“Nature-based Solutions for River Landscapes: categories, spatial characteristics, and effects on ecosystem services”

The concept of Nature-based solutions (NbS) could arguably alleviate water-borne challenges such as flood, droughts and water quality deficits in sustainable ways by harnessing ecological processes (Nesshöver et al., 2016). In addition, such NBS, have the potential to simultaneously safeguard biodiversity and enhance ecosystem services. While a great number of such NbS have already been developed in disciplines such as soil engineering, green infrastructure and river restoration, no systematic overview and characterization exists so far (European Commission, 2015; Raymond et al., 2016a). The objectives of this contribution are to provide a typology of NbS for water-borne challenges in river landscapes and to characterize the potential impacts of these NbS types on a selected set of ecosystem services. Our methods include a focused literature review of techniques that can be interpreted as nature-based solutions from a variety of sources such as ecological engineering, river restoration and European water regulations. With the techniques compiled, a typology of NbS was developed, based on a synthesis of prior suggestions from the literature. A spatial diagram is developed to explore the potential spatial expansion of and spatial relationships between the NbS types. The potential impacts of NbS types on selected ecosystem services are assessed through a Delphi-method to elicit expert opinions. We identify 15 types of NBS, ranging from riverbank control to floodplain restoration methods. The expert-based assessment of likely impacts on ecosystem services shows a differentiated picture, highlighting that NBS do not contribute automatically to the provision of all ecosystem services, but that substantial trade-offs may occur and need to be taken into account in planning and management. We close with recommendations for further research and practical application. Taken together, our research can provide an essential contribution to systemize the emerging scholarship on NbS in river landscapes, and to help in selecting appropriate NbS in practice.