model results.; Variogram analysis was used to forecast dominant operational scale and identify scale effects as a component for data analysis in environmental models. There is an unbounded relationship between elevation variance and resolution, with phosphorus loading having a bounded range at course scales, suggesting the influence of watershed-level processes. This is consistent with the study areas smooth topography. Kriging was examined as a re-scaling tool and performed poorly due to the anthropogenic nature of the land use. |
