Microbial and chemical quality assessment of the small rivers entering the South Baltic. Part I: Case study on the watercourses in the Baltic Sea catchment area.

The area of the Coastal Landscape Park (CLP) due to its location is extremely attractive touristic area. In the summer season, a significant increase in population density is observed, which influences surface water quality. Large numbers of tourists generate an increased amount of municipal wastewater, being treated in local treatment plants and discharged into rivers and streams. The paper presents preliminary research from summer 2016 on three watercourses ending in the Baltic Sea: Piaśnica, Karwianka and Czarna Wda rivers. It is a part of a long-term project conducted in CLP to assess surface waters quality. The scope of research included measurements of in situ parameters (temperature, conductivity, pH, dissolved oxygen). Chemical Oxygen Demand was determined using a spectrophotometer. Ion chromatography was used to determine ions concentrations (including biogenic compounds). Sanitary state of watercourses was assessed based on fecal coliforms abundance, which number was determined by the cultivation method. The determination of microbiological parameters such as: prokaryotic cell abundance expressed as total cells number (TCN), prokaryotic cell biovolume expressed as average cell volume (ACV), the prokaryotic biomass (PB) and prokaryotic cell morphotype diversity was determined using epifluorescence microscopy method. Results showed that water quality of Piaśnica and Czarna Wda rivers were affected by discharged treated wastewater. In the case of Karwianka River, the main pollution source could be surface runoff from fields and unregulated sewage management in this area. The conducted research confirmed the urgent need for better protection of this area to conserve both its ecosystem and value for tourism. 56 E. Bączkowska, A. Kalinowska, O. Ronda, K. Jankowska, R. Bray, B. Płóciennik, Ż. Polkowska wastewater). Studies have shown that tourism puts pressure on coastal areas around the world (Gössling et al. 2018). In Europe, similar studies are currently being carried out, demonstrating the need for continuous and wider monitoring of watercourses that flow into protected areas (Grabic et al. 2018). Global change and anthropogenic activities put a heavy strain on marine ecosystems. Scientists aim to answer the questions of how to protect the environment and biodiversity without inhibiting socio-economic development and increasingly popular tourism, for example in the Doñana National Park in Spain, very well described in the literature (García-Llorente et al. 2018). Researchers from Germany and Denmark who conducted research in the area of the Wadden Sea (Sylt-Rømø Bight, Norderaue tidal basin and Jade Bay), also proved that it is crucial to develop relevant management plans to protect and benefit from ecosystems (de la Vega et al. 2018). Wastewater entering the treatment plant is a habitat for various types of microorganisms, including pathogens (Cai and Zhang 2013). As a result of proper WWTP functioning, the physical and chemical quality of the effluent is higher than that of the influent, however, it is usually not subjected to any degree of disinfection before it is discharged into the receiver (Michałkiewicz 2018). This means that significant numbers of microorganisms can be released to the ecosystem in case of inappropriate WWTP operation, e.g., insufficient sludge settling or increased hydraulic load. The presence of various bacteria and other microorganisms is an important contribution to global biodiversity, and it is crucial to the functioning of ecosystems (Caruso et al. 2016). Different types of prokaryotic microorganisms can be found in different niches, and their development, growth or division possibilities are closely linked to the conditions offered by a particular ecosystem. It has been proven that prokaryotic cells can survive in extreme climate using the pollutants contained in glacial waters as a source of food (Kosek et al. 2018). Other studies show how microorganisms can develop in the oceanic depths or hydrothermal vents, depending on depth, temperature and pressure (la Ferla et al. 2012). Publications confirm that the prokaryotic communities can adapt and survive in various environmental conditions, and colonize even nutrient-poor or extremely hostile, acidic or boiling hot niches (Amin et al. 2017). Therefore, a question arises whether human-related bacteria, possibly released with the treated wastewater, can survive and develop in the receiver significantly deteriorating its quality. While many microorganisms in the ecosystem play an important role in the biodegradation of pollutants (Ostroumov 2017), which can originate from human activity, there is still a risk that this microbial community may contain pathogenic microorganisms that may have an adverse effect on the health and life of animals and people living in the vicinity of such reservoirs. Hel Peninsula and beaches of the Baltic Sea are example of such extraordinary places in Poland. Coastal Landscape Park (CLP) is located in the northern part of Poland and covers an area of almost 19 ha – over a half is covered by the waters of the Inner Puck Bay and marine coastal areas. It is one of the oldest (established in 1978) areas in Poland covered by this form of nature protection (Majdak 2008). Tens of thousands tourists visit the Park annually, and the number of accommodations increase each year (Borkowski 2019). During the summer season, over 500 thousand people visit the CLP and the nearby area. The population density in Puck County increases from about 150 people per sq. km to over 850 people per sq. km (Statistics Poland 2016a). Every year in the summer season, the Park authorities face the extremely difficult task to ensure that tourists visiting this area leave the place intact. Of course, despite all efforts, this does not always work. Apart from vandalism, illegal garbage disposal, lack of sanitary connections of seasonal accommodation spots, there are other factors that can have a negative impact on the ecosystem, which result only from such seasonal popularity of this area, e.g., the fluctuating amount of released treated wastewater. One of the most impacted environments are surface waters: rivers and lakes being very popular tourist destinations during the summer season (Krajewska and Fac-Beneda 2016). Rivers located in the northeastern part of Pomeranian Voivodeship are not under permanent control by the Coastal Landscape Park’s employees. Their catchment is not always within the Park’s area and the Park’s Board has no authority over the tributaries, therefore the protection and management are very difficult. Streams and ditches supplying bigger rivers usually pass-through agricultural areas and carry organic pollution from the farms and fertilizers from the fields (Wojciechowska et al. 2019). They flow through the CLP area, carrying pollutants straight into the Baltic Sea (Zaborska et al. 2019). They also receive treated effluent from local wastewater treatment plants. During the summer, when population density dramatically increases, thousands more cubic meters of wastewater flow into the wastewater treatment plants than in other periods of the year, which raises the question of whether during the holiday season the efficiency of wastewater treatment plants located in tourist areas is sufficient. There is need to apply a comprehensive protection program to the unique NPK area that will perfectly correspond to the priorities of the Regional Operational Program of the Pomeranian Voivodeship for 2014–2020 (ROP WP 2014–2020) funded by the European Union (EU) under the European Regional Development Fund (ERDF) and the European Social Fund (ESF). In 2015, preparations were initiated to assess the physicochemical and microbiological risks occurring in this area. Essential physicochemical and sanitary analyses (number of E. coli bacteria) were performed at selected measurement points. On the basis of preliminary observations, 40 measurement points were selected, and the scope of physicochemical and microbiological studies was extended. The CLP area was divided into two regions – catchments of the Piaśnica, Karwianka and Czarna Wda rivers which directly flow to the Baltic Sea (Part I) and rivers and smaller watercourses flowing to the Bay of Puck (Part II). The conducted research confirms the urgent need for better protection of this area to conserve both its ecosystem and value for tourism. The watercourses pass near the swimming areas and beaches, that are very popular in the summer season and may affect their quality. Moreover, due to the popularity of local tourism after the Covid-19 pandemic, these areas may still be used intensively in the future because of their unique tourist qualities. This paper discusses the analysis of the results of the research conducted in 2016 in the Part I area, the research of Microbial and chemical quality assessment of the small rivers entering the South Baltic. Part I: Case study... 57 the second area (Part II) is discussed in Baczkowska et al., 2022. Materials and Methods Study area In this study, three rivers: the Piaśnica River, Karwianka River and Czarna Wda River, which pass through the Coastal Landscape Park (CLP), were selected in consultation with the CLP management board to conduct physicochemical and microbiological analysis, based on the representative character of these rivers. The catchments of these rivers represent diverse physiographic conditions, e.g., isolated wetlands and coastal lowlands. The variety of relief conditions cause the occurrence of different types of soils, which entails different types of land use in the catchments. The Piaśnica River catchment is an area of 300 km2, mainly covered by forests. Agricultural use does not exceed 50% of the region. On the contrary, the smaller catchments of the Karwianka River (60 km2) and the Czarna Wda River (90 km2) are covered in 65% by agricultural land dominated by farmlands. Anthropogenically transformed areas c