The effects of urbanization on trophic relationships in constructed wetlands

Constructed stormwater wetlands are one strategy for mitigating the negative effects of urbanization on aquatic ecosystems. However, the biotic community in these wetlands generally is dominated by organisms able to tolerate poor water quality. Reduced macroinvertebrate diversity and abundance in comparison to natural wetlands, and prevalence of invasive species, such as Gambusia, can influence the flow of energy through food webs. We used stable-isotope analysis (δ¹³C and δ¹⁵N) of food webs to assess whether the amount of catchment urbanization (total imperviousness [imperviousness] 5 % catchment covered in impervious surfaces) influenced basal resources and trophic relationships in constructed wetlands in Melbourne, Australia. As imperviousness increased, the abundance and diversity of macroinvertebrates decreased significantly and the values of δ¹³C and δ¹⁵N recorded for fishes and macroinvertebrates increased significantly. An increase in imperviousness was associated with a decrease in the mean trophic position of fishes and an increase in the mean trophic position of macroinvertebrates. Our results suggest that sources of C differed between sites of low and high imperviousness and that N sources increased with increasing imperviousness. Our study provides an understanding of the likely consequences of disturbance associated with urbanization on the foodweb structure of constructed wetlands.