The most likely cause of this "regression" in ecological changes is a combination of land and road development around the site during the 1950s, which created runoff laden with road salt, and unusually high lake levels that raised the level of the water in the marsh.
(The most likely cause of this "regression" in ecological changes; is; a combination of land and road development around the site during the 1950s) (the 1950s; created; runoff laden with road salt) (unusually high lake levels; raised; the level of the water in the marsh)
The most likely cause of this "regression" in ecological changes the 1950s unusually high lake levels
is created raised
a combination of land and road development around the site during the 1950s
runoff laden with road salt
the level of the water in the marsh