1. Department of Geosciences, Virginia Tech , Blacksburg, VA 204061 , USA
2. Virginia Tech National Security Institute , Virginia Tech, Blacksburg, VA 24061 , USA
3. Institute for Water, Environment and Health, United Nations University , Hamilton, ON L8P 0A1, CA
4. U.S. Geological Survey, Pacific Coastal and Marine Science Center , Santa Cruz, CA 95060 , USA