Wetlands filter nutrients through a combination of physical, chemical, and biological processes that naturally remove or transform these substances as water flows through them. These processes include sedimentation, volatilization, sorption, and biological uptake.
Here's a more detailed breakdown:
1. Physical Processes:
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Sedimentation (Particle Settling): Wetlands slow down water flow, allowing suspended particles carrying nutrients (like phosphorus bound to soil) to settle out and accumulate in the sediment. This physical settling effectively removes particulate nutrients from the water column.
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Volatilization: Some nutrients, primarily nitrogen in the form of ammonia (NH3), can be converted into gaseous forms that are released into the atmosphere. This process, known as volatilization, removes nitrogen from the water.
2. Chemical Processes:
- Sorption (Adsorption/Absorption): Wetland soils, rich in organic matter and clay minerals, have the ability to bind nutrients through adsorption (surface adhesion) and absorption (uptake into the material). Phosphorus, in particular, can be effectively removed from the water through sorption onto soil particles. Iron and aluminum oxides in wetland soils also play a crucial role in phosphorus sorption.
3. Biological Processes:
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Plant Uptake: Wetland plants absorb nutrients like nitrogen and phosphorus from the water and sediment through their roots. These nutrients are used for plant growth and biomass production. When plants die and decompose, some of the nutrients are released back into the environment, but a portion becomes incorporated into the long-term organic matter storage in the wetland.
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Microbial Transformation: Microorganisms (bacteria and fungi) play a vital role in nutrient cycling within wetlands. They can transform nutrients into different forms through processes such as:
- Nitrification: Converting ammonia (NH3) to nitrate (NO3-).
- Denitrification: Converting nitrate (NO3-) to nitrogen gas (N2), which is then released into the atmosphere. This is a key process for nitrogen removal in wetlands.
- Phosphorus Solubilization/Immobilization: Microbes can influence the solubility of phosphorus, making it more or less available for plant uptake and other processes.
Summary:
Wetlands act as natural filters by employing physical processes like settling and volatilization, chemical processes like sorption, and biological processes involving plants and microbes to effectively remove and transform nutrients, thereby improving water quality.
