Once considered pristine forests, the mid-elevational forests of the eastern Andean flank are now known to have long histories of human occupation. Past habitations, such as the 'Lost City of the Amazon' in the Upano Valley of eastern Ecuador, were societally and temporally complex with sophisticated cultures emerging, flourishing, and disappearing. The cultures of the Upano Valley transformed local ecosystems, but whether lasting ecological changes from those activities persist in modern forests is not known. Here, using paleoecological reconstructions from Lake Cormorán, located immediately adjacent to the Upano Valley and within 10 km of an area of >300 km2 of abandoned mound complexes, we provide a timeline of human influence spanning the last 2770 years. We document the onset of maize cultivation c. 570 BCE, and changes in land use within the occupation phase that included slash-and-burn, slash-and-mulch, and silviculture. A gradual decline in forest exploitation presaged an apparent abandonment of the site c. 550 CE. A much later wave of land use that began about 1500 CE, coupled with abandonment and a succession influenced by a warmer and wetter climate, produced a distinctive forest composition unique to the last 120 years.

Nature based solutions (NbS) for flood regulation (e.g., forest restoration) need to be informed by the analysis of climate change and land-use/cover change (LUCC) effects on floods, but these effects are still poorly understood. In this study, it is hypothesized that effects of climate change and LUCC on floods exhibit an abrupt change at a threshold elevation with implications for forest restoration. The study was carried out in the Tena watershed located in Ecuadorian Amazon. Hydrological simulations were run using TETIS model for different climate and LUCC scenarios. Projected precipitation from the Global Climate Models (GCMs) under the SSP5-8.5 scenario of CMIP6 was assessed. Isolated and combined effects of climate change and LUCC on floods across an altitudinal gradient were analyzed at 42 flow sites. Obtained results confirm the hypothesis showing the existence of a threshold elevation at 590 m a.s.l., where abrupt changes on floods occurred. The effects of LUCC prevailed over the effects of climate change in the upper basin, while in the lower basin, effects of climate change prevailed, especially for small and medium flood events. The results suggest that native forest is priority in the area above the threshold elevation, informing restoration as a NbS for flood regulation in humid tropical basins in a context of climate change.

Microplastics (MPs), defined as plastic particles between 5 mm and 0.001 mm, are transported through the atmosphere and detected in diverse ecosystems, including remote cryospheric environments. However, their atmospheric accumulation rates remain largely unquantified. This study presents the first reconstruction of the accumulation of atmospheric MPs in a tropical Andean glacier over the course of a hydrological year, defined as the annual cycle delimited by δ18O isotope depletion rather than the calendar year. An 8-m ice core was collected from Glacier 15-α on the Antisana volcano in Ecuador and dated with δ18O values to cover this cycle. MPs were visually identified and quantified, and polymer types were determined via micro-FTIR analysis. Accumulation rates were estimated by modeling a linear correlation between concentration of MPs and core depth, where surface layers are the most recent. A total of 1762 MPs were identified in the ice core, classified as fibers and fragments. Polyethylene and polymethyl methacrylate were the most common polymers throughout the core. The accumulation rate more than doubled, rising from 140 MPs/L at the beginning to 292 MPs/L at the end. These results indicate progressive atmospheric deposition of MPs, with persistent accumulation recorded in the upper troposphere, above boundary layers where turbulent mixing and frequent Amazonian rainfall would typically remove particles. Persistent MPs in the upper troposphere underscore the atmosphere's role as both a global vector and reservoir, with wide-ranging implications for ecosystems and long-range exposure risks to humans and wildlife.

Changes in land-use practices have been a central element of human adaptation to Holocene climate change. Many practices that result in the short-term stabilization of socio-natural systems, however, have longer-term, unanticipated consequences that present cascading challenges for human subsistence strategies and opportunities for subsequent adaptations. Investigating complex sequences of interaction between climate change and human land-use in the past—rather than short-term causes and effects—is therefore essential for understanding processes of adaptation and change, but this approach has been stymied by a lack of suitably-scaled paleoecological data. Through a high-resolution paleoecological analysis, we provide a 7000-year history of changing climate and land management around Lake Acopia in the Andes of southern Peru. We identify evidence of the onset of pastoralism, maize cultivation, and possibly cultivation of quinoa and potatoes to form a complex agrarian landscape by c. 4300 years ago. Cumulative interactive climate-cultivation effects resulting in erosion ended abruptly c. 2300 years ago. After this time, reduced sedimentation rates are attributed to the construction and use of agricultural terraces within the catchment of the lake. These results provide new insights into the role of humans in the manufacture of Andean landscapes and the incremental, adaptive processes through which land-use practices take shape.

Over recent decades, anthropogenic forest fires have significantly altered vegetation dynamics in the Amazon region. While human activities primarily initiate these fires, their escalation is intricately linked to climatic conditions, particularly droughts induced by the warm El Niño phase. This study investigates the impact of meteorological and hydrological drought on forest fires in the Amazon, focusing on the role of groundwater and El Niño events. Utilizing comprehensive drought indicators at various soil depths and standardized precipitation indexes, the research spans from 2004 to 2016, revealing a consistent decrease in humidity conditions across surface soil moisture, root zone soil moisture, and groundwater storage levels. With its slower response to precipitation changes, groundwater emerges as a crucial factor influencing hydrological drought patterns in the Amazon. The spatial distribution of drought conditions is explored, highlighting areas with lower humidity concentrations in the northeast and a correlation between forest fires and positive rates of change in burned area fraction during El Niño events. Notably, the study underscores the substantial increase in burned area during the 2015–2016, characterized by a very strong El Niño. This nuanced understanding of groundwater dynamics and its interplay with El Niño events provides critical insights for developing a tailored fire risk index in the ecologically significant and vulnerable Amazon basin, subsidizing strategies for mitigating fire risk and enhancing preparedness.

Understanding how tropical systems have responded to large-scale climate change, such as glacial-interglacial oscillations, and how human impacts have altered those responses is key to current and future ecology. A sedimentary record recovered from Lake Junín, in the Peruvian Andes (4085 m elevation) spans the last 670,000 years and represents the longest continuous and empirically-dated record of tropical vegetation change to date. Spanning seven glacial-interglacial oscillations, fossil pollen and charcoal recovered from the core showed the general dominance of grasslands, although during the warmest times some Andean forest trees grew above their modern limits near the lake. Fire was very rare until the last 12,000 years, when humans were in the landscape. Here we show that, due to human activity, our present interglacial, the Holocene, has a distinctive vegetation composition and ecological trajectory compared with six previous interglacials. Our data reinforce the view that modern vegetation assemblages of high Andean grasslands and the presence of a defined tree line are aspects of a human-modified landscape.

Flood frequency and intensity depend on the interaction between climate change and land-use/land-cover change (LUCC). However, their isolated and combined interactions are poorly understood, limiting the assessment of forest-based regulation of flood dynamics as means of adaptation to climate change within stream networks. We aim to evaluate the isolated and combined effects of climate change and LUCC on flood dynamics in a 240 km Ecuadorian Amazon basin. Hydrological simulations were run using the TETIS model, including designed deforestation scenarios and projected precipitation derived from the Global Climate Model (GCM) IPSL SSP5-8.5 (CMIP6). Statistical analysis of stormflow alterations at 42 stream network points across the basin reveal a heterogeneous pattern of impacts. Obtained results show that the effect of climate change on floods is more homogeneous over the basin than that of LUCC. Moreover, LUCC effects are pronounced in the upper basin and climate change effects dominate over LUCC effects in the lower basin. An altitudinal transition zone (590 to 906 m.a.s.l) is detected, where the LUCC effects on stormflows are higher than elsewhere in the basin and higher than those of climate change. Additionally, close to additive interaction between climate change and LUCC is identified. The magnitude of changes in the lower basin is closely related to scale effects and ecosystem sensitivity, highlighting the importance of native forest in downstream flow regulation and flood control, with its significance expected to grow due to climate change interactions.

La carretera Puyo-Tena es propensa a deslizamientos de tierra debido a la geodinámica, geomorfología y materiales geológicos de la zona (afloramientos y estratos inestables). En los últimos años, este problema ha provocado de forma persistente la inutilización parcial o total de la carretera en numerosas ocasiones. El objetivo de la investigación fue generar un modelo cartográfico de susceptibilidad a deslizamientos a partir de variables como la pendiente, las formaciones geológicas, la cobertura y uso de la tierra, así como las distancias a fallas, carretera y ríos. El grado de incidencia de deslizamientos se estimó como la combinación lineal de las variables ponderadas mediante el proceso de jerarquía analítica. La importancia de este método semicuantitativo radica en su capacidad para desagregar un problema de decisión complejo en un modelo de decisión más simple y coherente. El modelo cartográfico resultante se reclasificó en cinco categorías de susceptibilidad: muy baja, baja, moderada, alta y muy alta. Los resultados mostraron que 17 km de los 80 km de la carretera Puyo-Tena tienen una alta probabilidad a deslizamientos, lo que equivale a 21,25% de la carretera. Además, dentro de este porcentaje, se determinó que existen quince regiones con alta probabilidad de deslizamientos debido a su ubicación en zonas con fuertes pendientes, litología porosa y permeable, gran cantidad de ríos y suelos agrícolas. Para la verificación del modelo se utilizó el área bajo la curva (en inglés AUC) de la característica operativa del receptor (en inglés ROC). Los resultados de la verificación mostraron que el modelo cartográfico para el áre de estudio tiene un valor de precisión de 83,7%. El modelo cartográfico de susceptibilidad a deslizamientos permitirá tomar las decisiones pertinentes para mitigar eventos potenciales que puedan poner en peligro a transportistas, bienes materiales y residentes de la zona.

Native forest deforestation has been identified as one of the main land cover changes affecting flood risk specially during small and moderate storm events. In this regard, forest protection and reforestation are considered a nature-based solution (NbS) for flood regulation. However, there is a lack of knowledge about the effects of different deforestation spatial patterns over floods. Effects of land cover changes on floods in a humid tropical basin within the Ecuadorian Amazon are assessed distinguishing forest location and forest fragmentation. The hydrological distributed model TETIS was applied to simulate the hydrological response of a basin to extreme storms having return periods of 1, 10 and 100 years, considering five land cover scenarios. The model was calibrated and validated using nine storm samples collected at a gauge station during the years 2018 and 2020. The simulated overland flow in hillslopes and stormflows within the river channel were analyzed to i) assess the statistical differences among all land use scenarios with the Kruskal-Wallis test; ii) assess the statistical differences among pairs of both location and fragmentation scenarios through the post-hoc evaluation Dunn test; iii) assess the statistical differences in relation to the baseline. Obtained results indicate that stormflow is less sensitive than overland flow to land cover changes. Forest location have more influence than forest fragmentation over both, overland flow and storm flows. Deforestation of the upper basin represents the worst scenario for flood regulation, thus protection of existing forest, as well as reforestation of deforested areas located in the upper watersheds is a priority for flood risk mitigation and forest conservation. The results enhance our understanding of ecosystem services provided by tropical Andean foothills forests.

Oxygen isotopes delta O-18 from a 13 m ice core derived from the Antisana volcano ice cap (0 degrees 28'S, 78 degrees 08'W), Ecuador, were analyzed to generate an age model based on isotopic fluctuations. The inferred age model spans c. 3.6 years, from 1993 to mid-1996, and corresponds to 3.6 cycles of isotopic fluctuations driven by seasonal change in precipitation in western Amazonia. A logarithmic transformation (LT) was performed on the ice core density data to remove the compression effect of accumulated snow affecting the temporal fluctuation of the isotopic signal. A wavelet analysis run on the decompressed isotope signal (LT) showed periodicities of 80, 40, and 20 corresponding to 12, 6, and 3 months, respectively. The results were compared against the isotopic record from the Chimborazo ice core data to validate its temporal match with a hydrological year. The LT isotopic signal showed a significant correlation with the Chimborazo isotopic data (r = 0.69 and p-value < 0.001). The methodology applied in this study allowed the reconstruction of 3.6 cycles (3.6 years), showing that age models can be derived from ice cores using oxygen isotope annual fluctuations in tropical glaciers.

Palaeoecological records suggest that humans have been in the Andes since at least 14 000 years ago. Early human impacts on Andean ecosystems included an increase in fire activity and the extinction of the Pleistocene megafauna. These changes in Andean ecosystems coincided with rapid climate change as species were migrating upslope in response to deglacial warming. Microrefugia probably played a vital role in the speed and genetic composition of that migration. The period from ca 14 500 to 12 500 years ago was when novel combinations of plant species appeared to form no-analogue assemblages in the Andes. By 12 000 years ago most areas in what are today the Andean grasslands were being burned and modified by human activity. As the vegetation of these highland settings has been modified by human activity for the entirety of the Holocene, they should be regarded as long-term manufactutred landscapes. The sharp tree lines separating Andean forests from grasslands that we see today were probably also created by repeated burning and owe their position more to human-induced fire than climatic constraints. In areas that were readly penetrated by humans on the forested slopes of the Andes, substantial modification and settlement had occurred by the mid-Holocene. In hard-to-reach areas, however, the amount of human modification may always have been minimal, and these slopes can be considered as being close to natural in their vegetation. This article is part of the theme issue 'Tropical forests in the deep human past'.

Monitoring studies are necessary to better understand the hydrological processes affecting the isotopic signature of cave waters, which are ultimately recorded in speleothems that are used as paleoclimate archives. This research examines changes in the isotopic composition (delta O-18 and delta H-2) of precipitation as it infiltrates through the epikarst and into the Jumandy cave, located in the western Amazon Basin (Ecuador). Meteorological and hydrological parameters were monitored outside and inside the cave, and isotope analyses were carried out in waters from rainfall, an underground river, and drip-water at two sampling sites in the cave between April 2019 and February 2020. At monthly timescale, the rainfall weighted isotopic composition monitored at our stations was strongly correlated with the mean precipitation amount. However, when considered at weekly time-steps, the correlation is only moderate. This implies that the variation of the isotopic composition in the study area cannot be interpreted exclusively as an amount effect. Isotopic values and back-trajectory modeling show that the isotopic signature was affected by the moisture source effect associated with upstream rainout. The moisture flux is dominantly from an east to northeast direction and moisture mainly originates over the Atlantic Ocean, passing through the Amazon Basin. A significant fraction of moisture is associated with local sources within the Amazon Basin. This aspect is confirmed by d-excess values of rainfall and the Local Meteoric Water Lines (LMWLs) that indicate an influence of the high evapotranspiration rate of the Amazon region on the isotopic composition of local rainfall. The infiltrated water resides for about three weeks in the epikarst and then pre-cipitates forming speleothems (residence time). However, this short residence time needs to be confirmed with a longer monitoring period. Despite the different magnitudes of the dripping rates, the isotopic values at the two monitored sites are similar. This suggests that the dripping discharge rate is affected by the karst structure, but the isotopic signature reflects the mixing of individual rainfall events above the cave. Therefore, ?18O in spe-leothems from these caves is mainly recording short-term precipitation changes linked to regional and large-scale atmospheric circulation.

Our understanding of the climatic teleconnections that drove ice-age cycles has been limited by a paucity of well-dated tropical records of glaciation that span several glacial–interglacial intervals. Glacial deposits offer discrete snapshots of glacier extent but cannot provide the continuous records required for detailed interhemispheric comparisons. By contrast, lakes located within glaciated catchments can provide continuous archives of upstream glacial activity, but few such records extend beyond the last glacial cycle. Here a piston core from Lake Junín in the uppermost Amazon basin provides the first, to our knowledge, continuous, independently dated archive of tropical glaciation spanning 700,000 years. We find that tropical glaciers tracked changes in global ice volume and followed a clear approximately 100,000-year periodicity. An enhancement in the extent of tropical Andean glaciers relative to global ice volume occurred between 200,000 and 400,000 years ago, during sustained intervals of regionally elevated hydrologic balance that modified the regular approximately 23,000-year pacing of monsoon-driven precipitation. Millennial-scale variations in the extent of tropical Andean glaciers during the last glacial cycle were driven by variations in regional monsoon strength that were linked to temperature perturbations in Greenland ice cores 1 ; these interhemispheric connections may have existed during previous glacial cycles.

Microplastic (MPs) contamination is ubiquitous in most terrestrial and aquatic ecosystems. Recently MPs have been reported at high altitudes which indicates that air masses can transport and deposit MPs in the surface snow of high mountain ecosystems, however, whether MPs typification and abundance can be influenced by direction and origin of air masses still remains an open question. Here we present the first report of MPs above 5000 m a.s.l from surface snow of a glacier in the tropical Andes. We collected surface snow along an elevational gradient, from 5000 to 5400 m a.s.l., in the Antisana Glacier, in the northern Andes cordillera of Ecuador to analyze MPs abundance and polymeric identification with the Fourier Transform Infrared (FTIR) and also to hypothesized the possible MPs sources in this remote area by comparing the oxygen and hydrogen stable isotopic ratio composition of the snow samples and by analyzing the wind direction. We observed an average of 131 +/- 24 MPs L-1 in our samples. Fibers corresponded to 70% of all MP shapes; FTIR results showed that MPs composition mainly included polyurethane, polyethylene, polyamide, polyester, and high-density polyethylene in surface snow. There were no statistically significant differences of MPs abundance among sampled elevations, and the isotopic ratio composition did not differ among locations. Our results suggest that MP that accumulated in the glacier may be transported from the east, across the Amazonia, by the prevalent eastward air flow. The absence of industrial cities at least 2000 km further east from Antisana, indicates that the remote Andean glaciers could constitute important depositional zones for long-distance transported contaminants. (c) 2021 Elsevier B.V. All rights reserved.

Microplastic contamination has become ubiquitous in terrestrial and marine environments. Recent studies have shown that the wind can transport and deposit microplastics in high mountain ecosystems, but microplastic contamination therein is unknown. Because mountain glaciers are the primary source of drinking water for large urban areas in the Andes, assessing recent and historical microplastic contamination is crucial. Surface snow can indicate recent microplastic deposition, whereas glacial ice cores can provide information on historical contamination. At mountain glaciers, the inhospitable conditions and the difficult accessibility are limiting factors for sampling. Therefore, sampling and laboratory analytical methods have to be integrated and planned ensuring replicability. Here, we present 1) a new methodology to identify sampling areas within the accumulation zone of a glacier to obtain samples of surface snow and ice cores; 2) a less-manipulative analytical technique for the preparation and isolation of microplastics derived from glaciers. In addition, we identified the minimum amount of sample necessary to obtain robust data on contamination by microplastics.

Humid montane forests are challenging environments for human habitation. We used high-resolution fossil pollen, charcoal, diatom and sediment chemistry data from the iconic archaeological setting of Laguna de los Condores, Peru to reconstruct changing land uses and climates in a forested Andean valley. Forest clearance and maize cultivation were initiated during periods of drought, with periods of forest recovery occurring during wetter conditions. Between ad 800 and 1000 forest regrowth was evident, but this trend was reversed between ad 1000 and 1200 as drier conditions coincided with renewed land clearance, the establishment of a permanent village and the use of cliffs overlooking the lake as a burial site. By ad 1230 forests had regrown in the valley and maize cultivation was greatly reduced. An elevational transect investigating regional patterns showed a parallel, but earlier, history of reduced maize cultivation and forest regeneration at mid-elevation. However, a lowland site showed continuous maize agriculture until European conquest but very little subsequent change in forest cover. Divergent, climate-sensitive landscape histories do not support categorical assessments that forest regrowth and peak carbon sequestration coincided with European arrival. Multi-proxy palaeoecological methods reconstruct phases of land clearance, maize cultivation and forest regrowth in the High Andes centuries before European incursion, and do not support the idea that forest regrowth and peak carbon sequestration were coincident with European arrival.

We present a 12,6700-yr limnological history of Lake Miski, a high-elevation lake in a wet section of the Peruvian Andes. While many shallow Andean lakes dried up during the mid-Holocene, loss-on-ignition, magnetic susceptibility, and diatom analysis showed that Lake Miski was a constant feature in the landscape. Overall, fluctuations in the fossil diatom communities of Lake Miski tracked changes in insolation, but this was not the only mechanism influencing observed variability. We identify periods when insolation and interactions with the Pacific Ocean may have played a role in structuring local climate and diatom assemblages. The true mid-Holocene Dry Event (MHDE) is manifested in this record between 8000 and 5000 cal BP, but the carbonate stratigraphy and the diatom community indicated that although the level of the lake decreased, it never completely dried out, instead there was higher availability of planktic habitat and stronger mixing than in much of the Holocene. High rates of biological change observed during the late-Holocene in other records from Peru associated with human amplification of climatic signals were not observed in Lake Miski, as this lake may have been too wet and remote to be strongly influenced by human activity. Because of the presence of a woodland microrefugium, Lake Miski was suggested to have been an unusually climatically stable and wet location during the regional drying associated with the MHDE. Our new limnological information provides additional insights relating to this discussion. The presence of the observed woodland apparently withstood fluctuations that induced state changes in the lake and diatom flora, underscoring that microrefugia do not equate to unchanging' hydrologies or climates.

Aim: To determine the palaeoecological influences of climate change and human land use on the spatial distribution patterns of Polylepis woodlands in the Andes. Location: Tropical Andes above 2,900 m between 2 degrees S and 18 degrees S of latitude. Methods: Pollen and charcoal data were gathered from 13 Andean lake sediment records and were rescaled by the maximum value in each site. The rescaled pollen data were used to estimate a mean abundance and coefficient of variation to show woodland expansions/contractions and woodland fragmentation over the last 20,000 years. The rescaled charcoal was displayed as a 200-year moving median using 500-year bins to infer the influence of fire on woodland dynamics at landscape scale. Pollen and charcoal were compared with speleothem, clastic flux and archaeological data to assess the influence of moisture balance, glacial activity and human impact on the spatial distribution of Polylepis woodlands. Results: Woodland expansion and fire were correlated with precipitation changes and glacier dynamics from c.20 to 6kcal bp (thousands of calibrated years before present). Charcoal abundances between 20 and 12 kcal bp were less common than from 12kcal bp to modern. However, human-induced fires were unlikely to be the main cause of a woodland decline centred at 11 kcal bp, as woodlands recovered from 10.5 to 9.5kcal bp (about twofold increase). Charcoal peaks analogous to those that induced the woodland decline at 11 kcal bp were commonplace post-9.5kcal bp but did not trigger an equivalent woodland contraction. An increase in the coefficient of variation after c.5.5 kcal bp suggests enhanced fragmentation and coincided with the shift from logistic to exponential growth of human populations. Over the last 1,000 years, Polylepis became hyper-fragmented with over half of sites losing Polylepis from the record and with coefficients of variation paralleling those of glacial times. Main conclusions: Polylepis woodlands formed naturally patchy woodlands, rather than a continuous vegetation belt, prior to human occupation in the Andes. The main factors controlling pre-human woodland dynamics were precipitation and landscape heterogeneity. Human activity led to hyper-fragmentation during the last c.1,000 years.

A new fossil pollen, Sporormiella, and sediment chemistry record from Lake Llaviucu, Ecuador, spanning the period from 16,280–9000 years Before Present, provides a high-resolution record of paleoecological change in the high Andes. The deglacial transition from super-páramo through páramo grasslands, to Andean forest is traced, with near-modern systems being established by c. 11,900 years ago. It is suggested that forest elements probably existed in microrefugial populations close to the ice front. Sporormiella is used as a proxy for megafaunal abundance, and its decline to background levels is inferred to indicate a local extinction event at c. 12,800 years ago. About 1800 years prior to the extinction, charcoal becomes a regular sedimentary component in this very wet valley. An early date for human activity in the valley is suggested, with the direct implication of humans in the extinction of the megafauna.