Assessment of the biological integrity of the native vegetative community in a surface flow constructed wetland treating industrial park contaminants

A study was conducted to evaluate the biological integrity of a constructed wetland receiving landfill leachate and stormwater runoff from the Burnside Industrial Park, Dartmouth, Nova Scotia. The biological integrity of the constructed wetland was tested in the second growing season using vegetative community monitoring. The metrics analyzed were species diversity, species heterogeneity (dominance) and exotic/invasive species abundance. There was no significant difference in the plant species diversity between the constructed wetland and the reference site. However, the constructed wetland supported a higher plant species richness than the reference site. The top three species in the constructed wetland were tweedy’s rush (Juncus brevicaudatus), soft rush (Juncus effusus) and fowl mannagrass (Glyceria striata). In total, these three species occupied 46.4% of the sampled population. The top three species in the reference site were soft rush (Juncus effusus), sweetgale (Myrica gale) and woolgrass (Scirpus cyperinus). In total, these three species occupied a more reasonable 32.6% of the sampled population. The reference site supported greater biological integrity as it had greater heterogeneity and a smaller abundance of exotic and invasive species compared to the constructed wetland (3.8% versus 10.7%). Although poor heterogeneity and the presence of weedy, exotic species can be a sign of degraded biological health and future problems, these are also common indicators of a system simply undergoing early succession. As the constructed wetland matures, its plant biodiversity may actually decrease, but its integrity, as measured by exotic and invasive species abundance as well as heterogeneity, is expected to increase, so long as invasive species present in the constructed wetland remain controlled through weeding during the first few growing seasons.