Search

We analysed a 24 cm long sediment sequence (past ~200 years) from an alpine lake (Tatra Mts., Slovakia) for chironomids, cladocerans, and diatoms to reconstruct the effects of a historically documented fish introduction. Our results indicate that fish introduction predated the age of the sequence, and thus, we did not cover the lake's fishless period. The individual proxies coincide in showing two main lake development stages. The first stage lasted until ~1950 CE and was interpreted as the stage when brown trout and alpine bullhead co-occurred. The extremely low concentration of cladocerans, the dominance of small-bodied chydorids, and the low share of daphnids, together with the low proportion/absence of large-bodied tanypod chironomids, suggest a strong effect of both species. The beginning of the next stage is probably related to the ban on fish manipulations and grazing in the catchment. A significant increase in the total abundance of cladocerans and of daphnids may indicate the extirpation of trout. The steep increase in thermally plastic chironomid taxa since the end of the 20th century indicates climate warming. Generally, while cladocerans primarily indicate fish manipulations, chironomids and diatoms mainly reflect other local and global environmental stressors. [ABSTRACT FROM AUTHOR]

Odonates are one of the best-known aquatic insect groups, with the renowned ability to reflect the quality of freshwater ecosystems. In the last few decades, major emphasis has been placed on the importance of secondary aquatic habitats as refugia for odonates. Biota of man-made habitats, especially dams, are burdened by countless negative anthropogenic impacts. Nevertheless, some habitat types appear to be able to support species with high conservation value. Here, we used generalised linear models to analyse the effects of several environmental characteristics, such as pH, conductivity, water area and perimeter of selected sites, to clarify the effects of drivers in terms of species richness of odonates. Water dams, flooded quarries, flooded gravel quarries and flooded sandpits have been compared based on the Dragonfly Biotic Index (DBI). We recorded 44 odonate species, including several red-listed ones, such as Epitheca bimaculata (Charpentier, 1825), Leucorrhinia caudalis (Charpentier, 1840) and L. pectoralis (Charpentier, 1825). Although the highest numbers of species were found at water dams, at such habitats, the lowest values of DBI were revealed. The fractional effect of habitat types on DBI was also proven to be significant. Increased conductivity resulted in a decrease of species richness. The positive correlation between habitat area and DBI was also proven to be significant. Our results indicate a high conservation value of different types of flooded quarries counter to water dams, based on the presence of several nationally threatened species with high values of DBI. [ABSTRACT FROM AUTHOR]