Natural Water Reservoirs as an Example of Effective Nature-Based Solutions (NBS)

*Ewelina Widelska, Barbara Sowińska-Świerkosz and Wojciech Walczak*

#### **Abstract**

Nature-based solutions (NBS) include actions that are inspired and/or powered by nature. The level of human intervention can vary from no or minimum intervention to the creation of the entire new ecosystems. One of the types of such solutions are natural water reservoirs (NWRs) with recreational and bathing functions, in which natural water self-purification processes are used. Mechanical, biological, and chemical self-purification processes are used to filter water in natural swimming pools. The elimination of nutrients (nutrients) and bacterial contamination takes place through the use of biological filter beds, usually planted with aquatic vegetation. Implementation of natural water reservoirs also showed a multitude of positive effects on the environment benefits including: enhancing the natural capital, promoting biodiversity, creating new habitats, mitigating water runoff, enhancing water resilience, contribution to urban heat island (UHI) mitigation, increasing air quality, and improvement of local climate.

**Keywords:** nature-based solutions, natural water reservoirs, natural systems

#### **1. Introduction**

Intensive urban development has an increasingly stronger impact on the nonurbanized environment. At the same time, cities and their inhabitants face a huge scale of challenges, such as: air pollution, the existence of the urban heat island (UHI), water excess or scarcity, loss of natural habitats, or social stratification. The use of Nature-based solutions is an effective means of dealing with many of these problems simultaneously [1].

The concept of Nature-based solutions (NBS) refers to solutions that are powered by nature and are implemented to manage natural systems in a way that balances benefits for both nature and society [2]. They were defined by International Union for Conservation of Nature [3] as "Actions to protect, sustainably manage and restore natural and modified ecosystems that address societal challenges effectively and adaptively, simultaneously providing human well-being and biodiversity benefit."

NBS include actions that are inspired and/or powered by nature. The level of human intervention can vary from no or minimum intervention to the creation of the entire new ecosystems [4, 5]. Therefore, as NBS can be considering establishment of protected areas or conservation zones, actions directed to controlling urban expansion, gardens and parks of different size, green roofs, and facades as well as creation of new waterbodies [6].

One type of such artificial waterbodies are natural water reservoirs (NWRs) with recreational and bathing functions, in which natural water self-purification processes are used. Mechanical, biological, and chemical self-purification processes are used to filter water in natural swimming pools. The elimination of nutrients and bacterial contamination takes place through the use of biological filter beds, usually planted with aquatic vegetation. Specified, specially selected for water parameters, mineral deposits are able to capture pollutants, pathogens as well as nutrients dissolved in water, mainly phosphates [7]. Therefore, NWR meets the most important criterion set to NBS: the conscious use of natural minerals and plants is a priority, not a supplement to conventional infrastructure.

Secondly, NBS are called as challenge-orientation action that contributes to alleviate well-defined environmental, societal, and economic problems [8]. Among them, however, IUCN [3] emphasized that NBS must effectively address societal challenges as well as result in a net gain to biodiversity and ecosystem integrity. Among most commonly mentioned challenge areas addressed by NBS are climate change adaptation and mitigation, disaster risk reduction, food and water security, human health and socioeconomic development, as well as environmental degradation and biodiversity loss [6, 9, 10]. Although the main goal of natural water reservoirs' implementation is directed to societal challenge, which can be named as "health and wellbeing," these waterbodies contribute to many others challenges. Regarding the environmental dimension, these waterbodies donate biodiversity enhancement by the introduction of native plant species associated with the aquatic environment. These plants together with water area create new aquatic and semiaquatic habitats that attract animal species, including amphibians, reptiles, and migrating birds [11]. Next to habitat creation function, natural water reservoirs face challenges such as disaster risk reduction and water management. They fulfill function of small retention waterbodies that collect rain and storm water and prevent against rapid water runoff from the urbanized areas [11]. Regarding the climate change adaptation and mitigation challenge, natural water reservoirs have direct impacts on greenhouse gas emissions via carbon storage and sequestration in vegetation, temperature cooling, and creation of shadows that impact human thermal comfort [12].

Implementation of natural water reservoirs also showed a multitude of positive effects on the environment benefits including: enhancing the natural capital, promoting biodiversity, creating new habitats, mitigating water runoff, enhancing water resilience, contribution to UHI mitigation, increasing air quality, and improvement of local climate [13]. The benefits provided by NBS may include different spatial scales: from area under action, through the surrounding areas, to the cityscape or even regional scale IUCN [3]. NWR are well known to provide a set of distinct benefits in relation to different special scales. Among cultural services are recognized benefits such as improvement of physical and mental health, increase of recreational value and educational opportunities, as well as tangible esthetic and spiritual benefits resulting from the contact with nature and people [11].
