What is a key function of vegetative buffer zones in watershed protection?

• A. They mainly increase surface runoff.
• B. They filter nutrients and sediments before reaching waterways.
• C. They solely provide aesthetic value.
• D. They increase evapotranspiration to degrade pollutants in air.

Answer: (B)

Vegetated buffer zones along streams act as natural filters that protect water quality. As runoff passes through the grassy, shrubby, or wooded strip, the vegetation slows the water, allowing sediment to settle out and preventing it from entering the water. The roots and soil biology uptake and transform nutrients like nitrogen and phosphorus, so less of these pollutants reach the stream. The buffers also promote infiltration, so more water soaks into the ground rather than running off, and they stabilize banks to reduce erosion. All of these effects combine to keep nutrients and sediment out of waterways, which is the central protective function in a watershed. The other options miss this main role: buffers don’t primarily increase runoff, aren’t just aesthetic, and aren’t designed mainly to degrade airborne pollutants via evapotranspiration.