Author(s): Shifteh Mobini; Amir Rezvani; Elisie Karesdotter; Zahra Kalantari

Linked Author(s): Shifteh Mobini, Zahra Kalantari

Keywords: 1. Nature-Based Solutions (NbS) 2. Small Stream Restoration 3. Water Quality Management 4. Biodiversity Enhancement 5. Expert Perspectives 6. Community Engagement 7. Ecosystem Services and Societal Benefits

Abstract: Book of Extended Abstracts 41st IAHR World Congress 22-27 June 2025 Singapore EVALUATING THE EFFECTIVENESS OF NATURE-BASED SOLUTIONS FOR SMALL STREAM RESTORATION Shifteh MOBINI1, Amir REZVANI2, Elisie KARESDOTTER3, Zahra KALANTARI4 1 Trelleborg Municipality Sweden 1 Lund University, Sweden 1email: shifteh. mobini@trelleborg. se 2,3, 4 Department of Sustainable Development, Environmental Science and Engineering (SEED), KTH Royal Institute of Technology, Sweden. 2email: rezvani@kth. se 3email: elisie@kth. se 4email: zahrak@kth. se ABSTRACT 1. Introduction Small streams play an essential role in maintaining ecosystem services, biodiversity, and water quality. Despite their significance, they have historically received less attention in research and management compared to larger river systems. Small streams, especially those flowing through agricultural landscapes, face a range of environmental stressors such as nutrient runoff, pesticide application, and physical modifications, all of which can degrade their ecological health and reduce the services they provide (Craig et al., 2008; Roni et al., 2008). In Trelleborg, a municipality in southern Sweden, several Nature-Based Solutions (NbS) have been implemented to restore and manage small streams (Figure 1). These NbS are designed to protect, manage, and restore ecosystems to address societal challenges, such as climate adaptation and biodiversity conservation while delivering co-benefits for nature and people (Cohen-Shacham et al., 2016; Kalantari et al., 2020). Some of the NbS applied in the region include wetland creation, stream remeandering, and riparian zone restoration, aimed at improving water quality, reducing nutrient inputs, and enhancing biodiversity in small streams. Figure 1. Map of the study area in Trelleborg, southern Sweden, showing the catchments included in this study. Managing small streams with NbS is especially critical in agricultural landscapes, as these areas are often the source of significant nutrient pollution, which small streams help to convey to larger water bodies (Sweeney et al., 2004). However, there is a substantial gap in the research regarding the long-term effectiveness of NbS, specifically in small streams, as much of the existing literature tends to focus on larger river systems or wetlands (Palmer et al., 2010). This study addresses this gap by evaluating the effectiveness of NbS interventions in six small streams in Trelleborg: Tullstorpsan, Stastorpsan, Albacksan, Dalkopingean, Gislovsan, and Vemmenhogsan. Understanding the outcomes of NbS in small streams is crucial for informing future restoration projects and enhancing the resilience of these ecosystems. The findings from this study will contribute to achieving the United Nations Sustainable Development Goals (SDGs), particularly SDG 6 (Clean Water and Sanitation) and SDG 13 (Climate Action), which highlight the need for sustainable water management and climate-resilient solutions (United Nations, 2015). Moreover, this study will provide guidance for urban planners, water resource managers, and policymakers working in regions where small streams face similar ecological and management challenges. 2. Methods This study utilizes a multi-disciplinary approach to evaluate the effectiveness of NbS in Trelleborg’s small streams, combining qualitative and quantitative methods. The methodology includes thoroughly reviewing historical NbS projects, expert interviews, NbS inventory creation, and spatial analysis using Geographic Information Systems (GIS). The following subsections describe each of the key methodological steps in detail. 2.1. Documentation Review A comprehensive review of existing documentation and reports on NbS projects in the Trelleborg region forms the foundation of this research. This includes analyzing Southwestern Skane Water Council reports, environmental impact assessments, and municipal records dating back over the last decade. These documents provide essential historical data on NbS implementations, such as wetland creation, shoreline protection, and stream remeandering, and help identify each project's key milestones and objectives. 2.2. Expert Interviews Semi-structured interviews were conducted with five key stakeholders involved in managing Trelleborg's small streams. This included three municipal experts and two external specialists, all with direct experience with NbS in the region. The interviews followed a flexible format, allowing for in-depth discussions on the successes, challenges, and long-term impacts of each NbS project. The primary focus of the interviews was to gather expert insights on: • The design and implementation process of NbS in small streams • The perceived effectiveness of these solutions in meeting their goals (e. g., reducing nutrient inputs, improving flood resilience) • Challenges encountered during implementation and lessons learned The interviews were transcribed and analyzed using thematic analysis, a qualitative method that allows researchers to identify, analyze, and report patterns within data. This helped contextualize the NbS projects' effectiveness from a practical, on-the-ground perspective. 2.3. NbS Inventory Creation A detailed inventory of all NbS implemented in the six streams was created, categorizing each solution by type and location. This inventory is a key data source for further spatial analysis and evaluation. Each NbS was evaluated based on its objectives, timeline, and key outcomes, as reported in the reviewed documents and expert interviews. This inventory provides a clear visual and descriptive database of all stream interventions. 2.4. GIS Spatial Analysis The spatial component of the analysis was conducted using ArcGIS Pro, which allows for the integration of various spatial data sets, including land use maps, stream delineations, and NbS locations. The analysis involved: • Catchment delineation: Identifying the boundaries of the six small streams using hydrological models and land use data. • Mapping NbS: Overlaying the locations of each NbS project on the catchment maps to visualize the spatial distribution of interventions. • Land-use impact assessment: Assessing how surrounding land use (e. g., agriculture, urbanization) influences the effectiveness of NbS, especially in terms of nutrient runoff and sediment transport. The GIS analysis also allowed for identifying spatial patterns, such as clusters of NbS projects or areas that remain under-addressed by current interventions. Additionally, it was used to model the potential expansion of NbS projects in areas where they might provide further ecological or flood-management benefits. 2.5. Data Integration and Analysis The qualitative data from the expert interviews were integrated with the quantitative spatial data using thematic coding. This technique allows for identifying recurring themes or challenges mentioned by experts and then comparing them with the physical and spatial characteristics of the NbS projects. For example, experts’ insights on nutrient reduction were cross-referenced with GIS data on nearby agricultural land use to evaluate the actual effectiveness of the projects in these areas. 3. Results/Findings This study anticipates several key findings that will provide insights into the performance of NbS in enhancing ecosystem services, supporting biodiversity, and managing flood risks in agriculturally impacted watercourses. Below is a summary of the anticipated results: 3.1. Comprehensive Inventory of NbS Types The creation of a detailed inventory across the six small streams is expected to reveal a variety of implemented NbS types. This inventory will help categorize each NbS by type, objective, and location, offering a clear understanding of how different interventions are applied based on specific stream characteristics and challenges (Table 1). 3.2. Performance of NbS Solutions It is anticipated that the study will identify key performance indicators for NbS effectiveness in small streams. For instance: • Nutrient Reduction: Wetlands and buffer zones are expected to be particularly effective in capturing nutrients from agricultural runoff, thereby improving water quality and reducing nutrient inputs into downstream ecosystems. • Biodiversity Enhancement: Stream remeandering and riparian restoration are likely to enhance habitat diversity, providing increased opportunities for species richness and ecological resilience in these streams. • Flood Management: NbS solutions such as remeandering and wetland creation are anticipated to improve flood resilience by increasing water retention capacity and reducing peak flows, particularly during storm events. These solutions can also enhance groundwater recharge, contributing to long-term water security in the region. 3.3. Spatial Patterns of NbS Implementation This project’s analysis will provide visualizations of spatial patterns, revealing areas with concentrated NbS efforts and potential gaps in coverage. This spatial data will allow for identifying clusters where multiple NbS projects are implemented within proximity, which could result in synergistic benefits. Conversely, the analysis may also highlight regions within the municipality where NbS coverage is limited, offering insights into areas for potential future interventions. 3.4. Key Success Factors and Challenges The study will identify essential success factors contributing to effective NbS implementation in small streams through expert interviews and thematic analysis. Anticipated success factors may include: • Stakeholder Engagement: Active involvement of local stakeholders, such as landowners and community groups, has been shown to improve project adoption and long-term sustainability. • Appropriate NbS Selection: Aligning specific NbS types with the unique characteristics of each stream is crucial for maximizing effectiveness. Additionally, challenges are expected to emerge from the interviews, particularly regarding resource limitations, regulatory barriers, and maintenance demands. These insights will highlight common obstacles in NbS implementation and provide lessons for future projects in similar regions. 3.5. Expert Perspectives and Lessons Learned Finally, the qualitative data from expert interviews will yield valuable perspectives on the perceived effectiveness of NbS in achieving ecological and societal goals. Experts’ insights into the adaptability, limitations, and observed benefits of each NbS type will provide practical knowledge for future projects. This study is expected to document lessons learned, particularly regarding the importance of adaptive management and continuous monitoring, which are crucial for maintaining the effectiveness of NbS in dynamic small-stream environments. Table 1. Summary of NbS Implementations across Six Streams in Trelleborg, Sweden. Stream Name Type of NbS Implementations Year Implemented Objectives Key Outcomes Notes on Implementation Tullstorpsan Wetland Creation 2009 - Reduce nutrient inputs to the Baltic Sea - Improve water quality - Reduce erosion - Minimize dredging need - Manage flooding - Enhance biodiversity - Promote outdoor recreation - Improved water quality, - visitor engagement, - Notable wetlands: Borringe mad, Jordberga demonstration site, Skateholm wetland; - Project initiated by landowners Stastorpsan Shoreline Protection Ongoing Protect water quality and natural habitats Enhanced biodiversity in Amossarna Part of the Amossarna water system within the catchment Albacksan - River meandering - Wetland creation/restoration 2007 - Improve flood management, - Enhance recreation - Increased recreational area, - Restored wetlands Implemented in Alback area with recreational improvements Dalkopingean - Erosion Protection, - Spawning Bed Creation, - Stream Cleaning - Flow concentrators 1990s - Protect trout spawning areas - Enhance trout habitat and production - Higher trout populations, - Improved habitat Implemented by Dalkopinge Fishing Conservation Association Gislovsan Shoreline Protection Ongoing Protect sensitive orchid flora Conservation of orchid species No major NbS implemented due to concerns over ecosystem impact Vemmenhogsan Pesticide Reduction 1990 Reduce agricultural runoff 90% reduction in pesticide leakage Collaboration with landowners References Cohen-Shacham, E., Walters, G., Janzen, C., & Maginnis, S. (2016). Nature-based solutions to address global societal challenges. IUCN: Gland, Switzerland, 97,2016-2036. https: //doi. org/http: //dx. doi. org/10.2305/IUCN. CH. 2016.13. en Craig, L. S., Palmer, M. A., Richardson, D. C., Filoso, S., Bernhardt, E. S., Bledsoe, B. P., Doyle, M. W., Groffman, P. M., Hassett, B. A., & Kaushal, S. S. (2008). Stream restoration strategies for reducing river nitrogen loads. Frontiers in Ecology and the Environment, 6 (10), 529-538. https: //doi. org/ https: //doi. org/10.1890/070080 Kalantari, Z., Ferreira, C. S. S., Deal, B., & Destouni, G. (2020). Nature‐based solutions for meeting environmental and socio‐economic challenges in land management and development. In (Vol. 31, pp. 1867-1870): Wiley Online Library. Palmer, M. A., Menninger, H. L., & Bernhardt, E. (2010). River restoration, habitat heterogeneity and biodiversity: a failure of theory or practice? Freshwater Biology, 55,205-222. https: //doi. org/https: //doi. org/10.1111/j. 1365-2427.2009.02372. x Roni, P., Hanson, K., & Beechie, T. (2008). Global review of the physical and biological effectiveness of stream habitat rehabilitation techniques. North American Journal of Fisheries Management, 28 (3), 856-890. https: //doi. org/https: //doi. org/10.1577/M06-169.1 Sweeney, B. W., Bott, T. L., Jackson, J. K., Kaplan, L. A., Newbold, J. D., Standley, L. J., Hession, W. C., & Horwitz, R. J. (2004). Riparian deforestation, stream narrowing, and loss of stream ecosystem services. Proceedings of the National Academy of Sciences, 101 (39), 14132-14137. https: //doi. org/https: //doi. org/10.1073/pnas. 0405895101 United Nations. (2015). Sustainable Development Goals. United Nations. https: //sdgs. un. org/goals

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Year: 2025