Плавнева амфіфітна рослинність пониззя Південного Бугу в умовах новітніх еколого-гідрологічних змін стану заплави

Abstract

In the course of systematic environmental investigations of the Southern Buh flooded areas, it has been revealed that marsh territories in the floodplain of the lower river flow existed and still partially exist only in the behind the dalles area – from the Chartala mouth to the Inhul mouth. In the investigated section of the watercourse, “classical” marshy ecotopes of the wetland marsh type still occur. In this specific region, there are 4 outsize marsh territories, with the largest among them Varyushyno-Kovalivskyi, having the area of about 1000 hectares. Taking into account the uniqueness and relative preservation of the natural marsh biocenoses in the Southern Buh lower reaches, the latter have repeatedly served as the object of scientific research. Unfortunately, there have not been conducted systematic ecological studies of the flora groups within the period of 2000-2018. Under these conditions, in the context of growing instability and the revival of cargo shipping in the Southern Buh lower reaches, scientific investigation of the fluvial vegetation as a reserve of primary natural vegetation is necessary and relevant. This fact caused the choice of this topic and specific research tasks. Accordingly, the aim of this work is to investigate the state and composition of the amphiphytic vegetation of the Southern Buh river floodplains in the conditions of the contemporary ecological and hydrological changes in the state of marshes by the case study of Kovalivskyi marsh area. Field, hydrological, soil and botanical surveys were carried out on various, heterogeneous in their ecohydrological characteristics, sections of Kovalivskyi marsh area – from the meadow sections of the marsh upper boundary to the lacustrine flowing and riverbed sections. As the basic material for preparation of this article, the author used actual data of her own field investigations of the marsh biotopes in Kovalivskyi marsh area, which were combined with the results of ecohydrological, bioclimatic and phytocenotic surveys of marshes conducted during 2012-2019 in different seasonal phases of the river watercourses and various vegetation states. The methods of field environmental, botanical and hydrological researches, the method of data systematic generalization and the method of comparative analysis were chosen as the main investigation methods. Analysis of available materials on the main characteristics of Kovalivskyi marsh area makes it possible to classify it as a natural river-lake formation of the eutrophic type (the biomass is estimated as 1050-1120 gm/season/m 2 ). It has been revealed that the diversion of the watercourse hydrological regime and the marsh siltness intensify the processes of biomass production solely at the expense of macrophytes, which dramatically inhibits the cycling of substances in the marsh ecosystem. The results of ecological, hydrological and bioclimatic surveys of the investigated region indicate that the current period is distinguished by the factor of growing aridity of the climate (an increase in average annual temperatures by 1.0-1.2°С), when in 2012-2018, the average annual precipitation rate in the lower reaches of the Southern Buh did not exceed 320-260mm. In addition, over the past 30 years, the relative annual air humidity dropped from 60-65% to 45-48%. Accordingly, the evaporation rate from the water surface increased from 625-700mm to 800-900mm, reaching 1020-1050mm in the summers of 2011, 2012 and 2015, which led to the decrease in surface runoff from 0.44mm to 0.17mm. Consequently, the unstable hydrological regime of the watercourse contributed to silt ing of a larger part of the floodplain and to extension of the most valuable in natural biodiversity marsh lakes in Kovalivskyi marsh area. Nevertheless, the latter retains the features of long-term and seasonal dynamism, demonstrating it by the species structure of local groups, which, according to the season, have different characteristics and corresponding phytodiversity. Phytocoenoses of free-flowing, submersed and emergent plants are typical for habitats of continued flowage. Among the ecological types of these phytocoenoses, aquatic plants predominate. Their typical representatives are: rigid hornwort ( Ceratophyllum demersum ), common duckmeat ( Spirodela polyrrhiza ), floating fern ( Salvinia natans ), common frogbit ( Hydrocharis morsus-ranae ), claspingleaf pondweed ( P. perfoliatus ) and longleaf pondweed ( P. nodosus ), straight vallisneria ( Vallisneria spiralis ), European white water lily ( Nymphaea alba ) and yellow water-lily ( Nuphar lutea ). The biotopes of partial flooding and excessive streamflow combine wetland complexes situated near river channels with thickets of tall-grass helophytes, that include emergent vegetation, the main representatives of which are common reed grass ( Phragmites australis ), clubrush ( Scirpus lacustris ), softstem bulrush ( S. tabernaemontani ), simplestem bur-reed ( Sparganium erectum ), narrowleaf cattail ( Typha angustifolia ), flowering rush ( Butomus umbellatus ), arrowhead ( Sagittaria sagittifolia ), European water-plantain ( Alisma plantago-aquatica ), sweet flag ( Acorus calamus ), and cyperus sedge ( Сarex pseudocyperus ). Generalized ecological and phytocenotic studies of higher aquatic vegetation in the investigated marsh area indicate that, in general, the factor of ecotope hydrological regime is the most essential and determining for the riverside aquatic vegetation to spread out. It is also closely connected with changes in the water level during the growing season and with the characteristics of the streamflow. In the course of geobotanical explorations of vegetation, natural rare vegetation groups of European white water lily (Nymphaea alba) and yellow water-lily (Nuphar lutea) , as well as floating fern (Salvinia natans) listed in the Red Data Book of Ukraine, Annex I of the Bern Convention and the International Union for Conservation of Nature (IUCN) Red List, were identified. The floral findings increase the sozological value of this territory. The generalization of the materials of the investigation of the vegetation state and composition in the Southern Buh lower reaches gives grounds to deduce that under the conditions of the current ecological and hydrological changes of the marshes, the amphiphytic vegetation is under the risk of extinction. The prospects for further investigations are related to the development of a complex of nature conservation measures aimed at preventing the destructive processes taking place in Kovalivskyi marsh area as the only preserved natural marsh area in the Southern Buh lower reaches.