Nature-Based Solutions (NBS) can offer a sustainable approach rooted in ecological engineering and systems thinking, utilizing natural processes to address water quality challenges in the Black Sea Region (BSR). NBS provides adaptable, scalable, and dynamic solutions. Beyond water quality enhancement, NBS also supports ecosystem services that benefit society.

Aligned with the Blueing the Black Sea program, the report centers on identifying NBS strategies pertinent to improving water quality within the Black Sea Region. While showcasing effective technologies for mitigating water pollution, broader considerations of approach are equally considered. By exploring frameworks and best practices, this document aims to aid policy leaders and professionals in navigating the implementation of NBS.

The unique geographical characteristics of the Black Sea Region, marked by limited mixing due to bathymetry and the Bosphorus Strait, set the stage for assessing pollution management strategies. The multifaceted nature of pollution in the Black Sea, influenced by various environmental parameters and diverse pollution sources offers insights into the complex challenge.

A primary methodology revolves around upstream pollution source interception, targeting urban, peri-urban, and rural areas to prevent pollutants from reaching the sea. Several key findings elucidate effective NBS techniques. Constructed wetlands, resembling natural processes, emerge as instrumental in sewage, stormwater, and industrial wastewater treatment. Strategies for sediment management, encompassing conservation, dune promotion, and innovative practices like sand borrowing, contribute to coastal preservation. Harmful algal blooms can be addressed with potential applications of algae in bioenergy and other domains.

The report culminates in a series of recommendations for propelling NBS development, encompassing aspects like cost-effectiveness, stakeholder engagement, analytical science, circular economy integration, blended finance, localized solutions, and digital innovation. This comprehensive exploration underscores the potential of NBS as a transformative force in enhancing water quality and environmental resilience within the Black Sea Region and beyond.

The Black Sea is notably Europe's most polluted sea, requiring diverse solutions to rectify its water quality issues. The Nature-based Solutions approach (NBS approach) emerges as a promising and inclusive strategy with wide-ranging co-benefits. This report aims to showcase the effective utilization of NBS to address water pollution in the Black Sea Region. NBS has gained global traction, offering significant potential for implementation and impact. Several organizations, including The World Bank, International Union for Conservation of Nature (IUCN), Global Center for Adaptation, The Nature Conservancy, International Water Association, and Ecoshape, are actively involved in developing or supporting NBS initiatives.

Despite the growing attention, existing NBS guidelines primarily focus on climate resilience, with fewer specifically targeting enhanced water stewardship, and even fewer addressing water quality. This document seeks to compile pertinent findings and present them in a manner specifically related to water quality in the Black Sea Region. In this context, "the region" encompasses the Black Sea itself, its rivers, and their respective catchments. The study encompasses the littoral countries of the Black Sea, including Romania, Bulgaria, Moldova, Türkiye, Georgia, and partially Ukraine.

This report is organized in a systematic manner to thoroughly explore the implementation and effects of Nature-Based Solutions (NBS) aimed at improving water quality in the Black Sea area. The introduction sets the stage by explaining the rationale behind NBS implementation and introduces the unique context of the Black Sea drainage basin. Recent developments and changes in the region are highlighted. The report then delves into pollution stream diagnostics, focusing on the identification, categorization, and prioritization of relevant pollution streams affecting the Black Sea. The NBS approach for the region is explored, encompassing stakeholder engagement, the identification of NBS typologies and technologies, opportunities for private and public sector involvement, and governance considerations. The heart of the report lies in the presentation of NBS case studies, categorizing them by rivers, coasts, and offshore areas, showcasing their applicability and success. NBS project financing is thoroughly examined, considering various funding mechanisms. The report concludes by summarizing key findings, drawing conclusions from the research, and providing recommendations to guide future NBS initiatives and policies for enhancing water quality and environmental resilience in the Black Sea Region.

The Black Sea, bordered by its tributaries and the Marmara Sea leading to the Mediterranean, faces environmental challenges marked by declining biological resources, reduced species diversity, and degraded landscapes. Human activities, including pollution, eutrophication, and unsustainable fishing, have jeopardized the ecosystem's health and recreational value. The confined water exchange and pollutant runoff from European rivers exacerbate plastic pollution. The Black Sea's unique features, such as its largest meromictic basin, anoxic lower layer, and intricate ecosystems, contribute to its complex state.

Efforts to manage pollution have progressed over time, with policy advancements and improved monitoring leading to reduced pollutant loads. However, recent studies caution that regional development may reverse these gains, potentially returning the Black Sea to its eutrophic state from the 1980s. Collaborative institutions like the Black Sea Commission and initiatives like the Common Maritime Agenda have emerged to address pollution, conservation, safety, and fisheries. Coastal planning, supported by ministerial declarations, has promoted sustainable coastal zone use. Ongoing commitments, such as the Regional Action Plan on Marine Litter and the Black Sea Integrated Monitoring and Assessment Programme, reflect the region's environmental dedication.

Recognizing the complexity of the Black Sea's challenges, comprehensive stakeholder engagement has been pursued through workshops and analyses. Focus primarily lies on littoral countries due to geopolitical events. The involvement of key players, regional organizations, expert communities, and international financial institutions, guided by the Mendelow matrix, ensures informed decision-making and cooperation. This inclusive approach fosters successful implementation of Nature-Based Solutions (NBS) within the region, aligning with economic development and environmental preservation goals.

Pollution in the Black Sea is a complex issue influenced by various factors. The region faces significant anthropogenic pressures, particularly in the northwest, leading to eutrophication and elevated chlorophyll-a concentrations due to partial sewage treatment and coastal tourism. The problem is compounded by detectable bilge oil dumping, possibly due to cost-cutting measures. Pollution enters the Black Sea Region through river systems and human activities can often exacerbate this by disrupting river dynamics. Traditional engineering solutions, although addressing some problems, can create new challenges, such as in the case of alterations to the Danube floodplain that have disrupted water quality regulation. Nature-Based Solutions (NBS) emerge as a holistic strategy to maintain vital water body integrity. Addressing pollution primarily involves targeting sources upstream in urban, peri-urban, and rural areas to prevent contamination from reaching the sea. Restoring natural systems and connectivity within aquatic ecosystems is recognized as effective.

Nature-based solutions in river, coastal, and open sea contexts hold the potential to counter various forms of pollution and ecological challenges in BSR. Constructed wetlands are engineered to treat various wastewater types, replicating natural wetland functions without releasing pollutants. Initially seen for tertiary treatment, they now serve as source control, preventing contamination or reducing sewer pollutants. Evolving into surface and sub-surface types, with the latter being more effective due to sediment contact, these wetlands mainly focus on nutrient removal, with vertical flow wetlands enhancing nitrogen removal. Managing sediment addresses floods, erosion, and habitat protection. Sediment is vital for river flow and habitats. Recognizing sediment changes is key for nature and society. Nature-based solutions involve beach preservation, dune reinforcement, and habitat improvement. Harmful algal blooms, caused by excessive nutrients, pose risks in the Black Sea, where human-induced biodiversity loss threatens marine life and oceans' ecosystem services. Algae harvesting for renewable energy and food production, along with initiatives that reintroduce key species, aim to restore depleted European seas, offering nature-based solutions to counter biodiversity loss and improve water quality.

The urgent need for addressing climate change demands more investment in Nature-based Solutions (NBS), which currently receive only 3% of global climate funds. Current annual allocations for NBS projects are approximately $133 billion, mostly from public financing. Private sector involvement is limited, focusing on sustainability and offsets. Challenges include cost uncertainty, lack of standardized revenue models, and investor understanding. Philanthropies, donors, and Development Finance Institutions are key actors in mobilizing funding, along with blended finance approaches combining public and private sources. Measuring impact and cost-benefit analysis will be crucial for private engagement and ensuring sustainability.

A governance framework for NBS in the Black Sea Region should emphasize integrated mechanisms for wastewater management, guided by relevant agencies and collaborative principles. Multi-level governance involving state agencies at different levels, along with non-state actors and communities, aims to ensure effective NBS implementation. Challenges include harmonization of policies influenced by EU directives, limited technical capabilities, and conflicting roles in enforcing environmental regulations. While green infrastructure and NBS align with global and EU frameworks, integration into national strategies varies among Black Sea countries. Moldova showcases NBS integration in policies emphasizing water use, biodiversity, and wetland restoration. Addressing land-based sources (LBS) pollution, responsible for over 80% of marine pollution, requires transboundary cooperation and action-oriented obligations to protect the Black Sea's ecological integrity.

Some key recommendations arise from the team’s analysis of case studies, NBS best practices, and context-specific observations about the Black Sea. They suggest prioritizing cost-effective methods like Vertical Flow Constructed Wetlands (VFTWs) and integrating them with traditional grey infrastructure for optimized performance. Stakeholder engagement is crucial throughout the project lifecycle to ensure community ownership and address challenges. Robust analytical science and cost-benefit analyses are emphasized to provide evidence of the social and ecological benefits of NBS. Multi-stakeholder collaboration involving local communities, governments, and private enterprises is encouraged for successful design and implementation, integrating NBS solutions into urban-rural contexts. A circular economy approach for resource recovery and managing trade-offs based on project goals is recommended. Lastly, leveraging blended finance mechanisms, combining grants and debt, is highlighted to attract private investment for sustained project success, especially for smaller-scale initiatives.

Nature-based Solutions, rooted in ecological engineering and earth sciences, relies on natural systems for sustainability. It employs systems thinking, analyzing natural stocks and flows in specific contexts, acknowledging spatial and temporal boundaries. The NBS approach stands in contrast with traditional engineering, but often strategically combines green and grey infrastructure. This allows them to be adaptable and dynamic, lacking a fixed recipe yet offering scalable and sustainable solutions. Beyond water quality, this approach can also enhance ecosystem amenities that benefiting human societies through regulating, provisioning, cultural, and supporting services. Overall, NBS can improve water quality, empower communities, enhance infrastructural resilience, all crucial in addressing problems posed by climate change.

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Before exploring specific solutions, it's crucial to adopt a clear approach once the problem is identified. A thorough understanding of the historical and present-day hydrology, causes, and types of pollution in the Black Sea has now been established. The application of a sound Nature-based Solutions approach (NBS approach) can help the practitioner tackle pollution issues of this scale and complexity.