Original article in English – http://www.constantinealexander.net/2016/06/constructed-wetlands-boost-biodiversity.html

Section of an artificial wetland for stormwater treatment which was constructed by the University of New Hampshire Stormwater Center. Image: University of New Hampshire Stormwater Center, 2012.

By Science for Environment Policy

Constructed wetlands are used in many countries as green infrastructure for wastewater treatment, but a new study suggests they can also be important sites for biodiversity.

This paper reports on a constructed wetland in an urban area of Italy that contributed to an increase in the number of plant species by over 200%. Researchers say the ability of constructed wetlands to boost biodiversity could support local development.

Natural wetlands are among the most biodiverse ecosystems on Earth, and constructed wetlands (i.e., reed bed treatment systems) are no exception.

Constructed wetlands are designed to mimic natural wetland systems and are used worldwide for wastewater treatment. Provided there is sufficient surface area, they can remove contaminants similarly to traditional systems, but with lower operating costs.

The study focused on a constructed wetland named EcoSistema Filtro (ESF), which was built in 2004 in Sardinia. The treatment wetland is located within the Molentargius-Saline Regional Natural Park, which is of international importance due to its high biodiversity (part of the Natura 2000 network and the Ramsar Convention on Wetlands).

ESF is a free-water surface constructed wetland covering an area of 37 hectares, and the treated water flows DIRECTLY into the natural park.

The researchers monitored data on plants growing in this constructed wetland over a period of eight years (2005-2013) by surveying three plots twice a year. At least once a month, a walkover survey was also conducted to collect data on each plant species observed. The researchers then compared data collected over the years to evaluate changes in flora during the development of the wetland ecosystem.

Plant colonization began shortly after the construction of the wetland and increased gradually, with the greatest increase during the first and second years. Over the eight years of the study (except at the turn of 2006/2007, when plants were mechanically removed as part of management measures), the number of recorded species steadily increased. The number of taxa increased by 14% each year.

In the final year of the study, researchers recorded 275 different plant species (an increase of 224% compared to the first year). The wetland flora accounted for more than half (54%) of the total flora of the regional park, including many endemic species. Six different groups of endemic plants benefited from the saline and nitrogen-enriched environment provided by the constructed wetland.

Researchers also recorded a significant number of alien species, which in 2013 represented 12% of the wetland's entire flora. The authors of the study suggest that these plants colonized the wetland from surrounding areas influenced by human activity. However, these alien species did not appear to have a negative impact on endemic species. Six percent of the observed plant species were protected, including two on the IUCN Red List of Threatened Species.

The researchers assume that the constructed wetland boasts such high species diversity due to its location (the interface between fresh and saline water), and also because it provides an ideal habitat for several species of migratory birds that CAN disperse seeds and plant fragments [1, 2].

This constructed wetland, although situated within a natural park yet surrounded by the disturbance of an urban environment, provides a nature-based solution that, besides wastewater treatment, brings additional benefits in terms of conserving and enhancing biodiversity.

This study demonstrates the positive impact that artificially created ecosystems CAN have on local biodiversity and highlighted the importance of protecting nature even during the operation of wastewater treatment plants (e.g., avoiding management interventions such as mechanical plant removal like that conducted at ESF). The researchers also believe that areas like this CAN greatly contribute to sustainable development in urban areas.

Lewis, L., Behling, E., Gousse, H., Qian, E., Elphick, C., Lamarre, J., Bêty, J., Liebezeit, J., Rozzi, R. & Goffinet, B. (2014). First evidence of bryophyte diaspores in the plumage of transequatorial migrant birds.PeerJ, 2, p.e424

Viana, D.S., Gangoso, L., Bouten, W. & Figuerola, J. (2016) Overseas seed dispersal by migratory birds.Proceedings of the Royal Society B: Biological Sciences. 283 (1822): 20152406

Citation: De Martis, G., Mulas, B., Malavasi, V. & Marignani, M. (2016); Can artificial Ecosystems enhance local Biodiversity? The case of a constructed Wetland in a Mediterranean urban context; Environmental Management 57 (5): 1088–1097; DOI: 10.1007/s00267-016-0668-4.