Subfossil chironomids (Diptera, Chironomidae) of lakes in the Tatra Mountains: an illustrated guide

Here we present a summary of subfossil chironomids (Diptera: Chironomidae) found in the surface sediments of 52 Tatra Mts. lakes (Slovakia, Poland). Head capsules of 73 morphotypes of 5 subfamilies are described and illustrated. In addition to the previously documented subfossils by Brooks et al. (2007), we present 15 new morphotypes: Diamesa Tatra-type A, Diamesa Tatra-type B, Pseudodiamesa branickii-type, Pseudodiamesa nivosa-type, Pseudokiefferiella parva, Brillia bifida-type, Cricotopus (Paratrichocladius) skirwithensis-type, Cricotopus (Cricotopus) tremulus-type, Cricotopus/Orthocladius I, Eukiefferiella brevicalcar-type, Eukiefferiella claripennis-type B, Orthocladius (Orthocladius) dentifer-type, O. (Mesorthocladius) frigidus, Orthocladius (Euorthocladius) sp. and Tanytarsini indet. Most of these types have possibly broad distribution patterns in Europe. We believe that due to specific features of each region, this paper will serve as a helpful manual for limnologists and paleolimnologists working not only in the Tatra Mts. but also in the whole Carpathian region.

Distribution of subfossil chironomids (Diptera, Chironomidae) along a water depth gradient in the shallow Lake Spore, northern Poland

Subfossil chironomid (Diptera, Chironomidae) remains are often used as indicators of lake level changes in palaeolimnological studies. However, their usefulness as a water depth proxy can vary between the sites, depending on the lake morphology, mode of taphonomic processes or amplitude of past water level fluctuations, among other factors. In this study, we have examined the distribution of subfossil chironomids in the shallow Lake Spore (northern Poland) to assess the influence of water depth on the fauna. Our aim was to evaluate the site-specific utility of subfossil chironomids for lake level reconstruction at Lake Spore. The subfossil chironomid assemblages in Lake Spore have heterogeneous distribution, suggesting they are predominately composed of remains deposited close to the sampling location. A strong relationship between the water depth and the chironomids is marked by the 25.12% variance explained by water depth in the taxonomic data. Moreover, according to generalized linear models (GLMs) out of 44 dominant taxa, 12 have significant relationships with water depth. However, the sensitivity of our chironomid fauna to water depth changes is not continuous along the entire depth gradient. The most abrupt assemblage change occurs at 2.6–3.7 m water depth, in proximity to the depth where macrophytes become less dense and finally disappear. We conclude that, despite these strong chironomid-water depth relationships, only major water level fluctuations can be satisfactorily reconstructed due to the limited turnover rates of the fauna along a depth gradient and relatively small amplitude of the lake level variations characteristic for East-Central Europe.

A major hydrobiological change in Dasht-e Arjan Wetland (southwestern Iran) during the late glacial – early Holocene transition revealed by subfossil chironomids

The late glacial – early Holocene transition is a key period in the earth’s history. However, although this transition is well studied in Europe, it is not well constrained in the Middle East and palaeohydrological records with robust chronologies remain scarce from this region. Here we present an interesting hydrobiological record showing a major environmental change occurring in the Dasht-e Arjan Wetland (southwestern Iran, near to Persepolis) during the late glacial – early Holocene transition (ca. 11 650 years cal BP). We use subfossil chironomids (Insecta: Diptera) as a proxy for hydrological changes and to reconstruct lake-level fluctuations. The Arjan wetland was a deep lake during the Younger Dryas marked by a dominance of Chironomus plumosus/anthracinus-type, taxa adapted to anoxic conditions of deep waters. At the beginning of the Holocene, a drastic decrease (more than 80% to less than 10%) of Chironomus plumosus/anthracinus-type, combined with diversification of littoral taxa such as Polypedilum nubeculosum-type, Dicrotendipes nervosus-type, and Glyptotendipes pallens-type, suggests a lake-level decrease and a more vegetalized aquatic environment. We compare and contrast the chironomid record of Arjan with a similar record from northwestern Iran. The palaeoclimatic significance of the record, at a local and regional scale, is subsequently discussed. The increase in Northern Hemisphere temperatures, inferred by geochemical data from NGRIP, at the beginning of the Holocene best explains the change from the Younger Dryas highstand to early Holocene lowstand conditions in the Dasht-e Arjan wetland. However, a contribution of the meltwater inflow from small local glaciers in the catchment basin is not excluded.

Historical development of three man-made reservoirs in a mining region: A story told by subfossil chironomids

Chironomid stratigraphic changes were studied in three man-made reservoirs situated in a region intensely used for mining in the past (Banska Stiavnica, Central Europe) The reservoirs were built in the first half of the 18th century and are remnants of a former hydro-energetic system that provided water for operating mining and smelting facilities until the 1920s. The dated sequence of sediment cores span the last 170–200 years, however the oldest sediments were not identified. A total of 58 taxa were recorded with the most common taxa being Cladotanytarsus mancus-type, Polypedilum nubeculosum-type, Procladius spp. and Tanytarsus spp. Changes in the subfossil assemblages suggest that all reservoirs followed similar developmental trends. The low number of chironomid remains and the prevalence of littoral and rheophilic taxa characterize the initial phase of reservoirs connected with severe water level fluctuations and unproductive conditions. A dramatic shift in both qualitative and quantitative structure of the chironomid assemblages correspond to the documented decline of mining activities in the region. The second period of the reservoir development is also connected to changes in sediment composition and an increase of sediment organic content. In this phase, chironomids indicate nutrient enrichment, developed profundal zone with oxygen depletion and a complexity of littoral habitats. Since the 1970s, changes in the assemblage structure indicate the reduction of the profundal fauna and increasing importance of littoral taxa. Despite the significantly different usage of the reservoirs after the mining phase (recreation and angling vs drinking water supply) the chironomid succession trajectories were fairly similar.

Subfossil chironomids from Kamchatka

Chironomid head capsules from surface sediments in Kamchatka reflect a rich and diverse fauna. We observed a relatively high abundance of head capsules from the subfamily<em> </em>Diamesinae. An unknown morphotype of Tanytarsini, 'Tanytarsini type klein'<em>,</em> was found in the lake sediments of two lakes from Central and southern Kamchatka.