Abstract
Urbanization impacts stream ecosystems globally through degraded water quality, altered hydrology, and landscape disturbances at the catchment and riparian scales, causing biodiversity losses and altered system functioning. Addressing the “urban stream syndrome” requires multiple mitigation tools, and rehabilitation of riparian vegetation may help improve stream ecological status and provide key ecosystem services. However, the extent to which forested riparian buffers can help support stream biodiversity in the face of numerous environmental contingencies remains uncertain. We assessed how a key indicator of stream ecological status, benthic diatoms, respond to riparian habitat conditions using 10 urban site pairs (each comprising of one unbuffered and one buffered reach), and additional urban downstream and forest reference upstream sites in the Oslo Fjord basin. Diatom communities were structured by multiple drivers including spatial location, land use, water quality, and instream habitat. Among these, riparian habitat condition independently explained 16% of variation in community composition among site pairs. Changes in community structure and indicator taxa, along with a reduction in pollution-tolerant diatoms, suggested tangible benefits of forested riparian buffers for stream biodiversity in urban environments. Managing urban impacts requires multiple solutions, with forested riparian zones providing a potential tool to help improve biodiversity and ecosystem services.
Highlights
Urbanization is a driver of global environmental change with a disproportionate impact on freshwater ecosystems [1,2]
Our case study focused on benthic diatoms, an important organismal group in stream–riparian networks, and we were able to demonstrate tangible benefits of forested riparian buffers in the urbanized Oslo basin
Studies have indicated that common diatoms in our study, such as Achnanthidium minutissimum, may be important sources of essential long-chain fatty acids that help fuel aquatic-terrestrial food webs [97,98,99]
Summary
Urbanization is a driver of global environmental change with a disproportionate impact on freshwater ecosystems [1,2]. Urbanization causes complex changes in stream hydrology, geomorphology and biogeochemical cycles, contributing to declines in biodiversity and altered system functioning [4,5,6]. Adjacent riparian zones in urban stream networks are often profoundly transformed through vegetation removal, bank reinforcement, imperviousness, and soil degradation leading to further impacts on stream ecosystems [7]. Changes due to urbanization often lead to catchment-wide impacts reaching far beyond the urban area [2], with cumulative effects driving changes in communities downstream [11]. There is great interest in developing effective management strategies to help reverse impacts of urbanization and improve biodiversity and ecosystem services in urban landscapes [12]
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