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How Wetlands Clean Water
Plants, microbes, and slow filtration
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Wetlands are nature’s water filters, found where land and water meet for part or all of the year. As muddy or polluted water moves through a marsh, swamp, or bog, its speed slows and many contaminants are trapped, absorbed, or broken down. This matters because wetlands help protect rivers, lakes, groundwater, and coastal waters from pollution. They also reduce flooding and provide habitat for birds, fish, amphibians, and insects.
A wetland cleans water through several connected processes. Sediment settles out when flowing water slows, plant roots hold soil in place, and microbes in wet soils break down some pollutants. Marsh plants take up nutrients such as nitrogen and phosphorus, which can otherwise cause algae blooms downstream. Wetlands such as the Florida Everglades and Louisiana marshes show how living ecosystems can support clean water, flood protection, and biodiversity at the same time.
Key Facts
- Wetlands slow moving water, allowing sediment and attached pollutants to settle to the bottom.
- Plants remove nutrients from water by absorbing nitrogen and phosphorus for growth.
- Microbes in wetland soils can convert nitrate to nitrogen gas through denitrification.
- Too much nitrogen or phosphorus can cause eutrophication, leading to algae blooms and low oxygen.
- Wetlands reduce flood peaks by storing water and releasing it slowly over time.
- Pollutant removal depends on water flow speed, plant density, soil type, temperature, and wetland size.
Vocabulary
- Wetland
- A wetland is an area where water covers or saturates the soil long enough to support water-loving plants and special soil conditions.
- Sediment
- Sediment is loose material such as soil, sand, and clay carried by water, wind, or ice.
- Runoff
- Runoff is water from rain, snowmelt, or irrigation that flows over land and can carry pollutants into waterways.
- Denitrification
- Denitrification is a microbial process that changes nitrate in water or soil into nitrogen gas.
- Eutrophication
- Eutrophication is the overgrowth of algae and aquatic plants caused by excess nutrients in a body of water.
Common Mistakes to Avoid
- Thinking wetlands only store dirty water is wrong because they actively filter, transform, and trap pollutants through plants, soils, microbes, and settling.
- Assuming all pollutants disappear completely is wrong because wetlands reduce many contaminants but can become overloaded if pollution levels are too high.
- Forgetting that slow water matters is wrong because fast-moving water does not give sediment enough time to settle or roots and microbes enough time to act.
- Treating nitrogen and phosphorus as always harmful is wrong because plants need these nutrients, but excess amounts can damage aquatic ecosystems downstream.
Practice Questions
- 1 A farm field sends runoff containing 80 kg of sediment into a wetland during a storm. If the wetland traps 65% of the sediment, how many kilograms of sediment continue downstream?
- 2 A wetland receives 120 g of nitrate in a day. Microbes remove 45 g through denitrification and plants take up 30 g. How many grams of nitrate remain in the water?
- 3 Explain why removing wetland plants could make downstream water quality worse, even if the wetland soil is still present.