Nature-based solutions (NBS) can protect, manage and restore natural or modified ecosystems. They are a multidisciplinary, integrated approach to address societal challenges and some natural hazards effectively and adaptively, simultaneously providing human well-being and biodiversity benefits. NBS applications can be easily noticed in circular cities, establishing an urban system that is regenerative and accessible. This paper aims to offer a review on NBS for urban water management from the literature and some relevant projects running within the COST Action ‘Implementing nature-based solutions for creating a resourceful circular city’. The method used in the study is based on a detailed tracking of specific keywords in the literature using Google Scholar, ResearchGate, Academia.edu, ScienceDirect and Scopus. Based on this review, three main applications were identified: (i) flood and drought protection; (ii) the water-food-energy nexus; and (iii) water purification. The paper shows that NBS provide additional benefits, such as improving water quality, increasing biodiversity, obtaining social co-benefits, improving urban microclimate, and the reduction of energy consumption by improving indoor climate. The paper concludes that a systemic change to NBS should be given a higher priority and be preferred over conventional water infrastructure.

There are considerable differences between the EU-15 countries and Central and Eastern European (CEE) countries in the application rate of phosphorus (P) fertilizer and manure as well as in the climate and erosion patterns, but the eutrophication of surface waters is a common problem. The availability of information on the contribution of the CEE countries to European surveys on eutrophication is not adequate, because the amount of data available from these countries is small. There is thus a need to compile more comprehensive data sets for better assessment. Recent changes in agricultural practices, and their impact on the trophic status of surface waters in CEE countries, have been evaluated using a few selected pressure and state indicators (phosphorus balance, phosphorus status and erosion of agricultural land, P loss risk index, chlorophyll a, total and orthophosphate content of water) by compiling and analysing data from the literature. In the CEE countries, small annual P balances ()7 to +6 kg P ha )1 ) and declining levels of soil available P (proportion of soils adequately supplied with P dropped to between 10 and 50% of total area) may lead to low yields and economic difficulties. Only 11% of the variation in total phosphorus (TP) in rivers studied could be attributed to the calculated P loss risk index, and thus to the impact of differences in the agricultural diffuse source P load. The generation of more consistent data sets should be pursued for the whole of Europe in order to derive more powerful indicators. A refined P index could be one of the best indicators of eutrophication. Recent changes in the trophic level of surface waters could be attributed to a large extent to the change in point source P loads, i.e. to the diminishing amount of P load from municipal and industrial wastewater. The short-term improvement of water quality in the CEE countries will require further improvements in wastewater treatment, but long-term improvement will only be achieved by reducing diffuse P losses from agriculture, possibly involving changes in the land use pattern and in farming practices.

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Natural heritage (NH) includes natural features that can be described as outstanding universal value at a national level. It refers to the importance of ecosystems, biodiversity, and geodiversity for their existence value, and the ecosystems can be considered as the spatial units for its mapping and assessment. The ecosystem services (ES) concept provides an appropriate basis in the form of assessment and mapping methods that enable linking the state of ecosystems with human well-being. Thus, it can be used as a platform to find solutions to the problems related to the conflicts between conservation and the use of the NH. In this paper, we aim to present the process of developing a methodological framework for mapping and assessment of ecosystem services provided by the natural heritage in Bulgaria for recreation and tourism. The conceptual framework of the ecosystem-based assessment of NH in Bulgaria is based on the assumption that the generation of NH for the needs of tourism can be presented as the linkages between the natural systems and tourism in the form of ES potential, flow, and demand. The results demonstrate that the NH can be presented as a spatial phenomenon conceptualized by the flows of benefits from ecosystems to people which contribute to human well-being. The mapping and assessment procedures are fully developed for application at a national level, while for the regional and local level, few pilot studies mark some basic foundations for further development.