High Altitude Lake and Hydrochemistry: A Study of Lam Dal and Six Consecutive Lakes of Dhauladhar, Himachal Himalaya, India

Increased human influence has warmed the atmosphere, ocean and land thereby resulting in widespread and rapid changes in the atmosphere, ocean, cryosphere and biosphere (IPCC, 2021). High altitude lakes are generally small and quite sensitive to natural and anthropogenic perturbations. The present work is a preliminary work to investigate different hydro chemical processes and factors that controls the geochemistry of a high altitude lake, Lam Lake (dal) and its consecutive six lakes flowing through the Chamba district, Himachal Pradesh. Two hundred and eighty (n=280) water samples were collected in the year 2017 during the pre-monsoon and post-monsoon season. The anion concentration for all the seven lakes followed the trend HCO3- > NO3- > Cl- > SO42- > PO43- whereas the order of cation concentrations was Ca2+> Mg2+> Na+> K+ for both the seasons. Less EC of the water samples shows its serene nature. Components of bicarbonate (HCO3-) were found to be the major anion whereas calcium (Ca2+) was found to be the major cation present in the lakes. Piper Plot and Durov plot indicated Ca2+ – HCO3- as the major hydrogeochemical facies with comparatively less contribution from Mg2+–HCO3- type. The dominance of Ca2+ – HCO3- over Mg2+– HCO3- reflects the possibility of the natural order of dominance in the geology of the catchment area. The low Na+ + K+/TZ+ (total cations) ratios and the high Ca2+ + Mg2+/TZ+ (total cations) and (Ca2+ + Mg2+)/(Na+ + K+) ratios showed dominance of carbonate weathering. The average carbon ratios during pre-monsoon and post-monsoon were found to be 0.97 and 0.98, respectively, suggesting that proton is primarily derived from the oxidation of sulphide involving carbonate dissolution. The baseline data generated for a high-altitude lake shows that weathering and erosion during monsoonal precipitation and snow melt runoff during ablation season are the main sources of the chemical composition of lake water. Further to trace the imprints of climate change and seasonal variations in the high-altitude lakes, long term monitoring is recommended along with isotopic tracer techniques.

DO RADIOCARBON AGES OF PLANT WAX BIOMARKERS AGREE WITH 14C-TOC/OSL-BASED AGE MODELS IN AN ARID HIGH-ALTITUDE LAKE SYSTEM?

ABSTRACT To elucidate the dynamics of terrestrial leaf waxes in a high-altitude lake system, we performed compound-specific radiocarbon analysis (CSRA) of long-chain n-alkanes in two sediment core sections from Lake Karakul (Pamirs, Tajikistan) and in surface soil samples from the catchment area. We aimed to answer the question whether the n-alkanes are delivered into the lake sediment with substantial delay due to storage in soils, which may cause a potential bias when used as paleoenvironmental proxies. In the surface soils, the CSRA results reveal an age range of n-alkanes from modern to 2278 ± 155 cal BP. In the two sediment core samples, three of the four n-alkane ages fell on the lower ends of the 1σ-uncertainty ranges of modeled ages of the sediments (based on AMS 14C-TOC and OSL dating results). We conclude that sedimentary leaf waxes represent compounds with intermediate turnover time in soils, for example originating from alluvial plains close to the shores. Overall, the results provide evidence that sedimentary leaf wax compounds in this cold and arid setting are potentially older than the conventional age model indicates, but these findings need to be interpreted in context of the generally large uncertainty ranges of such age models.

The Holocene lake-evaporation history of the afro-alpine Lake Garba Guracha in the Bale Mountains, Ethiopia, based on δ18O records of sugar biomarker and diatoms

In eastern Africa, there are few long, high-quality records of environmental change at high altitudes, inhibiting a broader understanding of regional climate change. We investigated a Holocene lacustrine sediment archive from Lake Garba Guracha, Bale Mountains, Ethiopia, (3,950 m asl), and reconstructed high-altitude lake evaporation history using δ18O records derived from the analysis of compound-specific sugar biomarkers and diatoms. The δ18Odiatom and δ18Ofuc records are clearly correlated and reveal similar ranges (7.9‰ and 7.1‰, respectively). The lowest δ18O values occurred between 10–7 cal ka BP and were followed by a continuous shift towards more positive δ18O values. Due to the aquatic origin of the sugar biomarker and similar trends of δ18Odiatom, we suggest that our lacustrine δ18Ofuc record reflects δ18Olake water. Therefore, without completely excluding the influence of the ‘amount-effect’ and the ‘source-effect’, we interpret our record to reflect primarily the precipitation-to-evaporation ratio (P/E). We conclude that precipitation increased at the beginning of the Holocene, leading to an overflowing lake between ca. 10 and ca. 8 cal ka BP, indicated by low δ18Olake water values, which are interpreted as reduced evaporative enrichment. This is followed by a continuous trend towards drier conditions, indicating at least a seasonally closed lake system.

A new species of Gammarus Fabricius, 1775 (Crustacea: Amphipoda: Gammaridae) from extreme high-altitude Lake Tong Tso, Qinghai-Tibetan Plateau

A new species of the genus Gammarus Fabricius, 1775 is described from Lake Tong Tso, an extreme high-altitude lake in the Qinghai-Tibetan Plateau. Gammarus pontual sp. nov. is considered part of the Gammarus lacustris G.O. Sars, 1863 group, which is characterized by having the inner ramus of uropod 3 longer than half the length of the outer ramus, and by having both rami covered with plumose setae. The new species stands apart from their congeners, mainly, by the following combination of characters: head with cephalic lateral lobe truncated; gnathopods 1-2 propodus weakly armed, with 1 stout seta defining palm; palm longer than posterior margin of propodus, with 1 main stout seta medially; pereopods 5-7 basis slender, posterior margin crenulate; epimeral plate 1 posterior margin produced into a short spine, facial ridge present; epimeral plates 2-3 posteroventral corner sharply pointed; uropod 3 rami covered with plumose setae, inner ramus about 80% the length of the outer ramus; telson apex with 2 stout setae on each side.

Spatiotemporal change of water level in ungauged high-altitude tropical lakes: a DInSAR approach

<p>Spatiotemporal characteristics of physical responses of lakes to external and environmental changes are still largely unknown due to the consistent lack of monitoring of water level and corresponding changes in water storage in lakes. Understanding these changes is a fundamental step in advancing regional management of natural and anthropogenic systems that depend on the water resources of lakes. As an illustrative example, we here report a case study involving lakes of the headwater topical Andes mountain range, which, despite guaranteeing water security to millions of downstream inhabitants, still remain significantly ungauged. We present a novel evaluation of the potential of Differential Interferometric Synthetic Aperture Radar DInSAR techniques for the spatiotemporal analysis of patterns of water level change in lakes such as the ones comprising these ungauged high-altitude lake systems. Time series of Sentinel-1B data for the years 2017 and 2018 were used to generate continuous interferograms representing water level changes in twenty-four lakes of the Cajas National Park, Ecuador. The relation of these water level changes with climatic and topographical factors were analyzed to validate the methodology, and determine any patterns of change and response to climatic drivers. We found relatively high Pearson correlation coefficients between regional precipitation and water level change as estimated from the interferograms. Furthermore, we found an important negative relationship between water level change, as obtained from the DInSAR phase, and lake surface area. The study revealed a spatial trend of this correlation in terms of the altitude of the lakes at the basin scale; that is, lower correlation values were found in the headers of the basins, whilst higher correlation values were found at lower basin altitudes. The results of the present study demonstrate the potential of DInSAR techniques based on Sentinel-1 data for the monitoring of hydrologic changes in open water surfaces, and the possible validation of the DInSAR results with precipitation when gauged water level data is missing. These results are a basis to propose monitoring strategies in ungauged high-altitude lake systems in regions with similar data gauging constraints. Future work will encompass the integration of ongoing water level gauging for further validation of the herein depicted lake water level estimation approach.</p>

Past and recent biodiversity profiling in ancient Lake Chalco Mexico by a metagenomics analysis

<p>For decades, paleoecological studies in lake sediments have focused on reconstructing the environments of the past and explaining phenomena linked to climatic variations. Recent advances in high-throughput DNA sequencing have allowed access to environmental DNA (eDNA) and ancient sedimentary DNA (sedaDNA) as a new and efficient proxy for past and present biodiversity. The basin of Mexico (BM) is located in the central part of the Trans-Mexican Volcanic Belt at 2,200 m a.s.l.; with the southern portion harboring the Chalco sub-basin. Lake Chalco is one of the last remaining natural aquatic ecosystems within the ever-expanding urban area surrounding Mexico City. The paleoenvironmental history of this lake has been previously characterized using sedimentological and geochemical proxies, as well as preserved microfossils (diatoms, pollen) with a temporal framework based on multiple radiocarbon dates. However, information for the remaining taxonomic groups and metabolic pathways remained unexplored. Here, we present the first metagenomics-based study for the Holocene in a high-altitude lake in Central Mexico –Lake Chalco. We explored the relationship between the lake’s paleoenvironmental condition and estimations of taxonomic and metabolic profiles across the sedimentary sequence (2.5 meters long). Multiple biological and abiotic variables revealed three main environmental phases: 1) a cool freshwater lake (FW1: 11,500-11,000 cal years BP), 2) a warm hyposaline lake (HS2: 11,000-6,000 cal years BP), and 3) a temperate, subsaline lake (SS3, <6,000 cal years BP). We describe the structure of the microbiota community and taxonomy richness turnover in the three Holocene paleoenvironmental phases. During the past 12 000 years BP the most abundant domains in Lake Chalco sediments were Bacteria, followed by Archaea, and Eukarya (36,722 genera). The analysis of functional proteins showed high biodiversity with a total of 27,636,243 proteins identified, but it was only possible to annotate 3,227,398 of them. Also, we identified several genes associated with some relevant pathways, such as methanogenesis. Altogether, this study allowed us to reconstruct the natural history of lake Chalco and its surroundings.</p>

Sedimentary dynamics and heavy metal deposition in central Pyrenean high altitude lakes during the last 2000 years

<p>High altitude mountain lakes archive high-resolution records of environmental variability (climatic and anthropic). The REPLIM project funded by the INTERREG program (POCTEFA 2014-2020) has implemented a network to understand current and past changes in Pyrenean lakes. In this work, we compare six high altitude lake records along a W- E transect in the South Central Pyrenees: Acherito (1877 m.a.s.l.), La Sierra (2022 m.a.s.l.), Sabocos (1900 m.a.s.l.), Marboré (2600 m.a.s.l), Urdiceto (2364 m.a.s.l.) and Cregueña (2633 m.a.s.l.).</p><p>In each lake we have analyzed short sediment cores across transects applying sedimentological (facies, grain size, sediment composition, thin sections), geochemical (XRF scanner, elemental and trace metals) physical (Magnetic Susceptibility), isotopic (δ<sup>13</sup>C and δ <sup>15</sup>N of bulk organic matter) and biological (diatoms) techniques. The age models have been constructed with <sup>137</sup>Cs, <sup>210</sup>Pb and <sup>14</sup>C dates.</p><p>The sedimentary dynamics and heavy metals depositional history for the last 2000 years provides a temporal context for recent changes. Sedimentary facies variability correlates with climate phases and reflect varied human pressures. In general, during the colder and more humid periods, usually associated with glacier advances (LIA and Late Antiquity LIA), higher surface runoff was generated and, therefore, sediment delivery to the lake increased, in some cases with deposition of coarser facies. Intense watershed disturbances due to human impact were noticeable in lower altitude lakes since early medieval times. All lakes show larger sediment rate variability during the last centuries, but the timing of the onset varies. Lakes located at higher altitudes (Marboré and Cregüeña) show larger changes in sedimentation rates and dynamics around the end of the LIA (ca. 1850 CE), while in lower altitude lakes (Sierra, Sabocos, Acherito) occurred later (ca. 1950 CE).  In most lakes, a significant increase in organic matter accumulation started at the end of the 19th century and the trend accelerated since mid 20th century. Diatom and isotopes analyses suggest an increase in lake primary productivity during the last decades. The results indicate that the combined impacts of climate change and increased human pressure in the Pyrenees at the end of the LIA had a greater impact on high-altitude lakes, but recent changes in the 20th century have affected the lakes at all altitudes</p><p>All lakes show a similar heavy metal deposition pattern, with enrichment during Roman and Medieval times and a progressive increase since the end of the 18<sup>th</sup> century (industrialization) and reaching its peak in the middle and late 20<sup>th</sup> century. Some metals, such as Pb, show a subsequent decline at the end of the 20<sup>th</sup> century related to the reduction of industrial emissions and the ban on leaded gasoline.</p><p>This integrated approach demonstrates the sensitivity of high altitude lake systems to record past changes and highlights the need for multi-archive studies to support regional reconstructions of past environmental and climate changes.</p>