Water purification depends on filtration and absorption by soil particles and living organisms in the water and soil. Human activities that compact soil, contaminate the water or alter the composition of organisms, degrade the purification process and can accelerate movement of unfiltered water through the system and into our water supplies.
- Wetlands: Many types of plants are specially adapted to different kinds of wetlands, and a large percentage of the nation’s imperiled plants and animals depend on wetlands for at least part of their life cycle. Wetlands commonly provide important benefits throughout the nation, such as:
- Flood Control:Some wetlands, particularly those on floodplains and in coastal areas, function in flood control by storing and decreasing the velocity of excess water during heavy rainfall. As water flows into wetlands, it naturally loses velocity as it collects and continues to spread out. Wetland vegetation provides another natural barrier to fast moving water and therefore aids in flood speed reduction. The result of wetland activity during floods is often decreased damage to surrounding areas.
- Silt Catchers: When flood waters are slowed by wetlands, they drop sediments among the roots and stems of the plants. This protects downstream waterbodies by preventing a dangerous build-up of gill clogging and egg damaging silt.
- Water Cleaners and Suppliers: Wetlands fed by groundwater further transport the water to streams that may otherwise dry up during warm summers or times of drought. Furthermore, wetlands absorb water during the wet seasons and gradually release it during dry seasons, and can thereby refill aquifers and other drinking water supplies. Wetlands not only supply water, but they cleanse it. When water enters a wetland, the wetland becomes a giant kidney, filtering out impurities before allowing the water to leave. Wetlands can remove 20 to 60% of metals in the water, trap and retain 80 to 90% of sediment from runoff and eliminate 70 to 90% of entering nitrogen. The wetland vegetation plays a large role in this filtering system as it uses its roots and stems to trap and gather sediments comprised of both chemicals and nutrients. (For further information: http://water.epa.gov/type/wetlands
- Erosion Control: Wetlands buffer shorelands against erosion because they are often located between water bodies and high ground. The roots of wetland vegetation bind the soil, putting a hold on it, while the plants themselves absorb the impact of waves.
- Riparian Forests. Riparian (streamside) forests act as “living filters” that intercept and absorb sediments, and store and transform excess nutrients and pollutants carried in runoff from adjacent lands. They can reduce the nitrogen concentration in water runoff and floodwater by up to 90%, and can reduce phosphorous by as much as 50%.
- Constructed Wetlands. Constructed wetlands mimic some of the filtration power of natural systems. They can be cost efficient for small communities but can not replace natural wetlands, and may not provide the many other wetland services (such as flood control and fish and wildlife habitat).