1. Department of Geography, The George Washington University, 2036 H St., NW, Washington, DC 20052, USA.
2. Department of Geography, Environment, and Spatial Sciences, Michigan State University, 673 Auditorium Rd., East Lansing, MI 48824, USA.
3. Department of Earth, Environment, and Geographical Sciences, Northern Michigan University, Marquette, MI 49855, USA.