1. a Clark Graduate School of Geography , Clark University , Worcester , MA , 01610 , USA
2. b Department of Geography and Environment , Rowan University , Glassboro , NJ , 08028 , USA
3. c Department of Geography , Rutgers, the State University of New Jersey , Piscataway , NJ , 08854 , USA
4. d Department of Environmental Sciences , University of Virginia , Charlottesville , VA , 22904-4123 , USA