The third- and second-from-last paragraphs reference a book found beside Lowell’s bunk: a copy of the “Conservation Pledge” from 1946 "when the magazine Outdoor

The third- and second-from-last paragraphs reference a book found beside Lowell’s bunk: a copy of the “Conservation Pledge” from 1946 "when the magazine Outdoor Life held a contest to encourage outdoors enthusiasts to dedicate themselves to the preservation of the America’s natural resources. The winning entry, the one that adorns Lowell’s wall aboard Valley Forge, was submitted by L.L. Foreman, a former ranch hand turned author of pulpy adventure Westerns. "The second-place winner of that 1946 contest? Rachel Carson." So there's a hint that the protagonist of Silent Running had actually read Carson's Silent Spring!