From wastewater to clean water — how do wetlands do it?
If you’ve been following our wetlands series, you already know that natural wetlands have been recognized for providing many benefits, including water quality improvement, food and habitat for wildlife, flood protection, shoreline erosion control, and opportunities for recreation. If you’re wondering how exactly wetlands go about improving water quality, also known as biofiltration, read on.
One of the simplest ways wetlands improve water quality is by filtering out sediment and decomposing plant matter as it comes into contact with wetland vegetation. Leaves provide friction to slow the flow of water, which allows for the settling of suspended solids and removal of related pollutants from the water column.
Using more complex processes, decomposers such as bacteria and fungi living on the exposed surfaces of the aquatic plants and soils can remove dissolved biodegradable material. This active decomposition and oxidation of inorganics produces final effluents with a characteristic low biological oxygen demand (BOD).
Why is this important you may ask? BOD is a measure of the oxygen required for the decomposition of organic matter and oxidation of inorganics such as sulfide. If BOD is high, low dissolved oxygen levels result, which can lead to the death of aquatic life.
Certain aquatic plants are very important in wetland processes because they pump atmospheric oxygen into their submerged stems, roots, and tubers. If you’ve ever disturbed wetland plants and wondered where those rising bubbles came from, now you know. The oxygen is utilized by the microbial decomposers attached to the aquatic plants below the level of the water. Plants also play an active role in absorbing nitrogen, phosphorus, and other compounds from the wastewater, preventing eutrophication (nutrient overloading).
Wetlands also do their part in removing fecal coliform bacteria and protozoans, as anyone who has had the misfortune of contracting beaver fever or other related illnesses can see the importance of. Bacteria attach to suspended solids that are then trapped by wetland vegetation. These organisms die after remaining outside their host organisms through degradation by sunlight, from the low pH of wetlands, and by protozoan consumption.
While wetlands have enormous potential to act as natural water treatment plants, diverting wastewater in need of treatment to a natural wetland could potentially have harmful effects. At least in part due to such concerns, there has been a growing interest in the use of constructed wetlands for wastewater treatment.
Simply put, a constructed wetland is a water treatment facility duplicating the processes occurring in natural wetlands as was just explained. If properly built, maintained and operated, constructed wetlands can effectively remove many pollutants associated with municipal and industrial wastewater and stormwater.
Although a primary purpose of constructed wetlands is to treat various kinds of wastewater, these facilities can serve other purposes as well. For example, research might be conducted to study and evaluate the workings of the wetland process. They can serve as wildlife sites to attract various animals and provide habitat. Also, a wetland can be a public attraction, welcoming visitors to explore its environmental and educational possibilities.
Not relying on concrete and steel, constructed wetlands usually can be built for less expense than other treatment options. Furthermore, with low-tech methods in place, no new or complex technological tools would be needed as plants and microorganisms are the active agents in the process. Constructed wetlands can vary greatly in size and function, serving municipalities, businesses and individual homes.
Currently the Resort Municipality of Whistler is considering installing a constructed wetland adjacent to, but isolated from, the White Gold Wetlands. The system would have the potential to treat surface run off from the village that is currently being directly drained into Fitzsimmons Creek via culverts or through the White Gold Wetlands in a controlled flow. The final decision on the project will be made in June when it will be determined if the water is indeed in need of treatment.
A final thought on the subject of biofiltration: While constructed wetlands have less impact on the environment than conventional water treatment plants, we shouldn’t forget that eliminating pollution at its source is always the best solution.
That’s all folks. If you still haven’t had enough of wetlands yet, join us for our final walking tour of the White Gold Wetlands. We’ll be meeting in the parking lot of The Boot Pub at 10 a.m. on Sunday.
For more information on our wetland initiatives, call AWARE at 604-932-4457 or e-mail us at aware@direct.ca .
Stay tuned for next week’s article as we present the steamy conclusion to our WET & WILD series: "Wetland Dreams" – a smoking feature on the River of Golden Dreams wetland corridor.
