Constructed wetlands can boost functional diversity

Posted on March 23, 2016

The success of freshwater restoration projects has typically been assessed by reference to structural ecosystem features, such as water quality and species diversity. To date, indicators of ecosystem function have seldom been used for restoration assessment, but this situation is likely to change with the growing recognition that ecosystem processes are reflected in the biological traits of aquatic organisms. Spanish researchers compared the functional diversity of macroinvertebrates in three artificial wetlands constructed 5–25 years earlier with that of three degraded natural wetlands on the floodplain of a regulated river. The study area was the Ebro River (NE Spain), which has been drastically affected by flood mitigation measures and agricultural and urban development. The project focussed on three riparian sites (each comprising one constructed and one natural wetland less than 1 km apart) in the river floodplain. Once excavated, the constructed wetlands (0.4-0.9 ha in area) were filled with water seeping from hillslope aquifers, and riparian vegetation was transplanted to the wetland banks to stabilise the shore and assist colonisation. At each site, the macroinvertebrate community was sampled in winter and spring, and its functional composition was described by reference to 11 biological traits, namely life cycle duration, the potential number of generations per year, aquatic stages, dispersal, resistance stages, locomotion and substrate relations, respiration, body size, reproduction, diet and feeding habits. Analysis showed that in the natural wetlands, macroinvertebrates tended to include relatively large deposit-feeding and predatory organisms with long life-spans, asexual reproduction and resistant forms such as cocoons. By contrast, the constructed wetlands featured more taxa with small bodies, short life-spans, active locomotion (e.g. swimmers, fliers), and species that reproduce via free eggs and feed by shredding or scraping. Taxonomic and functional richness were both significantly higher in constructed wetlands than in natural wetlands. These differences were partly explained by the fact that levels of inorganic nitrogen, phosphorus and organic matter (and thus the likelihood of eutrophication) were lower in the constructed wetlands. The greater prominence of pioneer and opportunistic species in constructed wetlands may have been helped by the presence of extra habitats in the form of gravel bottoms and submerged vegetation. These results increase confidence that wetland construction can boost the functional diversity of freshwater environments.

Reference: Espaňol, C. et al. 2015. Constructed wetlands increase the taxonomic and functional diversity of a degraded floodplain. Aquatic Sciences 77,27–44 .