| Abstract [eng] |
Lithuania is characterized by a dense river network – there are approximately 29,000 watercourses in the country, with a total length of around 64,000 km. Of these, more than 23,000 are shorter than 3 km, while about 5,367 rivers are longer than 3 km or have a catchment area greater than 5 km². The sub-basins of the Šventoji and Žeimena rivers, located in eastern Lithuania, are among the most important hydrographic units in the region. The rivers of these basins – Dubinga, Kiauna, Luknelė, Plaštaka, Skerdyksna, and Šešuola – are situated within a 60 km radius in the central part of eastern Lithuania and flow through diverse land use areas, forming an important system for assessing the impact of both natural and anthropogenic factors on aquatic ecosystems. Rivers play a crucial role in maintaining and preserving biodiversity. They provide habitats for a wide range of plants, fish, invertebrates, and other organism groups. The hydrological, physical, and chemical properties of rivers – such as water temperature, pH, substrate, dissolved oxygen, electrical conductivity, and salinity – directly influence the composition and functioning of biological communities within river ecosystems. Additionally, the habitats surrounding rivers – forests, meadows, agricultural lands, or urban areas – also shape the structure of these communities. Benthic macroinvertebrates living in rivers, including non-biting midges (Chironomidae), are particularly important due to their ecological plasticity and sensitivity to environmental changes. Chironomids are one of the most important and widespread insect groups in aquatic ecosystems, characterized by high species diversity and abundance. Their larvae are found in almost all freshwater habitats, and some species are adapted to extreme environmental conditions, such as high water temperatures (hot springs) or low pH (acidic waters). Chironomids fulfil key ecological functions: they decompose organic matter, their predatory larvae regulate macroinvertebrate populations, and they serve as a food source for fish, birds, and other animals. Due to their adaptability to a wide range of environmental conditions, they are valuable bioindicators. While globally Chironomidae are extensively studied – from systematics and phylogeny to their ecological roles and applications in water quality assessment – research on this group in Lithuania remains fragmented. To date, only one comprehensive paleoenvironmental study based on Chironomidae analysis has been conducted (Gastevičienė, 2022), along with a few species inventory surveys. In Lithuania, no studies have been conducted to assess the influence of ecological, environmental, and damming-related factors on chironomid diversity and abundance in rivers. In the Baltic countries, studies on Chironomidae diversity and ecology are conducted very fragmentarily, which limits the applicability of this aquatic macroinvertebrate group in environmental assessments. This dissertation provides the first systematic evaluation of Chironomidae diversity and distribution in relation to habitat characteristics and environmental factors across six rivers in central eastern Lithuania. For the first time, chironomid community structure was analysed under varying environmental and hydrological conditions, taking into account whether rivers were dammed or free-flowing. The obtained results not only contribute to the faunistic data of Lithuania, but also enable the further use of Chironomidae as a bioindicator group in assessing the ecological status of rivers and their anthropogenic impacts. |
