Question

which change may inappropriate land use, such as removing vegetation from hillsides and plowing fields parallel to a hillside, contribute to?

increase in erosion
decrease in amount of toxins in the soil
increase in weathering of the landscape
decrease in water runoff

Explanation:

Vegetation helps hold soil in place. Removing it and plowing parallel to a hillside (instead of contour - plowing which helps reduce erosion) makes soil more vulnerable to being washed or blown away. Weathering is a different process (physical/chemical breakdown of rocks). Removing vegetation doesn't decrease toxins (if anything, might expose soil to more pollutants). And without vegetation, water runoff usually increases as there's less to absorb the water.

Answer:

Increase in erosion