Influence of hydrological regim e of river on the species diversity of Charales in Steppe zone of Ukraine

Researchers on the species diversity o f charophytes (Charales, Charophyta) carried o ut in Kharkiv region (Eastern Ukraine) (Borysova, Gromakova, 2017) have revealed some interesting hydrological objects. Among them is the Bereka River with dense charophyte meadows. It is located in steppe zon e of Ukraine, thus a lot dry climate determines its unstable hydrological and hydrochem ical regimes. In summer a water level dramatic ally drops down that causes the considerable increase of salt load and drying up some reache s of river to lake-like water bodies. The lower reach of river (approximately 15 km near its mouth), transformed under constructio n of the Dnieper-Donbass canal, receives water from the Dnieper River and has stable hydro logical and hydrochemical regimes. The aim of the work is to study t he species diversity of charophytes in natural and transformed parts of the Bereka River with different hydrological and hydrochem ical rigimes. In 2013-2018 years during our fieldworks five species belonging to two genera were found, namely: Chara papillosa Kutz, C. connivens Salzm. ex A. Braun, C. contraria A. Braun ex Kutz, C. vulgaris L., and Tolypella glomerata (Desv.) Leonh. All spe cies formed dense populations in natural reaches of the Bereka River under unstable regime. While only C. vulgaris grew in the Dni eper Donbass canal under stable regime. T. glomerata is an annual charophyta growing in early spring. It forms numerous oospores in April -May an dies off in June. This species is rare for Ukrainian flora. Only three its stations in the Bereka River are known in Ukraine (Borysova, Gromakova, 2014). C. papillosa, C. connivens, C. contraria and C. vulgaris spread out there forming communities in June when general mineralization and sulfate salinization of water are getting hig her. Only two last species C. contraria and C. vulgaris keep growing in July-August. Thus, it is observed a natural replacement of freshwater species by brackish ones in connection with changing chemical composition of water in a small steppe river in summer.

Researchers on the species diversity o f charophytes (Charales, Charophyta) carried o ut in Kharkiv region (Eastern Ukraine) (Borysova, Gromakova, 2017) have revealed some interesting hydrological objects. Among them is the Bereka River with dense charophyte meadows. It is located in steppe zon e of Ukraine, thus a lot dry climate determines its unstable hydrological and hydrochem ical regimes. In summer a water level dramatic ally drops down that causes the considerable increase of salt load and drying up some reache s of river to lake-like water bodies. The lower reach of river (approximately 15 km near its mouth), transformed under constructio n of the Dnieper-Donbass canal, receives water from the Dnieper River and has stable hydro logical and hydrochemical regimes. The aim of the work is to study t he species diversity of charophytes in natural and transformed parts of the Bereka River with different hydrological and hydrochem ical rigimes. In 2013-2018 years during our fieldworks five species belonging to two genera were found, namely: Chara papillosa Kutz, C. connivens Salzm. ex A. Braun, C. contraria A. Braun ex Kutz, C. vulgaris L., and Tolypella glomerata (Desv.) Leonh. All spe cies formed dense populations in natural reaches of the Bereka River under unstable regime. While only C. vulgaris grew in the Dni eper Donbass canal under stable regime. T. glomerata is an annual charophyta growing in early spring. It forms numerous oospores in April -May an dies off in June. This species is rare for Ukrainian flora. Only three its stations in the Bereka River are known in Ukraine (Borysova, Gromakova, 2014). C. papillosa, C. connivens, C. contraria and C. vulgaris spread out there forming communities in June when general mineralization and sulfate salinization of water are getting hig her. Only two last species C. contraria and C. vulgaris keep growing in July-August. Thus, it is observed a natural replacement of freshwater species by brackish ones in connection with changing chemical composition of water in a small steppe river in summer.