Оригинальная модификация метода пробоподготовки озёрных отложений для изучения макроостатков личинок хирономид (Insecta: Diptera)

Abstract

Nonbiting midges (chironomids) comprise a globally distributed family of nematoceran flies with complete metamorphosis. They populate aquatic, semiaquatic, and, more rarely, terrestrial habitats and frequently dominate aquatic insect communities in both abundance and species richness. The larval stage is the longest life period (from several weeks to two years); the adults are ephemeral. All this makes chironomid larvae a very valuable object for investigation of ecological and paleoclimatic changes. The nearly six-year experience of work on the separation and investigation fossil remains of chironomid larvae showed that the generally accepted technique of processing samples of lake sediments has a significant drawback. The standard technique for preparation of samples from lake sediments cores for the study of remains of buried chironomid larvae (whole head capsules and mentums) includes treating the sediment with a 10 % KOH solution. After washing the treated samples on sieves, head capsules of chironomid larvae remain poorly washed from both the soil and alkali. It greatly complicates the work with detecting larva remains and their microscopy. The present article describes the original modification of the technique of chemical treatment of lake bottom sediments for the separating and investigation of the remains of non-biting midges larvae for paleoclimatic and paleoecological reconstructions. A distinctive feature of the developed method is that the precipitate is treated with an HF for 24 hours. Acid treatment of samples is carried out to remove the mineral content. It makes the sediment looser, liquid and less sticky. This significantly improves the quality of sample washing on sieves made of two-layer mill gas with a mesh size of 90-100 microns. The new method provides better washing of sediment samples, which contributes to a more complete separation of larva remains. When using the “alkaline” method, from 2–10 cm3 of wet sediment, about 50–100 (depending on the type of lake and the characteristics of sedimentation) head capsules of chironomid larvae can be selected. In the method we proposed, the standard sample volume was 0.5–2 cm3 of wet sediment. But, the content of the considered head capsules of chironomid larvae in the samples taken for analysis significantly exceeded the average achieved results due to their better washing from sediment. Proposed method is also suitable for treating sediments for palynological analysis. The inventory and the sample preparation algorithm are described and illustrated. Examples of photographic descriptions of the head capsules of larvae of some taxa of chironomids, made with a video eyepiece, are given.