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Lake Tzibaná is one of the largest (1.27 km2) and deepest (Zmax = 52 m) karstic lakes in the UNESCO’s Biosphere Reserve “Nahá-Metzabok” and in the Lacandon Forest, southeastern Mexico. It archives sediments from multiple sources and the inflowing Nahá River forms deltaic deposits. In 2019, the water level in Lake Tzibaná declined by ~ 15 m, persisting for 4 months and exposing the Nahá River Delta. A geophysical profile on the exposed delta revealed an accumulation of ~ 20 m of such deposits. Three sediment outcrops from an inactive channel in the Nahá River Delta, which ranged in height from 0.6 to 1.43 m, were sampled and a multi-proxy analysis of biological remains and geochemical variables was conducted. Four facies were observed: (1) massive-coarse sand, (2) fine sand, (3) dark leaf litter and (4) massive silty clay, each characterized by specific microcrustacean, testate amoebae and diatom taxa. Six dark leaf litter horizons were radiocarbon dated and revealed a complex depositional history including inverted ages making the establishment of an age model difficult. Nevertheless, past lake-level changes and the formation of the four facies match three characteristic water-level stages, which can also be observed on recent satellite images: (1) Massive-coarse sand deposits, with compositional and sedimentological characteristics of a shoreline environment and fluvial lateral banks, were formed during large-magnitude reductions in the lake level, similar to the one in 2019, (2) Interbedded layers of fine sand and dark leaf litter, currently found in low-energy fluvial environments, were formed during shorter and less pronounced decrease intervals, and (3) Massive silty clay, with distinctive microorganisms from low-energy lacustrine environments, is deposited during high water-level stages, when the delta is covered by water. Our findings illustrate how hydrological changes alter sedimentary dynamics in deltaic areas of lakes. Despite the complexity of their depositional processes, deltaic records can serve as a complementary source of paleolimnological information to records from distal zones due to their sensitivity to variations in water level, especially during extreme and prolonged desiccation events. Future research should attempt to combine evidences from deltaic and sediment sequences from deeper zones of Lake Tzibaná to reconstruct water-level variations during the entire Holocene. Understanding past lake-level reductions is not only relevant for the local indigenous communities but also crucial for the conservation of this ecosystem of international importance.

The lacustrine system developed in the basin of Mexico has been of great interest in studies of various geological and social disciplines. Its sediments preserve the history of the environmental changes that occurred during the late Quaternary. Between 2016 and 2018, a set of lacustrine sediment cores were collected in the Xochimilco sub-basin, located south of the basin of Mexico. From these sedimentary sequences, a master sequence was constructed that represents the upper 66.5 m of the lacustrine deposits. For the establishment of its stratigraphic column, 15 lithotypes were defined from their sedimentary components in which the clastic components made up of silicates dominate, mostly silt and clay in size. The most abundant biogenic fraction is diatoms that frequently form oozes, and ostracods are a common component in most of the sequence, which locally form hashes. Interbedded with the clastic and biogenic lithotypes are volcaniclastic deposits. Eight lithological units were defined based on their dominant lithotypes. The time scale of the sequence is still uncertain for the oldest sediments; however, it is estimated that it covers the last 300000 to 350000 years. From this temporality, environmental oscillations of millennial scales are inferred. Diatom-rich laminated sediments represent the deepest phases in the lake. The deposits with higher biogenic and authigenic calcareous components indicate the phases of higher ionic concentration during which the lake was shallower. The detailed analysis of the stratigraphy and the description of the sedimentary components in Xochimilco allows to establish an initial interpretation of the variations in the depositional environments, and provides the base from which the detailed studies of paleoclimatic indicators will be supported.

We analyzed multiple variables in recent sediments from 18 tropical, karst lakes in “Lagunas de Montebello” National Park, a Mexican Protected Natural Area and Ramsar site, to explore relationships between sediment characteristics and lake attributes: topography/location (mountain, surface-water-dominated vs. plateau, groundwater-dominated), morphometry (shallow vs. deep), and human activities (urbanization/agriculture). The study lakes fell into two groups: (1) pristine, oligotrophic, mostly located in the SE mountain terrain, and (2) impacted, eutrophic, in the NW plateau region. Sediment samples were collected from the central, deepest zone of each lake and analyzed for texture (grain size), carbonate content, and organic C and N. Water variables were measured in the water column overlying the sediment collection sites. Specific conductance, chlorophyll a, and total particulate carbon were higher in impacted, eutrophic plateau lakes than in pristine mountain lakes. Sediments, although composed mostly of silts, differed in grain size. Pristine, oligotrophic mountain lakes possessed coarser sediments, with a higher concentration of most likely recalcitrant organic carbon, than impacted, eutrophic plateau lakes. Topography/location is the primary factor that contributes to sediment differences, whereas eutrophication, caused by deforestation and agricultural runoff, is the second most important agent modifying sediment characteristics. The only pristine plateau lake, San Jose, had water quality similar to pristine mountain lakes, but finer sediments with lower organic C, N, and C/N. Comparison of San Jose sediments with those of impacted eutrophic plateau lakes indicated eutrophication has led to coarser sediments, as well as enrichment in CO3, organic C and N. Eutrophication-related sediment characteristics are valuable variables that can be used in paleolimnological studies to identify the onset of lake eutrophication in tropical karst water bodies.

Metagenomic and traditional paleolimnological approaches are suitable to infer past biological and environmental changes, however, they are often applied independently, especially in tropical regions. We combined both approaches to investigate Holocene Prokaryote and Eukaryote diversity and microbial metabolic pathways in ancient Lake Chalco, Mexico. Here, we report on diversity among a large number of lineages (36,722 OTUs) and functional diversity (27,636,243 non-clustered predicted proteins, and 6,144 annotated protein-family genes). The most abundant domain is Bacteria (81%), followed by Archaea (15%) and Eukarya (3%). We also determined the diversity of protein families and their relationship to metabolic pathways. The early Holocene (> 11,000 cal years BP) lake was characterized by cool, freshwater conditions, which later became warmer and hyposaline (11,000–6,000 cal years BP). We found high abundances of cyanobacteria, and fungi groups associated with mature forests in these sediments. Bacteria and Archaea include mainly anaerobes and extremophiles that are involved in the sulfur, nitrogen, and carbon cycles. We found evidence for early human impacts, including landscape modifications and lake eutrophication, which began ~ 6,000 cal years BP. Subsaline, temperate conditions were inferred for the past 5,000 years. Finally, we found nitrogen-fixing bacteria and protein-family genes that are linked to contaminated environments, as well as several fungal pathogens of crops in near-surface sediments.

Seasonal dry tropical forest (STDF) is a widespread vegetation type in western Mexico. Generally, this type of forest develops in semihumid habitats where lacustrine basins are scarce, preventing documentation of the vegetation history and forest dynamics using a paleoecological approach. Here, we present a palynological record from the Santa Maria del Oro crater lake, located within the distribution area of the STDF and the adjacent dry oak forest which gives insight into the changes in diversity and human impact at this tropical site. Pollen data, in combination with geochemical analysis and microcharcoal data from a lacustrine sequence, are used to discuss vegetation change and diversity in the plant assemblages related to drought or anthropogenic activity over the last 5000 years. Our results show three distinct periods of drought in the basin, from 4200 to 3850, 3100 to 2300, 1570 to 1100 and 300 cal year BP, with changes in vegetation composition mainly related to a decrease in taxa diversity during these periods. Based on the presence of maize pollen, two periods of human activity (3790–2160 and 280 cal year BP to present) were detected with an increase in herbaceous pollen used as a surrogate for deforestation. These two disturbance periods, pre-Columbian and postcolonial, occurred during wet conditions in the basin. Our results highlight the correlation between El Niño events, drought and fire with changes in the composition and diversity of STDF.

Lake Chalco lies south of the Basin of Mexico and has been the subject of studies related to Late Quaternary climate variability. In 2016, the International Continental Scientific Drilling Program “MexiDrill Project” recovered a 520-m sediment record from Lake Chalco. Magnetic susceptibility measurements revealed substantial changes in sediment physical properties between 343 and 285 m depth, suggesting changes in composition associated with fluctuations in the depositional environment. We targeted sediments in the 343–285 m interval for high-resolution facies analysis, to develop a model of Lake Chalco formation. We identified three facies associations, using sediment composition, texture, mineralogy and micro-morphological characteristics: (1) detrital facies, consisting of laminated silt, massive sand, stratified silty sand, clast-supported gravel and matrix-supported gravel; (2) biogenic facies, which include diatom ooze and bivalve coquina; and (3) volcaniclastic facies, represented by clast-supported pumice deposits. We propose that formation of Lake Chalco occurred in four stages, which we identified by changes in sediment characteristics. The first stage was an alluvial delta environment, in which debris and hyper-concentrated flows were the main sediment transport agents. The second was characterized by turbulent flows in a fluvial deltaic environment, which alternated with laminar flows associated with floodplains. The third stage was a time of fluvio-lacustrine transition in the basin, with formation of the previously identified Paleo-Chalco-I Lake, in response to wet conditions. During the fourth stage, a deep eutrophic lake formed (Paleo-Chalco-II), with an origin that appears to have been related to regional volcanism. Our working age-depth model indicates establishment of the lake at ca. 400 ± 46 ka. This paper presents the only available record of the transition from alluvial to lacustrine sedimentation of Lake Chalco. Our results allow us to establish (1) how the lake was formed and what the phases of its development were, (2) how a major volcanic event altered and transformed the lacustrine sedimentation, and (3) which climatic conditions dominated during the lake formation. The age for the onset of the lacustrine sedimentation in Chalco is for the first time constrained to around 400 ka. This enables to expand our knowledge of the climate for a time for which there is no information from terrestrial records of tropical North America.

In many temperate oligotrophic lakes, algal accumulations can form below the mixing zone. However, Deep Chlorophyll Maxima (DCM) have also been found in some eutrophic, tropical lakes and in this paper we aim to identify if they are recurrent features in these kinds of lakes and to recognize the factors that favor their formation. We analyzed 5 years of thermal stratification, water quality, and chlorophyll a concentrations in a tropical eutrophic lake in Central Mexico. Thermal stratification patterns were characteristic of warm monomictic lakes. Full water column deoxygenation during winter mixing was recorded in 3 of the analyzed years, and an increase of ~ 1 °C in the hypolimnion was detected between 2011 and 2015. DCM were detected in 4 out of the 5 studied years, at the top of the hypolimnion when the water column was stratified (spring–summer). This study is the first report of recurrent DCM formation in the northern limit of the Neotropics. It confirms that high light penetration is a necessary condition for DCM. Stratified nutrients with epilimnetic P depletion are also factors favoring DCM formation.

High-altitude lakes are sensitive to modern and past climate changes. Given their low-water temperatures, alkalinity, and nutrient levels, small climatic differences can strongly affect their water chemistry, and/or biodiversity. In central Mexico, there are only two high-altitude lakes, and both are within the crater of the Nevado de Toluca volcano. Here, we present a paleolimnological record from one of these lakes: La Luna. Previous paleoenvironmental work showed that it was sensitive to the Little Ice Age (LIA) cooling. Our results show that sediment accumulation began ~6900 to 6100 cal. yr BP under periglacial conditions and that lake conditions were established ~6000 cal. yr BP. One tephra layer was dated to ~5600 cal. yr BP, with no evidence of more recent volcanic activity. The early stages of this lake (6000–4700 cal. yr BP) contained Cladocera and diatom assemblages with different species composition than modern assemblages. This early stage community structure was related to more mesic conditions and cooler winters inferred by the high abundance of planktonic Aulacoseira nivaloides and of Chydorus cf. sphaericus. The establishment of modern limnological conditions after 4700 cal. yr BP is inferred from Cladocera and diatom assemblages similar to recent samples. A reduction in A. nivaloides and low magnetic-susceptibility values suggest lower lakes levels, a trend consistent with lower available moisture in central Mexico after 4000 cal. yr BP. The rest of the sequence shows the impact of two cold periods, the first one around 3000 cal. yr BP, identified by a new increase in Chydorus cf. sphaericus. The second was the larger impact associated with the LIA (AD 1350–1910), and an increase in Cavinula pseudoscutiformis and Pinnularia microstauron suggesting an increase in lake water pH. Also, organic matter and photosynthetic pigments increased during this period showing an increase in nutrient levels and productivity. Finally, the coldest interval during the LIA (AD 1570–1890) is identified by an important reduction in arboreal pollen concentration which points to a wider environmental impact of this cold event.

Geodiversity is recognized as one of the most important drivers of ecosystem characteristics and biodiversity globally. However, in the northern Neotropics, the contribution of highly diverse landscapes, environmental conditions, and geological history in structuring large-scale patterns of aquatic environments and aquatic species associations remains poorly understood. We evaluated the relationships among geodiversity, limnological conditions, and freshwater ostracodes from southern Mexico to Nicaragua. A cluster analysis (CA), based on geological, geochemical, mineralogical, and water-column physical and chemical characteristics of 76 aquatic ecosystems (karst, volcanic, tectonic) revealed two main limnological regions: (1) karst plateaus of the Yucatán Peninsula and northern Guatemala, and (2) volcanic terrains of the Guatemalan highlands, mid-elevation sites in El Salvador and Honduras, and the Nicaraguan lowlands. In addition, seven subregions were recognized, demonstrating a high heterogeneity of aquatic environments. Principal component analysis (PCA) identified water chemistry (ionic composition) and mineralogy as most influential for aquatic ecosystem classification. Multi-parametric analyses, based on biological data, revealed that ostracode species associations represent disjunct faunas. Five species associations, distributed according to limnological regions, were recognized. Structural equation modeling (SEM) revealed that geodiversity explains limnological patterns of the study area. Limnology further explained species composition, but not species richness. The influence of conductivity and elevation were individually evaluated in SEM and were statistically significant for ostracode species composition, though not for species richness. We conclude that geodiversity has a central influence on the limnological conditions of aquatic systems, which in turn influence ostracode species composition in lakes of the northern Neotropical region.

Geodiversity is recognized as one of the most important drivers of ecosystems characteristics and biodiversity globally. However, in the northern Neotropics, the contribution of highly diverse landscapes and geological history in structuring large-scale patterns of limnology and aquatic species associations remain poorly understood. We evaluate the interaction between geodiversity, limnology and freshwater ostracode assemblages to explore drivers of aquatic ecosystem structure from southern Mexico to Nicaragua. Cluster analysis based on geological, limnological, sedimentological and mineralogical characteristics of 76 aquatic ecosystems (karst, volcanic, tectonic) reveal two main limnological regions: (1) Karst terraces from the Yucatán Peninsula and northern Guatemala, and (2) volcanic terrains of the Guatemalan highlands, El Salvador and Honduras mid-elevations, and Nicaraguan lowlands. In addition, seven limnological subregions were recognized, attesting high limnological heterogeneity. Principal Component Analysis identifies water ionic and sediment composition as most influential for aquatic ecosystem classification and given their source of formation, we recognized geology as the fundamental determinant for large-scale limnological patterns. Multiparametric analyses based on biological data revealed that species association represent disjunct faunas. For instance, five species associations are closely related to limnological regions. Structural equation modelling reveals a strong influence of limnology and elevation on the biological composition, but geodiversity resulted in the most important driver. The confinement of species associations is attributed to regional lake geochemistry. We deduce a linear, continuous and primary influence of geodiversity for limnological structure, geochemical properties and aquatic biological composition in Lakes of the northern Neotropical region.

Se analizaron la abundancia relativa y la variabilidad morfológica de 4 especies y 1 variedad del género Aulacoseira (Bacillariophyceae) en sedimentos lacustres provenientes de lagos con diferentes características climáticas, morfométricas, fisicoquímicas y nivel trófico. Las afinidades ecológicas se investigaron a través del método de promedios ponderados y análisis de correspondencia canónica. Los resultados señalaron al gradiente de temperatura, salinidad y de nivel trófico como las principales variables que determinan la distribución de los taxones. Las especies del género tuvieron una distribución en aguas con pH circumneutrales levemente alcalinos y salinidades bajas. Aulacoseira granulata tuvo la mayor frecuencia de presencia y tolerancia por salinidades un poco más elevadas, A. ambigua alcanzó las abundancias relativas más altas, A. nivaloides se distingue por su afinidad a agua fría, de baja salinidad y bajo nivel trófico. Aulacoseira ambigua, A. granulata y A. granulata var. angustissima se distribuyen en ambientes de agua dulce, mesoeutróficos y A. pusilla tiene una afinidad por agua más turbia y con nivel más alto de fósforo. Este estudio aporta información sobre la variabilidad biológica y distribución ecológica de las especies dentro del género en lagos del centro de México.

Testate amoebae are bioindicators sensitive to environmental change, which show good preservation in sediments of low pH environments, such as high mountain lakes (LAM). The presence and diversity of testate amoebae were documented in surface sediments and sediment cores, dated with 210Pb, from the only 2 LAMs in Mexico (El Sol and La Luna), which have shown signs of recent human-induced changes. A total of 18 taxa were recorded and the main species observed in both lakes were Difflugia glans “glans” and D. globulosa. Specific richness and Shannon’s diversity index were higher in Lake El Sol than in the smaller, acidic and ultraoligotrophic Lake La Luna. The sediment cores recorded changes, during the last 20 to 25 years, in the composition of the testate amoebae communities (El Sol) and in their dominance (La Luna), as well as increased accumulation rate and concentrations of iron and organic carbon. These are signs of anthropogenic impact on the lakes, which should alert us to improve protection measures for these unique ecosystems, not only at the local (crater) level, but also with a more regional perspective.

Los lagos están entre los ecosistemas más sensibles al cambio climático, ya que el comportamiento termodinámico de su columna de agua es controlado por la marcha anual de la temperatura. Los lagos tropicales profundos presentan una columna de agua estratificada durante los meses más cálidos, sin embargo, en invierno esos estratos desaparecen al mezclarse la columna de agua. El patrón de mezcla de un lago se puede alterar cuando se presenta un incremento en la temperatura, ya sea debido al calentamiento global y/o durante el fenómeno meteorológico conocido como “El Niño”. El objetivo de este trabajo fue correlacionar cambios en el clima con los del lago La Alberca de Tacámbaro, Michoacán, México, durante un período que involucra dos eventos de “El Niño” (2009-2010 y 2015-2016) y con variaciones en las asociaciones de diatomeas preservadas en los sedimentos entre 1988 a 2015. El lago presentó un patrón de mezcla en invierno, con una termoclina somera en primavera que se profundiza en el otoño. Los datos muestran una tendencia que se refleja en la limitación de dos nutrientes, fósforo y nitrógeno (P y N), asociada con una menor mezcla vertical causada por años más calientes desde el 2000 y el efecto de los años en los que se presenta el fenómeno “El Niño”. Estos cambios correlacionan con un calentamiento del hipolimnion en 2015 comparado con 2009 y con alteraciones en la diversidad y composición de las diatomeas entre 1988 a 2015. Este estudio permitió documentar los cambios recientes del lago y asociarlos con el impacto del calentamiento global y los eventos de “El Niño”.

Forest fires, considered as free and not programmed fire propagation, are perturbations that greatly alter ecosystems. During fires, variable quantities of charcoal particles are produced by the burning vegetation, which can be later deposited in lacustrine basins. The traditional charcoal size particle model associates the > 100 µm primary particles to local fire events, within the watershed, and the < 100 µm particles are linked to regional fire events, outside the watershed. Fires can be related with favorable climatic conditions, but in tectonically active areas like the basin of Mexico, volcanism can also be a factor producing fires and charcoal particles. We document the history, intensity and frequency of fires recorded in the lacustrine sediments of lake Chalco (core CHAVII-11), by performing a high-resolution charcoal particle analysis in sediments deposited before and after three main volcanic events. The sources of these events had different distances to lake Chalco: Tláhuac tephra (TTH; 28690 years cal BP), probably produced by the Teuhtli volcano, was a local event; the Tutti Frutti Pumice (PTF; 17000 years cal BP) produced by the Popocatépetl volcano, was an extra-local event and the Upper Toluca Pumice (PTS; 12300 years cal BP) produced by the Nevado de Toluca volcano, was a regional event. Charcoal accumulation rates (CHAR) and distribution of size particles indicate that paleoclimate was a direct factor defining the intensity and recurrence of fires before and after volcanic activity, as climate defines vegetation type and density, and therefore fuel availability. Fires before and after the TTH were frequent, local and intense in comparison with fires reconstructed before or after the PTF and PTS events. CHAR values were lower during the more widespread PTF event, than for the local TTH event, although the highest CHAR values were recorded for the most distant, regional, and intense PTS event. These results show that charcoal accumulation rates during the volcanic events in central Mexico cannot be interpreted following traditional model of charcoal particle dispersion. This model have important restrictions in active volcanic regions such as central Mexico.

Diatom-based transfer functions for salinity, precipitation and temperature were developed using a training set that included data from 40 sites along central Mexico. These transfer functions showed good performance parameters and were subsequently applied to the previously published diatom record from lake Chalco, southern Basin of Mexico. Heinrich stadials (HS-3 to HS-0) were reconstructed as cold and dry events, with HS-2 representing the coldest and driest conditions, while HS-1 shows a complex bimodal cooling pattern. Orbital scale variability is also recorded. High and variable lake salinities from ∼34 to 29 ka BP (marine isotope stage 3, MIS-3) corresponded with times of maximum summer insolation and evidences of frequent fires. MIS-2 was identified as a cold period, with low lake salinity associated with low evaporation, with two cold intervals during the minima in spring (∼25.5 ka BP) and summer (∼20 ka BP) insolation. The ∼20 ka BP cold event together with HS-2 (24-23 ka BP), defined a bimodal maximum cooling during the last glacial maximum (LGM: 24.5–19.5 ka BP) within the range of pollen-based estimates, further supporting a maximum tropical cooling of 4–5 °C for the LGM. The deglacial (19.5–11.5 ka BP) showed the highest precipitation anomalies with three peaks that closely correlated with glacier advances in the nearby mountains (Iztaccihuatl). The early Holocene marked a change towards high lake salinities and the highest positive temperature anomalies (+3.5 °C) during a peak in summer insolation. Even though at orbital scale Chalco showed a nearly opposite trend to the record from the more southerly lake Peten-Itza (Guatemala), at millennial scale it showed a common pattern of cold and dry conditions during HSs, comparable to other tropical latitude sites in the northern hemisphere and further supporting the idea that there is a strong coupling between tropical and higher latitudes climates, in particular with the North Atlantic.

The aim of this study was to evaluate the mitigation of greenhouse gasses generated in the anaerobic digestion process of physicochemical sludges by evaluating the effect of CO2 supply and light in...

The occurrence of cyanobacterial blooms has increased globally over the last decades, with the combined effect of climate change and eutrophication as its main drivers. The seasonal dynamic of cyanobacterial blooms is a well-known phenomenon in lakes and reservoirs in temperate zones. Nevertheless, in the tropics, most studies have been performed in shallow and artificial lakes; therefore, the seasonal dynamic of cyanobacterial blooms in deep and eutrophic tropical lakes is still under research. We studied the seasonal variation of the phytoplankton community and the factors associated with Microcystis aeruginosa blooms along the water column of Lake Alberca de Tacámbaro, a warm monomictic crater lake located in Mexico, during 2018 and 2019. According to previous studies performed in 2006 and 2010, this lake was mesotrophic-eutrophic, with Chlorophyta and Bacillariophyta as the dominant groups of the phytoplankton community. During 2018 and 2019, the lake was eutrophic and occasionally, hypertrophic, a phenomenon likely associated with the increase of farmland area around the lake. The dominant species was M. aeruginosa, forming blooms from the surface to 10 m depth in winter, in the hypolimnion in spring and summer, and along the full water column in autumn. These findings suggest that M. aeruginosa in Lake Alberca de Tacámbaro displays seasonal and spatial population dynamics. Total phosphorus, dissolved inorganic nitrogen, water temperature and photosynthetically active radiation were the environmental factors related to M. aeruginosa blooms. Our results suggest that the changes in the structure of the phytoplankton community through time, and M. aeruginosa blooms in Lake Alberca de Tacámbaro, are mainly related to changes in land use from forest to farmland in areas adjacent to the lake, which promoted its eutrophication in the last years through runoffs. Comparative studies with other deep and eutrophic lakes will allow us to gain a deeper understanding of the dynamic of cyanobacterial blooms in natural and artificial water reservoirs strongly stressed by human activities.

For decades, paleoecological studies in lake sediments have focused on reconstructing the environments of the past and explaining phenomena linked to climatic variations. Recent advances in high-throughput DNA sequencing have allowed access to environmental DNA (eDNA) and ancient sedimentary DNA (sedaDNA) as a new and efficient proxy for past and present biodiversity. The basin of Mexico (BM) is located in the central part of the Trans-Mexican Volcanic Belt at 2,200 m a.s.l.; with the southern portion harboring the Chalco sub-basin. Lake Chalco is one of the last remaining natural aquatic ecosystems within the ever-expanding urban area surrounding Mexico City. The paleoenvironmental history of this lake has been previously characterized using sedimentological and geochemical proxies, as well as preserved microfossils (diatoms, pollen) with a temporal framework based on multiple radiocarbon dates. However, information for the remaining taxonomic groups and metabolic pathways remained unexplored. Here, we present the first metagenomics-based study for the Holocene in a high-altitude lake in Central Mexico –Lake Chalco. We explored the relationship between the lake’s paleoenvironmental condition and estimations of taxonomic and metabolic profiles across the sedimentary sequence (2.5 meters long). Multiple biological and abiotic variables revealed three main environmental phases: 1) a cool freshwater lake (FW1: 11,500-11,000 cal years BP), 2) a warm hyposaline lake (HS2: 11,000-6,000 cal years BP), and 3) a temperate, subsaline lake (SS3

The volcanic dammed Zirahuen Lake is one of the least eutrophic lakes in the state of Michoacan in the central Mexican highlands. Diatom-based records from two cores – one littoral in a water column of 15 m deep and one from the center of the ca. 40 m-deep lake – provide a sequence of environmental change spanning the last c. 12 ky. Diatom assemblages during the late Glacial are representative of shallow water or marsh-type environments, indicating lower lake levels in the lake margin. Fluctuating conditions occurred in the early Holocene, as evidenced by diatom assemblages in the central core, while an unconformity was observed in the littoral core between 12.1 and 7.2 ka BP associated with the damming of the lake as product of the development of the Magueyera volcano. The cores recorded a lake deepening and more stable lake levels between ca. 8.8 and 2 ka BP, with the planktonic Aulacoseira ambigua dominating the diatom assemblages. The lake deepening is associated with the last two La Magueyera lava flows that caused the final damming of the lake. These volcanic events increased hydrothermal activity and eutrophic conditions in the lake and favored increased silica availability for the Urosolenia eriensis blooms, with almost monospecific diatoms at c. 10.2 ka BP and again between 6.8 and 6.6 ka BP. Anthropogenic influence on the lake ecosystem is evident from c. 3.6 cal ka BP as increased catchment erosion. Significant changes from the mid-eighteenth century associated mainly with colonial copper smelting, deforestation, and recent intensification of land use in the catchment for avocado production are responsible for lake eutrophication.

The Basin of Mexico is a high elevation (2240 m asl), large (9540 km2), tectonic endorheic basin developed in the central-eastern Trans-Mexican Volcanic Belt. In 2016, the ICDP MexiDrill project recovered a total of 1152 m of sediments from a maximum depth of 520 m in Lake Chalco, in the SW of the Basin of Mexico. The upper 309.15 m (composite sequence, mc) are composed of fine-grained lacustrine sediments alternating with discrete visible tephra layers, and the lower 200 m are primarily volcaniclastic facies and basaltic lavas with some intercalated fluvial and alluvial facies. Initial lacustrine deposition started in the Chalco Basin, after the deposition of a thick volcaniclastic sequence, and continued until the lake was drained in recent centuries. Lake Chalco has remained as a shallow lake until the present day.

Globally, instrumentally based assessments of tsunamigenic potential of subduction zones have underestimated the magnitude and frequency of great events because of their short time record. Historical and sediment records of large earthquakes and tsunamis have expanded the temporal data and estimated size of these events. Instrumental records suggests that the Mexican Subduction earthquakes produce relatively small tsunamis, however historical records and now geologic evidence suggest that great earthquakes and tsunamis have whipped the Pacific coast of Mexico in the past. The sediment marks of centuries old-tsunamis validate historical records and indicate that large tsunamigenic earthquakes have shaken the Guerrero-Oaxaca region in southern Mexico and had an impact on a bigger stretch of the coast than previously suspected. We present the first geologic evidence of great tsunamis near the trench of a subduction zone previously underestimated as potential source for great earthquakes and tsunamis. Two sandy tsunami deposits extend over 1.5 km inland of the coast. The youngest tsunami deposit is associated with the 1787 great earthquake, M 8.6, producing a giant tsunami that poured over the coast flooding 500 km alongshore the Mexican Pacific coast and up to 6 km inland. The oldest event from a less historically documented event occurred in 1537. The 1787 earthquake, and tsunami and a probable predecessor in 1537, suggest a plausible recurrence interval of 250 years. We prove that the common believe that great tsunamis do not occur on the Mexican Pacific coast cannot be sustained.