Constructed Wetlands Overview
Constructed wetlands are just that. They are manmade wetlands utilized to better the environment through bio-filtration, habitat restoration or creation and reclamation of land. There are two major types of constructed wetlands. The first is the surface flow wetland. This type resembles a natural wetland in it aesthetics as well as its functionality. These keep a surface water depth that is not only visible but also creates the habitat for natural inhabitants to wetlands as well as the migratory animals that utilize these types of environments as they progress on their journeys. The second type of the sub-surface water flow wetland that utilizes filtration below the surface and the filtration is not exposed to the atmosphere (Keddy, 2010).
The construction of the two is very similar excluding the water levels and areas of filtrations. The design’s focus is accomplished through the engineered construction process to fully design and implement a wetlands habitat that will become as vibrant and sustainable as a natural occurring wetlands ecosystem. The composition includes an impermeable bottom layer that is made up of natural resources such as clay or other material or it could be composed of a synthetic material like PVC or rubber composition (Campbell and Ogden, 1999). The basic objective of this layer is to ensure the water does not seep or quickly leak out of the wetland area. This provided the framework for the wetlands and must work in conjunction with the other layers for the wetland to be successful. The next area is the substrate area that acts as a filter and is constructed of sand, gravel, clay and/or humus soils as well as a combination of the aforementioned.
The design criteria is based upon the needs of the area and what the exact form, fit and function the designing team wants to achieve at the end of the development. For example, if the primary objective is to use the constructed wetland as a water filtration area for wastewater. The area must take into consideration the amount of waste that will flow into the area, the amount of time it would take to filter that wastewater as well as the time it would take for the water to exit the wetland and return to a usable source. The size and filtration parameters would be designed around these key inputs. The secondary and tertiary benefits would be the habitat revitalization as well as the aesthetically pleasing environment that is created. Other factors to consider while constructing wetlands include the temperature and climate, evaporative process timing and precipitation that may impact the water levels in the wetlands and diminish the filtration qualities. The goal of the wetland creation is the development of a self-contained and self-sufficient ecosystem that provides intrinsic qualities of waste management, land reclamation, ecosystem generation and aesthetically pleasing landscapes.
The ecosystem itself is built upon not only the construction of the bottom and substrate areas but also that of the vegetative growth that is put in place with specific needs and purposes. The influent water travels into the wetland where a biological, chemical and physical reaction occurs. The water flows through the substrate creating a filtration effect on the water while the plant life transfers oxygen to the water table for the filter water to absorb. The treated water travels through the effluent piping system as cleaned water. This process has many critical parts to make it successful. One of those areas includes the plant life of the wetland. Constructed wetlands rely heavily on plant types such as cattails, reed, yellow iris, water soldiers, European white lily and Eurasian water-milfoil. There are benefits to each one of these plants. Initially cattails and common reed were used as a primary vegetative source due to their hearty ability to grow in sub-optimal locations, varying water depths, abundance and versatility to water types and composition. This was important to the wetlands project due in part to the types of water coming through the influent piping system. The influent system controls what comes into the wetlands but does not control the pH level, salinity, or contamination present. Another key aspect of the plant growth is the soil or source of nutrition the plants rely upon. When the constructed wetland is built the existing soil is removed and covered with nutrient stripped soil, clay or other composite material. This prevents unwanted variables being added to the ecosystem initially. The plants are then placed upon peat so that they have a bed of nutrition and growth opportunities.
Purpose and Benefits
The purpose of a constructed wetland is to provide a pretreatment to wastewater by creating an environment that filters, removes and decomposes bacteria in a way that looks natural and has beneficial qualities to the environment other than the bio-filtration qualities. The water leaving the wetland is now a higher quality effluent which requires the continued treatment of the water to be less demanding. The effluent leaves the wetland and travels to the next area for treatment but with less effort required for treatment the next area would have less demand. This in part due to the wetlands would decrease the overall demand for man-made treatment facilities due to the decreased amount of effort required. The constructed wetlands is an opportunity for on-site filtration needs with little maintenance and overhead. The cost of a constructed wetland is dependent upon the size and complexity that is incorporated into the system (Keddy, 2010). The key construction costs include earthwork, influent and effluent design and construction, distribution, linings, plants and substrate materials. While in some areas the construction cost may be slightly high, it does not directly compare in cost to that of a coal burning treatment facility. The maintenance and upkeep of a properly designed and implemented constructed wetland would be limited to vegetation maintenance, liner inspections and potential ecosystem maintenance if the proper aesthetics or performance is not maintained. Once established the maintenance and upkeep are minimal.
Other than the filtration qualities of the constructed wetlands there is also a revitalization effort that is incorporated into the creation of the wetland. With urbanization of areas all across the globe, the natural habitats that once served the same function as the wetlands are now overgrown with man-made constructions (Kadlec and Wallace, 2009). The positive impacts of urbanization, such as providing people with places to live and thrive, also have negative impacts on the environment. When the natural water filtration systems were removed, man-made treatment facilities were necessary. With the constructed wetlands the treatment facilities will be subsidized and newly formed ecosystems will generate. The ecosystems provide the areas that were removed by urbanization and ultimately replaced with a sustainable and fully incorporated area for plants, animals and humans to enjoy.
The aesthetics of the constructed wetland also play an important role in their acceptance and viability in areas that may not initially constitute and acceptable location. The wildlife, plant life, water flow and other key attributes add a slice of nature to the sprawling conformities of the urbanization movement. The function of the wetland coupled with the aesthetics allow for the perfect balance between form, fit and function into the lives of those that require the reclaimed water.
The constructed wetlands provide the opportunity to economically reclaim water through a bio-filter mechanism at a substantially lower cost that other treatment facilities. At the same time, the constructed wetland generates bio-diversity in an area that either incorporated the wetlands into their ecosystem or an area that requires the rejuvenation after it was utilized for other means. The constructed wetland provides multiple opportunities for revitalization, water treatment, environmental improvements and visually appeasing landscapes at a cost that is below that of other water treatment facilities. This provides a better alternative to subsidize and potentially become the primary water filtration system replacing current water treatment facilities.
Campbell, Craig S., and Michael Ogden. Constructed Wetlands in the Sustainable Landscape. New York: Wiley, 1999. Print.
Constanza, R. R., R. d’Arge, R. de Groot, S. Farber, M. Grasso, B. Hannon, K. Limburg, S. Naeem, R.V. O”Neill, J. Paruelo, R.G. Raskin, P. Sutton, and M. van der Belt “The value of the world’s ecosystem services and natural capital.” Nature 387:253-260. 1997. Print
Kadlec, Robert H., and Scott D. Wallace. Treatment Wetlands. Boca Raton, FL: CRC, 2009. Print.
Keddy, Paul A. Wetland Ecology: Principles and Conservation. New York: Cambridge UP, 2010. Print.