The effects of road crossings on stream macro-invertebrate diversity

Although it is well known that the increasing size of the human population has a negative effect on freshwater biodiversity, the subject of whether or how the intersection of roads and streams (hereafter road crossings) influence the diversity of stream macro-invertebrates is under-researched. To fill this gap in our knowledge, we collected stream macro-invertebrates from road crossings (bridges and culverts) and compared their diversity with upstream and downstream sections. We found that road crossings had negative effects on the richness and abundance of native macro-invertebrates, as well as on the number of protected taxa. Our results showed also that alien individuals were more abundant at road crossings. These findings support the assumption that road crossings contribute to the spread of alien species. The assessment of environmental variables indicated that road crossings caused habitat modifications, and based on these it can be assumed that habitat modifications and associated phenomena (e.g. pollutants and storm events) were the major drivers of the observed patterns in biodiversity. Our results fill a knowledge gap and contribute to the deeper understanding of the effect of road crossings on freshwater biodiversity.