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Herein, we report the discovery of a first-in-class chemotype 2-(alkylsulfonamido)thiazol-4-yl)acetamides that act as pan-selective inhibitors of cytidine 5'-triphosphate synthetase (CTPS1/2), critical enzymes in the

The residence time of carbon in terrestrial ecosystems, such as soils and freshwater, sets the pace of the terrestrial carbon cycle. Understanding export pathways and turnover times of soil organic carbon (OCSoil) is crucial to assess responses to climate and land use changes. Our study aims to quantify the average turnover time of OCSoil in the catchment of perialpine Lake Constance. Lake sedimentary sequences integrate organic carbon from their catchment and aquatic primary productivity. They act as both burial sites of organic carbon (OC) and time series archives of catchment processes. Thus, they can bridge the gap between plot scale observations, e.g., on soil carbon turnover, and observations made at the outlet of major river systems.Sedimentary organic carbon sources include aquatic primary productivity, OCSoil, and rock-derived (petrogenic) OC. Stable carbon isotopes (δ13C) can be used to identify the relative contribution of these pools. The 5700-year half-life of radiocarbon (14C) coupled with the atmospheric nuclear bomb spike in the early 1960s can be used to infer the age and turnover rate of the OC pools on millennial to annual timescales. Bulk OC isotope analysis of a varved sediment core spanning the past ca. 110 years at quasi-annual resolution was used to constrain the age of soil carbon delivered to Lake Constance. We combined the geochemical data with a Markov-Chain-Monte-Carlo-based approach to identify the most probable age structure of aquatic and soil-derived OC components and to quantify their respective contributions in addition to petrogenic OC.Radiocarbon analysis of sedimentary bulk OC reveals a well-defined but muted bomb spike in the early 1960s. However, bulk Δ14COC values remain below 0‰, implying a predominance of aged OC. Based on the δ13C-based three-component linear mixing model, we found these values to be the result of an OC mixture containing approx. 40% pre-aged soil carbon and up to 20% fossil petrogenic carbon. Accounting for these inputs, we estimated that soil-derived OC delivered to Lake Constance is centennial in age, implying interim storage prior or subsequent to erosion from the landscape.

The Radiocarbon Inventories of Switzerland (RICH) project aims to construct the first national-scale census of (radio)carbon across aquatic, terrestrial, and atmospheric reservoirs. Within the carbon cycle, inland waters play a crucial role with lakes integrating carbon from various sources within their catchments in addition to that fixed by local primary productivity. Here we will present radiocarbon measurements of water-column dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), and particulate organic carbon (POC) from 15 lakes across Switzerland covering a range of sizes, elevations, and trophic states. In addition, a year of monthly water column measurements from Switzerland’s two largest lakes - Lake Constance and Lake Geneva - reveal seasonal trends resulting from changes in productivity and river inflow. Preliminary results show that the average radiocarbon signature of DIC in both Lake Constance and Lake Geneva is depleted in 14C relative to atmospheric CO2, indicating a ca. 15-20% contribution from bedrock weathering (14C-dead carbon). The timeseries at Lake Constance builds on earlier measurements which have shown a decline in DI14C since the late 1960s due to decreasing concentrations of bomb radiocarbon in the atmosphere. DO14C values in Lake Constance are more enriched compared to DI14C, indicating the importance of terrestrial DOC sources. In contrast, DO14C values in Lake Geneva are similar to DI14C, consistent with lake primary productivity as the main source of DOC. Overall, variations in radiocarbon values between different lakes are much greater than seasonal variations observed in either Lake Constance or Lake Geneva. These results form the basis of a radiocarbon inventory of Swiss lakes and provide new insights into carbon cycling in these dynamic aquatic systems.

Currently, Holocene paleoclimate research shows discrepancies in the timing and extent of the so-called Holocene “climate optimum” (1). To better understand this phenomenon in the alpine region, we examine the mean annual air temperature (MAT) record based on the distribution of Glycerol Dialkyl Glycerol Tetraethers (GDGTs) in a 14-m long sediment core from Lake Rot, Switzerland. This small eutrophic monomictic lake is characterized by a seasonally anoxic hypolimnion. An age model based on 20 calibrated 14C dates shows that the top 10 m of sediments reflect the early, middle, and late Holocene (10 cal. ka BP to recent). To constrain environmental changes, we also look at total organic carbon (TOC), total inorganic carbon (TIC), total nitrogen (TN), and bulk organic matter δ13C and δ15N (n = 300). These indices give insight into the sources of organic matter in Lake Rot sediments. A stable and dominantly in-situ produced lacustrine source of organic matter is indicated by the range in C/N values (4-17) and d15N values (-0.37-5.84). Increasing TOC and δ13C values during the early Holocene (around 10 cal. ka BP), likely reflect elevated primary production in the lake during postglacial climate warming. Subsequently, high TIC values indicate a period with high calcite precipitation (10-8 cal. ka BP). Between 8-1.5 cal. ka BP, high TOC and very low TIC values indicate a dramatic change in the system, reflecting a higher production and/or conservation of organic matter. After this period, TOC decreases, showing a last increase in the top 50cm of the core, presenting signs of eutrophication. Lake Rot thus has experienced large changes in the last 10ka.From a subset of 63 samples, GDGTs are analysed to reconstruct MAT using the methylation index of brGDGTs (MBT’5ME). Using a lake calibration (2), reconstructed average MAT is 8.4℃ (RMSE = 2.1℃). The absence of large temperature changes during the Holocene highlights that the MBT’5ME-based reconstructed temperatures are not influenced by the large changes in water chemistry recorded by the bulk TOC and TIC values. Instead, the temperature reconstruction reflects stable Holocene temperature ranges, presenting no expressed “climate optimum” in this core. The most recent reconstructed temperature of 9.7℃ resembles actual measured MAT (10.7℃).Based on our results, the isoprenoid GDGT TEX86 is not applicable for the reconstruction of temperature in Lake Rot. This matches a recent study of perialpine lakes where the successful application of TEX86 was suggested to be limited to deep lakes (>100 m) (3). In addition, we will discuss whether production of in-situ brGDGTs in the water column and seasonality influence the sediment temperature record, as proposed by the authors and other studies (2,4). 1: Herzschuh et al., (2022). EGUsphere, 1-23.2: Russell et al., (2018). Organic Geochemistry, 117, 56-69.3: Damsté et al., (2022). Quaternary Science Reviews, 277, 107352.4: Loomis et al., (2014). Geochimica et Cosmochimica Acta, 144, 173-187.

Abrupt changes in the Atlantic meridional overturning circulation (AMOC) are thought to affect tropical hydroclimate through adjustment of the latitudinal position of the intertropical convergence zone (ITCZ). Heinrich Stadial 1 (HS1) involves the largest AMOC reduction in recent geological time; however, over the tropical Indian Ocean (IO), proxy records suggest zonal anomalies featuring intense, widespread drought in tropical East Africa versus generally wet but heterogeneous conditions in the Maritime Continent. Here, we synthesize proxy data and an isotope-enabled transient deglacial simulation and show that the southward ITCZ shift over the eastern IO during HS1 strengthens IO Walker circulation, triggering an east-west precipitation dipole across the basin. This dipole reverses the zonal precipitation anomalies caused by the exposed Sunda and Sahul shelves due to glacial lower sea level. Our study illustrates how zonal modes of atmosphere-ocean circulation can amplify or reverse global climate anomalies, highlighting their importance for future climate change., Science Advances, 9 (1), ISSN:2375-2548

Horn Richterswil, located along the shores of Lake Zurich, is contaminated by toxic metals. The area serves as a recreational public space today, but harboured several industries in the 19th and 20th centuries. This study of the lake’s sediments explains the risks and origins of the metal contaminants.

Intertidal sands are global hotspots of terrestrial and marine carbon cycling with strong hydrodynamic forcing by waves and tides and high macrofaunal activity. Yet, the relative importance of hydrodynamics and macrofauna in controlling these ecosystems remains unclear. Here we compare geochemical gradients and bacterial, archaeal, and eukaryotic gene sequences in intertidal sands dominated by subsurface deposit-feeding worms (Abarenicola pacifica) to adjacent worm-free areas. We show that hydrodynamic forcing controls organismal assemblages in surface sediments, while in deeper layers selective feeding by worms on fine, algae-rich particles strongly decreases the abundance and richness of all three domains. In these deeper layers, bacterial and eukaryotic network connectivity decreases, while percentages of clades involved in degradation of refractory organic matter, oxidative nitrogen and sulfur cycling increase. Our findings reveal macrofaunal activity as the key driver of biological community structure and functioning, that in turn influences carbon cycling in intertidal sands below the mainly physically controlled surface layer., PNAS Nexus, 1 (4), ISSN:2752-6542

Past temperature records are key tools for inferring climate dynamics and provide empirical data for testing climate models to improve our mechanistic understanding of natural climate variability. Unfortunately, very few quantitative records of pre-historic continental temperatures exist in Europe. Moreover, existing paleothermometers mainly provide mean annual or warm season temperatures, limiting our understanding of climate variability during the transitional seasons and winter. Alkenones are temperature-sensitive lipids produced by Isochrysidales algae, which have been used for decades to reconstruct quantitative changes in sea-surface temperatures. In lakes, they are not ubiquitous, but they have been increasingly reported in both saline and freshwater lakes worldwide, suggesting that there is great potential for alkenone-based paleotemperature reconstructions in lacustrine settings. Lacustrine alkenones have already been successfuly used to reconstruct paleotemperatures in high-latitude lakes. Depending on the timing of ice-out, they record winter/spring or summer temperatures. In our study, we found that a significant number of Swiss lakes contain lacustrine alkenones. Other studies in mid-latitude European lakes suggest that the peak of alkenone production occurs in spring. The monitoring of Lake St Moritz, an alpine lake in the South East of Switzerland, will allow determining the seasonality of alkenone production in mid-latitute high altitude lakes. Combining genetic analyses and the monitoring of physico-chemical parameters will provide more information about the ecology of the alkenone producers. Our first results suggest that we will be able to improve the understanding of alkenone production in freshwater lakes and to develop the first spring lake temperature reconstruction in Switzerland that extends beyond existing historical records.

Historical industrial activities at the Horn Richterwil, on the shore of Lake Zurich (Switzerland), caused widespread metal contamination on land and in the adjacent lake sediments. This study provides an estimation of the age and source of the contamination by using XRF core scanning, ICP-OES, and Hg-AFS for quantitative measurements of trace metals and MC-ICP-MS for the stable isotope analysis of mercury. Radiometric dating (137Cs, 210Pb, and Pu dating) of two proximal cores and varve chronology in a distal core suggest two different contaminations, one stemming from around 1960 (Zn, Cd) and an earlier one from 1880 (Cr, Cu, Hg, Pb, Sn). The XRF data suggest two different contamination pathways: one by landfill of contaminated soil and another one by industrial wastewater effluents. Maximum concentrations found within all samples are in the range of per mil (dry weight) for Cr, Cu, Hg, Pb, Sn, and Zn and lie within the top 10 cm of the sediment cores. The analysis of the mercury isotopic composition (δ202Hg and Δ199Hg) shows a significantly different signature for one of the cores, indicating a second mercury source. We could not identify the exact source or process leading to the isotopic fractionation of mercury, but the isotopic data confirm two different sources., Environmental Science and Pollution Research, 29 (57), ISSN:0944-1344, ISSN:1614-7499

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.

High-resolution proxy-based paleoenvironmental records derived from peatlands provide important insights into climate changes over centennial to millennial timescales. In this study, we present a composite climatic index (CCI) for the Hani peatland from northeastern China, based on an innovative combination of pollen-spore, phytolith, and grain size data. We use the CCI to reconstruct variations of the East Asian summer monsoon (EASM) intensity during the Holocene. This is accomplished with complete ensemble empirical mode decomposition (CEEMD), REDFIT, and cross-wavelet coherency analysis to reveal the periodicities (frequencies) of the multi-proxy derived CCI sequences and to assess potential external forcing of the EASM. The results showed that periodicities of ca. 300–350, 475, 600, 1075, and 1875 years were present in the Hani CCI sequence. Those periodicities are consistent with previously published periodicities in East Asia, indicating they are a product of external climate controls over an extensive region, rather than random variations caused by peatland-specific factors. Cross-wavelet coherency analysis between the decomposed CCI components and past solar activity reconstructions suggests that variations of solar irradiation are most likely responsible for the cyclic characteristics at 500-year frequency. We propose a conceptual model to interpret how the sun regulates the monsoon climate via coupling with oceanic and atmospheric circulations. It seems that slight solar irradiation changes can be amplified by coupling with ENSO events, which result in a significant impact on the regional climate in the East Asian monsoon area.

Land cover transformations have accompanied the rise and fall of civilizations for thousands of years, exerting strong influence on the surrounding environment. Soil erosion and the associated outwash of nutrients are a main cause of eutrophication of aquatic ecosystems. Despite the great challenges of water protection in the face of climate change, large uncertainties remain concerning the timescales for recovery of aquatic ecosystems impacted by hypoxia. This study seeks to address this issue by investigating the sedimentary record of Lake Murten (Switzerland), which witnessed several phases of intensive human land-use over the past 2000 years. Application of geophysical and geochemical methods to a 10 m-long sediment core revealed that soil erosion increased drastically with the rise of the Roman City of Aventicum (30 CE). During this period, the radiocarbon age of the bulk sedimentary organic carbon (OC) increasingly deviated from the modeled deposition age, indicating rapid flushing of old soil OC from the surrounding catchment driven by intensive land-use. Enhanced nutrient delivery resulted in an episode of cultural eutrophication, as shown by the deposition of varved sediments. Human activity drastically decreased towards the end of the Roman period (3rd century CE), resulting in land abandonment and renaturation. Recovery of the lake ecosystem from bottom-water hypoxia after the peak in human activity took around 50 years, while approximately 300 years passed until sediment accumulation reached steady state conditions on the surrounding landscape. These findings suggest that the legacy of anthropogenic perturbation to watersheds may persist for centuries.

Hydrogen isotope ratios of sedimentary leaf waxes (δ2HWax values) are increasingly used to reconstruct past hydroclimate. Here, we add δ2HWax values from 19 lakes and four swamps on 15 tropical Pacific islands to an updated global compilation of published data from surface sediments and soils. Globally, there is a strong positive linear correlation between δ2H values of mean annual precipitation (δ2HP values) and the leaf waxes n‐C29‐alkane (R2 = 0.74, n = 665) and n‐C28‐acid (R2 = 0.74, n = 242). Tropical Pacific δ2HWax values fall within the predicted range of values based on the global calibration, and the largest residuals from the global regression line are no greater than those observed elsewhere, despite large uncertainties in δ2HP values at some Pacific sites. However, tropical Pacific δ2HWax values in isolation are not correlated with estimated δ2HP values from isoscapes or from isotope‐enabled general circulation models. Palynological analyses from these same Pacific sediment samples suggest no systematic relationship between any particular type of pollen distribution and deviations from the global calibration line. Rather, the poor correlations observed in the tropical Pacific are likely a function of the small range of δ2HP values relative to the typical residuals around the global calibration line. Our results suggest that δ2HWax values are currently most suitable for use in detecting large changes in precipitation in the tropical Pacific and elsewhere, but that ample room for improving this threshold exits in both improved understanding of δ2H variability in plants, as well as in precipitation., Plain Language Summary: Past precipitation patterns are difficult to reconstruct, limiting our ability to understand Earth’s climate system. Geochemists reconstruct past precipitation by measuring the amount of heavy hydrogen naturally incorporated into the waxy coating of leaves, which is preserved in mud that accumulates in lakes, soils, and oceans. Heavy hydrogen in leaf waxes is strongly correlated with local precipitation, allowing us to learn about rainfall intensity, temperature, and cloud movement. However, no existing calibration studies include sites from the tropical Pacific, home to the most intense rainfall on the planet and populations that rely on rain for drinking water and farming. We measured heavy hydrogen in leaf waxes from tropical Pacific islands and show that although values are within the global calibration error, no precipitation relationship exists within the region. Plant type distributions do not explain the lack of correlation, which is best attributed to poorly constrained estimates of heavy hydrogen in local rain and the relatively small range of variability within the region. At present, heavy hydrogen from ancient leaf waxes can show large changes in past precipitation, but improved process‐level understanding is needed to use this tool to understand smaller changes in the tropical Pacific and elsewhere., Key Points: Leaf wax 2H/1H ratios are correlated with mean annual precipitation 2H/1H ratios globally, but not in the tropical Pacific. Deviations from the global relationship between precipitation leaf wax 2H/1H ratios cannot be predicted from palynological assemblages. Small range and large uncertainties in estimates of tropical Pacific precipitation 2H/1H ratios likely account for poor correlations., Swiss National Science Foundation, National Science Foundation (NSF) http://dx.doi.org/10.13039/100000001, Natural Environment Research Council (NERC) http://dx.doi.org/10.13039/501100000270, Department of Education and Training, Australian Research Council (ARC) http://dx.doi.org/10.13039/501100000923, http://10.0.15.89/ethz-b-000412154

Espiritu Santo is one of the 82 islands of the archipelago of Vanuatu and is the largest, highest, and most biodiverse of the insular country. Climatic changes linked to El Niño and extreme events such as cyclones and volcanic eruptions are a daily challenge in this remote area. These events can be recorded in sedimentary archives. Here we present a multi-proxy investigation of sediment cores retrieved from two small lakes located on the West coast of Espiritu Santo. Although the records span the last millennium, high-resolution radiocarbon dating of macrofossils reveals a rapid accumulation of sediment in the past 100 years. The high accumulation rate coupled with the high-resolution dating of freshwater sediments allows us to compare the 14C bomb curve with the biogeochemical proxies of the sedimentary records. The results can then be validated against written and oral historical records linked with the societal perception of recent environmental changes in this vulnerable ecosystem.

The Late Holocene marks a substantial cultural and economic transition in the eastern Eurasian Steppe and Altai Region with the dispersal of nomadic pastoralism. So far, paleoclimate conditions during this time remain unclear and controversial. Here, we present a high‐resolution 4.2 ka paleoclimate record from Lake Khar Nuur in the Mongolian Altai that is based on lake sediment proxies and biomarker compound‐specific δ2H analyses. Our results document increased aridity before ∼3.7 cal. ka BP, followed by two pronounced phases of warm and wet conditions from ∼3.5–2.8 to ∼2.3–1.5 cal. ka BP, and a strong increase in aridity since ∼1.5 cal. ka BP. Phases of warmer and wetter conditions coincide with a negative North Atlantic Oscillation, which has been responsible for advecting moisture into the region by more southerly‐displaced Westerlies and possibly favored the expansion of mobile nomadic pastoralism in the region., Plain Language Summary: Nomadic pastoralism is the dominant subsistence practice in the eastern Eurasian Steppe and Altai Region since the Late Bronze Age. Whether this had climatic reasons is one of the most intriguing question, because former climatic conditions are poorly understood in this important but understudied region. To address this issue, we established a hydrological record for the last ∼4.2 ka from a high‐altitude lake in the Mongolian Altai. Our findings provide evidence of exceptionally warm and wet conditions from ∼3.5–2.8 and ∼2.3–1.5 cal. ka BP. Those favorable climate conditions likely favored productive grasslands and the widespread dispersal of nomadic pastoralism in the eastern Eurasian Steppe and Altai Region., Key Points: A high‐resolution 4.2 ka paleoclimate record from Lake Khar Nuur in the Mongolian Altai, based on biomarker compound‐specific δ2H analyses. Our hydrological proxies record distinct changes in warm/wet and cold/dry conditions during the Late Holocene in the Altai Region: Pronounced warm/wet conditions from ∼3.5 to 2.8 cal. ka BP probably favored the widespread dispersal of nomadic pastoralism in the region., Ernst Abbe Stiftung, https://doi.org/10.1594/PANGAEA.936512

Ecological responses to past climate change as determined from palaeorecords offer insights into responses that may accompany future climate change. In arid and semi‐arid lands, the interactions between regional vegetation and climate change are not yet well understood, partly due to a lack of suitable palaeovegetation proxies that can provide accurate and continuous tracers for past vegetation dynamics. To gain a better understanding of long‐term vegetation dynamics, this study employs a multiproxy approach applied to sand‐palaeosol sediments of northeastern China's Songnen grasslands. Phytolith analyses and data on the stable carbon isotope composition (δ¹³C) of organic matter are used to reconstruct palaeovegetation composition, namely, the changing abundance of C₃ and C₄ species, whereas a geochemical weathering index (Fed/Fet ratios) tracks past East Asian summer monsoon (EASM) intensity. The phytolith assemblages and indices and δ¹³C of the soil indicate that C₄ species' abundance has been increasing in the Songnen grasslands since the mid‐Holocene, although C₃ vegetation is still dominant. Statistically significant negative correlations between the δ¹³C data and Fet/Fed ratios suggest that continuous weakening of the EASM since the mid‐Holocene may be responsible for the ¹³C‐enrichment of the sediments in the Songnen grasslands. Field vegetation surveys, modern topsoil phytoliths and δ¹³C calibration data indicate that the expansion of C₄ species since the mid‐Holocene is mainly due to their ability to cope with aridity when growing season temperature is not undergoing a significant decrease. Future precipitation decreases in arid and semi‐arid lands should make C₄ species more competitive in the grasslands of northeastern China. Highlights A continuous grassland landscape history is reconstructed from a sand‐palaeosol sequence via phytolith analysis. Multiple independent approaches were used to reconstruct past EASM intensity and palaeovegetation patterns. Phytolith and δ¹³C analyses indicate an increase in C₄ species since the mid‐Holocene. Aridification drives the increase in C₄ species within the grassland ecosystem.

High-resolution lake and reservoir bathymetric surveys can pinpoint locations that may experience underwater landslides (subaquatic sedimentary mass movements). These can pose a risk to underwater and shoreline infrastructure. This paper outlines an approach for using spatial variation in sedimentary patterns to identify areas susceptible to subaquatic mass movements in lakes and reservoirs. This study focusses on Lake Biel (Switzerland), which has experienced a protracted history of upstream alteration of river flow. Altered flow patterns increase risk of unstable sedimentary features and subaquatic mass movements. Data from sediment traps and cores, Acoustic Doppler Current Profilers and results from a 3D hydrodynamic model gave a consistent picture of spatial and temporal variation in weather-related sedimentation. Erosion caused by short-term rain events contributes the largest proportion of sediments to the lake. Strong rain events combine with typical wind patterns to drive lake circulation. The net effect results in preferential sedimentation onto a steeply sloping shelf prone to subaquatic slides. The integrated approach outlined here incorporates short- and long-term sediment dynamics to provide a systematic assessment of lake sedimentation and potential mass movement hazards. This research represents a first step in developing a risk-evaluation tool for aquatic hazard evaluation., Water Resources Management, 34 (13), ISSN:0920-4741, ISSN:1573-1650

Previous studies have shown that microbially produced methane can be a dominant carbon source of lacustrine sedimentary macrofauna in eutrophic lakes, most likely through grazing on methane-oxidizing bacteria. Here we investigate the contributions of different carbon sources to macrofaunal biomass across five lakes in central Switzerland that range from oligotrophic to highly eutrophic. Macrofaunal communities change with trophic state, with chironomid larvae dominating oligotrophic and tubificid oligochaetes dominating eutrophic lake sediments. The 13C-isotopic data suggest that the average contribution of methane-derived carbon to the biomass of both macrofaunal groups is similar but consistently remains minor, ranging from only ∼1 % in the oligotrophic lake to at most 12 % in the eutrophic lakes. The remaining biomass can be explained by the assimilation of detritus-derived organic carbon. Low abundances of methane-cycling microorganisms in macrofaunal specimens, burrows, and surrounding sediment based on 16S ribosomal RNA (rRNA) gene sequences and copy numbers of genes involved in anaerobic and aerobic methane cycling (mcrA, pmoA) support the interpretation of isotopic data. Notably, 16S rRNA gene sequences of macrofauna, including macrofaunal guts, are highly divergent from those in tubes or sediments. Many macrofaunal specimens are dominated by a single 16S rRNA phylotype of Fusobacteria, α-, β-, γ-, or ε-Proteobacteria, Bacteroidetes, or Parcubacteria. This raises the question of whether dominant lake macrofauna live in so far uncharacterized relationships with detrital organic-matter-degrading bacterial endosymbionts.

Objective The aim of this study was to evaluate the analytical performance of the Alinity®c Abbott compared to the Architect® immunoassay system for the determination of drugs having a narrow therapeutic index. Methods Valproic acid, amikacin, gentamicin, phenobarbital and vancomycin were analyzed using Particle-Enhanced Turbidimetric Inhibitor Immunoassay (Petinia), phenytoin and theophylline were analyzed using an immunoenzymatic method and a colorimetric method was performed to quantify lithium. The methods were validated according to the total error approach. Seven validation standards were analyzed in quintuplet during four days to establish the limits of the methods. Dilution integrity and interferences (hemolysis and high concentrations of bilirubin and lipids) were also tested. Depending on the analyte, the results obtained for twenty to forty patients on the Alinity® were compared to those obtained on the Architect®. Results The bias and the coefficients of variation for repeatability and for intermediate precision were lower than 15% for all drugs. Accuracy profiles were acceptable (acceptance limits fixed at 30%) in the validated ranges. The lower limits of quantification (LLOQ) were similar to those determined by Abbott except for gentamicin for which we determined a LLOQ at 1.22 mg/L while Abbott determined it at 0.5 mg/L. All assays diluted linear and analyte concentrations were not affected by interferences. Concentrations obtained for real samples on the Alinity®c are comparable to those obtained on the Architect®ci. Conclusions The analytical validation of a method suitable for therapeutic drug monitoring of drugs on the Alinity®c meets the requirements of European Medicines Agency.

Autochthonous calcite precipitation is an important process for C-fixation in hard-water lakes, which is mainly induced by the photosynthesis of planktonic microorganisms. Among these, the widespread calcifying green alga Phacotus lenticularis (Ehrenberg) Diesing contributes to biogenic calcite precipitation in temperate regions. Its role in carbonate precipitation needs to be investigated, because there are no studies dedicated to the quantitative contribution of Phacotus shells to long term carbonate sequestration in hard-water lake sediments. In order to fill this gap, the Phacotus shell content in the sediments of four German hard-water lakes was determined and compared to the fraction of Phacotus shells in the total suspended autochthonous calcite of the euphotic zone.It was found that the Phacotus shells contributed at least 10% to the autochthonous carbonate precipitation in the upper water column in three investigated lakes. During a Phacotus mass occurrence with a cell density of 1.8 × 106 Ind L-1 in Lake Hopfensee, even 59% of the 3.6 mg L-1 total carbonate concentration consisted of Phacotus shells. In contrast to this high amount, the topmost basinal sediment contained a Phacotus shell content between 80 and 36,252 individuals per mg dry sediment, representing only 0.02% to 2.28% of the total carbonate sediment content. In a gravity core from Lake Grosser Ostersee, dating back ~150 years, the Phacotus shell content was continuously below 0.24% whereas the shell diameters remained equal to those of living individuals found in the water column proving that Phacotus shells are capable to persist in the sediment after deposition.A main reason for the large discrepancy between Phacotus shell abundance in the euphotic zone and in sediment was found to be the gross authigenic carbonate precipitation, which dilutes the sedimenting Phacotus shells that accumulate exclusively during short and intensive population peaks in summer. Additionally, dissolution of the carbonate shells during sedimentation was proven to be a relevant factor in Lake Igelsbachsee by means of reducing the number of Phacotus shells reaching the lake bottom. These facts explain that short-term high Phacotus carbonate contents of the total suspended carbonate in the water column do not mirror the contribution of Phacotus shells in the sedimentary record.

During the “Paleoanthropocene”, humans have become one of the major factors affecting Earth surface processes, with intensified soil erosion being one of the most notable human-induced process. Especially semi-arid regions are vulnerable to human-induced soil erosion and landscape changes, which is particularly true for the Mongolian Altai, where extensive pastoralism and the rise of nomadic empires strongly influenced landscape changes. So far, only little is known about the impact of humans in the Mongolian Altai and whether landscape changes are naturally or human-driven. Therefore, our study investigates a 5 ka sediment core from Lake Khar Nuur, which is located at ~2500 m a.s.l. in the Mongolian Altai. More specifically, we carried out a biogeochemical multi-proxy approach to disentangle between natural and anthropogenic signals in the Khar Nuur sediments, which includes extensive 14C-dating, XRF analyses, CNS analyses and their stable isotopes, and fecal sterols.For the 5 ka sediments from Khar Nuur, XRF, Corg and bulk δ13C results show alternating phases of in-situ produced aquatic sediments/organic material versus increased terrestrial input from the catchment. Since no hardwater effect is observed for Khar Nuur sediments, phases of dominated in-situ aquatic production (i.e. high Ca/Ti ratios, higher Corg and positive bulk δ13C values) gave 14C-ages close to the timing of sediment deposition/biomass formation. In contrast, during phases of increased terrestrial input (i.e. low Ca/Ti ratios, low Corg and negative bulk δ13C values), 14C-ages become successively older and show larger age offsets compared to their timing of deposition in the lake. Thus, clear evidence is given that old organic carbon became mobilized from the catchment soils by increased soil erosion during three terrestrial phases from ~4.3 to 3.7 cal. ka BP, ~3.2 to 2.8 cal. ka BP and ~2.0 to 0.7 cal. ka BP. Abundances of fecal sterols start to increase at ~2 cal. ka BP, and human and herbivore feces strongly increase until ~1 cal. ka BP. This increase in fecal sterols falls directly into the last erosive phase between ~2.0 to 0.7 cal. ka BP and indicate that soil erosion during that time was mainly human-induced by increased pastoralism. Moreover, beginning human presence at ~2 cal. ka BP corresponds to the Xiongnu (the Huns), whereas the strongly increased anthropogenic activity in the region at ~1 cal. ka BP falls into a period where Turks, Uighurs and Mongols are present in western Mongolia and the Altai. Thus, soil erosion and landscape changes in the Mongolian Altai are strongly driven by the rise of pastoralism and nomadic empires during the late Holocene.

Salto Grande is a large South American reservoir on the border between Uruguay and Argentina that was impounded in 1979 and experiences recurrent, massive cyanobacteria blooms. A water-monitoring program was initiated 20 years after the dam was built, hence the causes and onset of cyanobacteria blooms remain poorly known. We collected two sediment cores from the old river channel in the reservoir (z = 17 m) and used physical, chemical and biological variables in the sediments, along with existing limnological data, to explore the history of cyanobacteria in the sub-tropical water body. Cyanobacteria fossil pigments were present at low concentrations during the first 24 years after impoundment, but more than doubled thereafter. Phytoplankton abundance tracked shifts in cyanobacteria pigment concentration, indicating an overall increase in all primary producers. Several sediment variables indicate a decline in water quality after 2003, such as increases in the number of photosynthetic sulfur bacteria and a reduction in sediment magnetic susceptibility. Akinetes (dormant cyanobacteria cells, Order Nostocales) in recent reservoir deposits were abundant and five species germinated under laboratory conditions, underscoring the ability of akinetes to initiate cyanobacteria blooms. The germinated assemblage reflected closely the composition of cyanobacteria blooms in the reservoir. Recorded increases in air temperature and decreases in wind speed, together with other variables (e.g. nutrients), can promote the large, recurrent cyanobacteria blooms. Invasion of the bivalve Limnoperna fortunei apparently promoted cyanobacteria blooms by preferential feeding on other phytoplankton taxa, and perhaps by altering nutrient concentrations and ratios. This work highlights the potential for using multiple variables in sediment cores from large reservoirs to better understand the responses of biota to multiple environmental stressors. Fil: Gangi, Daniela. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina Fil: Plastani, María Sofía. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina Fil: Laprida, Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina Fil: Lami, Andrea. Centre National de la Recherche Scientifique; Francia Fil: Dubois, Nathalie. No especifíca; Fil: Bordet, Facundo. No especifíca; Fil: Gogorza, Claudia Susana. Universidad Nacional del Centro de la Provincia de Buenos Aires. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires. - Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires; Argentina Fil: Frau, Diego. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; Argentina Fil: de Tezanos Pinto, Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Botánica Darwinion. Academia Nacional de Ciencias Exactas, Físicas y Naturales. Instituto de Botánica Darwinion; Argentina

Lake sediments are globally important carbon sinks. Although the fate of organic carbon in lake sediments depends significantly on microorganisms, only few studies have investigated controls on lake sedimentary microbial communities. Here we investigate the impact of anthropogenic eutrophication, which affects redox chemistry and organic matter (OM) sources in sediments, on microbial communities across five lakes in central Switzerland. Lipid biomarkers and distributions of microbial respiration reactions indicate strong increases in aquatic OM contributions and microbial activity with increasing trophic state. Across all lakes, 16S rRNA genes analyses indicate similar depth-dependent zonations at the phylum- and class-level that follow vertical distributions of OM sources and respiration reactions. Yet, there are notable differences, such as higher abundances of nitrifying Bacteria and Archaea in an oligotrophic lake. Furthermore, analyses at the order-level and below suggest that changes in OM sources due to eutrophication cause permanent changes in bacterial community structure. By contrast, archaeal communities are differentiated according to trophic state in recently deposited layers, but converge in older sediments deposited under different trophic regimes. Our study indicates an important role for trophic state in driving lacustrine sediment microbial communities and reveals fundamental differences in the temporal responses of sediment Bacteria and Archaea to eutrophication.

River engineering projects are developing rapidly across the globe, drastically modifying water courses and sediment transfer. Investigation of the impact of engineering works focuses usually on short-term impacts, thus a longer-term perspective is still missing on the effects that such projects have. The 'Jura Water Corrections' - the largest river engineering project ever undertaken in Switzerland - radically modified the hydrological system of Lake Biel in the 19th and 20th Century. The deviation of the Aare River into Lake Biel more than 140 years ago, in 1878, thus represents an ideal case study to investigate the long-term sedimentological impacts of such large-scale river rerouting. Sediment cores, along with new high-resolution bathymetric and seismic reflection datasets were acquired in Lake Biel to document the consequences of the Jura Water Corrections on the sedimentation history of Lake Biel. Numerous subaquatic mass transport structures were detected on all of the slopes of the lake. Notably, a relatively large mass transport complex (0 center dot 86 km(2)) was observed on the eastern shore, along the path of the Aare River intrusion. The large amount of sediment delivered by the Aare River since its deviation into the lake likely caused sediment overloading resulting in subaquatic mass transport. Alternatively, the dumping since 1963 in a subaquatic landfill of material excavated during the second phase of river engineering, when the channels flowing into and out of Lake Biel were widened and deepened, might have triggered the largest mass transport, dated to 1964 or 1965. Additional potential triggers include two nearby small earthquakes in 1964 and 1965 (M-W 3 center dot 9 and 3 center dot 2, respectively). The data for this study indicate that relatively large mass transports have become recurrent in Lake Biel following the deviation of the Aare River, thus modifying hazard frequency for the neighbouring communities and infrastructure.

Compound specific hydrogen isotope ratios (2H/1H) of lipid biomarkers preserved in sediments are used as paleohydrologic proxies. However, several variables, including contributions from different source organisms and their growth rates, can influence 2H/1H fractionation between lipids and source water. Significant uncertainties remain about how these factors combine to produce the net 2H/1H signal exported to sediments. To assess the influence of phosphorus availability on 2H/1H ratios of lipids accumulating in lake sediments, we analyzed surface sediments and sediment traps from ten central Swiss lakes representing a wide range of trophic states. In agreement with results from laboratory cultures, 2H/1H fractionation for the diatom biomarker brassicasterol (24-methyl cholest-5,22-dien-3β-ol) increased in more productive lakes (0.6 ± 0.1‰ per μg/L total P in sediment traps and surface sediments). In contrast, 2H/1H fractionation for phytol, the isoprenoid side-chain moiety of chlorophyll, decreased with increasing total P (−0.4 ± 0.1‰ per μg/L total P in sediment traps), suggesting that different biochemical mechanisms are responsible for changes in 2H/1H fractionation for each type of isoprenoidal lipid. Opposing changes in 2H-fractionation for sterols and phytol cause their 2H/1H ratios to converge as total P increases. This response may be a new tracer for phytoplankton growth conditions and is not influenced by the source water isotope value. Interpreting the 2H/1H ratios of short to long chain (C14–C30) n-alkanoic acids and n-alkanols is complicated by likely contributions from heterotrophs and/or vascular plants. These values generally did not correlate with lake water isotopes, nor did their fractionation factors correlate with total P. For most lipids there was no significant difference between sediment trap and surface sediment 2H/1H ratios. However, n-C14–n-C18 fatty acids were 2H-enriched in the surface sediments, most likely due to degradation in the water column. Our results indicate that interpretations of short-chain fatty acid 2H/1H ratios as a water isotope signal likely require supporting information about ecological conditions and community structure, but that paired H isotope measurements of phytoplankton-derived sterols and phytol may be developed as a proxy for phytoplankton growth.

We describe herewith the case of a patient presenting to the emergency department for worsening ear–nose–throat symptoms. As chemsex was evocated by the family, patient’s serum was submitted to a new psychoactive substances screening. After a simple liquid–liquid extraction, serum was injected on a high-resolution mass spectrometer using quite usual conditions (C18 column, gradient mode with acidic buffer, methanol and acetonitrile). An almost perfect match with 2-aminoindane (2-AI) was observed considering that the precursor ion was present in the sample but absent in the commercial library. Literature concerning 2-AI is sparse, and further investigations were undertaken. After injection of the reference standard, a small retention time shift has been observed (0.3 min) between the standard and the sample. The case was only closed while spiking the sample with the standard, giving rise to two distinct peaks. As a result, 2-AI was then considered as absent from the sample and death was attributed only to infection. Moreover, a rapid liquid chromatography–tandem mass spectrometry method dedicated to 2-AI was developed. It generated the same false-positive result highlighted by significant differences observed in ion ratios (2.37 for the sample versus 6.62 for the neat standard).

Purpose Nowadays, (−)-cannabidiol (CBD) is gaining popularity for the treatment of various problems and can be found easily in many stores in Belgium. However, such product must comply with the law: if the total tetrahydrocannabinol (THC) content [(−)-Δ9-tetrahydrocannabinol + (−)-Δ9-tetrahydrocannabinolic acid A (THC-A)] is higher than 0.2%, it is considered as narcotic by the Belgian legislation. In this context, we have developed a method to quantify major cannabinoids (THC, THC-A, CBD, cannabidiolic acid, cannabigerolic acid, cannabigerol and cannabinol) in plant material. Methods After drying, a liquid-liquid extraction was performed on plant materials, followed by dilutions. Extracts were analyzed by ultra-high-performance liquid chromatography combined with a photodiode array detector. Mobile phases consisted of methanol and 0.1% formic acid in water applied in a 16-minute gradient mode. After validating the method, it was applied to 213 samples seized by the police in CBD shops. Results The method fulfilled the criteria in terms of specificity, calibration curve, precision, trueness and dosing range. Total THC content ranged from 0.14 to 1.17% (median 0.38%) with 110 samples exceeding the Belgian legal threshold of 0.2%. The amounts measured in the samples varied greatly, some were 6 times below the amount labelled on the packaging, others showed a concentration 4 times higher than stated on the package. Same strain also showed concentration differences from shop to shop. Conclusion Our method was successfully validated and applied to samples seized in CBD shops. Half of the products exceeded the Belgian legal threshold. THC and CBD concentrations discrepancies showed that products sold in CBD shops are not pharmaceutical grade.

International audience; Freshwater ecosystems are under new and increasing threats from anthropogenic change. Ability to detect and predict consequences of environmental perturbations on ecosystem function and water quality is limited by the lack of empirical data over relevant time scales. Paleoecological records present a unique opportunity to broaden understanding of ecological transitions over decadal to millennial timescales. This study tested the occurrence of regime shifts to track changes throughout the lake food web beyond the typical instrumental era, using both "traditional" paleoecological proxies (e.g., cladoceran zooplankton, zoobenthos, and pigments) and more recently developed molecular genetic methods based on sedimentary DNA. We used sediment cores from the perialpine Lake Joux (Swiss Jura), where the history of human settlement and land-use practices in the catchment has been well documented since the Medieval period. Paleoecological evidence revealed an abrupt and unprecedented biological reorganization in the second half of the 20th century, following several centuries of relatively stable communities despite growing human pressure. Time-varying autoregression computed using dynamic linear modelling identified this transition, triggered by the onset of rapid cultural eutrophication in the 1950s, as a true regime shift. Since this time, despite decades of re-oligotrophication, biotic communities of Lake Joux have not returned to pre-disturbance composition, most likely due to other confounding factors, including climate warming, that may prevent the lake from returning to an earlier equilibrium state. Paleoecological reconstruction further suggested that cladocerans responded earlier to disturbance, which is highly relevant for lake monitoring and management strategies.

The Joux Valley (Swiss Jura Mountains) has a rather unusual history of human occupation, characterized by tardive but extensive settlement since the Late Middle Ages, followed by an intensive period of industrial development. To estimate the links between human activities and environmental consequences, sediment cores were retrieved in Lake Joux and submitted to a multiproxy analysis (high-resolution photographs, magnetic susceptibility, density, x-ray fluorescence, grain size, organic geochemistry, 14C, 210Pb and 137Cs dating). The diversity of anthropication phases, defined from historical data, is clearly recognized in the lake archive. The record suggests the region was mainly under climatic influence until the end of the 13th century. The growth of settlements in the valley and the associated massive deforestation is recorded by increasing terrestrial inputs, reflecting large-scale soil destabilization, which subsequently persists despite the transition from farming to industrial activities. Autochthonous contributions then dominate the record, both in response to climatic and anthropogenic influences. Construction works conducted at the outlet of the lake affected water flow, sedimentation and aquatic community (macrophytes, ostracods) dynamics. The substantial increase of anthropogenic heavy metals (Fe, Zn, Pb) recorded during the 20th century could reflect the development of the watch-making industry in the area, as well as the use of leaded gasoline. Historical information facilitated interpretation of the observed paleolimnological evolution in the context of varied coexisting human activities. This study highlights the importance of applying an integrated paleolimnological-historical approach in order to establish clear links between well-defined human activities and their subsequent environmental responses through time.

Sampling site, technique, and time influence postmortem drug concentrations. In 57 cases, we studied drug concentration differences as follows: subclavian vein-dissection/clamping versus blind stick, femoral vein-dissection/clamping versus blind stick, right cardiac chamber, and popliteal vein-dissection and clamping only. Cases were distributed in group #1 (all cases with both techniques), group #2 (dissection/clamping), and group #3 (blind stick). Sampled drugs were diazepam, methadone, morphine, and their metabolites. To assess PMR, mean concentrations and ratios were calculated for each group. Time-dependent variations of blood concentrations and ratios were also assessed. Results indicate that site, method, and time may influence postmortem distribution interpretation in different ways. Popliteal blood seems less subject to PMR. In conclusion, our study is the first to evaluate concurrently three main aspects of PMR and confirms that the popliteal vein may represent a site that is more resistant to the changes seen as a result of PMR.

Even though human-induced eutrophication has severely impacted temperate lake ecosystems over the last centuries, the effects on total organic carbon (TOC) burial and mineralization are not well understood. We study these effects based on sedimentary records from the last 180 years in five Swiss lakes that differ in trophic state. We compare changes in TOC content and modeled TOC accumulation rates through time to historical data on algae blooms, water column anoxia, wastewater treatment, artificial lake ventilation, and water column phosphorus (P) concentrations. We furthermore investigate the effects of eutrophication on rates of microbial TOC mineralization and vertical distributions of microbial respiration reactions in sediments. Our results indicate that the history of eutrophication is well recorded in the sedimentary record. Overall, eutrophic lakes have higher TOC burial and accumulation rates, and subsurface peaks in TOC coincide with past periods of elevated P concentrations in lake water. Sediments of eutrophic lakes, moreover, have higher rates of total respiration and higher contributions of methanogenesis to total respiration. However, we found strong overlaps in the distributions of respiration reactions involving different electron acceptors in all lakes regardless of lake trophic state. Moreover, even though water column P concentrations have been reduced by ∼ 50 %–90 % since the period of peak eutrophication in the 1970s, TOC burial and accumulation rates have only decreased significantly, by ∼ 20 % and 25 %, in two of the five lakes. Hereby there is no clear relationship between the magnitude of the P concentration decrease and the change in TOC burial and accumulation rate. Instead, data from one eutrophic lake suggest that artificial ventilation, which has been used to prevent water column anoxia in this lake for 35 years, may help sustain high rates of TOC burial and accumulation in sediments despite water column P concentrations being strongly reduced. Our study provides novel insights into the influence of human activities in lakes and lake watersheds on lake sediments as carbon sinks and habitats for diverse microbial respiration processes., Biogeosciences, 16 (19), ISSN:1726-4170

Leaf wax n-alkanes are increasingly used for quantitative reconstructions of past environmental changes. However, this is complicated in sediment archives with associated hydrological catchments since the stored n-alkanes can have different ages and origins. Direct 14C-dating of the n-alkanes has a great potential to derive independent age information for these proxies, allowing their correct paleoenvironmental interpretation. This holds also true for fluvial sediment-paleosols sequences (FSPS), where the n-alkane signal is divided into (i) a catchment signal that is deposited with fluvial sediments, and (ii) an in-situ signal from local biomass that increasingly dominates (paleo)soils with time. Therefore, age and origin of n-alkanes in FSPS are complex: In fluvial sediment layers they can be pre-aged and reworked when originating from eroded catchment soils, or originate from organic-rich sediment rocks in the catchment. In (paleo)soils, besides an inherited contribution from the catchment they were formed in-situ during pedogenesis and originate from local biomass. Depending on the different relative contributions from these sources, the n-alkane signal from an FSPS can show variable age offsets between its formation and final deposition. During this study, we applied compound-class 14C-dating to n-alkanes from a fluvial sediment-paleosol sequence (FSPS) along the upper Alazani River in eastern Georgia with Jurassic black clay shales in its upper catchment. Our results show that pre-heating the n-alkanes with 120 °C for 8 h before 14C-dating effectively removed the shorter chains (

Lacustrine sediment sequences were obtained from Lagunas Verde and Gemelas Este, two small lakes located east of the southern Patagonian Ice Field and close to the village of El Chalten, in Argentinian Patagonia. Four tephra layers were identified in each of the short sediment sequences and characterised using individual glass-shard tephra chemistry to determine provenance. Bulk sediment geochemistry and diatom assemblages were analysed to understand the impact of the tephra deposits on the lake ecosystems. Age-depth models for the cores were established by 137Cs and 210Pb dating. Tephra deposits in Laguna Gemelas Este were dated to AD 1986–1998, 1943–1968, 1927–1955, and 1849–1892, and the tephra deposits in Laguna Verde were dated to AD 1940–1970, 1888–1934, 1871–1920, and 1536–1669, the latter interval determined by extrapolation. All tephras had similar geochemical composition and originated from volcanoes in the northern Austral Volcanic Zone. Tephra units were attributed to known historical eruptions and all but one, most likely, were from Lautaro Volcano (49°01′S; 73°33′W). The age of the youngest tephra (AD 1986–1998) from Laguna Gemelas Este points to Viedma Volcano (49°22′S; 73°19′W) as a possible source. Volcanic eruptions had a larger impact on Laguna Verde than on Laguna Gemelas Este, as expressed by changes in δ15N values and diatom communities during tephra deposition. These shifts are explained by perturbations of the nitrogen cycle in the lake, associated with shifts in lacustrine primary production. Primary producers may have been affected by increased water turbidity caused by the ash fall, and consequently, used less nitrogen. Diatom assemblages in Laguna Verde showed marked reductions in numbers of planktonic/tychoplanktonic taxa, in favour of epiphytic/benthic diatom taxa, when tephra was deposited. This contrasts with Laguna Gemelas Este, in which epiphytic/benthic diatom species were generally more abundant and decreases in abundances of planktonic/tychoplanktonic taxa were not as strongly linked to tephra layers as in Laguna Verde. At Laguna Gemelas Este, flatter relief, greater fetch and/or drier climate may have contributed to generally less ecosystem variability, resulting in seemingly less environmental response to volcanic eruptions than in Laguna Verde.