All of the following can contribute to the watershed except *rivers *oceans *rainfall *groundwater

Groundwater

A watershed can be defined as a land filled with shallow water. The water in the water shed comes from a source of free flowing water like rivers and ocean, which gets drained further into another water source to make up a large water body.

The watershed is formed due to surface runoff, which means that the water from source of water like river, ocean and rainfall moves over the surface of earth and gets deposited in the watershed. Groundwater is a source of water, that exhibit accumulation of water underneath the earth crust. The water seep inside the earth crust through small pores present in aggregate of subsurface soil and rocks. This water remain as a underground reservoir, it can come out until the reservoir found and dig open. Therefore, it cannot cause surface runoff to become the part of any other water source and cannot contribute to the watershed.

sheep is a herbivore animal whereas grasshopper belongs to the class chordates but both of them feed on greens.  

if grasshopper and sheep feeding on a pasture land, i do not think both of them will have any impact on each other. however, the number of the species can make difference. since sheep feed on greens, there is a possibility there left no pasture land for the grasshoppers or they may get extinct.