USING ECOREGIONAL BOUNDARIES TO ORGANIZE UNITED STATES KARST AREAS AT THE REGIONAL SCALE

Based on our compiled database of potentially karstic areas, soluble rocks (carbonates and evaporites) directly underlie approximately 15% of the land area of the United States. We are currently working on non-lithologic schemes to further organize and classify these potential karst areas. Development of karst systems and features in these areas is the product of a complex and dynamic interplay of physical and chemical conditions and factors in four dimensions. Karst scientists have worked towards developing algorithms describing intensity of karstification, as well as predictive models for karst development in particular landscapes. However, application of these efforts in other areas is often disappointing because of differences between key variables in disparate karst systems. Karst development is affected by both epigenic (processes originated at the surface) and hypogenic (deep subsurface) conditions. As part of a hierarchical geographic classification scheme for karst lands in America States we are using the Omernick Ecoregion System for North America. Ecoregions are areas with similar climate, physiography, geology, soils, and other natural features. The hierarchy includes, from more general to more detailed, Level I, II, III, and IV ecoregions. These give us a framework for organizing karst terrains into areas affected by similar epigenic conditions at a regional scale. In addition, ecoregions are natural areas and can be mapped continuously across political boundaries. Data and documentation for these ecoregions may be accessed via the National Atlas at: http://nationalatlas.gov/mld/ecoomrp.html. Spatial boundaries of many of the traditionally defined North American karst areas align reasonably well with Level III ecoregions. Level IV areas are more detailed but not yet available for the entire nation. We believe that this organization will help establish better geographic references to karst regions and provide a framework for definition of regional-scale karst systems characterized by internally similar genesis and physio-chemical settings. Level III or IV ecoregions may be appropriate sizes for applying multivariate characterizations of karst development, and also for practical applications of karst-land management guidelines and practices.