## 2 Materials and Methodology  
### Lake Markakol: Importance of Microplastics Studies  
Lake Markakol is a high mountain lake located in the Markakol National Nature Reserve which is known as a unique nature site. The choice of this lake is justified by its geographical location and its status within the UNESCO World Network of Biosphere Reserves [66]. Lake Markakol belongs to the lakes of intra-mountain depressions and is located 1447 m above sea level, being a a so-called \"background water body\" in Kazakhstan because it counts as undisturbed and is relatively less vulnerable to anthropogenic pollution [67; 68]. Detection of plastic pollution is a unique and important objective even in Central Asia. It demands both more public attention and resonance and the continuation of research and the fight against plastic pollution.  
The mountain ridges around Lake Markakol have heights 2000-3000 m above sea level. The catchment area of the lake is 1180 km\({}^{2}\), the surface area of the lake is 455 km\({}^{2}\), and its volume is 6.5 km\({}^{3}\). The lake is 38 km long and 19 km wide with a maximum depth of 27 m, while its average depth is 14.3 m [69; 70]. The lake is famous for its unique flora and fauna, including rare and endemic fish species such as lenok and grayling. The lake is surrounded by the Markakol Reserve, which was founded to protect and preserve the local ecosystems. The lake's water surface and the adjacent forest and mountain areas provide favorable conditions for many species of birds, mammals and plants.  
The lake is a flowing lake as it is fed by several large tributaries (Urunkhaika, Topolevka, Tikhushka, Zhirelka, Elowka and Matabai) and 27 small streams feeding the lake with water from the surrounding mountains, while the Kalzhyr River flows out of it [68; 69; 71].  
Lake Markakol's area is characterized as the coldest region in Kazakhstan, with a minimum temperature of \(-55\)\({}^{\circ}\)C and only 162 warm days per year. According to data from the official website of the Republic State Institution \"Markakol State Nature Reserve\" [69], ice formation on the lake occurs in November-December, and opening and complete clearing of ice occurs by the end of May. According to Kazhydromet's observations, the average long-term air temperature values for January and July were \(-22.0\)\({}^{\circ}\)C and \(14.5\)\({}^{\circ}\)C, respectively. Consequently, the choice of time for the field campaign took into account the climatic features and characteristics of Lake Markakol. This is why the summer period was the most suitable time period for the field work.  
The water in the lake is fresh. It is an important source of drinking water and a habitat for various species of flora and fauna.  
Despite the fact that Lake Markakol is located in a remote, mountainous area, there are several settlements in the vicinity of the lake, including the village of Markakol and small villages in the surrounding areas, like Urunkhaika and Zharma.  
Like many natural objects, Lake Markakol faces the impact of anthropogenic activities such as poaching and eco-tourism. Thus, popular tourist trips among nature lovers and an increasing number of tourists during the summer months have led to increased pressure on the ecosystem of the lake, such as through the dumping of solid household waste and food residue in the surrounding lakes and, of course, abandoned poachers' fishing nets.