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Understanding climate and monsoonal dynamics on the Tibetan Plateau is crucial, as recent hydrological changes, evidenced by rising lake levels, will be accelerated by current global warming and may alter aquatic habitats and species inventories. This study combines chironomid assemblages with sedimentological, mineralogical and geochemical data of a short sediment core (37.5 cm) from the highaltitude (>4,733 m asl), saline (9 g L-1) and shallow (~5 m water depth) Shen Co, located in the southern part of the central Tibetan Plateau. The predominantly littoral, species-poor (10 chironomid morphotypes) chironomid assemblages are dominated by salt-tolerant taxa, that are highly sensitive to lake level fluctuations and macrophyte vegetation dynamics, making them ideally suited for tracking lake level changes over time. Results indicate a period (from ca. 1830 to 1921 CE) of drier conditions with low runoff and high evaporation rates in the Shen Co catchment, as indicated by a dominance of low-Mg calcite and dolomite and increased Ca/Fe and Sr/Rb ratios. This resulted in a decline in lake levels, an increase in salinity and the periodic occurrence of desiccation events at the sampling site. The first chironomid morphotype to appear after the dry period is Acricotopus indet. morphotype incurvatus, which indicate still low (<2 m) but rising lake levels after 1921 CE due to increasing runoff and a lower evaporation/precipitation ratio, as reflected by coarser grain size, higher quartz content and increased TN, TOC and Al/Si ratios. A replacement of A. indet. morphotype incurvatus by Procladius is observed as lake level rise continued after 1950 CE. The highest lake level is proposed for the period since 2006 CE. From 1955 to 1960 CE and from 2011 to 2018 CE, the presence of the phytophilic taxon Psectrocladius sordidellus-type supported abundant macrophyte growth. These changes are consistent with climate reconstructions from the northern and central Tibetan Plateau, indicating warmer and wetter climate conditions since the beginning of the 20th century, which have led to an increase in lake level in a number of Tibetan lakes. Our study specifically highlights 1920 and 1950 as years with enhanced precipitation. This can be attributed to strong overlapping multidecadal cycles of Westerlies and monsoon systems. This study demonstrates the significance of studying small, shallow lakes, as they frequently contain aquatic communities that respond more rapidly to the changes in the lake system. In addition, this study expands our understanding of the ecology of Tibetan chironomid morphotypes, highlighting this group's potential as paleolimnological proxies for investigating past environmental and climatic changes. [ABSTRACT FROM AUTHOR]

Lake Morenito located in the Argentinean Patagonia has been exposed to climatic, volcanic, and anthropogenic impacts for the last decades. In particular, the damming of the lake and the eruption of the Calbuco/Puyehue Volcanoes in AD 1960 played an important role in the lake's history. A 80-cm-long sediment core from Lake Morenito spanning more than 100 years was studied for chironomids, stable isotopes, and organic geochemistry to investigate how natural and anthropogenic stressors impacted the lake. Chironomid assemblages display large changes around AD 1950, with the appearance of the warm-adapted Chironomus and the replacement of Apsectrotanypus by Ablabesmyia, indicating a shift to warmer conditions. By that time and up to the present, an increasing trend of δ15N coupled with a decrease of δ13C points to shifts in the carbon and nitrogen cycles associated with human activities. It is evident that the onset of human activities during the 1950s following by the lake damming in AD 1960 had significant effects on the chironomid assemblages and the geochemical composition of sediments which is reflected in the progressive deterioration of the lake ecosystem. [ABSTRACT FROM AUTHOR]

The ecology of aquatic protists such as testate amoebae is poorly known worldwide, but is almost completely unknown in lakes of the northern Neotropics. To address this knowledge gap, we analyzed testate amoebae (Amoebozoa: Arcellinidae) in lakes of the Lacandón Forest, one of the most biodiverse parts of southern México. We set out to evaluate the diversity of testate amoebae communities and assess whether testate amoebae taxa are reliable indicators of environmental variables dissolved oxygen and water depth. We collected 17 surface sediment samples from a range of water depths in six lakes across the Naha-Metzabok Biosphere Reserve, northeastern Chiapas state. We identified 15 testate amoebae taxa distributed across seven genera. Eleven were identified to species level and four to strain (infra-subspecific level), and taxa were distributed unevenly among samples. Distribution of taxa in samples was related to dissolved oxygen (DO) concentration in the water measured near the sediment surface. Arcella discoides and Centropyxis aculeata strain "aculeata" were the most tolerant of low oxygen concentrations, whereas the other taxa require higher DO levels. The influence of oxygen was also seen at the assemblage level. Sites with low DO concentrations had Shannon Diversity Index (SDI) values <1.5, an indication of stressful ambient conditions. We identified two species assemblage types, which are distinguished by their oxygen concentration requirements. Assemblage 1 was more diverse and possessed species that are intolerant of low oxygen concentrations, whereas Assemblage 2 possessed fewer, rarer, opportunistic species that tolerate stressful conditions. Low oxygen concentrations are related to water depth and the combination of these two variables is important in determining the composition of testate amoebae assemblages in Lacandón Forest lakes. Quantitative relationships between testate amoebae assemblages and water depth will enable use of sedimented amoebae remains for paleolimnological inference of past water level changes in lakes of the Lacandón Forest. [ABSTRACT FROM AUTHOR]

Paleoecological studies are crucial for understanding ecosystem disturbance and resilience dynamics. However, nearly all the research related to the response of aquatic communities to disturbances has been developed at short-term ecological scales. In this study, we investigate the long-term response of chironomid insects of two lakes, to volcanic and other environmental disturbances that have taken place during the last 200 years. The studied lakes, Lake Verde and Lake Toncek, are located in the Nahuel Huapi National Park (northern Patagonia, Argentina), under contrasting environmental settings. Our results show that the main driver of faunal changes in both lakes is volcanism. Indeed, after the impact of the 1960 Puyehue/Calbuco volcanic events, the chironomid assemblage of Lake Verde recovered to initial conditions showing high resistance and a strong resilience to the impact. In this lake, the canopy, the presence of macrophytes, and the dynamic of the watershed are important determinants of resilience providing habitats for species colonization and/or by giving refugia to the community. Contrarily, chironomid assemblages from Lake Toncek did not recover to the original state after the impact of the ash. This lake is located above the tree line, and therefore it is highly probable that the lack of vegetation cover in the basin offered no protection for the aquatic environment, leaving the ecosystem highly exposed to the effect of the volcanic ashes. Subordinate to the effects of the volcanism, rising temperatures in the last 50 years and/or increasing human activities in the area, especially in L. Toncek, may also be responsible for the changes in chironomid assemblages. [ABSTRACT FROM AUTHOR]

Abstract: In the Southern Hemisphere, the lack of quantitative temperature records hampers the understanding of climate change since the Last Glaciation and refrains the comparison with the Northern Hemisphere records. To provide quantitative data, a 63-lake chironomid transfer functions was developed in Patagonia. Mean annual air temperature (MAT) was one of the most important factors explaining the distribution of chironomids while precipitation did not have any significant relationship with chironomid assemblages. The MAT model had a r 2 of 0.64, a RMSE of 0.83 and a maximum bias of 1.81°C, comparable to other transfer functions of this size. This model was applied to the Lake Potrok Aike (PTA) chironomid records which consisted of only four taxa (Phaenopsectra, Cricotopus, Smittia and Polypedilum). The chironomid-inferred air temperatures were colder-than-the-average (10.8°C) during the Lateglacial with the coldest temperatures (9°C in average) during the Antarctic Cold Reversal (ACR). Between ca. 8000 and 3500cal. years BP, the chironomid-inferred air temperatures were warmer-than-the-average with a decreasing trend. From ca. 3500cal. years BP to the present, the chironomid-inferred temperatures oscillated around the average. The difference between the chironomid-inferred air temperature in the surface sample and the climate normal (1961–1990) was 0.6°C, suggesting that chironomids are sensitive enough to quantitatively reconstruct MAT at PTA. The general pattern of temperature changes reconstructed by the PTA chironomid record corresponded well to other quantitative records in the Southern Hemisphere. The results presented here show that investing in the development of chironomid transfer functions for quantitative climate research in the Southern Hemisphere is valuable. [Copyright &y& Elsevier]

This study investigates the palaeoecological record (δ18O, δ13C, pollen, plant macrofossils, chironomids and cladocera) at Lake Bled (Slovenia) sedimentary core to better understand the response of terrestrial and aquatic ecosystems to Late-glacial climatic fluctuations. The multi-proxy record suggests that in the Oldest Dryas, the landscape around Lake Bled was rather open, presumably because of the cold and dry climate, with a trend towards wetter conditions, as suggested by an increase in tree pollen as well as chironomid and cladocera faunas typical for well-oxygenated water. Climatic warming at the beginning of the Late-glacial Interstadial at ca. 14,800 cal yr BP is suggested by an increase in the δ18O value, the appearance of Betula and Larix pollen and macrofossils, and a warmth-adapted chironomid fauna. With further warming at ca. 13,800 cal yr BP, broad-leaved tree taxa (Quercus, Tilia, Ulmus), Artemisia, and Picea increase, whereas chironomid data (Cricotopus B) suggest lowering of lake levels. After 12,800 cal yr BP (and throughout the Younger Dryas), the climate was colder and drier, as indicated by lower δ18O values, decline of trees, increase of microscopic charcoal, xerophytes and littoral chironomids. A warmer climate, together with the spread of broad-leaved tree taxa and a deeper, more productive lake, mark the onset of the Late-glacial/Holocene transition. These results suggest that terrestrial and aquatic ecosystems at Lake Bled were very dynamic and sensitive to Late-glacial climatic fluctuations. [ABSTRACT FROM AUTHOR]