How do conservationists make use of watersheds and ecozones?

Conservationists make use of watersheds by preserving them so that they can be used to supply the drinking water of local inhabitants, for spawning grounds say for salmon, and perhaps for irrigation as long as the re-charge is greater than or equal to the discharge. Ecozones can be used to protect habitats for wildlife so they can flourish or at least not become extinct. 

Its decreasing because of illnesses

Answer (d) may increase or decrease porosity through dissolution or deposition;