Freshwater ecosystems and the aquatic ecosystem services (recreation, water quality, flood control) that they provide are affected by not only direct human activities (wetland draining, canalization) but also indirect ones at the interfaces between terrestrial and aquatic ecosystems (riparian zones) as well as in the entire watershed (land-use change). These environmental changes are also coupled with climate change that affect precipitation, temperature, and run-off which in turn impact negatively habitat quantity and quality, species diversity locally (punctual effects) and regionally (cumulative effects). In urban areas, riparian zones provide important ecosystem services for recreational purposes (hiking paths and bike lines along streams), wildlife habitat, and nutrient retention and contaminant sequestration. Hence, it is important to quantify the degree of local and regional threats (road crossing, stream temperature, wetland drainage) to the maintenance of aquatic network functions (hydrology) and aquatic ecosystem services (recreation along riparian zones) in urban watersheds.
To study the stream connectivity, the dendritic network approach has been proven powerful to quantify functional (species dispersal) connectivity. Here, we integrate a multiscale framework and network approach to determine the combined the effects of landscape alteration and fragmentation on species persistence (alpha-diversity), species movement (beta-diversity) within stream (fish) and across wetlands (amphibian) in urban watersheds.
Stream fish communities from 159 sites across five watersheds in Toronto (Canada) and complete barrier inventories on the watersheds were used to assess the relative effects of land-use and connectivity for each watershed at the segment-level and at the regional-level. Generalized mixed linear models were used to test how diversity is affected by land-use and connectivity. Then we assess how storm water ponds can help maintain connectivity for amphibians in urban areas given increasing urbanization and traffic volume in one watershed.
Overall, results show the importance of considering scale specific effects when assessing the effects of land-use and fragmentation on community structure. Alpha diversity is related to local habitat variables, whereas beta diversity is related to network size and the level of dendritic connectivity. Storm water ponds facilitate increased habitat connectivity for amphibians in urban areas, but they can have negative effects on local populations due to low habitat quality. Using these approaches, we determine the resilience of urban watersheds to maintain aquatic ecosystem services (recreation and species habitat) in Toronto.