Aquatic vegetation of the lakes of the Kolyma River upstream valley (Magadan Region)

The information on the syntaxonomic diversity of the aquatic vegetation in the upper Kolyma River valley, located in the northeast of Russia, is summarized. The territory is a well-developed valley throughout its length, featuring an island floodplain and several terraces above it. This landscape hosts numerous oxbow and thermokarst lakes with aquatic communities which were studied to varying degrees — while the aquatic flora is one of the most extensively studied compare to other Far East areas, only some information has been obtained on the aquatic macrophyte species composition, distribution and ecology. The objective of this study is to compile the information gathered to date on the syntaxonomic diversity of aquatic vegetation in the upper reaches of the Kolyma River, The study area is in the Kolyma River valley between the confluence points of the Kulu and Ayan Yuryakh rivers (62.29887 N, 147.72886 E), and the upper pool of the Kolyma Reservoir (61.89122 N and 148.61855 E) (Fig. 1). The water bodies on floodplain terraces are diverse: thermokarst lakes, formed due to local soil subsidence caused by the thawing of underground ice or icy soils, oxbow and oxbow-thermokarst lakes, overgrown quarries; small thermokarst pools in sites of abandoned gold mining enterprises. Field work in eight large lakes and several dozens of small ones was carried out in the period of the lowest water level (summer dry season) — end of June–July. The area of sample plots as determined based on community size, with those less than 100 m2 being described within their natural limits. The research conducted in the Tenkinsky district of the Magadan region in the upper reaches of the Kolyma iver between 2008 and 2019 was based on 143 geobotanical relevés made by the author. Computer program Juice 7.0.45 (Tichý, 2002) was used for data treatment. The syntaxonomic classification was based on general works on aquatic vegetation, and species were primarily assigned to associations following their dominance (Vegetace…, 2011; Chepinoga, 2015; Mucina et al., 2016). The coenotic diversity of aquatic vegetation in the studied lakes is 11 associations in three alliances, two orders and two classes (Tables 1–5). Ten associations belong to the class Potamogetonetea, and one — to the class Littorelletea (Fig. 3–10). Seven associations are put in the alliance Potamogetonion.1. Myriophylletum sibirici Taran 1998 — rare communites in large oxbow-thermokarst lake Orotuk on the first terrace above the floodplain at 0.9 m depth. It is found in Eastern Siberia, including Transbaikalia and Yakutia, and is likely more widely distributed in the Kolyma River Valley within the local range of dominant (Chepinoga, 2015; Gogoleva et al., 2017). 2. Potamogetonetum berchtoldii Krasovskaya 1959 — extremely rare communites, found only in oxbow-thermokarst lake Mikhailovo on the first terrace above the floodplain, at 0.9 m depth. 3. Ranunculo circinati–Potamogetonetum friesii Weber-Oldecop 1977 — Potamogeton friesii communities in shallow sites of mesotrophic lakes with muddy bottoms, recorded only in oxbow-thermokarst lake Tumul-1 at 1.2 m depth. 4. Potamogetonetum graminei Lang 1967 — communities of grass pondweed, with some leaves submerged and some on esfloating on the water surface. This community is described in the large oxbow lake Podkova, located on the first terrace above the floodplain. 5. Potamogetonetum perfoliati Miljan 1933 — communities of pierced-leaved pondweed, typically with a two-layer structure, which are commonly found in several large oxbow-thermokarst lakes on the terrace above the floodplain and thermokarst lakes on the second above-floodplain terrace with muddy bottoms at 1.0–1.5 m depths. 6. Potamogetonetum praelongi Hild 1959 — communities of white-stemmed pondweed, typically recorded in all large oxbow-thermokarst lakes and several oxbow lakes with slimy bottom at 1.5–2.3 m depth. 7. Potamogetonetum tenuifolii Kipriyanova et Lashchinsky 2000 — communities of northern pondweed with Nymphaea tetragona as a companion, easily found in various types of lakes, including small thermokarst reservoirs in the sites of abandoned gold mining enterprises. Three associations within the alliance Nymphaeion albae.1. Nupharetum pumilae unite communities of small cow lily with Nymphaea tetragona as subdominant species that very rare in study area. 2. Nymphaeetum tetragonae — communities of holarctic relict species four-angled water lily, often found in various types of lakes, including small oxbow reservoirs. 3. Potamogetonetum natantis — common floating pondweed communities whidespread in the boreal zone of the North-East of Russia. Communities of amphibious helophytic perennial Sparganium hyperboreum in shallow waters are included in the ass. Sparganietum hyperborei Teteryuk, Lavrinenko et Kipriyanova 2022, within the alliance Sparganion hyperborei in the order Littorelletalia Koch 1926, the class Littorelletea Br.-Bl. et Tx. ex Westhoff et al. 1946 (Lavrinenko, D’yachkova, 2021; Teteryuk, Lavrinenko et Kipriyanova, 2022). Communities formed by relict species Nymphaea tetragona, Nuphar pumila and Ceratophyllum demersum, listed in the Red Book of the Magadan Region require protection (Red Data..., 2019).