Conclusions and Recommendations

Each NBS can either be combined with other NBS or with grey infrastructure to improve water quality. The combination depends on many parameters such as influent wastewater characteristics, treatment yield (nutrient removal), land availability and energy. For example, as in case of Restoring the Gârla Mare and Vrata wetlands, Romania or the largest river restoration project in Europe-Restoration of the Emscher River, stream restoration can be coupled with other management approaches such as constructed wetland, ponds, enhanced agricultural practices and sewer repair.

Engaging a diverse group of stakeholders, including potential investors, at every stage of planning, design, and decision-making is crucial to ensure the successful incorporation of Nature-based Solutions (NBS) and foster community ownership. Understanding the varying needs of stakeholders as well as constraints of specific investors during the design phase is crucial. For example, in case of Restoring the Gârla Mare and Vrata wetlands, Romania, due to changes of opinions by stakeholders and permitting issues, this project took considerably longer than planned. It shows the importance to allocate enough time to engage stakeholders and analyse the area from multiple perspectives such as protected species and habitats, hydrology, legal rights of the land and resources and economic development potential.

NBS-coupled grey infrastructure (or grey-green infrastructure) can provide multiple benefits to communities. For example in Dinxperlo (Netherlands) combining CW with a grey infrastructure (e.g.WWTP) improves the overall performance of the WWTP in the catchment as well as offer additional ecosystem services and benefits to nature and society bridging the ecological and landscape gap between the WWTP and the receiving water body.

Strong analytical science and cost-benefit analysis has a key role either as evidence to convince decision makers or as leverage points to influence policy. Besides the capability of NBS to enhance water quality, many social and ecological co-benefits bring NBS to the forefront with their provided value and encourage decision makers to invest or policy makers to include NBS as a promising solution rather than an optional luxury.

NBS are usually initiated by designers or consultants who work with developers and governments. Due to the implicit and necessary collaborative effort with local stakeholders and authorities, a multi-stakeholder approach with clear governance is needed. Thinking only about who can invest is not sufficient, multiple actors are needed for design, implementation, and operation. It is important to engage with multiple stakeholders and specially to incorporate it to urban-rural life through community networks and civil society organisations.

NBS can be used in circular economy approach together with their potential trade-offs. NBS often allow resource recovery, such as energy recovery from biomass, water reuse and sludge reuse with many existing potential trade-offs in line with local context and project objectives. In the case of Orhei Municipality, Moldova, considering the energy recovery from biomass and nutrient recovery co-befits, higher investment costs were needed to meet local regulations and to locate the treatment plant close to reuse site (crop fertigation or anaerobic digestion).

Although specific context of each NBS influence which success factors can play a role in increasing bankability, blended finance can be used to attract private investors for NBS projects which cannot deliver sufficient risk adjusted returns. In particular, small-scale NBS projects cannot be viable due to a lack of interest from investors because of costly process of securing guarantees for long-term or lack of proper feasibilities where blended finance can help to share risk between public, private and development finance. Some successful NBS as in Orhei Municipality, Moldova can be replicated within similar contexts, which is based on a close partnership with WB, EIB, local government as well as private companies.

Constructed wetlands are indicated in many cases as being one of the best choices to enhance water quality irrespective to community size when land is available at an affordable cost. For example, Orhei Municipality, Moldova case confirms that a well-designed and planned decentralized approach can help to adopt NBS (CW) for large size cities.

NBS such as constructed wetlands work in all kinds of climates. All conventional wastewater treatment is biologically based, and biological reactions slow down at low temperatures. Proper technical solutions (e.g. increasing treatment area, insulating from heat loss, deepening installation for freeze protection, and/or recirculating the water to keep it from freezing) can be adopted if high nitrification is required in cold seasons.

NBS has shown to be essential in regulating not only water quality but has significant co-benefits often being the linking pin between disparate groups (stakeholders) and the environment in which they reside or share with nature itself. Its promise also lies in its scalability, cost-effectiveness, versatility and adaptability. Together with strong policy, enforcement and clear governance, makes for a very strong approach to solve not just water quality in the Black Sea, but makes contributions to all other aspects of sustainability due to the co-benefits. As increased green financing becomes available, this sector is poised to grow and with that comes the need for increased capacity building. It is noted that NBS is still nascent in both the public and private sector and better understanding of its potential needs to be more broadly recognised (even in technically oriented circles, due to lingering scepticism). However, with increasing deployment, a more obvious business case, more data, improved standards of living and mandates such as SDGs, these sentiments are turning in favour of NBS.

Every habitat or terrain type has a suitable solution and can be further tailored to accommodate local conditions and customs. This report has shown the power of cascades, combining modular solutions, such as modernized WWTPs, with constructed wetlands which can purify the wastewater further and if connected to a (wild) river thereafter, would be able to reach a water quality that the rest of the natural ecosystem can handle before ultimately draining into the Black Sea. If sediments were not being eroded due to canalisation and industrialization this would further the cause to allow excess nutrients to naturally be taken up or be broken down by biota that. If enough time (retention ponds) is given to allow for the same processes these again improve the chances for water to be in a cleaner state before reaching the sea. If coastal communities are involved in decision making or spatial planning through stakeholder engagement, they tend to choose for sustainable solutions rather than yet another commercial development with little shared benefit for the community. All the factors mentioned in this report when combined give the Black Sea a very good chance to be restored. In basic terms, NBS can only work as well as the opportunity allows for them to thrive – much like nature itself.

Digital innovations play a significant role in enhancing Nature-based Solutions (NBS) for water quality improvement. Geospatial technologies, while not strictly nature-based themselves, are essential in monitoring, designing, and controlling NBS initiatives, both remotely and directly. Through tools like remote sensing, satellite imagery, and geographic information systems (GIS), stakeholders can monitor water bodies and surrounding landscapes, identify areas of concern, and track changes in water quality over time. By involving these digital solutions, decision-makers can better understand environmental challenges and make informed choices during the planning and implementation of NBS projects.

Data-driven approaches, facilitated by advanced data analytics and machine learning algorithms, have proven instrumental in improving water quality through NBS. By analysing large datasets, these technologies reveal valuable insights into water quality dynamics, identify patterns, and predict trends. Moreover, the effectiveness of NBS interventions can be assessed, allowing stakeholders to optimize their design and implementation strategies. Examples like WATSON (Water Analytics for Treatment Operations) demonstrate how data analytics and machine learning can be employed to optimize water treatment processes and enhance water quality. These digital tools provide essential support in the sustainable management of water resources.

The integration of sensor technologies, such as IoT devices and sensor networks, enables real-time monitoring of crucial water quality parameters like temperature, pH, dissolved oxygen, and nutrient levels. Deployed in rivers, lakes, and other water bodies, these sensors provide continuous data streams, offering valuable information about water quality variations. Additionally, mobile applications and citizen science initiatives actively engage the public in monitoring water quality and contributing data. Platforms like iNaturalist empower individuals to report observations and collect water quality data, fostering public awareness and participation in NBS efforts. By leveraging these digital technologies, stakeholders can create a more comprehensive and holistic understanding of water quality dynamics and develop effective NBS strategies accordingly.