Soil maps generate reliable Quaternary geologic map

Geologists, archeologists, anthropologists, ecologists, engineers, and natural resource managers routinely use National Cooperative Soil Survey (NCSS) data across field sciences. Researchers at Iowa State University decided to test the reliability of this data as applied in geology, and sought to create the best possible Quaternary geology map of the Des Moines Lobe solely using NCSS data. Their broader goal was to create the map to explore how the rich level of detail in the Soil Survey Geographic (SSURGO) database can be used to serve many other areas of study. Bradley A. Miller (Environmental Programs, Iowa State University), C. Lee Burras (Dep. of Agronomy, Iowa State University), and William G. Crumpton (Dep. of Ecology, Evolution, and Organismal Biology, Iowa State University) categorized soil map units with respect to geologic units and successfully created a detailed Quaternary geologic map for the Des Moines Lobe. Their map showed strong agreement with existing Quaternary geologic maps while adding a user-controlled level of scale. The results are published in the Winter 2008 issue of Soil Survey Horizons.

Digital county soil maps were obtained from the USDA-NRCS Soil Survey Geographic (SSURGO) Database, and a database was constructed that categorized each soil series that appeared in the selected counties for surface geologic attributes. The database key was based on terms found in the online Official Series Descriptions, and the database was then linked to the SSURGO shapefile in ESRI's ArcGIS 9.2 software. The soils were displayed by grouping categorized soil into 15 geologic units. Quaternary geologic maps that were available in a GIS format were used to compare the new Quaternary geologic map for level of agreement and detail.

The resulting map communicates many of the spatial intricacies of the Des Moines Lobe landform with the 15 map units based on geologic units. The display of these map units shows detailed features of ground moraine, stagnation moraine, glacial lakes, outwash, and loess deposits.

The researchers envision widespread use of the method, given the generally good agreement with the existing Quaternary geologic maps and the inclusion of finer detail and user-controllable scale. The development of keys that relate soil survey terminology to information of geologic interest will allow soil survey to be a quick and easy reference for geologic inquiry. The same concept can be applied to any discipline affected by soil properties.

Source: Soil Science Society of America