| Streamside (riparian) buffer zones are among our best management tools for mitigating the unwanted effects of land use on streams, rivers, and lakes. Forested buffer zones help preserve aquatic ecosystem health by removing excess nutrients lost from upland soils, shading water surfaces, and providing terrestrial organic matter that supports aquatic food webs. Yet, the effectiveness of riparian buffers as a conservation tool varies based on how they are designed. In Sweden, a legacy of intensive forestry has given rise to buffers dominated by coniferous trees (e.g., spruce), which may not promote good water quality and diverse aquatic communities (1). For this reason, current policy recommends prioritizing broadleaf trees (e.g., birch) along our waterways (2). While there may indeed be benefits to increasing the plant diversity and ‘deciduousness’ of riparian zones, the consequences of doing this have never been tested in the Swedish landscape. Without this evidence, it is difficult to push forward clear sets of recommendations to public and private landowners.
Advancing innovative approaches to riparian buffer design is crucial to water conservation, but also captures key aspects of soil conservation, and is thus central to the 2021 theme for Oscar and Lili Lamms research call. To achieve this end, this PhD project will test the significance of prioritizing broadleaf trees in riparian buffer zones for water quality, stream ecosystem ‘functioning’, and aquatic food web structure. Our specific research objectives include:
1. Test the relative ability of broadleaf versus coniferous trees to promote nutrient filtration/retention in riparian soils.
2. Evaluate how increasing broadleaf cover influences key ecosystem functions in streams, including aquatic metabolic activity and nutrient retention.
3. Assess relationships between broadleaf cover, invertebrate biodiversity, and the trophic complexity of stream food webs.
To meet these objectives, we have assembled a supervisory team of experts in riparian ecology, stream ecosystem science, and buffer management in the Swedish landscape. Our project will integrate ‘whole-system’ estimates of ecosystem functioning in streams with different buffer properties, isotopic tools to address trophic dynamics of aquatic communities, and a novel mesocosm experiment to explore mechanisms under controlled conditions – all aimed at testing whether broadleaf vegetation enhances how buffer zones carry out their most vital functions. Results from this work will reveal how new approaches to managing boreal forest landscapes might promote the plant, soil, and aquatic processes that collectively underpin healthy streams and rivers. Finally, our research team has a clear record of advancing ideas for buffer design and engaging stakeholders to achieve policy change. The PhD student recruited for this project will have the opportunity to participate in this dialog and gain experience in efforts to translate scientific understanding into practical application.
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