How does a wetland work?

A wetland is one of nature's many ways of treating water. Wetlands can be found all over the world, both natural and constructed. A wetland essentially serves to remove contaminants from water flowing through it. This can be accomplished in several ways:

• Nutrient uptake by wetland plants
• Denitrification by bacteria
• Nutrient settling due to decreased flow velocities

Plant's role in a wetland ecosystem

The plant life found in a wetland system is incredibly important to the function of the wetland. These plants are the real driving force for improvement of water quality. Plants need certain nutrients (like nitrogen) to grow, and these nutrients are found in abundance in stormwater runoff. The root systems of the plants absorb these nutrients, removing them from the effluent flow. Figure 4 provides a visual representation of this process.

The denitrification process

Denitrification in a wetland refers to the process of reducing nitrate (NO_3-) concentrations from the influent flow by bacteria in the soil. These bacteria convert nitrate to molecular nitrogen (N₂), which is then able to dissipate into the atmosphere. This process is critical to reducing nitrate concentrations in stormwater before it reaches the lake.

Nutrient Settling

By holding water and slowing flow, a wetland system is able to allow the settling of nutrients into the soil. These nutrients are those that are unusable to plants, and are heavy enough to sink down into the soil. Phosphorous is an example of one of these nutrients, with an atomic mass of 30.97u. This is an important step in the phosphorous cycle. Additionally, heavy metal ions that have made their way into the wetland can settle into the soil and be prevented from entering the lake. Figures 4 and 5 provides a diagram of the nutrient settling process.