Step 1: Among the four options, succession and natality belong to plant/population ecology, while water resources is a general environmental science term, none of which are specifically tied to Barrell.
Step 2: Joseph Barrell's specific and well documented contribution to earth science was coining the term lithosphere for the strong, brittle outer shell of the Earth that sits above the weaker, plastic asthenosphere.
This terminology is still used today in plate tectonics and physical geography.
