Andean Lakes Research Articles

Evaluation of the water quality of a high Andean lake using different quantitative approaches

This study assessed a high Andean lake's trophic state and water quality using methodologies with eutrophication and water quality indexes. Water samples were collected at six points in the lake, with a monthly frequency, for three winter and three summer months. Dissolved oxygen, pH, phosphates, nitrates, transparency, chlorophyll-a, fecal coliforms, biological oxygen demand (BOD), temperature, and turbidity were determined at each point. The trophic state of the lake was categorized by applying the Organization for Economic Cooperation and Development (OECD) eutrophication index, Carlson's trophic state index (CTSI) and trophic index (TRIX). In addition, National Sanitation Foundation water quality index (NSF-WQI), Canadian Water Quality Index (CCME-WQI) and Oregon Water Quality Index (OWQI) were used to evaluate water quality. Results indicated that the lake had a high level of eutrophication, suggesting an excessive accumulation of nutrients in the water. CTSI and TRIX index showed that the lake was in a hyper-eutrophic state, while according to the OECD methodology, the trophic state related to phosphorus and transparency was hypereutrophic, and according to chlorophyll, it varied from mesotrophic to eutrophic. The NSF index classified the lake with average quality, the CCME index indicated fair water quality, and the OWQI classified it as very poor. Therefore, the water quality of the high andean lake assessed by eutrophication and water quality indexes presented significant differences based on physicochemical characteristics. The human influence was identified as the main cause of eutrophication, including tourism and agriculture. These results suggest that measures should be taken to reduce human activity in the area and control pollution in the lake.

Responses to arsenic stress by the Andean benthic-extremophile cyanobacteria Rivularia halophila

Microorganisms living in naturally arsenic (As)-enriched environments exposed to extreme conditions play an active role in As mobility by influencing chemical speciation or inducing dissolution of As-bearing phases. In this work, the cyanobacterium Rivularia halophila was evaluated in its capability to tolerate, accumulate and biotransform As species. R. halophila was isolated from a hypersaline and high-altitude Andean Lake characterized by high geogenic As content in the sediments and water. Cultures of R. halophila were exposed to concentrations of As(V) and As(III) up to 15,000 and 200 ppm, respectively. Results showed that R. halophila effectively tolerated high As doses (IC50: 8500 and 70 ppm for As(V) and As(III) respectively), responding with a gradual decrease in growth and chlorophyll content. Cell damage and reactive oxygen species (ROS) only significantly increased at 5000 ppm of As(V) and 20 ppm of As(III), demonstrating an extreme adaptation to both As species. Moreover, As accumulation was significantly higher in As(III) treatment (i.e., 9.500 ppm) than in As(V) (i.e., 480 ppm). The main representative As-bearing phases in the biomass fractions were determined using micro-focused X-ray photoelectron spectroscopy. Three main As-bearing phases were identified: arsenate, arsenite and As(III)-S (mostly associated with sulfur). The redox evolution of As-bearing phases in the biomass fractions, coupled with increase of bulk As content and ROS activity, suggest that active bioaccumulation and transformation of As by R halophila occurs during environmental stress conditions.

Compositional Changes in Sediment Microbiota Are Associated with Seasonal Variation of the Water Column in High-Altitude Hyperarid Andean Lake Systems.

The lacustrine systems of La Brava and La Punta, located in the Tilopozo sector in the extreme south of Salar de Atacama, are pristine high-altitude Andean lakes found along the central Andes of South America. This shallow ecosystem suffers from permanent evaporation, leading to falling water levels, causing it to recede or disappear during the dry season. This dynamic causes physicochemical changes in lakes, such as low nutrient availability, pH change, and dissolved metals, which can influence the composition of the microbial community. In this study, we used a metataxonomic approach (16S rRNA hypervariable regions V3 to V4) to characterize the sedimentary microbiota of these lakes. To understand how the water column affects and is structured in the microbiota of these lakes, we combined the analysis of the persistence of the water column through satellite images and physicochemical characterization. Our results show a significant difference in abiotic factors and microbiota composition between La Punta and La Brava lakes. In addition, microbiota analysis revealed compositional changes in the ecological disaggregation (main and isolated bodies) and antagonistic changes in the abundance of certain taxa between lakes. These findings are an invaluable resource for understanding the microbiological diversity of high Andean lakes using a multidisciplinary approach that evaluates the microbiota behavior in response to abiotic factors. IMPORTANCE In this study, we analyzed the persistence of the water column through satellite images and physicochemical characterization to investigate the composition and diversity in High Andean Lake Systems in a hyperarid environment. In addition to the persistence of the water column, this approach can be used to analyze changes in the morphology of saline accumulations and persistence of snow or ice; for example, for establishing variable plant cover over time and evaluating the microbiota associated with soils with seasonal changes in plants. This makes it an ideal approach to search for novel extremophilic microorganisms with unique properties. In our case, it was used to study microorganisms capable of resisting desiccation and water restriction for a considerable period and adapting to survive in ecological niches, such as those with high UV irradiation, extreme drought, and high salt concentration.

Anthropogenic activities in the páramo trigger ecological shifts in Tropical Andean lakes

AbstractA robust understanding of the impact of anthropogenic activities on high-altitude tropical aquatic ecosystems is key for the conservation and protection of the Tropical Andean biodiversity hot spot. We present the results of a multiproxy study of lake sediments from the high Andean páramo of El Cajas National Park, a UNESCO biosphere reserve in Ecuador. The main site, Laguna Pallcacocha, is well known for recording El Niño–driven clastic flood layers that are triggered by high-intensity rainfall anomalies from the eastern Pacific. The second site, Laguna El Ocho, does not contain clastic laminations, providing a control. The records show abrupt shifts in diatom assemblages ca. AD 1991 in both high-elevation Andean lakes accompanied by local changes in páramo composition that suggest a sudden nutrient enrichment of the environment. The diatom assemblages from Laguna Pallcacocha, in relation to the clastic input events, are remarkably stable and do not show evident El Niño signals at the analysed resolution. Based on comparison with the nonlaminated El Ocho record, we deduce the main source of this nutrient enrichment to be the construction of a heavily transited road that runs through the park, while climate warming played secondary role by amplifying its effects.

Detecting hydrologic distinctions among Andean lakes using clumped and triple oxygen isotopes

Oxygen isotope distributions from lacustrine carbonates provide insights into climate and hydrological change, but it is difficult to isolate the influences of catchment precipitation δ18O, water temperature, and evaporation on lacustrine carbonate δ18O values. Recent work shows the potential for using a combination of clumped (Δ47) and triple oxygen isotope (Δ′17O) measurements to identify the roles of temperature and evaporation on carbonate δ18O values in lakes, allowing precipitation δ18O values to be inferred and facilitating paleoclimate reconstructions. However, modern calibration of this approach has been mostly limited to arid regions with a high ratio of evaporative losses over inputs (XE) and low relative humidity (h<0.7). Developing this tool for paleoclimate and paleoelevation reconstructions requires expanding the modern calibrations to a greater range of climatic and hydrologic conditions. We sampled four lakes in different hydrologic states under a single, high humidity climate regime (h=0.7–0.9) in the Lake Junín region of central Peru. Clumped isotope temperatures from lake carbonates reflect water temperatures during carbonate formation. Lake hydrology is the main control on the Δ′17O values of carbonates and waters: Δ′17O values are lowest in the larger lakes with higher XE when compared to smaller, headwater lakes where evaporation is minimal and Δ′17O is indistinguishable from that of precipitation. Reconstructed unevaporated catchment precipitation δ′18O (δ′18Orucp) values from lake waters rely on accurate characterization of λlake, the triple oxygen isotope evaporation slope. We explore the influence of humidity on λlake using both new observations and modeled data. Accounting for local humidity improves λlake estimates, which allows for more accurate reconstructions of δ′18Orucp. We generate a δ′18Orucp value of −15.2±2.1‰ from modern carbonates and waters (n=15) in the Lake Junín region, which is similar to amount weighted mean annual precipitation −14.1 (±2.2‰). This study illustrates that (1) Δ′17O can be used to differentiate between lakes with differing XE in humid climates, (2) lake carbonate Δ′17O and δ18O values can be used to evaluate the influence of evaporation on lake water δ18O values in a range of climates, and (3) modeling λlake under appropriate humidity conditions improves δ′18Orucp estimates from lake carbonate Δ′17O.

Spatiotemporal distribution of physicochemical parameters and toxic elements in Lake Pomacochas , Amazonas, Peru

Lakes are water bodies that play an essential role as water sources for humanity, as they provide a wide range of ecosystem services. Therefore, this study aimed to evaluate Lake Pomacochas, a high Andean lake in the north of Peru. A variety of parameters were studied, including physicochemical parameters such as temperature (T°C), dissolved oxygen (DO), potential hydrogen (pH), electrical conductivity (EC), turbidity, total dissolved solids (TDS), biochemical oxygen demand (BOD), alkalinity, and chlorides hardness; the concentrations of nitrates, nitrites, sulfates, and ammonium; elements such as aluminum (Al), calcium (Ca), magnesium (Mg), sodium (Na), potassium (K), and boron (B); as well as metals and metalloids such as zinc (Zn), cadmium (Cd), copper (Cu), lead (Pb), and arsenic (As). In addition, pH, Zn, and Cu were evaluated at the sediment level. It is important to note that all parameters evaluated in the water matrix showed significant differences in the seasonal period and depth levels. In comparison, the parameters evaluated at the sediment level had no significant differences between the seasonal period and sampling points. As for the seasonal period, the variables that were higher for the dry season were electrical conductivity, total dissolved solids, and lead while that for the wet season were biochemical oxygen demand, zinc, magnesium, turbidity, calcium, dissolved oxygen, temperature, and potential hydrogen. At the depth levels, parameters such as total dissolved solids, lead, and arsenic had similar behavior for the three depths evaluated. According to national standards, latent contamination by cadmium and lead was found in the lake water from the ecological risk assessment. However, by international standards, all sampling stations showed a high level of contamination by cadmium, lead, zinc, copper, and arsenic, which represents a potential risk for the development of socioeconomic activities in the lake. At the same time, the evaluation of sediments did not present any potential risk.

Neoliberal Lakeside Residentialism: Real Estate Development and the Sustainable Utopia in Environmentally Fragile Areas

This article exposes the central role played by neoliberal real estate development in the transformation of two lakeside cities in southern Chile. The concept of neoliberal lakeside residentialism addresses the ways in which commercialisation of the natural world in tourism hotspots is comprehensively reshaping the environmentally fragile Andean lake district. Specifically, we hypothesise that this green utopia is rapidly becoming a dystopia as a result of the aggregate effects of real estate development on environmental sustainability. In order to analyse these tensions, we conduct a case study in the districts of Villarrica and Pucón, both located within the Lake Villarrica watershed. There is evidence of territorial metamorphosis of the Araucanía Region as areas popular with tourists are increasingly being closed off by large-scale real estate operations. We find that this “anomalous” rate of urbanisation is indeed affecting sustainability in the territory, both environmental and social, concluding that regulation of these processes is needed in order to preserve both the natural and cultural wealth of the study area.

Using Stable Water Isotope Composition (δ18O and δ2H) to Track the Interannual Responses of Arctic and Tropical Andean Water Bodies to Rising Air Temperatures

AbstractLakes in the Arctic and tropical Andes are experiencing some of the largest temperature increases on the planet with coeval marked limnological changes, but little data exist on water balance parameters from these regions. Here, we present a unique data set of water stable isotope composition (δ18O and δ2H) from a suite of 49 water bodies in the Canadian Arctic (Resolute Bay, Cornwallis Island, and Cape Herschel, Ellesmere Island) and the tropical Andes (Cajas National Park, Ecuador) spanning various years from 2009 to 2016. We show that an increase in air temperature over the study period resulted in evaporative enrichment of water isotopes in most Arctic sites highlighting the significance of evaporative losses to small Arctic ponds during the prolonged ice‐free summers now experienced in this part of the world. Exceptions include some Arctic waterbodies that received abundant snowmelt and large, ice‐covered lakes less prone to evaporation. Data from the Andean lakes indicated evaporative effects were minimal due to abundant precipitation. These data, in combination with limnological records and paleolimnological research from each region, provide a holistic view on how freshwater ecosystems are responding to recent warming in climatically sensitive Arctic and Andean environments.

Proteomic Signatures of Microbial Adaptation to the Highest Ultraviolet-Irradiation on Earth: Lessons From a Soil Actinobacterium.

In the Central Andean region in South America, high-altitude ecosystems (3500–6000 masl) are distributed across Argentina, Chile, Bolivia, and Peru, in which poly-extremophilic microbes thrive under extreme environmental conditions. In particular, in the Puna region, total solar irradiation and UV incidence are the highest on Earth, thus, restraining the physiology of individual microorganisms and the composition of microbial communities. UV-resistance of microbial strains thriving in High-Altitude Andean Lakes was demonstrated and their mechanisms were partially characterized by genomic analysis, biochemical and physiological assays. Then, the existence of a network of physiological and molecular mechanisms triggered by ultraviolet light exposure was hypothesized and called “UV-resistome”. It includes some or all of the following subsystems: (i) UV sensing and effective response regulators, (ii) UV-avoidance and shielding strategies, (iii) damage tolerance and oxidative stress response, (iv) energy management and metabolic resetting, and (v) DNA damage repair. Genes involved in the described UV-resistome were recently described in the genome of Nesterenkonia sp. Act20, an actinobacterium which showed survival to high UV-B doses as well as efficient photorepairing capability. The aim of this work was to use a proteomic approach together with photoproduct measurements to help dissecting the molecular events involved in the adaptive response of a model High-Altitude Andean Lakes (HAAL) extremophilic actinobacterium, Nesterenkonia sp. Act20, under artificial UV-B radiation. Our results demonstrate that UV-B exposure induced over-abundance of a well-defined set of proteins while recovery treatments restored the proteomic profiles present before the UV-challenge. The proteins involved in this complex molecular network were categorized within the UV-resistome subsystems: damage tolerance and oxidative stress response, energy management and metabolic resetting, and DNA damage repair.

Climatic and Ecological Changes in the Subtropical High Andes During the Last 4,500 Years

The effects of climate change may be more evident in mountainous areas. In these areas, an increase in temperature and a decrease in precipitation can reduce the amount of snow, which represents a source of water for human consumption and vegetation. To analyze the effects of climate change on vegetation, it is possible to examine the climate–vegetation relationship in the past and observe the influence of variation in temperature and precipitation on the dynamics of plant communities. The aim of the present work was to describe the climate–vegetation dynamics of the last 4,500 years in the high subtropical Andes of Chile (30°S). The paleoclimatic reconstruction was carried out through the analysis of fossil pollen and macroscopic carbon obtained from sediment cores from two high Andean lakes. The dynamics of the vegetation was analyzed taking into account the alpha and beta diversity. The pollen and carbon records showed three contrasting periods during the last 4,500 years. From the beginning of the sequences until ∼1900 cal. yr BP, relatively dry climatic conditions are suggested, with a slight trend toward more humid conditions after 2,700 cal. yr BP. Pollen records from ∼1900 to ∼600 cal. yr BP suggest wetter conditions than today. Finally, relatively arid conditions have reappeared in the last ∼600 years. The diversity analysis showed that the climate mainly influences the composition of taxa in the communities (beta diversity) and not the richness (alpha diversity). In periods of dry/wet transition and vice versa, beta diversity changes. On the other hand, richness remains relatively constant throughout the record.

Human practices behind the aquatic and terrestrial ecological decoupling to climate change in the tropical Andes

Anthropogenic climate change and landscape alteration are two of the most important threats to the terrestrial and aquatic ecosystems of the tropical Americas, thus jeopardizing water and soil resources for millions of people in the Andean nations. Understanding how aquatic ecosystems will respond to anthropogenic stressors and accelerated warming requires shifting from short-term and static to long-term, dynamic characterizations of human-terrestrial-aquatic relationships. Here we use sediment records from Lake Llaviucu, a tropical mountain Andean lake long accessed by Indigenous and post-European societies, and hypothesize that under natural historical conditions (i.e., low human pressure) vegetation and aquatic ecosystems' responses to change are coupled through indirect climate influences—that is, past climate-driven vegetation changes dictated limnological trajectories. We used a multi-proxy paleoecological approach including drivers of terrestrial vegetation change (pollen), soil erosion (Titanium), human activity (agropastoralism indicators), and aquatic responses (diatoms) to estimate assemblage-wide rates of change and model their synchronous and asynchronous (lagged) relationships using Generalized Additive Models. Assemblage-wide rate of change results showed that between ca. 3000 and 400 calibrated years before present (cal years BP) terrestrial vegetation, agropastoralism and diatoms fluctuated along their mean regimes of rate of change without consistent periods of synchronous rapid change. In contrast, positive lagged relationships (i.e., asynchrony) between climate-driven terrestrial pollen changes and diatom responses (i.e., asynchrony) were in operation until ca. 750 cal years BP. Thereafter, positive lagged relationships between agropastoralism and diatom rates of changes dictated the lake trajectory, reflecting the primary control of human practices over the aquatic ecosystem prior European occupation. We interpret that shifts in Indigenous practices (e.g., valley terracing) curtailed nutrient inputs into the lake decoupling the links between climate-driven vegetation changes and the aquatic community. Our results demonstrate how rates of change of anthropogenic and climatic influences can guide dynamic ecological baselines for managing water ecosystem services in the Andes.

Composite microbialites: Thrombolite, dendrolite, and stromatolite associations in a modern environment, Pozo Bravo lake, Salar de Antofalla, Catamarca Puna, Argentina

ABSTRACT Pozo Bravo is a high-altitude Andean lake that harbors modern microbialites thriving in hypersaline conditions in the Salar de Antofalla, one of the driest sites on Earth and located in the Puna region of Catamarca, northwest Argentine. Due to the lake physiography, microbialites are restricted to a narrow belt following Pozo Bravo lake variations. Microbialites exhibit a wide range of external morphologies including domal, discoidal, tabular, and horseshoe-like bioherms which vary considerably in size, as well as large biostromal terraces. As documented by other studies on modern microbialites, external morphology appears to be mainly the product of the environmental setting. In Pozo Bravo lake, high evaporation rates and hypersalinity (driven by high temperature and strong winds), water-level fluctuations, and lake-bottom topography are major controlling factors. The distinctive feature of Pozo Bravo microbialites is their internal structure, showing a gradual transition from a thrombolitic core to dendrolitic structures and to a sharply overlying stromatolitic layer within a single microbialite. We suggest that these various microbialite textures represent a gradual change within an environmental gradient based on lake-level variations, and the influence of these environmental factors on biological activity, mainly by cyanobacteria and diatoms. The study of this site is particularly relevant given that it represents an active system where progressive changes in microbialite type (from thrombolites to dendrolites and stromatolites) are recorded, providing an excellent natural laboratory to study these textural changes from a mechanistic perspective, and it may provide insights for better understanding of the microbialite geological record. In addition, given that these systems are threatened by human activities (mining of lithium-rich brines), its study and preservation are necessary.

Low-decomposition rates of riparian litter in a North Patagonian ultraoligotrophic lake

Littoral zones of lakes are important for carbon and nutrient recycling because of the accumulation and decomposition of organic matter (OM) coming from terrestrial and aquatic plants. Here, we aimed to study OM decomposition from the most abundant riparian trees (Nothofagus dombeyi and Myrceugenia exsucca), and an emergent macrophyte (Schoenoplectus californicus), in the littoral zone of an ultraoligotrophic North-Patagonian Andean lake. We analysed the initial 2-days leaching, and litter mass loss and litter nutrient changes after one year of decomposition in a litter-bag experiment. The three studied species had very slow decay rates (k < 0.005 day−1), and initial nutrient release by leaching was not related to differences in decomposition rates. However, differences in leaf traits (lignin content) were related to interspecific variation in decomposition rates. The highest decomposition rates were observed for the macrophyte S. californicus, the species with the lower lignin content, while the opposite was observed in the Myrtaceae M. exsucca. In the three studied species, nitrogen content increased during decomposition. Our results indicated that in the shore of ultra-oligotrophic lakes, litter remains for long periods with net nutrient immobilization, thus OM of the riparian vegetation represents a carbon and nutrient sink.

Phenotypic plasticity of clonal populations of the freshwater jellyfish Craspedacusta sowerbii (Lankester, 1880) in Southern Hemisphere lakes (Chile) and the potential role of the zooplankton diet

AbstractThe freshwater jellyfish Craspedacusta sowerbii (Lankester, 1880) is a global invader of lakes. Empirical and experimental evidence indicate that the environmental factors that govern the global expansion of Craspedacusta and the development of jellyfish blooms are temperature, meso‐eutrophic character and food availability in lakes. In newly colonised lakes, the medusa stage of C. sowerbii feeds preferentially on medium‐sized (0.2–2.0 mm in diameter) microcrustaceans, for example Daphnids and copepods. Clonal populations of this invader have recently been recorded in several Andean lakes of northern Patagonia (40°S). Here, we report for the first‐time synchronous blooms of clonal populations of C. sowerbii in two nordpatagonian lakes with similar habitat and water quality but with different types of zooplankton as food supply for jellyfish. Jellyfish populations in these lakes showed notable differences in body size, as well as in the colour of the gonads. We speculate that the observed differences of the medusa populations reflect phenotypic plasticity and could be mediated by the quality of the diet, which was the main environmental factor that differed between the studied lakes. Both lakes are inhabited by microcrustaceans, but in one lake, the highly coloured symbiotic ciliate Stentor amethystinus was also present, amounting to almost 52% of total zooplankton biomass. This type of food source for jellyfish blooms of C. sowerbii is for the first time reported in the world. The invasion process of clonal jellyfish in north Patagonian lakes represents a unique opportunity to study the potential role of diet quality in inducing plasticity responses to environmental stress derived from climate change.

The role of different natural and human-related habitats for the conservation of birds in a high Andean Lake

The role of different natural and human-related habitats for the conservation of birds in a high Andean Lake

Unmanned aerial vehicle, and GIS tools, to monitor the reproduction of the flamingo Phoenicopterus chilensis (Aves: Phoenicopteridae)

Introduction: High Andean flamingos also known as parihuanas, are species of recurrent presence in the high Andean areas which find this area as an important resting, feeding and in some cases breeding area The species recorded here correspond to Phoenicoparrus jamesi, Phoenicoparrus andinus and Phoenicopterus chilensis, the latter being the most abundant and common. During the censuses performed during 2018 and 2019, in the high Andean lake of Salinas, Ramsar site, located within the Reserva Nacional Salinas y Aguada Blanca in Southern Peru, atypical behaviors of these birds were recorded in a sector of the lake, observing reproductive courtship and the settlement of colonies of P. chilensis. Objective: The study aimed to confirm and evaluate reproductive events of P. chilenesis (Chilean flamingo) through the use of an unmanned aerial vehicle (UAV) and image processing tools using geographic information systems. Methodology: Monitoring was conducted during 2018 and 2019 to breeding colonies of P. chilensis, we used a UAV Phantom 4 testing different flight altitudes to avoid disturbing the birds and performed records of aerial photographs and GIS post-processing with the creation of panchromatic images for the identification and counting of individuals and eggs automated, and manual verification. Results: During 2018 were identified nests and presence of six eggs, this occurred between March and June where the event was interrupted not observing chicks or juveniles during this period, for 2019 the breeding was more successful, where a higher number of eggs were counted (40-66) and with the formation of three reproductive colonies with 4 185 adult individuals, also verified the presence of chicks and juveniles that reached a maximum of 1 491 individuals. Conclusions: We confirmed two continuous reproductive events of P. chilensis in the Salinas lake, where during 2019 was the most successful incorporating several new individuals to the initial population, likewise the methodology applied in the image processing allowed differentiating between adult individuals and eggs but did not allow differentiating juveniles, however, the images directly acquired by the UAV allow distinguishing the types of individuals to perform a manual count.

Ecological resilience in tropical Andean lakes: A paleolimnological perspective

AbstractLittle is known about whether changes in lake ecosystem structure over the past 150 years are unprecedented when considering longer timescales. Similarly, research linking environmental stressors to lake ecological resilience has traditionally focused on a few sentinel sites, hindering the study of spatially synchronous changes across large areas. Here, we studied signatures of paleolimnological resilience by tracking change in diatom community composition over the last 2000 years in four Ecuadorian Andean lakes with contrasting ecoregions. We focused on climate and anthropogenic change, and the type of biological responses that these changes induced: gradual, elastic, or threshold. We combined multivariate ordination techniques with nonlinear time‐series methods (hierarchical generalized additive models) to characterize trajectories of community responses in each lake, and coherence in such trajectories across lakes. We hypothesized that remote, high‐elevation lakes would exhibit synchronous trends due to their shared climatic constraints, whereas lower elevation lakes would show less synchronous trends as a consequence of human density and land‐cover alteration. We found that gradual and elastic responses dominated. Threshold‐type responses, or regime shifts, were only detected in the less remote lake, after a long period of gradual and elastic changes. Unexpected synchrony was observed in diatom assemblages from geographically distant and human‐impacted lakes, whereas lakes under similar broad‐scale environmental factors (climate and ecoregion) showed asynchronous community trajectories over time. Our results reveal a complex ecological history and indicate that Andean lakes in Ecuador can gradually adapt and recover from a myriad of disturbances, exhibiting resilience over century to millennial timescales.

Patterns of alluvial deposition in Andean lake consistent with ENSO trigger

The laminated sediment record from Laguna Pallcacocha, Ecuador, is widely used as a sensitive recorder of past variability in the El Niño-Southern Oscillation. However, limited knowledge of local meteorology, hydrogeomorphic processes, and the lateral variability of the lacustrine stratigraphy have resulted in some ambiguity in proxy interpretation. In this study, we report new high-resolution meteorological data, hydrogeomorphic mapping of the catchment and geochemistry of the lake’s sediments. We show that the fine clastic layers are deposited from alluvial activity in the catchment related to intensive rainfall events originating from the Pacific. Frequency analyses of the geochemistry of the sediments indicates that the clastic layers in L. Pallcacocha fall into the characteristic ENSO frequency band and most likely record Eastern Pacific and Coastal Pacific El Niño events. We also illustrate that recent debris flow deposition has resulted in an abrupt avulsion of the main fluvial channels, redirecting sediment input between the lake’s two basins and possibly influencing the lithostratigraphy of the sediment package of L. Pallcacocha.

Carbon fixation and rhodopsin systems in microbial mats from hypersaline lakes Brava and Tebenquiche, Salar de Atacama, Chile.

In this work, molecular diversity of two hypersaline microbial mats was compared by Whole Genome Shotgun (WGS) sequencing of environmental DNA from the mats. Brava and Tebenquiche are lakes in the Salar de Atacama, Chile, where microbial communities are growing in extreme conditions, including high salinity, high solar irradiance, and high levels of toxic metals and metaloids. Evaporation creates hypersaline conditions in these lakes and mineral precipitation is a characteristic geomicrobiological feature of these benthic ecosystems. The mat from Brava was more rich and diverse, with a higher number of different taxa and with species more evenly distributed. At the phylum level, Proteobacteria, Cyanobacteria, Chloroflexi, Bacteroidetes and Firmicutes were the most abundant, including ~75% of total sequences. At the genus level, the most abundant sequences were affilitated to anoxygenic phototropic and cyanobacterial genera. In Tebenquiche mats, Proteobacteria and Bacteroidetes covered ~70% of the sequences, and 13% of the sequences were affiliated to Salinibacter genus, thus addressing the lower diversity. Regardless of the differences at the taxonomic level, functionally the two mats were similar. Thus, similar roles could be fulfilled by different organisms. Carbon fixation through the Wood-Ljungdahl pathway was well represented in these datasets, and also in other mats from Andean lakes. In spite of presenting less taxonomic diversity, Tebenquiche mats showed increased abundance and variety of rhodopsin genes. Comparison with other metagenomes allowed identifying xantorhodopsins as hallmark genes not only from Brava and Tebenquiche mats, but also for other mats developing at high altitudes in similar environmental conditions.

Phosphate-Arsenic Interactions in Halophilic Microorganisms of the Microbial Mat from Laguna Tebenquiche: from the Microenvironment to the Genomes.

Arsenic (As) is a metalloid present in the earth's crust and widely distributed in the environment. Due to its high concentrations in the Andean valleys and its chemical similarity with phosphorus (P), its biological role in Andean Microbial Ecosystems (AMEs) has begun to be studied. The AMEs are home to extremophilic microbial communities that form microbial mats, evaporites, and microbialites inhabiting Andean lakes, puquios, or salt flats. In this work, we characterize the biological role of As and the effect of phosphate in AMEs from the Laguna Tebenquiche (Atacama Desert, Chile). Using micro X-ray fluorescence, the distribution of As in microbial mat samples was mapped. Taxonomic and inferred functional profiles were obtained from enriched cultures of microbial mats incubated under As stress and different phosphate conditions. Additionally, representative microorganisms highly resistant to As and able to grow under low phosphate concentration were isolated and studied physiologically. Finally, the genomes of the isolated Salicola sp. and Halorubrum sp. were sequenced to analyze genes related to both phosphate metabolism and As resistance. The results revealed As as a key component of the microbial mat ecosystem: (i) As was distributed across all sections of the microbial mat and represented a significant weight percentage of the mat (0.17 %) in comparison with P (0.40%); (ii) Low phosphate concentration drastically changed the microbial community in microbial mat samples incubated under high salinity and high As concentrations; (iii) Archaea and Bacteria isolated from the microbial mat were highly resistant to arsenate (up to 500 mM), even under low phosphate concentration; (iv) The genomes of the two isolates were predicted to contain key genes in As metabolism (aioAB and arsC/acr3) and the genes predicted to encode the phosphate-specific transport operon (pstSCAB-phoU) are next to the arsC gene, suggesting a functional relationship between these two elements.