The work on the initial version of ecological regions for the conterminous US, subsequently becoming Level III, was conducted in the mid-1980s by Omernik and published in 1987. This work was "based on the hypothesis that ecosystems and their component display regional patterns that are reflected in spatially variable combinations of causal factors. These causal factors include climate, mineral availability (soils and geology), vegetation, and physiography. Although these factors interact, the importance of each factor in determining the character of ecosystems varies from place to place." Omernik argued that "by analyzing a combination of small scale maps of the important causal factors and of integrative factors (such as land use), distinct regional patterns of ecosystems can be perceived" (quotations in this paragraph from Omernik 1987). These level III ecoregions have been used for assessment and management of rivers and lakes in Minnesota (Heiskary and various others 1987, 1988, 1989, 2008, 2019; Ramstack and others 2004; Anderson and others 2016). The work on Level IV described here was conducted under the aegis of the Omernik system and started with the Omernik Level III ecoregions as a basis. The method of discovery is described in some detail in Omernik and Griffith's 2014 paper. The process in Minnesota included in the early stages two visits to Minnesota to talk with potential users of more detailed ecoregions. Many maps of relevant phenomena were assembled from some materials already available at the US EPA research laboratory in Corvallis, and from sources online. Some of the maps that have been used are represented in Appendix M. Also considerable literature was assembled on soils, vegetation, wildlife, geology, and geography. The references in the report list most of these documents. With these many materials to assist, patterns among them were studied and compared until the accumulated knowledge suggested the appropriate division of the Level III regions into subregions, with possible minor changes to the boundaries of Level III also. This process, as with any regionalization process, cannot be considered a final reckoning of the ecoregionality of Minnesota because not only will further knowledge affect possible changes, but the forces of change interact in complex ways and change themselves in spatial distribution and importance. Omernik, J.M., 1987, Ecoregions of the conterminous United States (map supplement): Annals of the Association of American Geographers, v. 77, p. 118-125, scale 1:7,500,000.
Omernik, James M, Glenn E Griffith. 2014. Ecoregions of the Conterminous Unites States: Evolution of a Hierarchical Spatial Framework. Environmental Management 54:1249-1266.
Heiskary, S A, C B Wilson, D P Larsen. 1987. Analysis of regional patterns in lake water quality: Using ecoregions for lake management in Minnesota. Lake and Reservoir Managment. 3:337-344.
Heiskary, S, W W Walker Jr. 1988. Developing nutrient criteria for Minnesota lakes. Lake and Reservoir Management 4:1-9.
Heiskary, S, C B Wilson. 1989. The regional nature of lake water quality across Minnesota: an analysis for improving resource management. Journal of the Minnesota Academy of Sciences 55:71-77.
Heiskary, Steven, Bruce Wilson. 2008. Minnesota's approach to lake nutrient criteria development. Lake and Reservoir Management 24:282-297.
Heiskary, Steven A, Kristofor Parson. 2019. Regionalization of Minnesota's rivers for application of river nutrient criteria. Minnesota Pollution Control Agency. 32 pages. URL: https://www.pca.state.mn.us/sites/default/files/wq-s6-18.pdf
Ramstack, Joy M, Sherilyn C Fritz, Daniel R Engstrom. 2004. Twentieth century water quality trends in Minnesota lakes compared with presettlement variability. Canadian Journal of Fisheries and Aquatic Sciences 61:561-576.
Anderson, Pam, and 18 others. 2016. Guidance Manual for assessing the quality of Minnesota surface waters for determination of impairment: 305(b) report and 303(d) list. Minnesota Pollution Control Agency. 77 pages.
AUTHOR: Denis White, retired US EPA; courtesy faculty, Geography Program, Oregon State University. COLLABORATORS AND CONTRIBUTORS: Glenn Griffith, US Geological Survey; James Omernik, USGS Geological Survey; Alan Woods, retired; Steve Heiskary, Retired MN PCA. CITING THE Report: White, Denis. 2020. Ecological Regions of Minnesota: Level III and IV maps and descriptions. 22 pages text, 69 pages appendices. Ecoregion Links |
