What is one major effect of runoff?

• A. Humus formation
• B. Soil enrichment
• C. Mineral deposition
• D. Erosion

Answer: (D)

Runoff is the movement of surface water after rainfall, and its main impact on rangeland soils is erosion: the wearing away and removal of the topsoil by that flowing water. As water runs over bare or vegetated ground, it can detach soil particles and transport them downslope or into nearby waterways. This loss of the nutrient- and structure-rich top layer reduces soil productivity, alters soil structure, and can lead to gullies and sedimentation in streams.

Humus formation happens as organic matter decomposes and stabilizes in the soil, not as a direct result of surface water moving across the land. Soil enrichment isn’t the typical result of runoff either; runoff commonly washes nutrients away rather than concentrating them in the soil where you want them. Mineral deposition can occur where water slows and drops its carried minerals, but that’s a secondary effect and not the primary consequence of runoff on the land. The predominant outcome to focus on is erosion.