Constructing wetlands to sanitize rivers and produce green energy

A new study from researchers in the Netherlands demonstrates that wetlands can be constructed in strategic locations to clean up rivers while producing enough biomass to serve as a clean energy source. In the Netherlands, like much of the world, surface runoff, particularly from agriculture, has polluted rivers with nutrients.

To address this issue, Bastiaan Meerburg and fellow researchers planted a field with the marsh plant common reed, Phragmites australis, and then redirected a near-by nutrient rich stream into the newly constructed wetland. The water was held in the wetland for a period of time before being released back into the stream.

Common reed is able to grow in the water and absorb nutrients which are removed from the system as the plant is harvested. The researchers measured water quality at both the intake and outtake of the wetland and found that as much as 47% of the nitrogen and 45% of the phosphorus was removed. They discovered that higher nutrient loads resulted in higher levels of removal.

The constructed wetland was also highly productive. After only one year of growth post-establishment 221 g/m2 biomass had accumulated and after two years, the amount increased to 903 g/m2. These findings show that constructed wetlands can provide a useful tool to prevent eutrophication in surface waters while generating a potentially valuable crop for farmers.

However, the researchers also caution that “choosing the moment of harvesting may have important consequences for the soil-plant-microbe system, especially on aspects as nutrient-removal, methane emission, filter regeneration and biomass production,” although this was not examined in the study. The researchers were able to determine that the amount of time the water remained in the system (residence time) affected the degree of sanitation efficiency.

The study provides additional empirical evidence that multifunctional wetland systems can be constructed to provide multiple benefits to society. In addition to nutrient retention and biomass production, the constructed wetlands in the study provided flood protection by storing water. With sea level rise from climate change, flood management is predicted to become increasingly important, particularly in the Netherlands where over half of its land already sits at an elevation below sea level. 

-Reviewed by Evyan Borgnis

Meerburg, B., Vereijken, P., Visser, W., Verhagen, J., Korevaar, H., Querner, E., Blaeij, A., & Werf, A. (2010). Surface water sanitation and biomass production in a large constructed wetland in the Netherlands Wetlands Ecology and Management DOI: 10.1007/s11273-010-9179-x