Case Study of Selected Nature Swimming Pools in the South Moravian Region

312 © The Author(s) 2021. This is an open access article distributed under the terms of the CC BY-NC-ND license. https://content.sciendo.com/view/journals/eko/eko-overview.xml Ekológia (Bratislava) - Journal of the Institute of Landscape Ecology, Slovak Academy of Sciences CASE STUDY OF SELECTED NATURE SWIMMING POOLS IN THE SOUTH MORAVIAN REGION TEREZA POLOPRUTSKÁ1, MICHAL NOVÁČEK 2, PETRA OPPELTOVÁ1 1Department of Applied and Landscape Ecology, Faculty of Agronomy, Mendel University in Brno, Zemědělská 1, 613 00 Brno, The Czech Republic 2Institute of Computer Aided Engineering and Computer Science, Faculty of Civil Engineering, Brno University of Technology, Veveří 95, 602 00 Brno, The Czech Republic; e-mail: michal.no[email protected]  Corresponding author Received: 18 May 2021 / Accepted: 14 September 2021 Abstract Poloprutská T., Nováček M., Oppeltová P.: Case study of selected nature swimming pools in the South Moravian Region. Ekológia (Bratislava), Vol. 40, No. 4, p. 312–324, 2021. Nature swimming pools are asought-after alternative to conventional swimming pools. Their natural water purification system, without the need for chemicals, is beneficial to health and environmentally friendly. Designing such a nature swimming pool is a complex matter because it requires coordination of a number of effects, which can easily cause an imbalance in the entire system. This work uses the case study method to analyse the overall condition of three nature swimming pools in the South Moravian Region during the second half of the swimming pool operation season. Key words: water, swimming area, regeneration area, nutrients, water trophy. Introduction Nature swimming pools are an alternative to conventional swimming pools which utilise chemical water treatment methods. The water in nature swimming pools is not cleaned chemically, but biologically and mechanically (Littlewood, 2005). This difference has benefits in the form of a healthy bathing environment, which does not have any negative impact on human health because no chlorine is used (Bernard et al., 2009). However, it also has specific limitations, which include a limited number of bathers and stricter requirements for the correct design of the swimming pool in order to achieve a balanced ecosystem (Pavlis, 2017). Design of a nature swimming pool and its maintenance are problematic because efforts need to be made to keep the amount of nutrients in this system as low as possible (Association of nature swimming pools and ponds, 2014). It is difficult to rectify the amount of nutrients in such acomplex nature system. Extensive technologies and chemical additives are used to treat water by conventional water management methods (Bratby, 2016). We essentially wish to avoid use of these technologies in nature swimming pools. This is why, the design is based on natural water treatment methods (Sperling, 2007), which we apply on various scales using with the least possible technology. The main natural processes utilised in nature swimming pools are filtration, which can remove substances depending on the filtration material used (Karczmarczyk et al., 2019), removal of substances utilising vegetation (Guardia-Puebla et al., 2019) and potentially sedimentation in swimming pools without water circulation systems. There are a number of factors influencing these natural processes, and it is, therefore, very difficult to design a water ecosystem such that it remains balanced and meets our requirements (Pavlis, 2017). In contrast to the conventional chemical method of water purification, all changes using the natural purification method take place much more slowly and after a specific interval, which is why the stability of the ecosystem is so important. This paper contains an analysis of the condition of three selected nature swimming pools in the South Moravian Region. These are locations in the municipalities of Oslavany, Kovalovice and Bohuslavice u Kyjova. The general design of nature swimming pools and swimming ponds includes a main swimming area for users and a regeneration area, which is intended for removing contaminants (nutrients) from the swimming area (Von Berger, 2010). Depending on the type, artificial swimming pools can be divided into nature swimming pools and swimming ponds (Association of nature swimming pools and ponds, 2014). Nature swimming pools are a closed system with an assured water circulation system. Swimming ponds do not have a circulation system and contain standing water (Association of nature swimming pools and ponds, 2014). On the basis of this definition, all the analysed artificial natural pools are nature swimming pools. Due to their nature, nature swimming pools contain oligotrophic water (Association of nature swimming pools and ponds, 2014), which is water with a low nutrient content (Pitter, 2015). The overall nature swimming pool system consists of a closed water circulation system, when water from the swimming Vol. 40, No. 4, p. 312–324, 2021 doi:10.2478/eko-2021-0033 313 area is continuously pumped into the regeneration area, where the nutrients it contains are removed utilising a filtration and biological treatment system (utilising phytoplankton, zooplankton and macrophytes) (Baumhauer, Schmidt, 2008). This system has no outflow and water can only be added to the pool when it evaporates. The water added to the pool should contain as few nutrients as possible to maintain its oligotrophic nature (Pavlis, 2017). In the public nature swimming pools of the Czech Republic, the water samples have to be collected and analysed on a monthly basis as per the requirements of the relevant Regional Hygiene Station (Decree No. 238/2011 Coll., 2011). In this case, key indicators are the amount of Escherichia coli, water transparency and the amount of Enterococcus. These parameters are crucial for the health of bathers (Giampaoli et al., 2014). However, they may not serve as evidence of the complex condition of the nature swimming pool. Fig. 1. Locations of the examined nature swimming pools. Source: Open Street Map. Type of swimming pool P-total (mg/l) pH (-) Ratio of regeneration area to swimming area (%) Standing watera 1 <0.035 8.0–8.5 40:60 2 <0.035 8.0–8.5 50:50 3 <0.035 8.0–8.5 50–60:50–40 Circulating water 4 <0.010 8.0–8.5 70:30 5 <0.010 8.0–8.5 up to 100:0 Table 1. Chemical composition and geometric parameter values of a swimming pool recommended by the standards (Association of nature swimming pools and ponds, 2014). Note: aIn swimming pool type 3, the circulation system is used for a maximum of 2 hours a day. Ekológia (Bratislava) 2021: 40(4): 312–324 314 Fig. 2. Swimming section of the nature swimming pool in Oslavany. Source: author’s archive. Fig. 4. Swimming section of the nature swimming pool in Kovalovice. Source: author’s archive. Fig. 3. Filtration walls with vegetation in the regeneration section in Oslavany. Source: author’s archive. Fig. 5. System of dams in the regeneration section in Kovalovice. Source: author’s archive. Fig. 6. Linear-shaped regeneration section in Bohuslavice u Kyjova. Source: author’s archive. Fig. 7. Cascade in the regeneration section in Bohuslavice u Kyjova. Source: author’s archive. Ekológia (Bratislava) 2021: 40(4): 312–324 315 The main indicator of water pollution from the water management aspect is the presence of nutrients (Håkanson, Bryhn, 2008). In the presence of high concentrations of key nutrients, which are especially nitrogen and phosphorus compounds, algae and cyanobacteria reproduce excessively in the water, thereby causing the water quality to decline (McGriff, McKinney, 1972). The result of this abundant reproduction is mainly a decline in water transparency, which results in unsatisfactory hygienic conditions for operation of the facility. This poor condition may be caused by an increased presence of nutrients, whereas the decline in degree of water transparency is a consequence of this poor condition (Håkanson, Bryhn, 2008). There are some recommended standards for designing swimming ponds and nature swimming pools in the Czech Republic. These standards give the geometric parameters and the chemical and physical indicators recommended for construction (Association of nature swimming pools and ponds, 2014). The values of these indicators are given in Table 1. However, there are no general methods that can be used to create a nature swimming pool design and guarantee a specific water quality. This is particularly because of the complexity of the entire issue as there are a number of issues that affect water quality in a nature swimming pool. Material and methods The nature swimming pools were chosen with regard to the distances between them. They are all located in the South Moravian Region. This means that relatively similar climatic conditions can be assumed. They are also located at similar altitudes. Access to each complex was arranged in advance with the operator. Access was always assured before opening. This eliminated the direct impact of bathers on the results of research. The locations of the analysed nature swimming pools are clearly given in Fig. 1. Oslavany The nature swimming pool in Oslavany is located in the complex of the local château at an above-sea-level of approximately 220m.a.s.l. This is the newest nature swimming pool in the investigated sample (constructed in 2019). This is also the nature swimming pool with the largest swimming and regeneration area. The complex also contains sanitary facilities and a shower with cold water from the water mains next to the nature swimming pool. A bored well provides additional water. The swimming area (Fig. 2) is divided into a deep swimming section with an area of approximately 600 m2 and a depth of 2.5m and a shallow section with a depth of up to 1.4 m and an area of approximately 600 m2. The total volume of the swimming section is approximately 1.450 m3. The pool is lined with exterior swimming pool sheeting and embedded into a concrete shell, with vertical walls on one side and a gradual entrance inclined into the water on the other side. Water is removed from the surface of the swimming section using skimmers and pumped into the pre-treatment zone. This nature swimming pool is the only one of the examined group with a pre-treatment system before the regeneration zone, which filters the water through fabric and subsequently aerates it using compressors. The pre-treated water is then pumped into the regeneration zone (Fig. 3). The regeneration section, with an area of approximately 515m2 and a volume of 375 m3, contains a layer of gravel on the bottom and also a number of thin, separate, vertical walls made from filtration material with a cover of vegetation, which is visible in Fig. 3. These walls are located in the direction of the natural water flow and prolong the time the water stays in this section. The maximum number of visitors to the swimming pool at one time is limited. The management of the complex does not keep long-term records of the number of visitors. Kovalovice The nature swimming pool in Kovalovice is located on the bank of Kovalovice stream, at an above-sea-level of approximately 270m.a.s.l. This nature swimming pool was the first nature swimming pool to be established in the Czech Republic in 2007. This is the second biggest (by area) swimming pool in the examined sample. The complex also contains sanitary facilities, including cold water showers. A bored well supplies additional water. The swimming area (Fig. 4) consists of a small paddling pool and a large swimming pool. The paddling pool is separated from the main pool and was not the subject of this research. The main swimming pool, with an area of approximately 1000 m2 and a volRegeneration section Swimming section Regeneration and swimming area ratio Vol. (m3) Area (m2) Depth (m) Vol. (m3) Area (m2) Max. depth (m) Regeneration area:swimming area Oslavany 375 515 0.7 1450 1200 2.5 30.0:70.0 Kovalovice 250 500 0.5 3700 1000 4.2 33.3:66.7 Bohuslavice 50 175 0.3 780 574 2.85 23.4:76.6 Table 2. Geometric parameters of the examined nature swimming pools. Shower Aeration Long-term records of the number of visitors Water filtration through screen Oslavany Yes Yes No Yes Kovalovice Yes No Yes Yes Bohuslavice Yes No Yes No Table 3. Presence of facilities for visitors and the method of treating water in the examined complexes. Ekológia (Bratislava) 2021: 40(4): 312–324 316 Fig. 8. Collection sites and depiction of functionality in a diagram of the nature swimming pool in Oslavany. The deep part of the swimming section is coloured dark blue and the shallow part is coloured light blue. Source: author’s archive. Fig. 9. Collection sites and depiction of functionality in a diagram of the nature swimming pool in Kovalovice. The deep part of the swimming section is coloured dark blue and the shallow part is coloured light blue. Source: author’s archive. Ekológia (Bratislava) 2021: 40(4): 312–324 317 ume of 3700 m3, has an elliptical shape with a gradual incline into the water up to a depth of 1.0 m. The entrance incline crosses into a deep pool with vertical walls, which reaches a depth of 4.2m. This is, therefore, the deepest of the examined nature swimming pools, with the greatest volume. The surface of the pool consists of a pebble in cement screed on the shallow, inclined banks and concrete blocks lining the deep section, without a finishing layer. The water is removed from the surface of the swimming section through three skimmers into the regeneration zone, where it is filtered at the inlet through a very rough screen, without fabric. The water can also be pumped from around the perimeter of the deep swimming section (at approximately the middle of the depth) and also by a pipe from the bottom of the pool. There are three pumps installed in the complex for moving the water. The regeneration zone is of rectangular shape, with an area of approximately 500 m2 and a volume of 250 m3 (the volume is determined on the basis of the depth of the mud bottom of the regeneration section). The entire area is dammed by a transverse system of dams (Fig. 5), which are planted extensively with vegetation. This nature swimming pool has the greatest proportion of vegetation per area of regeneration section. The density of the vegetation within the area of the regeneration section also assures significant slowing of the water flow. The water is filtered through a fine fabric at the outlet from the regeneration section. The management of the complex determines the maximum number of visitors and keeps long-term records of the number of visitors. Bohuslavice u Kyjova The nature swimming pool in Bohuslavice u Kyjova is located on the steep, north-facing slope of a mountain, at an above-sealevel of approximately 230 m.a.s.l. It originated by conversion of a former conventional swimming pool into a nature swimming pool. The conversion was executed in 2013. This is the smallest (by area and volume) swimming pool of the sample of examined swimming pools. There are sufficient sanitary facilities and also a cold water shower in the complex due to the previous function of the area. The swimming section originated on the site of the pool at the previous conventions facility. This pool, of a rectangular shape, was retained, but one side was modified and a gradual incline into the water was created. There is a filtration bed built into the site of the incline, which no longer fulfils its role, however. The pool has an area of 574 m2 and a volume of 780 m3. The maximum depth at the transition site of the pool is 1.2 m. The depth of the main swimming pool is 2.85 m. The entire bottom of the pool is covered in swimming pool sheeting. The water is removed from the surface into the regeneration section using three skimmers and a pump, possibly from the filtration bed using a pump. The regeneration section is usually in the form of a linear element (trough), which overcomes a height difference of over 2 m, over a length of approximately 80 m, which is visible in Fig. 6. This height difference is overcome using a system of small dams (see Fig. 7) over which the water overflows. This is a soFig. 10. Collection sites and depiction of functionality in a diagram of the nature swimming pool in Bohuslavice u Kyjova. The deep part of the swimming section is coloured dark blue and the shallow part is coloured light blue. Source: author’s archive. Ekológia (Bratislava) 2021: 40(4): 312–324 318 lution created tailored for the sloping terrain. The total area of the regeneration section is approximately 175 m2, with a volume of approximately 50 m3. The bottom of the trough of the regeneration section is partially filled with substrate and planted with abundant vegetation. However, the height of the substrate and the depth of the water are very small and the water only remains in the regeneration zone for a short period. The management of the complex in Bohuslavice u Kyjova keeps a long-term record of the number of visitors. The nature swimming pool is supplied with water from the local water mains.A clear definition of the geometric parameters of the individual analysed nature swimming pools is given in Table 2. Along with the geometric parameters, additional information was also obtained concerning the equipment and functioning of the nature swimming pools, which could affect the quality of the water. This information given in Table 3. Samples were taken four times from two nature swimming pools and three times from one swimming pool, at intervals of approximately 2 weeks between the collection of samples. Samples of water were taken from the regeneration section and from the swimming section of each nature swimming pool. Samples from the regeneration section were collected right in front of the inlet into the swimming section. Samples from the swimming section were always collected from the opposite end to the inlet and also outside the reach of the skimmers. The collection sites are presented in Figs 8–10. During collection at the specific site, the quality of the water was analysed using a Hach multimeter, which was used to establish the values of the amount of dissolved oxygen in water, the pH value and temperature. This was followed by actual collection of samples for analysis of N-NO3, P-PO4, total phosphorus and chlorophyll-a. All probes and containers that came into contact with the collected water were always carefully rinsed with distilled water. The collection sites, including the schematic diagram of the functionality of the nature swimming pools, are depicted in Figs 8–10.All the samples were subjected to a laboratory analysis arranged by Povodí Vltavy. The accredited laboratory of the Povodí Vltavy, State Enterprise, carried out the laboratory analysis. The obtained values of the chemical indicators were processed into tables, for which the median value and standard deviation were calculated. The median values of the chemical indicators, with designation of 25 and 75% quantile, for the regeneration and swimming sections of each of the examined swimming pools are expressed graphically. The median of the values obtained is marked in red, the 25% quartile defined by the bottom boundary of the blue rectangle and the 75% quartile is designated by the upper boundary of the rectangle of the box graph. The minimum and maximum measured values are also entered into the graph. Results and discussion The results of laboratory analysis are presented in Table 4. A total of four samples were collected for the nature swimming pools in Oslavany and Kovalovice. Only three samples were collected for the nature swimming pool in Bohuslavice. Comparison of the median individual chemical indicators in the examined nature swimming pools is depicted in the following figures: total phosphorous in Fig. 11, N-NO3 values in Pool Zone N-NO3 (mg/l) P-PO4 (mg/l) P-total (mg/l) Chlorophyll-a (μg/l) O2 (mg/l) pH (-) Oslavany Regeneration section 13.0 <0.010 0.011 7.1 8.41 6.51 18.0 <0.010 0.013 24.0 7.29 6.33 14.0 <0.010 0.017 4.8 6.65 6.95 14.0 <0.010 0.013 25.0 9.70 7.60 Swimming section 17.0 0.55 0.012 8.1 10.06 7.40 18.0 <0.010 0.019 41.0 11.98 8.16 14.0 <0.010 0.013 17.0 9.19 7.40 5.0 <0.010 0.015 28.0 11.21 8.41 Kovalovice Regeneration section <0.1 <0.010 0.014 17.0 8.85 6.55 0.2 <0.010 0.021 10.0 2.63 6.48 0.6 <0.010 0.014 7.3 2.84 6.81 0.7 <0.010 0.012 4.4 8.73 6.66 Swimming section <0.1 <0.010 0.014 22.0 12.34 6.65 0.1 <0.010 0.023 17.0 8.19 7.13 0.4 <0.010 0.014 8.2 7.63 7.09 0.6 <0.010 0.012 4.4 10.19 6.81 Bohuslavice Regeneration section 1.5 <0.010 0.007 1.9 8.59 7.58 2.9 <0.010 0.009 6.0 9.17 7.26 2.5 <0.010 0.011 4.6 10.00 7.29 Swimming section 1.4 <0.010 0.013 4.7 8.05 7.04 2.1 <0.010 0.019 21.0 10.03 7.25 1.6 <0.010 0.009 16.0 11.51 6.95 Table 4. Results obtained from analysis of samples. Ekológia (Bratislava) 2021: 40(4): 312–324 319 Fig. 11. Comparison of total phosphorus values in the regeneration and swimming sections. Source: author’s archive. Fig. 12. Comparison of N-NO3 values in the regeneration and swimming sections. Source: author’s archive. Ekológia (Bratislava) 2021: 40(4): 312–324 320 Fig. 13. Comparison of dissolved oxygen values in the regeneration and swimming sections. Source: author’s archive. Fig. 14. Comparison of pH values in the regeneration and swimming sections. Source: author’s archive. Ekológia (Bratislava) 2021: 40(4): 312–324