The wetland ecosystem is different from the ecosystems of other water bodies like the ponds, streams and lakes. Wetlands are inundated by water permanently or seasonally. These lands have unique vegetation of aquatic plants that are adapted to hydric soil.
A rich and healthy wetland ecosystem has a wide diversity of plants and animals that act as filtering systems in removing sediments and impurities from water making it cleaner.
Hence the right option for this question is a