The Ecological Role of Roadside Stormwater Ponds - Potential to Support Biodiversity

The increased recognition that roads may impair the aquatic environment and ecosystems has led to a shift from conventional drainage systems toward blue-green solutions such as stormwater ponds. Research on blue-green stormwater solutions has until now mainly focused on water quantity and quality. The aim of this study was to explore the ability of highway stormwater ponds to provide suitable habitats and support, especially macroinvertebrate biodiversity, and to identify the key environmental variables that affect biological community composition and the number of taxa, utilizing data at regional and global scales. Ultimately, this research informs design recommendations for stormwater systems that simultaneously provide multiple ecosystem services. The results of this thesis indicate that larger ponds are better for supporting aquatic biodiversity due to a more heterogeneous environment and the ability to dilute pollutants. Also, the presence of other ponds in the vicinity of the stormwater ponds can facilitate the movement of invertebrates between ponds through increased connectivity. An apparent negative effect of pollution levels on the macroinvertebrate community composition was observed, but not on the biodiversity measured as the number of taxa or Shannon index. The analyses based on the datasets identified using both morphology and DNA metabarcoding demonstrated that DNA metabarcoding captured and identified more than twice the number of taxa compared to morphological identification. Application of DNA metabarcoding greatly increases the number of species identified at each sampling site, thereby providing more accurate information regarding the way the ponds function and how they are affected by management. Subsequently, the differences in the macroinvertebrate community composition between different types of ponds were compared at the regional and global scale. The results indicated that environmental characteristics, especially conductivity and pH, were different between different types of ponds. Alpha and gamma diversity were similar or even higher in manmade ponds compared to natural ponds due to very different macroinvertebrate communities. Moreover, generally ponds exhibited high levels of spatial heterogeneity, which subsequently enhances gamma diversity. In summary, stormwater ponds have the potential to provide suitable habitats to foster biodiversity. When such systems are created, larger ponds should be built to provide more heterogeneous habitat and dilute harmful pollutants. Additional ponds should also be created in the vicinity of the ponds, thereby promoting aquatic biodiversity through higher connectivity. Although stormwater ponds accumulate pollutants due to their primary functions, this pollution retention process creates a unique environment within the stormwater ponds, which are more suitable for taxa that are moderately to strongly tolerant to pollutants and that may not be found in natural ponds. In this way, stormwater ponds constitute an option in the areas along the highway so that they could combine water treatment properties with providing a suitable habitat for aquatic organisms.