Perception of ecosystem services provided by nature-based solutions (NBS) to address tourism-related challenges in coastal cities: The case of Seferihisar (TUR) and Aveiro (PRT)

Abstract

While tourism facilitates economic growth in coastal regions, the intense pressures it creates make these areas more vulnerable. Seasonal increases in the number of visitors to coastal areas—which, due to their proximity to water, have become the city's most vulnerable zones—lead to a range of problems, including the overburdening of infrastructure beyond its carrying capacity, excessive water use, waste management issues, damage to marine ecosystems caused by pollutants and improper diving, water pollution, the destruction of cultural heritage, and the loss of local identity. Nature-based solutions are highly effective in managing serious events such as the climate crisis, rising sea levels, and floods. In addition to benefits such as rainwater storage, flood control, and habitat creation, nature-based solutions can also be used for recreational activities. The 2010 report The Economics of Ecosystems and Biodiversity (TEEB) argues that the services provided by nature have economic value. In this regard, TEEB has made the economic value of resources—often described as free and unlimited—visible. Nature-based solutions (NBS), characterized as solutions that mimic nature, provide various ecosystem services just as nature does on its own. However, while NBS provide solutions to many fundamental urban problems such as the climate crisis, natural disasters, and global warming, they have not yet been systematically evaluated in terms of tourism pressures and tourism-related challenges. On the other hand, the EU NBS Handbook highlights a gap in the literature by overlooking the effectiveness of NBS in addressing tourism-related challenges (TRC). It is believed that leveraging nature-based solutions to alleviate tourism pressures in coastal cities will provide a dual benefit: demonstrating how to adapt to tourism's destructive pressures on nature while simultaneously enhancing tourism's appeal. By acknowledging the existence of carrying capacity, NBS should be used to develop policies that prevent tourist crowds from concentrating solely in coastal areas and instead help distribute the density across the city as a whole.This study focuses on two case studies—Seferihisar (TUR) and Aveiro (PRT)—to examine the effectiveness of Nature-Based Solutions (NBS) provided by ecosystem services to address tourism-related challenges (TRC) in coastal cities. Since both case studies involve coastal settlements, the study sought to answer the questions: "Do Nature-Based Solutions (NBS) provide specific ecosystem services (ES) capable of addressing particular tourism-related challenges (TRC) in coastal cities?" and "If so, which specific tourism-related issues can be effectively mitigated by the ES provided by these prioritized NBS?" To establish a supply-demand balance, eight tourism-related challenges (TRC) that may be encountered in coastal cities were first identified. The TEEB framework was used as an ecosystem services classification to address the demand created by TRC. Of the 17 subcategories, two were excluded based on relevance, leaving 15 services to be considered. For the ecosystem services supply score, 13 NBS that could be linked to TRCs were identified. Examples of nature-based solutions were sourced from the UNaLab, INCCA, and Urban Nature Atlas (UNA); qualitative data on the ecosystem services they provide were converted into quantitative data through frequency counts, and optimized to align with the 0–5 scale used for ecosystem services. In this process, a supply matrix on a scale of 0-5 was created using a four-stage standardization method in which qualitative application examples were converted into quantitative data. Following this, in the online workshop conducted for the Seferihisar (TUR) and Aveiro (PRT) case studies, academics' ecosystem service demands (ES Demand) regarding TRC were collected. In the matching process, the mathematical alignment between the participants' demand scores and the supply scores in the literature was measured using the Mean Square Error (MSE) method. Within this scope, participants were asked to select the top-3 out of eight tourism-related challenges in order of priority via Google Forms, and to rate the ecosystem services provided by NBS capable of addressing these TRC on a 0–5 scale. After the ratings were completed, the average of ES demand scores for the first three tourism-related problems of the Seferihisar (TUR) and Aveiro (PRT) case studies was calculated using the Mean Square Error (MSE) method alongside the ES supply scores obtained from UNaLab, INCCA, and UNA sources..As a result of this analysis, it was determined that the solution that matches most optimally with infrastructure load and pollution in both case study regions is Constructed Wetlands (NBS-2).The evaluations regarding the first half of the workshop are as follows: Based on the scores assigned in the Seferihisar (TUR) case study, the priority TRC were identified as overburdened infrastructure (TRC-7), seawater pollution (TRC-2), and loss of local identity (TRC-6). To address these challenges, the following solutions were proposed: constructed wetlands (NBS-2); green corridors, boulevards, and group of tree/single lines (NBS-4); rain gardens (NBS-3); and the restoring mangroves, beaches and dunes (NBS-7), along with the creation of ponds, canals, and waterfront parks (NBS-5) were selected for the local climate and air quality regulation (ES 2.1), wastewater treatment (ES 2.4), freshwater (ES 1.3), recreation and mental and physical health (ES 4.1), and habitat for species (ES 3.1) services they provide. However, participants were able to opt for a different solution through a consensus reached in their own discussion rooms by presenting a meaningful rationale rather than relying solely on the results of the calculations. Accordingly, in the Seferihisar case study, an assessment was conducted for the second phase, specifically regarding overburdened infrastructure (TRC-7) and seawater pollution (TRC-2). The priority TRC identified in the Aveiro (PRT) case study are coastal erosion (TRC-4), loss of local identity (TRC-6), and overburdened infrastructure (TRC-7). To address these challenges, the same NBS typologies were utilized for the tourism (ES 4.2), moderation of extreme events (ES 2.3), aesthetic appreciation and inspiration for culture, art, and design (ES 4.3), erosion prevention and maintenance of soil fertility (ES 2.5), and wastewater treatment (ES 2.4) services they provide. In the Aveiro case study, a detailed assessment was conducted for the second phase specifically regarding the restoring mangroves, beaches and dunes (NBS-7); green corridors, boulevards, and group of tree/single lines (NBS-4); beach nourishment (NBS-12); and rain gardens (NBS-3).In the second half of the workshop, the suitability, feasibility, co-benefits, trade-offs, and impact levels of the identified NBS were discussed.The solutions of restoring mangroves, beaches and dunes (NBS-7) and beach nourishment (NBS-12) were assessed as having the highest impact and suitability in combating coastal erosion. However, it was determined that these solutions entail significant socio-ecological trade-offs, including the risk of ecological degradation due to the temporary closure of public beaches and the use of incompatible sand quality.To address challenges such as overburdened infrastructure (TRC-7) and seawater pollution (TRC-2), constructed wetlands, green corridors, and rain gardens have emerged as the most prominent solutions. While constructed wetlands were found to be effective in filtering surface runoff before it reaches the sea, their applicability in densely built-up coastal areas was assessed as low due to land requirements and a lack of qualified maintenance personnel. Additionally,, it has been noted that rain gardens left unmaintained can quickly turn into urban dumping grounds. On the other hand, the Aveiro group assessed the feasibility of green corridors as low due to a lack of space. This confirms that the success of NBS is largely dependent on spatial and managerial contexts. The filtration of stormwater or the integration of carbon sinks into the city can be hindered by spatial constraints. For example, rain gardens—which are necessary to address infrastructure issues—face resistance because they have the potential to reduce pedestrian crossings or park areas in already crowded tourist districts. Additionally, the risk of "greenwashing"—which refers to the application of NBS merely as an aesthetic attraction to attract new real estate investments rather than for its ecological function—has been identified as a critical barrier to the sustainability of these solutions.Following the completion of the workshop, semi-structured interviews were conducted with officials from the Climate Change and Zero Waste Directorate and the Disaster Affairs Directorate regarding the applicability of the identified NBS in Seferihisar Municipality. The primary objective of the semi-structured interview was to identify the obstacles that solutions—evaluated in a theoretical context without any restrictive factors—face or may face in being implemented on the ground.During the interviews, officials from the municipal departments were asked about the suitability, feasibility, co-benefits, trade-offs, and impact level of the solutions selected for the Seferihisar case study, specifically from the perspective of municipal administration.The semi-structured interviews confirmed that the theoretical effectiveness of NBS often conflicts with practical municipal constraints such as budget limitations, maintenance capacity, and land scarcity. Additionally, officials noted that the implementation process of these solutions could take a long time due to low motivation among the local population, that the process might get bogged down in bureaucratic hurdles, and that these areas risk being used as dumping grounds by industries, factories, or other facilities unless regular maintenance is provided. To enhance coastal resilience against tourism-related challenges, decision-makers must come together to explore feasible solutions in both theory and practice, and foster a culture of stakeholder participation. The developed NBS-ES-TRC matrix serves as a decision-support tool for local governments, enabling them to manage the trade-offs of nature-based solutions. Future coastal planning should prioritize "co-creation" strategies that combine expert knowledge with local government capacities, ensuring that nature-based solutions not only reduce environmental degradation but also sustainably enhance the carrying capacity and social well-being of tourism-dependent communities. Another important point to note for future studies is database representativeness. In the matrix created, while calculating the supply scores provided by nature-based solutions, the fact that urban solutions (rain gardens, green roofs, and walls, etc.) are numerically much more abundant in the databases, whereas coastal-focused solutions are relatively underrepresented, has created a limitation. The inability to prioritize coastal solutions according to the selected tourism-related challenges and their relegation to the background in the scoring system stems from the lack of existing application examples in the literature. At this point, it has been concluded that greater emphasis should be placed on nature-based solutions, particularly for the sustainable management of coastal areas.