Which is a principal role of wetlands in water quality protection and flood control?

• A. Wetlands filter pollutants, trap sediments, store floodwaters, and reduce peak flows.
• B. Wetlands primarily increase evaporation and decrease biodiversity.
• C. Wetlands act as primary sources of greenhouse gas emissions with no flood control.
• D. Wetlands only provide habitat and have no effect on water quality.

Answer: (A)

The main idea is that wetlands protect water quality and help control floods by acting as natural treatment systems and sponges. Water moving through a wetland slows down, allowing sediments to settle out and pollutants or nutrients to be taken up by plants or broken down by microbes. This filtration and biogeochemical processing reduce turbidity and contaminant loads before water enters streams and rivers. At the same time, the wetland’s soils and vegetation store excess water during heavy rains, releasing it gradually and thereby lowering the peak flows downstream. This combination—cleaner water and reduced flood peaks—is the principal way wetlands contribute to both water quality protection and flood control.

Other statements don’t fit because wetlands are not primarily about evaporation or biodiversity loss; they actually support high biodiversity and evapotranspiration is a part of their function but not the main water-quality/flood-control role. They are not just sources of greenhouse gases with no flood control; while methane can be produced, wetlands also store carbon and provide flood storage. And wetlands do more than just provide habitat; they actively improve water quality through filtration and sediment trapping, so saying they have no effect on water quality is incorrect.