Mark Nelson

 (born 1947) is an American ecologist and author based in Santa Fe, New Mexico. His research focuses on closed ecological system research, ecological engineering, restoration of damaged ecosystems, and wastewater recycling. The founding director of the Institute of Ecotechnics in 1973, Nelson was one of the eight original crew members of Biosphere 2 in 1991 and served as the Director of Earth and Space Applications for the project until 1994.