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Alpine lakes located in high-altitude mountainous regions act as vital sentinels of environmental change. Remote-sensing-based identification of these lakes is crucial for understanding their response to climate variations and for assessing associated disaster risks. However, the complex terrain and weather conditions in these areas pose significant challenges to accurate detection. This paper proposes a method that leverages the high precision of deep learning for small lake and lake boundary extraction combined with deep learning to eliminate noise and errors in the identification results. Using Sentinel-2 data, we accurately identified and delineated alpine lakes in the eastern Himalayas. A total of 2123 lakes were detected, with an average lake area of 0.035 km². Notably, 76% of these lakes had areas smaller than 0.01 km². The slope data is crucial for the lake classification model in eliminating shadow noise. The accuracy of the proposed lake classification model reached 97.7%. In the identification of small alpine lakes, the recognition rate of this method was 96.4%, significantly surpassing that of traditional deep learning approaches. Additionally, this method effectively eliminated most shadow noise present in water body detection results obtained through machine learning techniques. [ABSTRACT FROM AUTHOR]

Carbon burial patterns in lakes and their dynamic changes significantly impact terrestrial carbon sink fluxes and global carbon budgets. In this study, multi-indicator analysis of sediment core samples (P1, P2, and P3) from Pipahai Lake was conducted. Integrating the chronological sequences of 210Pb and 137Cs, we identified the historical changes and spatial characteristics of total organic carbon (TOC) and inorganic carbon (TIC) burial in Pipahai Lake since 1884. The results show that the TOC content was higher than that of the TIC. They exhibited an increasing trend with decreasing depth. Linear regression results indicated that the variation of TOC is less directly affected by precipitation (R = 0.39) and temperature (R = 0.58), while temperature may have a greater impact on TOC. From 1884 to 1995, nutrients were not the primary factor influencing changes in TOC. The synchronous variation in TIC and TOC contents reflects a higher contribution of external inputs to carbon burial in the Pipahai Lake basin. After 1996, nutrients may have begun to affect variations in TOC. The TOC primarily originates from distal aeolian transport or autochthonous sources, though human activity has played a role in its evolution. The TIC content is controlled by the TOC content and autochthonous sources. This study will contribute to the understanding of the carbon cycling dynamics and their influencing mechanisms in a high-altitude lake ecosystem. [ABSTRACT FROM AUTHOR]

Understanding the variability and related dynamic mechanisms of the Indian summer monsoon evolution over the past millenniums is crucial for disaster prevention and mitigation in the context of strengthening global warming. Here, we present a high‐resolution hydroclimate reconstruction over the past 3110 years in northwestern Yunnan Province, southwestern China, based on grain size analysis using the End‐member modeling algorithm and other environmental proxies. The results indicate that the temperature in northwestern Yunnan Province generally decreased since 3110 cal. yr BP, aligning with other temperature records on regional and global scales. Precipitation in the study area remained relatively stable before 1000 cal. yr BP, but exhibited an obvious out‐phase change compared with the temperature records over multidecadal to centennial timescale. While after 1000 cal. yr BP, the precipitation steadily increased, revealing the hydroclimate pattern of notably dry Medieval Warm Period (MWP) and relatively wet Little Ice Age (LIA) in the study area. The decoupling combination of temperature and precipitation spanning the MWP and LIA in southwestern China contrasts with that in the East Asian summer monsoon area and the Indian subcontinent which is also controlled by the Indian summer monsoon, indicating the spatial heterogeneity of precipitation in the Asian summer monsoon region. The discussion about dynamic mechanisms points out that solar activity emerges as a significant factor influencing regional temperature changes, and El Niño‐Southern Oscillation and Intertropical Convergence Zone migration jointly impact the precipitation change in the study area and the hydroclimate discrepancy in the Asian summer monsoon region. Plain Language Summary: Knowledge of the Indian summer monsoon evolution over the past millennium is vital for addressing the challenges posed by global warming. In this study, we present a high‐resolution hydroclimate reconstruction covering the last 3110 years in northwestern Yunnan Province, southwestern China. Using the End‐member Modeling Algorithm and multiple environmental proxies, we found a general temperature decrease since 3110 cal. yr BP, consistent with global and regional trends. Before 1000 cal. yr BP, precipitation in the study area remained stable but showed a distinct antiphase pattern with temperature variations over multidecadal to centennial timescales. After 1000 cal. yr BP, precipitation steadily increased, revealing a notably dry Medieval Warm Period (MWP) and a relatively wet Little Ice Age (LIA). The decoupling of temperature and precipitation during the MWP and LIA in southwestern China contrasts with the East Asian summer monsoon and the Indian subcontinent, highlighting the spatial heterogeneity of precipitation in the Asian summer monsoon (ASM) region. Our discussion on dynamic mechanisms highlights the significant role of solar activity in regional temperature changes and the joint impact of El Niño‐Southern Oscillation and Intertropical Convergence Zone migration on precipitation in the study area and the broader ASM region. Key Points: Precipitation change in the study area was indicated by the relative proportion of end membersDecoupling warming and monsoon precipitation in northwestern Yunnan Province was revealedEl Niño‐Southern Oscillation and Intertropical Convergence Zone migration jointly impact the hydroclimate discrepancy in the Asian summer monsoon region [ABSTRACT FROM AUTHOR]

Alpine (high mountain) ecosystems with extreme weather conditions and complex karstic geology, hosting extensive aquifers, are the two main characteristics of Taurus Mountain ranges, also affecting the distribution of living biota. Understanding these systems are important since they are potentially diverse but poorly explored habitats and are possible water source in the region, especially considering projected further aridification trends. Here, Lake Yeşilgöl (altitude 1815 m asl), a groundwater fed karstic lake at Mount Akdağ, is described in terms of its physical limnology and benthic freshwater ostracod assemblages for the first time. Three freshwater (podocopid) ostracod species were recorded: Fabaeformiscandona brisiaca (Klie, 1938), Neglecandona neglecta (Sars, 1887) Krstić, 2006 and Ilyocypris bradyiSars, 1890 in the surface sediment. Ostracods are in high abundance. According to the population structure of those species, I. bradyiSars, 1890 and N. neglecta (Sars, 1887) Krstić, 2006 are inhabiting this lake. Although F. brisiaca (Klie, 1938) is the most abundant ostracod species, it might be distributed/transported to the lake via groundwater. F. brisiaca (Klie, 1938) is the first record form Turkey and might be part of the meio-fauna of karstic groundwater of Taurus Mountains. Trace metals (Pb, Zn, Cd, Cu, and Ni) were measured in the surface sediment of the main lake basin and in the subsamples of the littoral short core. They are detectable low concentration. Atmospheric contamination does not yet appear to be an environmental threat at this remote alpine site in Western Taurus Mountains, in the south west Anatolia. This study measures basic physical limnological parameters in the lake water column and describes freshwater ostracods and trace metal concentrations in the surface sediments and in the short cores of an alpine, karst,groundwater-fed lake located in south-west Turkey. [ABSTRACT FROM AUTHOR]

The diel vertical migration of zooplankton includes downward migration to deep water during the day and upward migration to surface water at night. Diurnal downward migration has been well explained; zooplankton migration to surface water at night remains unclear. This study aimed to explore the reason of the nocturnal upward migration of the calanoid copepod Arctodiaptomus sp. In Lake Heihai, an alpine lake (elevation 4,090 m above sea level) without predators.Herein, we present the vertical profiles of the lake, including water temperature, chlorophyll a (Chl‐a), fatty acids, and astaxanthin synthesis precursors (ASPs) of seston in the water column. The distributions and concentrations of fatty acids and astaxanthin in Arctodiaptomus sp. were characterised through field investigations during the day and at night. Meanwhile, the effect of ultraviolet radiation (UVR) on ASPs in seston was explored through indoor experiments.Lake Heihai had the characteristics of low temperature, low food availability, high transparency, and high UVR intensity. Arctodiaptomus sp. was distributed in water layers below 6 m during the day and throughout the water column at night. Arctodiaptomus sp. accumulated large amounts of fatty acids, especially polyunsaturated fatty acids (PUFAs), and inhibitors of fatty acid oxidation–astaxanthin in the cold alpine lake. The concentrations of lutein, a kind of ASP, and PUFAs in seston were highest in surface waters. The indoor experiment verified that UVR can enhance the synthesis of ASP.The calanoids migrated to surface waters at night to obtain ASPs and PUFAs in seston, which were at high concentrations in surface waters. PUFAs and ASP may be of high food quality for zooplankton in alpine lakes. The findings indicated that the upward migration of Arctodiaptomus sp. at night was driven by the high quality of food sources (PUFAs and ASP) in surface waters. Arctodiaptomus sp. adapts behaviour and physiology to the environment of the alpine lake.We explored why zooplankton migrated to surface waters at night from the perspective of their physiological characteristics and adaptability to the environment. Our findings provide a new way to investigate the diel vertical migration of zooplankton, especially in alpine lakes. [ABSTRACT FROM AUTHOR]

Fish introduction into fishless high-altitude lakes has detrimental effects on biodiversity. Removal of alien fish through intensive fishing is cost-intensive and difficult to achieve in productive lakes. Lake Sulzkarsee is the only lake in the National Park Gesäuse, Austria, and was an important breeding site for amphibians until the lake was stocked with fish in the late 1970s. Salmonids were eradicated in 2005, but the lake remained degraded by the introduced minnows (Phoxinus sp.). In 2018, the lake was drained through a siphon pipe and then by pumping out water with dirt water pumps. The deepest part was treated with slaked lime, but several hundred adult minnows survived in sediment crevices and reproduced in the following season. After drainage, the phytoplankton biomass increased. Indicator species, such as Daphnia longispina and amphibians, showed signs of recovery, but they went back to an impacted state when minnows recovered after the failed eradication attempt. Purse seines proved to be the most efficient gear to catch minnows. These results indicate that deep mountain lakes are difficult to drain efficiently. Sediment treatment is required to eliminate all fish. [ABSTRACT FROM AUTHOR]

Alpine lakes, which include glacial and nonglacial lakes, are widely distributed in high mountain areas and are sensitive to climate and environmental changes. Remote sensing is an effective tool for identifying alpine lakes over large regions, but in the case of small lakes, the complex terrain and extreme weather make their accurate identification extremely challenging. This paper presents an automated method for alpine lake identification developed by leveraging deep learning algorithms and multi-source high-resolution satellite data. The method is able to detect the outlines and types of alpine lakes from high-resolution optical and Synthetic Aperture Radar (SAR) satellite data. In this study, a total of 4584 alpine lakes (including 2795 glacial lakes) were identified in the Eastern Himalayas from Sentinel-1 and Sentinel-2 data acquired during 2016–2020. The average area of the lakes was 0.038 km2, and the average elevation was 4974 m. High accuracy was reported for the dataset for both segmentation (mean Intersection Over Union (MIoU) > 72%) and classification (Overall Accuracy, User's and Producer's Accuracies, and F1-Score are all higher than 85%). A higher accuracy was found for the combination of optical and SAR data than relying on single-sourced data, for which the MIoU increased by at least 12%, suggesting that the combination of optical and SAR data is critical for improving the identification of alpine lakes. The deep learning-based method demonstrated a significant improvement over traditional spectral extraction methods. [ABSTRACT FROM AUTHOR]

The Holocene temperature discrepancy between paleoclimate reconstructions and climate model simulations—known as the Holocene temperature conundrum—calls for new high‐quality Holocene temperature records at high elevations. Here, we present a quantitative Holocene mean annual air temperature record based on a site‐specific branched glycerol dialkyl glycerol tetraethers calibration from a small remote alpine lake on the southeastern Tibetan Plateau. The record reveals a temperature history comprising a relatively cool early Holocene (before 7 ka) followed by a warmer mid‐ to late‐Holocene (after 7 ka), which was likely linked to increasing local annual insolation and greenhouse gases. Three cold events punctuated the general warming trend ca. 10.4 ka, 3.7 ka, and 1.7 ka BP, and correspond closely in time to ice rafting events in the North Atlantic, and to episodes of volcanism and/or unusual solar activity. The entire Holocene temperatures are cooler than the previously identified anthropogenic warming from 1990–2015 AD. Plain Language Summary: The scarcity of high‐quality, quantitative Holocene temperature records from terrestrial archives, especially at high elevations, such as the Tibetan Plateau, limits our understanding of the temperature history of the Holocene. Here, we present a molecular fossil‐based mean annual air temperature record for the last 12,000 years from sediments preserved in a small remote alpine lake. The new record shows that the early Holocene was relatively cool and was followed by a warmer mid‐ to late‐ Holocene, which is consistent with results from climate modeling studies. This Holocene warming trend was probably due to increases in regional annual solar radiation and additional radiative forcing of greenhouse gases. The reconstruction captures the anthropogenic warming of the past 25 years (1990–2015 AD) and shows it to be unusual during the past 12,000 years. Key Points: An unreported cooler early Holocene (before 7 ka BP) temperature record was presented at high elevations on the southeastern Tibetan PlateauThe entire Holocene mean annual temperatures are cooler than the previously identified anthropogenic warming at this site from 1990 to 2015 ADThree multi‐centennial cold events centered on 10.4, 3.7, and 1.7 ka BP are observed in the record [ABSTRACT FROM AUTHOR]

As essential parts of the unique ecosystem of Tibetan Plateau (TP), the sizes and associated physical properties of alpine lakes have long been investigated. However, little is known about one of the most critical biogeochemical properties, i.e. the Chlorophyll-a (Chl-a) concentrations. Here, for the first time, we presented a comprehensive investigation of the temporal–spatial variations in Chl-a in 82 lakes (>50 km2) across the entire TP region, based on MODIS observations in the period of 2003–2017. The results showed that the 82 lakes exhibited an average long-term mean Chl-a of 3.3 ± 4.3 mg m−3, with high Chl-a lakes concentrated in the eastern and southern inner TP basin and northeastern parts of the TP. An interannual trend analysis revealed that lakes exhibiting (significantly) decreasing Chl-a trends and (significantly) increasing Chl-a trends were comparable in numbers but differed in distribution patterns. A correlation analysis indicated that at least 70% of the interannual variability in Chl-a values of lakes was significantly correlated with one of the four environmental factors (wind speed, ice cover duration, lake water surface temperature and surface runoff) and lake size. In addition, glacier meltwater tended to reduce lake Chl-a while salinity levels showed minor influences. [ABSTRACT FROM AUTHOR]

Glacial lake outburst floods (GLOFs) represent one of the most serious hazard and risk in deglaciating high mountain regions worldwide and the need for GLOF hazard and risk assessment is apparent. As a consequence, numerous region- and nation-wide GLOF assessment studies have been published recently. These studies cover large areas and consider hundreds to thousands of lakes, prioritizing the hazard posed by them. Clearly, certain simplification is required for executing such studies, often resulting in neglecting qualitative characteristics which would need manual assignment. Different lake dam types (e.g., bedrock-dammed, moraine-dammed) are often not distinguished, despite they control GLOF mechanism (dam overtopping/dam breach) and thus GLOF magnitude. In this study, we explore the potential of easily measurable quantitative characteristics and four ratios to approximate the lake dam type. Our dataset of 851 lakes of the Cordillera Blanca suggests that while variances and means of these characteristics of individual lake types differ significantly (F-test, t-test), value distribution of different geometrical properties can't be used for the originally proposed purpose along the spectra. The only promising results are obtained for extreme values (selected bins) of the ratios. For instance, the low width to length ratio indicates likely moraine-dammed lake while the high value of ratio indicating round-shape of the lake indicates increased likelihood of bedrock-dammed lake. Overall, we report a negative result of our experiment since there are negligible differences of relative frequencies in most of the bins along the spectra. [ABSTRACT FROM AUTHOR]

Non-invasive techniques such as seismic investigations and high-resolution multibeam sonars immensely improved our understanding of the geomorphology and sediment regimes in both the lacustrine and the marine domain. However, only few studies provide quantifications of basin wide-sediment budgets in lakes. Here, we use the combination of high-resolution bathymetric mapping and seismic reflection data to quantify the sediment budget in an alpine lake. The new bathymetric data of Lake Brienz reveal three distinct geomorphological areas: slopes with intercalated terraces, a flat basin plain, and delta areas with subaquatic channel systems. Quasi-4D seismic reflection data allow sediment budgeting of the lake with a total sediment input of 5.54 × 106 t sediment over 15 years of which three-quarter were deposited in the basin plain. Lake Brienz yields extraordinarily high sedimentation rates of 3.0 cm/yr in the basin plain, much more than in other Swiss lakes. This can be explained by (i) its role as first sedimentary sink in a high-alpine catchment, and by (ii) its morphology with subaquatic channel-complexes allowing an efficient sediment transfer from proximal to distal areas of the lake. [ABSTRACT FROM AUTHOR]

Two widespread drivers of change in high-elevation lakes are climate warming and atmospheric nitrogen deposition, which may have interactive effects on aquatic ecosystems. Using an outdoor mesocosm experiment at 2900 m above-sea level along the Colorado Front Range, we investigated the individual and combined effects of realistic increases in temperature (ambient versus 2.4 °C increase) and nitrogen concentrations (three levels) on lake plankton and hydrochemistry. Relative to the low temperature treatment, enhanced temperatures decreased the overall density of Daphnia pulicaria by ~ 40% and of gravid females specifically by ~ 20%. Increased nitrogen also reduced Daphnia density, especially in the low-temperature treatments, leading to a significant nitrogen-by-temperature interaction. The calanoid copepod Hesperodiaptomus shoshone, in contrast, was unaffected by experimental manipulations of temperature and nitrogen, and declined in abundance over time regardless of treatment. Chlorophyll-a increased to a maximum in week 4 and was unaffected by the temperature manipulation, suggesting that observed effects on Daphnia were likely direct physiological responses to warming rather than bottom-up effects. Nitrate additions caused transient increases in chlorophyll-a, which converged across treatments by the end of the study as nutrients were assimilated. Nitrogen additions also led to progressive increases in dissolved organic carbon concentrations throughout the experiment. Our results suggest that warming has the potential to reduce zooplankton production, consistent with observed decreases in large-bodied Daphnia density with decreasing elevation in the Colorado Rockies. Future work should evaluate how the observed effects on plankton communities scale-up to natural lakes, particularly the relative importance of species-specific stress responses versus indirect food web effects. [ABSTRACT FROM AUTHOR]

The Tibetan Plateau (TP) has encountered rapid warming, with more than 50% of lakes expanding and 80% of glaciers retreating. Melting glaciers are known as a secondary source of pollutants, but the dynamics and release features of water‐soluble emerging chemicals have not been studied in the TP. Glacial ice and snow, meltwater runoff, rain, and lake water were collected in Nam Co basin, in the central TP. The total concentrations of perfluoroalkyl acids (PFAAs) were 1,413 pg/L for glacial ice, followed by 1,277 pg/L for meltwater runoff, 980 pg/L for lake water, and 616 pg/L for rain. Perfluorobutanoic acid is dominant in runoff and glacial ice, while lake water contained high proportions of perfluorobutane sulfonate and perfluorooctane sulfonate. During the melting season, meltwater runoff generally had greater PFAAs concentrations, and the PFAAs release fluxes were strongly related to the glacial melt intensity. Due to the direct input of PFAAs by melted glaciers, south shore of Lake Nam Co contained higher PFAAs concentrations. The estimated input fluxes of PFAAs to the lake by rain and glacial and nonglacial runoff were 1,425, 1,342, and 2,192 mg/day, respectively. Taken together, these evidences suggest that melting glaciers are sources of PFAAs, while the lake is the receptor. Given the continuity of glacial melt and high concentrations of water‐soluble emerging pollutants in glacier, the melting process will increase the risks of emerging pollutants to freshwater sources and should be of great concern. Key Points: The PFASs released by glaciers have become a secondary source of PFASs in Lake Nam Co in the central Tibetan PlateauPFAA transport dynamics in glacial runoff is related to the chain length of PFAAs and the melting process of ice and snowPrecipitation and glacial and nonglacial runoffs contribute 27.1%, 28.7%, and 44.2% of the total annual PFAAs input in Lake Nam Co, respectively [ABSTRACT FROM AUTHOR]

High-altitude lake sediments can be used as natural archives to reconstruct the history of pollutants. In this work, the temporal distribution of polycyclic aromatic hydrocarbons (PAHs) was determined in a sediment core collected from the southern Tibetan Plateau (TP), which was dated by using the 210Pb dating method and validated with the 137Cs fallout peak. The concentrations of the anthropogenic PAHs (Σ8PAH) in the sediment core ranged from 0.83 to 12 ng/g dw, and the fluxes of the Σ8PAH were in the range of 2.1-27 g/cm2/year. The temporal variations in the concentration and input flux of anthropogenic PAHs were low with little variability before the 1950s, and then gradually increased from the 1950s to the 1980s, and an accelerated increase was observed after the early 1980s. The content of total organic carbon played an insignificant role in affecting the time trends of PAHs in the sediment core. Diagnostic concentration fractions of PAH components indicate PAHs in the lake sediment of the southern TP which are mainly from biomass burning and/or from long-range atmospheric transport. [ABSTRACT FROM AUTHOR]

As part of an investigation of the sources of aliphatic hydrocarbons to the sediments of alpine Lake Ximencuo, leaves of the eight dominant vascular plants were collected and their hydrocarbon contents were analyzed. A series of unsaturated aliphatic hydrocarbons were identified in the plant leaves; in particular, Festuca sp. contain a series of n-alkadienes that have rarely been reported in previous studies. The comparison of n-alkane proxies (ACL27-33, ACLT, Paq, and CPI) and δ13Corg among plant leaves, surface soils, and lake sediments suggests that organic proxies have been altered to varying degrees during the transport and burial process of organic materials. It is believed that microbial reworking and source changes have great impacts on organic proxies in the alpine lake system. In addition, the cluster analysis for plant leaves depending on n-alkane compositions and the ACLT proxy generates similar results. Accordingly, we postulate that the average chain length of plant waxes might be a potential indicator of plant classification in regions such as the Qinghai-Tibet Plateau. [ABSTRACT FROM AUTHOR]

Based on analyses of multiple molecular markers (18S rDNA, ITS1, ITS2 rDNA, rbcL), an alga that causes red snow on the melting ice cover of a high-alpine lake in the High Tatras (Slovakia) was shown to be identical with Chlainomonas sp. growing in a similar habitat in the Tyrolean Alps (Austria). Both populations consisted mostly of smooth-walled quadriflagellates. They occurred in slush, and shared similar photosynthetic performances (photoinhibition above 1300 µmol photons m-2 s-1), very high levels of polyunsaturated fatty acids (PUFA, 64% and 74% respectively) and abundant astaxanthin accumulation, comparable to the red spores of Chlamydomonas nivalis (Bauer) Wille. Physiological differences between the Slovak and Austrian populations included higher levels of α-tocopherol and a 13Z-isomer of astaxanthin in the former. High accumulation of secondary pigments in the Slovak population probably reflected harsher environmental conditions, since the collection was made later in the growing season when cells were exposed to higher irradiance at the surface. Using a polyphasic approach, we compared Chlainomonas sp. with Chlamydomonasnivalis. The latter causes ʻconventionalʼ red snow, and shows high photophysiological plasticity, with high efficiency under low irradiance and no photoinhibition up to 2000 µmol photons m-2 s-1. Its PUFA content was significantly lower (50%). An annual cycle of lake-to-snow colonization by Chlainomonas sp. from slush layers deeper in the ice cover is proposed. Our results point to an ecologically highly specialized cryoflora species, whose global distribution is likely to be more widespread than previously assumed. [ABSTRACT FROM AUTHOR]

Sediment cores from four lakes across the Tibetan Plateau were used as natural archives to study the time trends of organochlorine pesticides (OCPs). The total concentrations of dichlorodiphenyltrichloroethane (ΣDDT) and hexachlorocyclohexane isomers (ΣHCH) were in the range of 0.04–1.61 and 0.08–1.88 ng/g based on dry weight (dw), while the input fluxes were in the range of 0.3–236 and 0.7–295 pg/cm2/y in the core sediments, respectively. The input fluxes of ΣDDT and ΣHCH generally peaked in sediment layers corresponding to the 1970s–1990s and peaked in top sediment layers. The ratio of α/γ-HCH decreased in the top layer sediments, implying that the contribution of lindane (pure γ-HCH) has been increasing in recent years. In addition, the ratio of o,p′-DDT/p,p′-DDT increased significantly over the last 15–20 years, suggesting that dicofol (characterized by high ratio of o,p′-DDT/p,p′-DDT about 7.0) has recently become a relatively more important source of DDT compared to technical DDT itself. The time trends of OCPs recorded in lake sediments examined the impact on such remote alpine regions by human activities. [ABSTRACT FROM AUTHOR]

Increased phosphorus (P) export from sediments to the overlying water column is a significant factor driving the variation of phytoplankton in productivity and community structure in lakes. However, the lack of long-term instrumental data often impeded analyses attempting to associate dynamics of phytoplankton with variation of internal P loading. Here, elements and lipid biomarkers were analyzed in a sediment core from Lake Heihai, a small, deep, and ultraoligotrophic alpine lake in Haba Mountain, Yunnan Province, SW China. The data document incredible enrichment of element iron (Fe) in the sediment, whose concentrations are much higher than those of other common major elements including titanium (Ti), aluminum (Al), calcium (Ca), and magnesium (Mg). This finding, together with the abundance correlation between P and Fe ( n = 30, R = 0.783) suggested that P was probably retained in sediments through sorption with micro-layer of FeOOH at the sediment-water interface. The P/Ti ratios, P/Fe ratios, and P/total organic carbon (TOC) ratios all declined in the sediment since 1980, perhaps indicating increased P release from sediments to the overlying water column initiated by hypolimnion anoxia and sulfidic, which is presumably triggered by regional climate warming since the 1980s. The P-rich bottom water can be injected into photic zone during wind-driven mixing and overturn of the water column, although its frequency and intensity might decline due to stronger water column stratification in warming climate. In response, diatoms exhibited a rapid increase of productivity at this time, because diatoms have a storage vacuole and thereby nutrients such as P can be concentrated and used for cell division long after they are depleted in the bulk fluid. Elevated diatom biomass produced shading of light penetration, allowing for a low productivity for dinoflagellates. This study deepens our understanding of the impact of climate warming on lake systems and highlights the element biogeochemical cycle contributing to the variation of nutrients in the lake water column. [ABSTRACT FROM AUTHOR]

The hydrochemistry of alpine lakes reflects water characteristic and its response to climatic change. Over 300 water samples had been collected from 52 sites of 5 lakes and 7 inflowing rivers in the Yamzhog Yumco Basin, South Tibet, during 2009-2014, basing which the hydrochemical regime and its mechanism were analyzed along with the adoption of hydrological investigations in 1979 and 1984 as well. Results revealed that the waters were hard with weak alkalinity for the Yamzhog Yumco Basin. Most of them were fresh, and the rest were slightly saline. The hydrochemical types of 5 lakes (i.e., Lake Yamzhog Yum Co, Puma Yum Co, Bajiu Co, Kongmu Co, and Chen Co) were SO -HCO -Mg-Na, HCO -SO -Mg-Ca, SO -Mg-Na, SO -HCO -Ca, and SO -Na-Mg-Ca, respectively. As for rivers, HCO and SO were the major anions, and Ca was the dominant cation. Lake Yamzhog Yum Co, the largest lake in the basin, exhibited remarkable spatial variations in hydrochemistry at its surface but irregular changes with depth. The weathering of evaporates and carbonates, together with evaporation and crystallization, were the major mechanisms controlling the hydrochemistry of waters in the Yamzhog Yumco Basin. Global warming also had significant impacts on hydrochemical variations. [ABSTRACT FROM AUTHOR]

To provide a theoretical basis for alpine source lake protection, ten samples were taken from each lake annually from 2012 to 2015. Each year, the various species of nitrogen and phosphorus nutrients were measured. The average contents of nitrate nitrogen, ammonia nitrogen, nitrite nitrogen, total phosphorus, and total nitrogen in the four lakes are 0.195-0.0 mg/L, 0.038-0.143 mg/L, 0.004-0.168 mg/L, 0.006-0.740 mg/L, and 0.050-0.547 mg/L, respectively. The total phosphorus contents in Eling Lake, Longbao Lake and Sea Star were higher than Class I water quality standards, and the total nitrogen contents in Eling Lake, Sea Star and Zhaling Lake were higher than Class I water quality standards as well. The concentration contour maps of the nitrate nitrogen, ammonia nitrogen, nitrite nitrogen, total phosphorus and total nitrogen showed that the indicators of the four lakes in the east, the west, and the center of the lake did not have the same trend. From 2012 to 2015, each of the measured nutrients showed a rising trend year by year. The four lakes are polluted by both endogenous and exogenous pollution, and it is necessary to limit the exogenous pollution and protect the alpine lakes immediately. [ABSTRACT FROM AUTHOR]

Global environmental change has affected aquatic ecosystems of the southeast Tibetan Plateau during the past 200 years, altering the composition and biomass of primary producers (e.g. algae). However, the response of primary consumers (e.g. cladocerans) to this recent environmental forcing is not well documented. Samples of cladoceran remains from sediment traps (1-year deployment), surface sediments covering a range of water depths and a short 22.5-cm sediment core were analysed in a small, remote alpine lake (Moon Lake) in Sichuan Province (SW China). Littoral forms, notably Chydorus sphaericus and Acroperus harpae, together with Daphnia pulex dominated the cladoceran community. Remains of these cladocerans were well represented in the sediment core assemblages as indicated by their relative abundance in the surface sample. There was a marked increase in the abundance of D. pulex and total cladoceran fluxes in the sediment core from ca. 1880 AD, coinciding with the changes in diatom assemblages and pigments. Analysis of the multi-proxy data (cladocerans, diatom, pigment, total organic carbon, C/N ratio, air temperature and atmospheric NO records) suggests that both direct and indirect climatic forcing, coupled with enhanced nutrient supply (e.g. NO deposition) effects on primary producers have changed cladoceran community dynamics in Moon Lake over the last ~200 years. [ABSTRACT FROM AUTHOR]

Over a period of 34 years (1954-1987), a total of 11.9 million glass eels were stocked all over Austria to improve the yields of commercial fishermen and to make the lakes more attractive for anglers. Nearly half (48%) of the imported glass eels were introduced into natural, previously eel-free Alpine lakes until stocking ceased in 1988. Twenty-five years later, their occurrence could be verified in 56% ( N = 22) of the Austrian Alpine lakes larger than 50 ha and mean body length had increased to 66 cm. Eels from seven selected Austrian Alpine lakes exhibited a yearly mean increase in length between 0.6 and 1.5 cm, indicating a comparatively poor growth compared with the majority of eel populations from within their natural distribution range. At the same time, high expectations in developing a flourishing eel fishery were not met. In all but one lake, the harvest remained below 3% of the total yearly catch and salmonids remained the dominant target species. During peak harvest in the 1980s, it exceeded 8% in mesotrophic Wallersee (2600 kg). Simulations of stock development indicated that the yield could have been improved, but contrary to earlier expectations eels never became important for local cuisine and catches remained too low for the development of a profitable export business. On the other hand, eels may have contributed to the loss of small-bodied fish taxa. [ABSTRACT FROM AUTHOR]

Sediments from Lake Petit (2200 m a.s.l., Southern Alps) are particularly relevant for analysis of coupled landscape palaeoecology and palaeolimnology. Diatom assemblages, organic matter composition of sediments (total nitrogen and organic carbon) and Pediastrum boryanum concentrations were obtained from a 144-cm-long core, enabling the reconstruction of the aquatic ecosystem over nearly the last 5000 cal. BP. From 4800 to 4300 cal. BP, Lake Petit was a stable diatom-productive water body dominated by alkaliphilous diatoms (Staurosirella pinnata). During this period, nutrients and cations were supplied by the chemical weathering of podzols that developed under conifer woodlands. This overall stability was suddenly interrupted at 4200 cal. BP by a major detrital pulse that was probably climate linked (4200 cal. BP event) and that triggered a drop in diatom productivity and diversity. From 4100 to 2400 cal. BP, diatom productivity progressively decreased, whereas Pediastrum developed. Diatom assemblages were more diversified (predominance of Pseudostaurosira robusta, P. brevistriata and P. pseudoconstruens) and reflected a regime of continuous erosion, whereas slopes were colonised by grazed grasslands. Finally, from 2400 cal. BP to the present day, diatom assemblages reveal a slight acidification and nutrient enrichment of waters concomitant with increasing human pressure in the catchment. These results demonstrate the close links between ecosystems and the ready propagation of disturbances throughout watersheds that might lead to abrupt regime shifts in such alpine environments. [ABSTRACT FROM AUTHOR]

The combined effect of external environment and energy allocation strategy of the organism on longevity can be exceptional. In a cold oligotrophic fishless habitat, individual Daphnia can live for over a year, several times the usual Daphnia lifespan. This extreme lifespan is in part a consequence of the overwintering strategy which includes storing resources and delaying reproduction until another spring. Yet, contrasting strategies may be applied by Daphnia, resulting in over twofold differences in lifespan within a single habitat. We identify physiological mechanisms mediating such differences in longevity in closely related Daphnia of two lineages coexisting within a high altitude lake, testing the predictions that long-lived animals stay in colder waters and have lower metabolic rates, irrespective of temperature. Vertical distribution of the animals was assessed during three summer stratification seasons, and metabolic activity was measured as oxygen consumption and RNA:DNA ratio. The results not only support our predictions but also reveal that habitat choice is dependent on reproductive status rather than genotype. The young individuals of the overwintering lineage may delay reproduction in part by staying in colder waters than the reproducing adults, which together with low intrinsic metabolic rates may underlie the longevity of Daphnia of this lineage. [ABSTRACT FROM AUTHOR]

ABSTRACT Lakeshores are under increasing pressure from human activities, which cause extensive hydromorphological alterations. In this article, a method is described for assessing those alterations by using physical criteria developed in relation to the response by the lakeshore ecosystem, using benthic invertebrates as indicators. Two alpine lakes (Lake Bled and Lake Bohinj, Slovenia) were used as a case study. Both lakes are subjected to varying levels of physical alterations and lakeshore uses, which are described using alteration variables for four lakeshore zones: littoral zone, shoreline zone, riparian zone and lakeshore region. On the basis of these four variables, a Lakeshore Modification Index (LMI) was developed as a weighted sum of all variables. The weights were based on each variable's explanatory power regarding the distribution of benthic invertebrate taxa using canonical correspondence analyses. Both the LMI and all four lakeshore zone alteration variables showed significant ( p < 0.01) negative correlations with species richness, but the LMI showed the strongest correlation (Pearson r = −0.086, p < 0.01). Differences existed in the level of alteration of the two lakes, with Lake Bled being more altered than Lake Bohinj; Lake Bled also exhibited the highest values for all four alteration variables and the highest LMI score. With the use of a classification system with five equidistant LMI classes, a difference was observed between the lakes in the distribution of LMI classes (two-sample Kolmogorov-Smirnov test Z = 5.714, p < 0.01). An assessment and classification of lakeshore modifications based on physical criteria, similar to that given by the LMI, can provide an important tool for lake management in practice, where a reliable method for assessing pressures is needed to support decision-making. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The 'All Taxa Biodiversity Inventories' (ATBIs) project coordinated by the European Distributed Institute of Taxonomy (EDIT) aims to achieve a baseline biodiversity assessment of flora and fauna in those regions characterized by a lack of knowledge and a high potential for biodiversity. Within the framework of the ATBIs, the aim of this study was to analyse the diatom flora and ecology of a complex of freshwater ecosystems in the Maritime Alps Natural Park (Italy), designated as a Special area of Conservation under the European Habitat Directive. We sampled epilithic and epiphytic diatoms in different habitats in 24 sites: shallow lake, springs, and streams. Our analysis resulted in a list of 138 diatom taxa, highlighting the great biodiversity and the complex structure of the investigated diatom communities. The taxa list included a wide range of uncommon species, including some recorded for the first time in North-Western Italy. Among the different habitats the highest level of diversity was found in the more lentic waters, in particular in limnocrene springs. These results show that the diatom communities of pristine and undisturbed high-mountain environments are rich and complex, despite the severe environmental conditions. [ABSTRACT FROM AUTHOR]

Daphnia middendorffiana has an arctic, circumpolar distribution, with some isolated southerly populations restricted to mountainous areas, including the Alps. In this paper, new records of Daphnia middendorffiana on the Alps are reported. The species was regularly recorded in several samples collected from 2006 to 2009 in four high altitude lakes in the Gran Paradiso National Park (GPNP) during the ice free period. This is the third finding for the Alps and the described populations are the largest. Chemical and morphometric features of the lakes are provided, the morphology of the Daphnia middendorffiana from GPNP is described as well as some aspects concerning its ecology. The studied lakes are small, oligotrophic (total phosphorus ranged from 0 to 7 µdg L-1) and well preserved from acidification risk (pH ranged from 6.45 to 8.14). D. middendorffiana is the largest zooplanktonic crustacean inhabiting the Alpine lakes in GPNP reaching 3.43 mm in length; the morphological analysis noted some differences within the studied populations; however there is a clear resemblance to the only Alpine population previously described (from Central Alps, Bognanco Valley, Lake Campo IV) and to the arctic populations. D. middendorffiana in GPNP lives at low density levels, reaching higher densities in late August and early September. No males have been found during the sample campaign confirming its ability to produce asexual viable diapauses eggs. This study confirms the attitude of this species for cold and oligotrophic waters and increases the current knowledge on the geographical distribution, morphology and ecology of this species in Alpine environments. The finding of D. middendordorffiana in the GPNP poses interesting issues concerning the phylogeography of Alpine Daphnia middendorffiana, as well as raising need for conservation efforts aimed at keeping the populations safe from several global and local threats, such as climate warming and the ecological impact of alien species. [ABSTRACT FROM AUTHOR]

The existence of bacterioneuston in aquatic ecosystems is well established, but little is known about its composition and dynamics, particularly in lakes. The bacterioneuston underlies extreme conditions at the air–water boundary, which may influence its dynamics in a different way compared with the bacterioplankton. In this study, we assessed quantitative changes in major bacterial groups of the surface microlayer (SML) (upper 900 μm) and the underlying water (ULW) (0.2–0.5 m depth) of an alpine lake during two consecutive ice-free seasons. Analysis of the bacterial community composition was done using catalyzed reporter deposition FISH with oligonucleotide probes. In addition, several physicochemical parameters were measured to characterize these two water layers. Dissolved organic carbon was consistently enriched in the SML and the dissolved organic matter pool presented clear signals of photodegradation and photobleaching. The water temperature was generally colder in the SML than in the subsurface. The bacterial community of the SML and the ULW was dominated by Betaproteobacteria and Actinobacteria. The bacterial community composition was associated with different combinations of physicochemical factors in these two layers, but temporal changes showed similar trends in both layers over the two seasons. Our results identify the SML of alpine lakes as a microhabitat where specific bacterial members such as of Betaproteobacteria seem to be efficient colonizers. [ABSTRACT FROM AUTHOR]

The quality and interpretability of the paleobiological record depends on the preservation of morphological and geochemical fossils. Siliceous microfossils and sedimentary pigments are often cornerstones in paleoecology, although the microbial and geochemical processes conducive to their preservation remain poorly constrained. We examined sediments from an alpine lake in Banff National Park (Alberta, Canada) where diatom frustules are completely dissolved within 50 years of deposition. Diatom dissolution, silica recycling, and diagenetic alteration of algal pigments were investigated, in conjunction with porewater geochemistry and microelectrode profiling of the sediment–water interface. Analysis of sediment trap material showed ~90% of biogenic silica (BSi) production is lost prior to burial. Silica flux calculations, based on dissolved silica (as H4SiO4) in pore-waters, show a further ~6% of total BSi is returned to the water column from the upper 4 cm of sediments, implying that only ~4% of total BSi is permanently archived in sediments. In situ sediment pH and O2 profiles reveal that aerobic respiration by bacteria fully consumes oxygen by a depth of 4 mm into the sediment, with associated strong pH and redox gradients. During sedimentation and early diagenesis, diatoms undergo loss of extracellular polymeric substances that coat their frustules, promoting silica dissolution and leading to the loss of the microfossil record by a depth of 3.25 cm. Sedimentary pigments similarly undergo rapid degradation, but diatom-related carotenoids persist below the depth of silica dissolution. This work provides new insights on diagenetic processes in lakes, with broad implications for the interpretation of sedimentary proxies for algal production. [ABSTRACT FROM AUTHOR]

Plankton in mountain lakes are confronted with generally higher levels of incident ultraviolet radiation (UVR), lower temperatures, and shorter growing seasons than their lower elevation counterparts. The direct inhibitory effects of high UVR and low temperatures on montane phytoplankton are widely recognized. Yet little is known about the indirect effects of these two abiotic factors on phytoplankton, and more specifically whether they alter zooplankton grazing rates which may in turn influence phytoplankton. Here, we report the results of field microcosm experiments that examine the impact of temperature and UVR on phytoplankton growth rates and zooplankton grazing rates (by adult female calanoid copepods). We also examine consequent changes in the absolute and relative abundance of the four dominant phytoplankton species present in the source lake ( Asterionella formosa, Dinobryon sp., Discostella stelligera, and Fragilaria crotonensis). All four species exhibited higher growth rates at higher temperatures and three of the four species (all except Dinobryon) exhibited lower growth rates in the presence of UVR versus when shielded from UVR. The in situ grazing rates of zooplankton had significant effects on all species except Asterionella. Lower temperatures significantly reduced grazing rates on Fragilaria and Discostella, but not Dinobryon. While UVR had no effect on zooplankton grazing on any of the four species, there was a significant interaction effect of temperature and UVR on zooplankton grazing on Dinobryon. Discostella and Dinobryon increased in abundance relative to the other species in the presence of UVR. Colder temperatures, the presence of zooplankton, and UVR all had consistently negative effects on rates of increase in overall phytoplankton biomass. These results demonstrate the importance of indirect as well as direct effects of climate forcing by UVR and temperature on phytoplankton community composition in mountain lakes, and suggest that warmer climates and higher UVR levels may favor certain species over others. [ABSTRACT FROM AUTHOR]

The salinization of Mirror Lake in the White Mountains of New Hampshire has been ongoing steadily since Interstate 93 (I-93) was built through the NE subcatchment of the lake in the fall and winter of 1969–1970. Salt added to I-93 during winter as a deicer has been transported to the lake by different quantified, hydrologic pathways, but primarily from the Northeast Tributary, which was intersected by I-93. Now, surprisingly, after the New Hampshire Department of Transportation has spent more than $500,000 on recent structural modifications to divert salt from I-93 away from the Northeast subcatchment of Mirror Lake, applications of salt to a small, town road traversing the other two subcatchments for the lake and servicing a new housing development, have become the major source of salt to the lake. Streamflow from these two subcatchments currently provides more than three times as much salt to the lake as from I-93, and the salt concentration in the lake continues to rise. [ABSTRACT FROM AUTHOR]

In May 2005, an epidemic of the cestode Triaenophorus crassus occurred in the Salvelinus umbla population of Lake Grundlsee, an oligotrophic Austrian Alpine Lake. Based on catches with a standardized multi-mesh gillnet survey 53% of S. umbla were infected with up to 17 cysts of T. crassus per fish. This is the first documented record of an epidemic of this tapeworm in S. umbla. [ABSTRACT FROM AUTHOR]

We analysed a 42 cm long sediment record from Lej da la Tscheppa, a high-altitude lake (2,616 m a.s.l.) in the Upper Engadine valley (Switzerland) for subfossil diatoms, chironomids and pollen. The chronology of the top 21 cm of the record was established using 210Pb analysis using a constant-rate-of-supply model, and validated with 137Cs measurements and the content of spheroidal carbonaceous particles. A tentative chronology for the lower part of the core was obtained through extrapolation of the sedimentation rates in the uppermost part of the record. Pollen assemblages in the record reflect regional changes in forestation and land-use patterns in the Upper Engadine valley and show no evidence of significant local human activity in the lake’s catchment. Diatom assemblages record a distinct increase in planktonic taxa since the early 19th century, suggesting a decrease in the duration of ice-cover. In contrast, chironomid assemblages remained stable during a large part of the record. We applied an established chironomid-based July air temperature transfer function and a newly developed diatom-based spring air temperature transfer function to reconstruct past seasonal air temperature changes at Lej da la Tscheppa. The reconstructions indicate a diatom-inferred warming trend in spring temperatures during the past ca. 400 years, whereas chironomid-inferred summer temperatures suggest a slight cooling trend. These biota-based reconstructions are in good agreement with the centennial-scale temperature trend in an independent reconstruction of regional temperatures in the Upper Engadine region based on instrumental records and documentary proxy evidence from the Alps. Our results suggest that, in high-altitude lakes, independent chironomid- and diatom-based seasonal temperature reconstruction is possible and can be successfully used to track seasonal temperature trends. [ABSTRACT FROM AUTHOR]

Major and trace elements, minerals, and grain-size were analysed from the early to mid-Holocene (12 to 4 ky BP) period of a sediment core from the Alpine lake Oberer Landschitzsee (ObLAN, 2076 m a.s.l.), which is located on predominantly crystalline bedrock on the southern slopes of the Austrian Central Alps. Geochemistry and mineralogy were compared with diatom-inferred (Di-) ‘date of autumn mixing’ ( Amix), DOC, pH, and selected indicator pollen species from the same sediment core. Principal components analysis (PCA) indicated a positive correlation between processes triggered by temperature and precipitation (e.g., lake mixing, DOC). PCA grouped indicators of physical weathering and enhanced catchment run-off (sand, quartz, feldspar), elements of weathering (e.g., Ti, Rb, Mn) under dryer conditions (clay to silt fractions), and elements that probably were related to changes in redox conditions (Cu, Fe, S, Zn). The duration and height of the snow-pack played an important role in this high-alpine environment, affecting weathering, erosion, pH, and lake stratification. Low Alnus viridis pollen abundance, together with markers for increased elements of erosion, indicated extensive snow-pack. Changes in S coupled with As, and elements indicating increased weathering, reflected climate oscillations. LOI was affected by productivity and erosion. High (late) Di– Amix coupled with increased Di-DOC indicated prolonged summers with increased productivity. Cold and wet (snow-rich) phases and subsequent melting caused low pH and a decoupling of the significant linear correlation between sedimentary Ca and Di-pH. Weathering and leaching during climate deteriorations opposed the long-term trend in a loss of cations and forced in-lake alkalinity generation during the following lake warming. Overall, the multi-proxy study indicated complex climate-driven processes within different time-scales (long-term trends, climate oscillations, seasonality). The climate oscillations within 12–5 ky BP corresponded well with the cool and wet phases known from central Europe suggesting a dominant common Atlantic climate impact. When Mediterranean climate established between 5 and 4 ky BP, its influence on the southern slopes of the Alps increased. [ABSTRACT FROM AUTHOR]

Sägistalsee is a small lake located at the modern tree-line in the Swiss Alps. A 13.5 m long core taken in the central part of the 9.5 m deep basin consists of clayey silts and sands and dates back to about 9000 cal. BP. These sediments have a low organic content that steadily increases from 4–8% loss-on-ignition at 550 °C towards the top of the core, whereas the carbonate content decreases from 20 to about 10% loss-on-ignition at 950 %C. We outline the aims of an interdisciplinary research project centred on the Holocene sediments of Sägistalsee. We also present information about the lake, its sediments, and its catchment that forms the basis for different biotic and abiotic multi-proxy studies carried out on the sediments of Sägistalsee. [ABSTRACT FROM AUTHOR]

Phytoplankton seasonal and long-term succession can be described and functionally classified by associations similar as in terrestrial vegetation studies. Such a concept has to include 'climax' into pelagic succession which in turn leads to the question to what extent steady state assemblages occur and if during periods of dynamic equilibrium can be identified. Here we explore the situation with respect to the above question for deep, nutrient poor, alpine lakes in Austria. We first track the long-term development of phytoplankton biomass, their taxonomic structure and their relation to total phosphorus and chlorophyll-a as predictors of trophic state over the past 35 years. We then analyse this data set for coherent algal associations which can be ascribed to trait separated functional groups according to Reynolds et al. (2002). A three year period of stable environmental conditions has then be extracted from the progression of trophic state indices, having similar dominating species each year. These years were finally analysed for steady state conditions according to definitions given in Sommer et al. (1993). During thermal stratification, achievement of an equilibrium could be ruled out although coexistence of several dominating species lasted for several weeks. Habitat templates were constructed from environmental variables prior to biomass peaks for two species important in summer assemblages, the dinoflagellate Ceratium hirundinella and the diatom Fragilaria crotonensis. In summary, functional groups proved to be a valid and useful concept to describe species succession of phytoplankton in deep alpine lakes while pelagic climax is much less clear and steady state conditions were never met. [ABSTRACT FROM AUTHOR]

Lake Ilchir is an alpine lake located 1963 m above sea level in the mountain ranges of eastern Sayan, eastern Siberia. Observations are presented from October 1998 to September 1999 in order to provide the phytoplankton and zooplankton community structures. Sixty-six taxa of phytoplankton and 66 taxa of zooplankton were recorded. Of much interest was the finding of rare species, such as the dinoflagellate Gymnodinium coeruleum, the diatoms Pliocaenicus costatus and Cyclotella tripartita, and the calanoids Acanthodiaptomus tibetanus and Arcthodiaptomus (S.) paulseni. [ABSTRACT FROM AUTHOR]

The epiphytic invertebrates found on Potamogeton perfoliatus L. in Traunsee, an oligotrophic Alpine lake in Austria, were investigated in August and October 1998 in order to study the impact of industrial tailings discharged into the lake. 113 taxa were found, 54 could be identified to the species level. Their total abundance varied between ca. 190,000 and 1,138,000 ind. m-2 lake bottom area. This epiphytic assemblage was dominated by Dreissena polymorpha and Sida crystallina, which resulted in a very low overall species diversity. Multivariate statistical analyses revealed significant differences in the community structure between three sites, each of them was located at a different distance from the site of industrial waste emission. These differences were interpreted as variations which reflect the patchiness within highly structured habitats rather than as being the result of the industrial pollution. [ABSTRACT FROM AUTHOR]

The absence of Potamogeton lucens L. in an area of Traunsee, Austria, which is heavily impacted by industrial sludges was related to these deposits. The hypothesis that P. lucens L. is affected by the industrial tailings was confirmed by growth experiments of the translocated plants in the field. At the unpolluted reference site of the lake, the plants grew better, they were longer and produced more leaves than at the emission site. [ABSTRACT FROM AUTHOR]

Traunsee, an oligotrophic Alpine lake, has suffered from inputs of industrial tailings (soda- and salt-mining industries) for several decades. The effects of the industrial sludges on the spatial distribution of the littoral and profundal invertebrate fauna was investigated along three transects at five dates. In the littoral zone, no negative impacts were found. A distinct gradient in faunal composition and diversity was, however, observed along a profundal transect relative to the distance from the waste emission. Near the industrial input, the enhanced pH, the substrate instability, and the poor sediment quality for substrate- and deposit-feeders were the main factors that lower or prohibit colonization of the industrial sludges. Along a transitional zone between the waste emission and the deepest basin, recolonization was delayed, but did occur as soon as layers of a few mm natural sediment seal the sludge. Mobile, epibenthic organisms are the first to settle these areas, whereas recolonization by tube-building oligochaetes and chironomids requires thicker sealings of the industrial sludges. Differences in the abundance of benthic invertebrates at different profundal sites were not only related to the waste emission, but also to the influence of the main tributary, the River Traun. The enhanced availability of allochthonous organic matter was probably responsible for high densities of tubificids near the inlet in the South of Traunsee. Moreover, a higher proportion of tolerant oligochaete and ostracod species in the lower profundal outside the influence of the industrial tailings was interpreted as reflecting the increased trophy of Traunsee in the 1970s, which forced sensitive species to shift to the upper profundal when the oxygen climate deteriorated. [ABSTRACT FROM AUTHOR]

The ecosystem response of Lake Redó (Central Pyrenees) to fluctuations in seasonal air temperature during the last two centuries was investigated by comparison of reconstructed air temperatures with the sediment record. Fine slicing allowed a resolution of 3–6 years according to the 210Pb dating, although it was still difficult to easily investigate the response to air temperature forcing, since extreme fluctuations in temperature occur on interannual time-scales. However, the resolution was sufficient to show responses on decadal and century scales. An overall tendency to warming in mean annual temperature in the Central Pyrenees has been caused by summer and in particular by autumn increases. Many of the measured sediment variables apparently responded to these long term trends, but the significance of the relationships was highly conditioned by the structure of the data. The variables responding most on the finer time scales were the microfossils. For diatoms, chironomids and chrysophytes the main variability correlated to summer and to autumn temperatures. For two planktonic species, Fragilaria nanana and Cyclotella pseudostelligera, we found a link of their variability with temperature fluctuations in their growing months (September and October, respectively). This relationship appeared at a certain point during a general warming trend, indicating a threshold in the response. On the other hand, no significant changes in the dominant species could be linked to temperature, nor in any significant subgroup of the 180 diatom species present in the core. In contrast, for most chironomids (particularly Paratanytarsus austriacus, Heterotrissocladius marcidus and Micropsectra radialis) a negative relationship with summer temperature extended throughout the studied period. This response of the whole group gives chironomids a more robust role as indicators for recording temperature changes on long time-scales (e.g., through the Holocene) and for lake signal inter-comparison. Finally, our results indicated that, in all cases, there was a significant resilience to high frequency changes and hysteresis despite extreme fluctuations. Although we were dealing with organisms with one or many generations per year, their populations seemed to follow the decadal trends in air temperature. [ABSTRACT FROM AUTHOR]

A radiocarbon-dated core, NC, taken in the alpine Blue Lake in the Snowy Mountains of southeastern Australia provides a Holocene record of sedimentation that consists mainly of organic clays. Two types of quartz grains are recovered from 81 samples from the core. One type consists of angular grains, with frequently shattered faces, which originates from granitic lithologies present within the small catchment area of the lake. The other type is characteristically rounded to subrounded, often textured with frequent silica coating and is considered to have been deposited within the lake and its catchment by aeolian processes. These aeolian grains are thought to have been transported along the main dust path that ferries aeolian dust from the Mallee region, west of the Snowy Mountains, as far as the southeastern Tasman Sea. Aeolian grains with the largest size occur over approximately the last 1.6 ka of the Holocene and this indicates an increase of climatic instability, with arid phases that commenced about 3.5 ka. At 2 ka, a wet period in southeastern Australia coincided with low aeolian input at Blue Lake. The period of consistent reduced aeolian activity spans the 7.6 to 5.5 ka interval at Blue Lake. [ABSTRACT FROM AUTHOR]

A short sediment core from the deepest part of an alpine lake (Lake Chuna, Kola Peninsula, northwestern Russia), covering about the past 200 yrs of sediment accumulation, was analysed for chironomid head capsule remains. The lake has been receiving acidic precipitation and heavy metals loading from the atmosphere since the 1940's. A total of 22 chironomid taxa were recorded. The most important taxa were typical elements of oligotrophic lakes, i.e. Micropsectra insignilobus, Paratanytarsus penicillatus, Stictochironomus spp. and Heterotrissocladius marcidus. Based on the cluster analyses results for the reconstructed environmental variables and chironomid communities, three developmental stages were distinguished from the lake history: (1) Natural ontogeny stage (before ~1945); (2) Initial stage of anthropogenic ontogeny (~1945-~1982); and (3) Anthropogenic ontogeny stage (~1982-~1996). During the first period, the changes in the chironomid fauna were characterized as an anthropogenically undisturbed community, with M. insignilobus dominating (46-66%). The changes during the second period reflected the initial phase of anthropogenic succession associated with the beginning of acidification and heavy metal pollution. The main species showed opposite distributional patterns in this period; the abundance of the group M. insignilobus/ Stictochironomus spp. decreased, whereas the abundance of P. penicillatus/ H. marcidus increased. The third period was characterized by a major shift in the faunal assemblages, from M. insignilobus to other dominant species including P. penicillatus (19-30%). The increases of Orthocladiinae relative abundance and total organic content in the uppermost sediment layers may be explained by a decrease in lake productivity. The decreases of cold-stenothermal taxa Stictochironomus spp. and M. insignilobus in the uppermost sediment layers can be explained by the global warming during the 20th century. The lake ecosystem is likely to be affected by both inputs of airborne contaminants and climate changes. [ABSTRACT FROM AUTHOR]

Seasonal changes in blood erythrocytes and lymphocytes were investigated in Arctic char from a remote high mountain lake at an altitude of 2344 m. Despite striking seasonal differences of environmental conditions the erythrocyte numbers remained constant during the year. Lymphocytes, however, displayed a distinct seasonal pattern with low abundance during the period of ice-cover (about 7 months) and high abundance in summer. During winter the circulating blood contained lymphocytes with damaged organelles and membranes, and almost exclusively mature red cells with a high density. With rising water temperature in July/August (11°C), however, high-density (old) cells almost disappeared, the proportion of immature cells dramatically increased, and the capacity to responding to handling stress decreased. We conclude that in summer the accelerated erythropoiesis (recruitment of red blood cells) compensates for the reduced life span of red blood cells. [ABSTRACT FROM AUTHOR]

The gill structure of Arctic char from a low ionic (1-2 μmol Cl-) high mountain lake (2344 m above sea level) showed distinct seasonal changes. From spring to early winter chloride cells (responsible for ion uptake) were numerous, and during summer gill epithelia were highly hypertrophic resulting in a thick blood-to-water barrier. This gill morphology is typical for fish from soft water habitats and reflects osmoregulatory responses. In mid-winter, however, both chloride cell numbers and epithelia thickness were reduced and comparable to the situation in freshwater with high ionic contents. This pattern correlated with seasonal fluctuations of water chemistry. The most significant correlation was found with CO2 which accumulated under the ice cover, reaching a tenfold oversatturation. The concentration of Ca, Na, and Cl varied only by a factor of two or less and the correlation with the epithelial thickness was much weaker. [ABSTRACT FROM AUTHOR]

The species diversity and changes in the structural dynamics of the algal flora from the alpine lake Nesamovyte has been studied for 100 years. During the period of investigations, 234 species (245 infraspecific taxa) were revealed to cover more than 70% of the modern species composition of the studied lake. The modern biodiversity of algae is characterized by an increase in the number of widespread forms, a change from the baseline "montane" complex in comparison to the beginning of the 20th century. Nevertheless, the Nesamovyte Lake still has a unique algae composition that is typical for high-mountainous European lakes. The presence of a different complex of conventionally arctic species of algae, in particular, diatoms is discussed. Structural changes in the taxonomic composition of the algal flora of the lake as well as in the complex of the leading genera, species and their diversity are revealed. An ecological analysis of the algal species composition of the lake showed vulnerability and degradation to the ecosystem of the lake. On this basis, the issue regarding the question of protection and preservation of the algae significance and uniqueness of the flora of algae in the Nesamovyte Lake are discussed. [ABSTRACT FROM AUTHOR]

Tourism pressure on protected areas with attractive landscapes leads to environmental modifications. Eutrophication poses the main threat to the quality of water in alpine lakes. Even small inflows of biogenic elements can disrupt the ecological balance of these ecosystems. The aim of this study was to verify the hypothesis that recreational activities and easy access to alpine lakes contribute to changes in their ecological status. This hypothesis was verified by analyzing the presence of hydromacrophytes in two lakes of the Tatra National Park (Poland). The analysis was carried out along segments of hiking trails which were evaluated for accessibility to the studied lakes. Underwater surveys were carried out during scuba diving expeditions in 2012–2016. Submerged vegetation was evaluated in both lakes. This is the first study in Poland and one of the few projects in the world to have relied on such extensive support from scuba divers to generate highly accurate measurements. The study demonstrated that lake bottoms were extensively covered by Potamogeton friesii in the vicinity of trail segments with easy access to lakes. Our results show that tourism pressure contributes to the growth of aquatic vegetation in some areas of alpine lakes. We relied on our findings to propose several modifications to the routes of the evaluated tourist trails to minimize the impact of anthropogenic pressure on the studied lakes. [ABSTRACT FROM AUTHOR]

Exceptionally large (up to 4.0 mm) Daphnia middendorffzana were collected with a bottom-closing net while sampling benthos in Pipit Lake,Alberta. Such large D. middendorffiana have not been observed in plankton samples collected from the lake over the past 30 years, nor have such large individuals been reported in the literature. Stable nitrogen isotope ratios (81SN) of the large Daphnia were 4.5%o higher than smaller Daphnia from higher in the water column, indicating that the spatially separated Daphnia may use different food sources. The large Daphnia had Hesperodiaptomus resting eggs and nauplii in their guts, while the smaller Daphnia higher in the water column had mainly phytoplankton in their guts. Our findings highlight the need to use several different kinds of sampling gear to completely assess the fauna of a lake. [ABSTRACT FROM AUTHOR]