Where does the term “ecological literacy” come from?

Disinger and Roth (1992) claim that Charles Roth coined the term in 1968.
However, these authors also suggest that 20+ years of research have not helped to clarify the term: there is still no agreed upon definition.

Disinger, J. F., & Roth, C. E. (1992, November). Environmental Literacy. ERIC/CSMEE Digest. Retrieved October 16, 2001 from http://www.ericse.org/digests/dse92-1.html

Morrone, M.; Manci, K. & Carr, K. (2001). Development of a metric test group differences in ecological knowledge as one component of environmental literacy, Journal of Environmental Education, 32(4), 33-42.