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Abstract Freshwater fishes are among the most threatened taxa worldwide owing to changes in land use, species introductions, and climate change. Although more than half of the freshwater fishes in the Chilean Mediterranean ecoregion are considered vulnerable or endangered, still little is known about their biogeography. Fishes of the family Perciliidae are endemic of this region and ideal cases to study potential implications of global warming given their endangered conservation status, small size, restricted range, and limited dispersal capacity in fragmented habitats. Here, we model the spatial distribution of habitats for Percilia irwini and P. gillissi under current (1970–2000) and future (2050–2080) climatic scenarios (SSP245, SSP585). We implement maximum entropy (MaxEnt) models adapted for stream networks using high-resolution datasets of selected geophysical and climatic variables. At present, both species inhabit relatively low-quality habitats. In the future (SSP585), suitable habitats for P. irwini are predicted to be reduced drastically (99%) with potential local extirpations in its northern range. Similarly, up to 62% of suitable habitats for P. gillissi would also be reduced in the future. Our study provides insights about assessing future threats and vulnerability of endemic, endangered, range-restricted, and small-bodied freshwater species in this region and elsewhere.

The application of the Multispectral Instrument (MSI) aboard Sentinel-2A/B constellation for assessing water quality in Chilean lakes represents an emerging area of research, particularly for the environmental monitoring of optically complex water bodies. Similarly, atmospheric correction processors applied to aquatic environments, such as the Case 2 Networks (C2RCC-Nets), are notably underrepresented. This study evaluates the capability of C2RCC-Nets using different neural networks—Case-2 Regional/Coast Color (C2RCC), C2X-Extreme (C2X), and C2X-Complex (C2XC)—to estimate Secchi depth in Lake Lanalhue (eutrophic), Lake Villarrica (oligo-mesotrophic), and Lake Panguipulli (oligotrophic). The evaluation used different statistical methods such as Spearman’s correlation and normalized error metrics (nRMSE, nMAE, and nbias) to assess the agreement between satellite-derived data and in situ measurements. C2XC demonstrated the best fit for Lake Lanalhue, with an nRMSE = 33.13%, nMAE = 23.51%, and nbias = 8.57%, in relation to the median ground truth values. In Lake Villarrica, the C2XC neural network displayed a moderate correlation (rs = 0.618) and error metrics, with an nRMSE of 24.67% and nMAE of 20.67%, with an nbias of 4.21%. In the oligotrophic Lake Panguipulli, no relationship was observed between estimated and measured values, which could be related to the fact that the selected neural networks were developed for very case 2 waters. These findings highlight the need for methodological advancements in processing satellite-derived water quality products for Chile’s optical water types, particularly for very clear waters. Nonetheless, this study underscores the need for model-specific calibration of C2RCC-Nets, as lakes with different optical water types and trophic states may require tailored training ranges for inherent optical properties.

This study marks the first recorded case of TiO2 nanoparticle pollution in Chilean rivers, indicating significant progress in understanding the distribution of nanowaste and its effects on a global scale. By investigating four different locations, including the outlet of a wastewater treatment plant during summer, winter and spring, the research revealed varied concentrations of TiO2 nanoparticles, with a notable range between 17.6 µg L−1 during the summer and 22.9 µg L−1 in spring in downstream river sections. The study used transmission electron microscopy to characterize nanoparticles, observing sizes between 10 and 206 nm, and an EDS detector confirmed titanium proportions of 4.84 % to 20.35 % by dry weight. These TiO2 nanoparticles, predominantly in Rutile and Anatase forms, denote a significant environmental presence, especially considering the low population densities of the sampling areas. The findings highlight the urgent need for international awareness and routine monitoring of nanowaste, advocating for preventive actions in the production of nanomaterials and adaptive management strategies in tune with the dynamic nature of water systems and environmental changes, both for places densely and sparsely populated.

This study examines the dynamics of limnological parameters of a South American lake located in southern Chile with the objective of predicting chlorophyll-a levels, which are a key indicator of algal biomass and water quality, by integrating combined remote sensing and machine learning techniques. Employing four advanced machine learning models (recurrent neural network (RNNs), long short-term memory (LSTM), recurrent gate unit (GRU), and temporal convolutional network (TCNs)), the research focuses on the estimation of chlorophyll-a concentrations at three sampling stations within Lake Ranco. The data span from 1987 to 2020 and are used in three different cases: using only in situ data (Case 1), using in situ and meteorological data (Case 2), using in situ, and meteorological and satellite data from Landsat and Sentinel missions (Case 3). In all cases, each machine learning model shows robust performance, with promising results in predicting chlorophyll-a concentrations. Among these models, LSTM stands out as the most effective, with the best metrics in the estimation, the best performance was Case 1, with R2 = 0.89, an RSME of 0.32 µg/L, an MAE 1.25 µg/L and an MSE 0.25 (µg/L)2, consistently outperforming the others according to the static metrics used for validation. This finding underscores the effectiveness of LSTM in capturing the complex temporal relationships inherent in the dataset. However, increasing the dataset in Case 3 shows a better performance of TCNs (R2 = 0.96; MSE = 0.33 (µg/L)2; RMSE = 0.13 µg/L; and MAE = 0.06 µg/L). The successful application of machine learning algorithms emphasizes their potential to elucidate the dynamics of algal biomass in Lake Ranco, located in the southern region of Chile. These results not only contribute to a deeper understanding of the lake ecosystem but also highlight the utility of advanced computational techniques in environmental research and management.

In this study, we employ in situ, meteorological, and remote sensing data to estimate chlorophyll-a concentration at different depths in a South American freshwater ecosystem, focusing specifically on a lake in southern Chile known as Lake Maihue. For our analysis, we explored four different scenarios using three deep learning and traditional statistical models. These scenarios involved using field data (Scenario 1), meteorological variables (Scenario 2), and satellite data (Scenarios 3.1 and 3.2) to predict chlorophyll-a levels in Lake Maihue at three different depths (0, 15, and 30 m). Our choice of models included SARIMAX, DGLM, and LSTM, all of which showed promising statistical performance in predicting chlorophyll-a concentrations in this lake. Validation metrics for these models indicated their effectiveness in predicting chlorophyll levels, which serve as valuable indicators of the presence of algae in the water body. The coefficient of determination values ranged from 0.30 to 0.98, with the DGLM model showing the most favorable statistics in all scenarios tested. It is worth noting that the LSTM model yielded comparatively lower metrics, mainly due to the limitations of the available training data. The models employed, which use traditional statistical and machine learning models and meteorological and remote sensing data, have great potential for application in lakes in Chile and the rest of the world with similar characteristics. In addition, these results constitute a fundamental resource for decision-makers involved in the protection and conservation of water resource quality.

In this study, we combined machine learning and remote sensing techniques to estimate the value of chlorophyll-a concentration in a freshwater ecosystem in the South American continent (lake in Southern Chile). In a previous study, nine artificial intelligence (AI) algorithms were tested to predict water quality data from measurements during monitoring campaigns. In this study, in addition to field data (Case A), meteorological variables (Case B) and satellite data (Case C) were used to predict chlorophyll-a in Lake Llanquihue. The models used were SARIMAX, LSTM, and RNN, all of which showed generally good statistics for the prediction of the chlorophyll-a variable. Model validation metrics showed that all three models effectively predicted chlorophyll as an indicator of the presence of algae in water bodies. Coefficient of determination values ranging from 0.64 to 0.93 were obtained, with the LSTM model showing the best statistics in any of the cases tested. The LSTM model generally performed well across most stations, with lower values for MSE (2), RMSE (

Phytoplankton is considered a strong predictor of the environmental quality of lakes, while Chlorophyll-a is an indicator of primary productivity. In this study, 25 LANDSAT images covering the 2014–2021 period were used to predict Chlorophyll-a in the Villarrica lacustrine system. A Chlorophyll-a recovery algorithm was calculated using two spectral indices (FAI and SABI). The indices that presented the best statistical indicators were the floating algal index (R2 = 0.87) and surface algal bloom index (R2 = 0.59). A multiparametric linear model for Chlorophyll-a estimation was constructed with the indices. Statistical indicators were used to validate the multiple linear regression model used to predict Chlorophyll-a by means of spectral indices, with the following results: a MBE of −0.136 μ, RMSE of 0.055 μ, and NRMSE of 0.019%. All results revealed the strength of the model. It is necessary to raise awareness among the population that carries out activities around the lake in order for them to take policy actions related to water resources in this Chilean lake. Furthermore, it is important to note that this study is the first to address the detection of algal blooms in this Chilean lake through remote sensing.

Inland water is fundamental for the conservation of flora and fauna and is a source of drinking water for humans; therefore, monitoring its quality and ascertaining its status is essential for making decisions in water resources management. As traditional measuring methods present limitations in monitoring with high spatial and temporal coverage, using satellite images to have greater control over lake observation can be a handy tool and have satisfactory results. The study of chlorophyll-a (Chl-a) has been widely used to ascertain the quality of the inland aquatic environment using remote sensing, but in general, it depends on the local conditions of the water body. In this study, the suitability of the Sentinel-2 MSI sensor for Chl-a estimation in a lake in south-central Chile is tested. An empirical approach is proposed, applying multiple linear regressions, comparing the efficiency and performance with L1C and L2A products, separating the equations constructed with spring-summer and fall-winter data, and restricting Chl-a ranges to those measured in the field to generate these regressions. The algorithms combining spectral bans proved to have a good correlation with Chl-a measured in the field, generally resulting in R2 greater than 0.87 and RMSE and MAE with errors less than 6 μg L−1. The spatial distribution of Chl-a concentrations at the study site was obtained based on the proposed equations.

The diffuse attenuation coefficient of photosynthetically active radiation is an important inherent optical property of the subaquatic light field. This parameter, as a measure of the transparency of the medium, is a good indicator of water quality. Degradation of the optical properties of water due to anthropogenic disturbances is a common phenomenon in freshwater ecosystems. In this study, we used four algorithm-based Landsat 8 OLI and Sentinel-2A/B MSI images to estimate the diffuse attenuation coefficient of photosynthetically active radiation in Lake Villarrica located in south-central Chile. The algorithms’ estimated data from the ACOLITE module were validated with in situ measurements from six sampling stations. Seasonal and intralake variations of the light attenuation coefficient were studied. The relationship between the diffuse attenuation coefficient of photosynthetically active radiation, meteorological parameters, and an optical classification was also explored. The best results were obtained with QAA v6 KdPAR Nechad (R2 = 0.931, MBE = 0.023 m−1, RMSE = 0.088 m−1, and MAPE = 35.9%) for spring and QAA v5 Kd490 algorithms (R2 = 0.919, MBE = −0.064 m−1, RMSE = −0.09 m−1, and MAPE = 30.3%) for summer. High KdPAR values are associated with the strong wind and precipitation events suggest they are caused by sediment resuspension. Finally, an optical classification of freshwater ecosystems was proposed for this lake. The promising results of this study suggest that the combination of in situ data and observation satellites can be useful for assessing the bio-optical state of water and water quality dynamics in Chilean aquatic systems.

We reported the presence of Peridiniopsis borgei Lemmermann in La Encantada lake (Province of Huaura) and studied the specimens using optical and scanning electron microscopical techniques. The population of P. borgei showed a variation in the number and degree of development of the marginal ridges. This is the first illustrated report of the species in Perú

Abstract Background The invasive diatom Didymosphenia geminata (Lyngbye) M. Schmidt has received considerable attention in recent years due to its rapid geographic expansion and massive proliferation, which have altered habitat availability for benthic species and triggered negative effects on stream ecosystems. We evaluated the changes in the community structure of phytobenthos caused by the temporal variation in D. geminata coverage, in addition to the environmental variables correlated with the temporal variation of this invasive microalga in the Andean sector of the Biobio River basin, Chile. Methods Environmental parameters were measured during the austral summer of 2014–2015, when phytobenthos samples were collected and used to develop a relative abundance matrix of taxa by calculating species richness and Shannon diversity. Multivariate techniques were used to establish the relationships among environmental variables, including D. geminata coverage, and the phytobenthic community. Results Massive proliferation of D. geminata occurs during summer (December–January). According to multiple regression analysis, electrical conductivity, temperature and total phosphorus were the variables that best explained the variation in D. geminata coverage. When D. geminata coverage was over 50%, phytobenthic species richness was significantly higher than at the uninvaded site, without a significant change in Shannon diversity. In addition, the % coverage of this invasive microalga and total phosphorus concentration were variables that differentiated phytobenthic communities among the study sites. Conclusions Environmental factors such as conductivity, temperature and total phosphorus concentration influenced the temporal variability of D. geminata mats. In addition, the massive growth of this invasive diatom caused a higher species richness without altering Shannon diversity. Our results suggest that the spatio-temporal variability of D. geminata correlated with environmental variables will help predict the habitat suitability of this alga in other Andean rivers and allow a better understanding of ecological habitat alterations.

Lake temperature has proven to act as a good indicator of climate variability and change. Thus, a surface temperature analysis at different temporal scales is important, as this parameter influences the physical, chemical, and biological cycles of lakes. Here, we analyze monthly, seasonal, and annual surface temperature trends in south central Chilean lakes during the 2000–2016 period, using MODIS satellite imagery. To this end, 14 lakes with a surface area greater than 10 km2 were examined. Results show that 12 of the 14 lakes presented a statistically significant increase in surface temperature, with a rate of 0.10 °C/decade (0.01 °C/year) over the period. Furthermore, some of the lakes in the study present a significant upward trend in surface temperature, especially in spring, summer, and winter. In general, a significant increase in surface water temperature was found in lakes located at higher altitudes, such as Maule, Laja and Galletué lakes. These results contribute to the provision of useful data on Chilean lakes for managers and policymakers.

Remote sensing was used as an early alert tool for water clarity changes in five Araucanian Lakes in South-Central Chile. Turbidity records are scarce or unavailable over large and remote areas needed to fully understand the factors associated with turbidity, and their spatial-temporal representation remains a limitation. This work aimed to develop and validate empirical models to estimate values of turbidity from Landsat images and determine the spatial distribution of estimated turbidity in the selected Araucanian Lakes. Secchi disk depth measurements were linked with turbidity measurements to obtain a turbidity dataset. This in turn was used to develop and validate a set of empirical models to predict turbidity based on four single bands and 16 combination bands from 15 multispectral Landsat images. The best empirical models predicted turbidity over the range of 0.3–12.3 NTUs with RMSE values around 0.31–1.03 NTU, R2 (Index of Agreement IA) around 0.93–0.99 (0.85–0.97) and mean bias error (MBE) around (−0.36–0.44 NTU). Estimation maps to analyze the temporal-spatial turbidity variation in the lakes were constructed. Finally, it was found that the meteorological conditions may affect the variation of turbidity, mainly precipitation and wind speed. The data indicate that the turbidity has slightly increased in winter–spring. These models will be used in the future to reconstruct large datasets that allow analyzing transparency trends in those lakes.

Mediante un análisis histórico-documental se reconstruyeron las condiciones ambientales del lago Vichuquén y su entorno entre los siglos XIX-XXI. Los resultados obtenidos permitieron determinar transformaciones del paisaje natural como consecuencia de la actividad humana. Se pudo establecer que hasta fines del siglo XIX la intervención ambiental habría sido moderada, momento en que comenzó a intensificarse notoriamente debido a la explotación mercantil de recursos naturales y al cambio de uso de suelo. Desde mediados del siglo XX, la ocupación ribereña del lago con fines turísticos-recreacionales incrementó severamente la degradación ambiental del ecosistema léntico, aumentando su nivel de trofía. Se verificó además la importante incidencia de algunos fenómenos naturales en la dinámica del complejo lacustre de Vichuquén.

Paleolimnological reconstructions from the mid and high latitudes in the Southern Hemisphere are still relatively scarce. Anthropogenic impacts have evidenced trophic state changes and an increase in cyanobacterial blooms in the lacustrine system of San Pedro de la Paz in the last decades. Here, we reconstructed primary production and sedimentological changes spanning the past 2500 years in two coastal lakes in Mediterranean Chile. A multiproxy approach including sedimentological, biogenic silica, carbon and nitrogen isotopes and fossil pigments analysis in sediment cores was performed in Laguna Grande (LGSP) and Laguna Chica de San Pedro (LCSP). A marked change in the sedimentology of the lakes, likely related to the terrigenous sediment inputs derived by a transition from an arid condition in the mid-Holocene to a more humid condition in the late Holocene that favoured arboreal forest establishment at 100 BC–AD 150. A period of low primary production was identified between 850 to 1050 AC for LCSP, suggesting moist and cold conditions that were possibly related to La Niña events. In recent decades, there have been increases in primary production, probably resulting from anthropogenic disturbances. These likely include the clearance of native vegetation, the introduction of exotic tree species, and urbanisation, which in turn, resulted in nutrient inputs and hence eutrophication. We conclude that an integrated management program for both lakes is urgently needed.

Novoa, V., Rojas, O., Arumí, J. L., Ulloa, C., Urrutia, R., & Rudolph, A. (marzo-abril, 2016). Variabilidad de la huella hídrica del cultivo de cereales, río Cachapoal, Chile. Tecnología y Ciencias del Agua, 7(2), 35-50. Se evaluaron los efectos de la variabilidad climática en el consumo de agua para la producción agrícola de cereales, a través del cálculo de la huella hídrica, metodología que consideró tres escenarios de precipitación: (a) año húmedo, (b) año normal y (c) año seco, y bajo dos condiciones de rendimiento (constante y disminución de 20%, proyectando el efecto de cambio climático), en tres secciones de la cuenca del río Cachapoal. Además, se calculó el agua virtual y la productividad aparente del agua para evidenciar el efecto de la variabilidad climática en la productividad del consumo del agua en el cultivo de cereales. El análisis de percentiles determinó que el año 2005 correspondió a húmedo, 2006 a normal y 2007 a seco. La huella hídrica de los cereales, bajo un rendimiento constante, fue mayor en el año húmedo con 1 064 m3 /ton; en cambio, con una disminución del rendimiento, fue mayor en el año seco (1 633.9 m3 /ton). Para ambas condiciones, la mayor huella hídrica azul se estimó en un año seco y la mayor huella hídrica verde en un año húmedo. Sin embargo, no se observaron diferencias entre las secciones de la cuenca. En un año húmedo se habría exportado la mayor cantidad de agua virtual con 14 325 000 m3 /año, y se habría producido la menor productividad aparente del agua, 92.8 $/m3 , información fundamental para determinar sistemas agrícolas sustentables.

A nivel global la temperatura de los ríos sigue siendo tema de investigación en ecología fluvial, pero el conocimiento de su variabilidad espacio-temporal en diversos sistemas fluviales aún es limitada y en algunos casos desconocida. Este estudio tuvo por objetivo comparar el régimen térmico natural de dos ecosistemas fluviales andinos con diferente vegetación ribereña (estepa y bosque de Nothofagus dombeyi). La temperatura en ambos sitios fue registrada con una resolución de 15 min desde enero a julio de 2011. La temperatura media, máxima y rango diario del agua mostraron diferencias significativas, con valores más bajos en el río con presencia de N. dombeyi. En relación al ciclo diario, se observó un leve retraso en la temperatura mínima y adelanto en la máxima para el río con bosque nativo. La realización de monitoreos continuos mediante sensores de temperatura permitió determinar contrastes en el régimen térmico y sugiere que la sombra generada por el dosel reduce la radiación solar que recibe el río y la temperatura máxima (± 4 °C) en ríos andinos. Asimismo, la conservación de la cobertura boscosa de N. dombeyi en la zona andina podría ser importante para moderar y mitigar la ocurrencia de temperaturas más altas a consecuencia de los escenarios de calentamiento global proyectados para la zona.

A strong socio-economic development pressure in South Chile will more and more cause an impact to the present lakes and rivers. Nevertheless, our knowledge concerning the ecological structure and the microbial self-purification capabilities of these lacustrine water bodies is scant but essential for a future sustainable development of land and water use. We studied Lake Laja, a lake already heavily impacted by water diversions for hydropower generation and irrigation. Typical for the Andean region Lake Laja is an oligotrophic water body, limited by nitrogen nutrients. Only very low chlorophyll a and particulate organic carbon (POC) concentrations and a small abundance and biomass of bacteria (mainly ultramicrobacteria) and heterotrophic flagellates were encountered. Weak trophic interrelations were derived from a high bacteria-to-heterotrophic flagellate ratio. For the ten investigated extracellular enzymes (alkaline phosphatase, leucine, arginine-, glycine and tyrosine-aminopeptidase, α-, β-D-glucosidase, α-, β-D-galactosidase, N-acetyl-β-D-glucosaminidase), with the exception of α-D-glucosidase, a broad range of organic matter degradation activities was proven. Probably, due to the N-limitation, organic nitrogen hydrolysing extracellular enzymes reached activities on average of 45 % compared to other studies in oligotrophic waters. The possible effect of N-limitation on extracellular enzyme activities was more pronounced by cell specific extracellular enzymatic activity rates, which exceeded those of other oligotrophic water bodies on average by factor 2. The overall activities of all microbial extracellular enzymes studied proved to be dominated by the dissolved free external enzymes (up to 98 %) over the ectoenzymes which are associated with particulate organic matter (bacterial cell walls, particles, and aggregates). It is concluded that future socio-economic changes, dealing with watershed human intervention (accelerating inorganic and organic loads) as well as global change (temperature and precipitation changes) could lead to significant changes in the ecology of Lake Laja.La gran presión generada por el desarrollo socioeconómico del sur de Chile, está causando cada vez más un mayor impacto en los lagos y ríos allí presentes. Sin embargo, el conocimiento de la estructura ecológica y la capacidad microbiana de autodepuración de los cuerpos de agua lacustres es escasa, pero esencial para un futuro uso sostenible de los recursos agua y suelo. Se estudió el lago Laja, por ser un cuerpo de agua muy afectado por la extracción de agua para la generación de energía hidroeléctrica y el riego. Como es característico de la región andina, el lago Laja es oligotrófico limitado por nutrientes nitrogenados. Se encontraron bajas concentraciones de clorofila a y carbono orgánico particulado (POC), así como bajas abundancias y biomasa de bacterias (principalmente ultramicrobacteria) y de flagelados heterotróficos. Interrelaciones tróficas débiles se determinaron de la relación bacterias y flagelados heterotróficos. Para las diez enzimas extracelulares estudiadas (fosfatasa, leucina-, arginina-, glicina- y tirosina-aminopeptidasa, a-, b-D-glucosidasa, a-, b-D-galactosidasa, N-acetyl-b-D-glucosaminidasa), con la excepción de α-β-glucosidase, se analizó un amplio rango de actividad de degradación sobre la materia orgánica. Probablemente, debido a la limitación de nitrógeno, el N-orgánico hidrolizado por enzimas extracelulares alcanzó una actividad promedio de 45 %, comparada con otros estudios en aguas oligotróficas. El posible efecto de la limitación de N en la actividad enzimática extracelular, fue más pronunciado en las tasas de la actividad enzimática extracelular específicas, las cuales excedieron en un factor promedio de dos a las de otros cuerpos de aguas oligotróficos. En general, la actividad de todas las enzimas extracelulares microbianas estudiadas resultaron estar dominadas por enzimas externas disueltas libres (hasta el 98 %), más que por ectoenzimas asociadas a partículas de materia orgánica (paredes celulares de bacterias, partículas y agregados). De esta manera es posible concluir que los futuros cambios socioeconómicos, reflejados en el incremento de cargas orgánicas e inorgánicas, así como el efecto del cambio global (cambios en temperaturas y precipitaciones), podrían provocar cambios significativos en la ecología del lago Laja.

TanDEM-X digital elevation model (DEM) is a global DEM released by the German Aerospace Center (DLR) at outstanding resolution of 12 m. However, the procedure for its creation involves the combination of several DEMs from acquisitions spread between 2011 and 2014, which casts doubt on its value for precise glaciological change detection studies. In this work we present TanDEM-X DEM as a high-quality product ready for use in glaciological studies. We compare it to Aerial Laser Scanning (ALS)-based dataset from April 2013 (1 m), used as the ground-truth reference, and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) V003 DEM and SRTM v3 DEM (both 30 m), serving as representations of past glacier states. We use a method of sub-pixel coregistration of DEMs by Nuth and Kääb (2011) to determine the geometric accuracy of the products. In addition, we propose a slope-aspect heatmap-based workflow to remove the errors resulting from radar shadowing over steep terrain. Elevation difference maps obtained by subtraction of DEMs are analyzed to obtain accuracy assessments and glacier mass balance reconstructions. The vertical accuracy (± standard deviation) of TanDEM-X DEM over non-glacierized area is very good at 0.02 ± 3.48 m. Nevertheless, steep areas introduce large errors and their filtering is required for reliable results. The 30 m version of TanDEM-X DEM performs worse than the finer product, but its accuracy, −0.08 ± 7.57 m, is better than that of SRTM and ASTER. The ASTER DEM contains errors, possibly resulting from imperfect DEM creation from stereopairs over uniform ice surface. Universidad Glacier has been losing mass at a rate of −0.44 ± 0.08 m of water equivalent per year between 2000 and 2013. This value is in general agreement with previously reported mass balance estimated with the glaciological method for 2012–2014.

This study reports the presence of the diatom Stephanodiscus minutulus (Kützing) Cleve & Möller for the frst time in Chilean continental waters; it is a taxon reported in many aquatic systems in Europe and North America and there are only scanty records from South America (Argentina). The species was found in a sedimentary profle collected from Lake Laja (Andes Mountains), Central Chile. The principal morphological features of S. minutulus are described, and comments about its relationship with other closely related taxa are given.En este estudio se señala la presencia de la diatomea Stephanodiscus minutulus (Kützing) Cleve & Möller por primera vez para aguas continentales de Chile; es un taxón muy común en diversos sistemas acuáticos de Europa y Norteamérica, y para Sudamérica sólo existen escasos registros en Argentina. La especie fue encontrada en un perfl sedimentario colectado en el Lago Laja (Cordillera de los Andes), Chile central. Se describen las principales características morfológicas de S. minutulus y se entregan comentarios sobre su relación con otras especies cercanas.

Chironomid assemblages and sedimentological parameters (grain size, organic content, mineralogy) of a short sediment core from Lake Galletué (38°41' S, 71°17' W) were analysed. The sedimentary record includes one volcanic ash (tephra) layer, which has a completely different composition than the host sediment in terms of organic content, grain size, and mineralogy. According to the geochronology (210Pb and 137Cs), this ash layer corresponds to the eruption of Llaima Volcano in 1956-1957. The tephra deposition had an impact on chironomid assemblages producing, among other changes, an increase in Parakiefferiella and a decrease in Ablabesmyia, although no noticeable change was detected in the diversity index. When compared with other studies, our results also show an impact in terms of the presence of chironomid head capsules within the tephra. The presence of these head capsules could result from the effects of percolation, since the coarse grain size of the tephra particles provides large interstitial spaces. The recovery in the abundances of some taxa after the tephra input, suggests the lake is probably restoring the conditions prevailing before the tephra fallSe analizan las asociaciones de restos sub-fósiles de quironómidos y los parámetros sedimentológicos de un núcleo sedimentario del lago Galletué (38°41' S, 71°17' O). Es evidente en este núcleo la presencia de un estrato de sedimentos volcánicos (tefra) de una composición distinta en el contenido deµmateria orgánica, en el tamaño de partícula y en la mineralogía, respecto de los sedimentos del lago. De acuerdo a la geocronología isotópica (210Pb y 137Cs), los sedimentos de esta tefra podrían corresponder a la erupción del volcán Llaima de 1956-1957. Por otra parte la depositación de esta tefra también provocó un cambio en las asociaciones de quironómidos, siendo evidente el aumento de Parakiefferiella y la disminución de Ablabesmyia dentro del estrato de tefra. Si bien nuestros resultados, al igual que estudios previos, registran un cambio en las asociaciones de quironómidos debido a la entrada de sedimentos volcánicos, un aspecto diferente es la presencia de cápsulas cefálicas dentro de la tefra. Una posible explicación a tal diferencia podría ser la percolación de los restos de quironómidos por los espacios intersticiales de la tefra. La recuperación en la abundancia de algunos taxa luego de la depositación de la tefra, sugiere que el lago restablecería las condiciones existentes previo a la caída de la tefra

La presente investigación realizó una reconstrucción de la evolución trófica de Laguna Grande de San Pedro (VIII Región, Chile) durante el último siglo, a través del análisis estratigráfico de diatomeas y registros geoquímicos preservados en un núcleo de sedimento obtenido en el lago. Los resultados obtenidos señalan que la comunidad de diatomeas ha variado su composición a través del tiempo, reconociéndose cuatro períodos distintos, que representan cada uno de ellos una condición trófica diferente. Por otra parte, los registros geoquímicos aumentan sus tasas de acumulación hacia los estratos superficiales del perfil, evidenciando un aumento de la productividad hacia la actualidad. De acuerdo a lo anterior, es posible concluir que la productividad de Laguna Grande ha experimentado importantes cambios, evolucionando desde un sistema oligo-mesotrófico (período más antiguo) a uno eutrófico (período reciente). Los cambios más drásticos habrían sucedido en las últimas décadas, como respuesta al fuerte desarrollo de actividades forestales y de urbanización en la cuenca de este sistemaThis research reconstructs the trophic evolution of Laguna Grande de San Pedro (VIII Region, Chile) during the last century, through both the stratigraphic analyses of diatom remains and geochemical parameters preserved in a sediment core obtained in this lake. The results obtained show that the community of diatoms has changed its composition throughout time, showing four different periods, representing each one a distinctive trophic condition. On the other hand, the geochemical records increase their accumulation rates to the profile surface layers, making evident an increase of the productivity to the present time. In this context, it is possible to conclude that the productivity at Laguna Grande has experienced significant changes, evolving from an oligo-mesotrophic system (earlier period) to an eutrophic one (recent period). The most drastic changes would have happened during the last decades, as response to both the intense development of urbanization and forest activities in the basin of this lake

Diatom, hydrocarbons and fatty acid sedimentary records were used for reconstructing the recent (last 150 years) palaeolimnological history of Laguna Chica of San Pedro (Concepción, VIII Región, Chile). Cluster analyses (Constrained Incremental Sum of Squares) on the diatom data revealed three distinct periods. The first period (1883-1940's) showed a pronounced increase in sedimentation rate and a slight increase in organic matter accumulation. In this period, eutrophic species (Aulacoseira granulata and Staurosira construens) became increasingly dominant. From the 1940s until the 1970s the diatom signal is more equivocal: after the initial decrease in the relative abundance of A. granulata and S. construens their numbers fluctuate without a clear pattern. Sedimentation rates strongly fluctuate in this period. From 1978 onwards eutrophic species are in decline while indicators of oligotrophic conditions, such as Cyclotella stelligera and Aulacoseira distans, become more abundant. This shift in the lake trophic status could not be attributed to a reduction in the nutrient load from the catchment and we hypothesize that the invasion of the lake by the submersed macrophyte Egeria densa has altered nutrient availability to the plankton communities. This is in agreement with the hydrocarbons and fatty acid analyses which demonstrate a shift in carbon number distributions from short chain alkanes and alkanoic acids (typical for microalgae) to long chain molecules (characteristic for higher plants) in the upper layers of the lake sedimentSe realizó la reconstrucción histórica de los últimos 150 años de Laguna Chica de San Pedro (Concepción, VIII Región, Chile), a través de la utilización de los restos de diatomeas, hidrocarburos y ácidos grasos contenidos en la columna de sedimento. El análisis estratigráfico de las diatomeas reveló la presencia de tres períodos diferentes. El primer período (1883-1940's), mostró un marcado aumento de las tasas de sedimentación y un leve aumento en la acumulación de materia orgánica; en este período se registra un incremento de las especies eutróficas (Aulacoseira granulata y Staurosira construens). Desde los años cuarenta hasta la década del setenta el cambio en la comunidad de diatomeas fue más evidente y las tasas de sedimentación variaron fuertemente. A partir de 1978 disminuyen las especies eutróficas y aumentan las indicadoras de condiciones oligotróficas (Cyclotella stelligera y Aulacoseira distans). El cambio en el estado trófico del lago, no se atribuye a una reducción de los aportes de nutrientes desde la cuenca, sino que se hipotetiza que la invasión de la macrófita Egeria densa, alteró la disponibilidad de nutrientes en las comunidades planctónicas. Esto concuerda con el análisis de hidrocarburos y ácidos grasos, registrándose una mayor concentración de compuestos de cadena larga (característicos de plantas superiores) en los estratos superficiales, mientras que en los estratos más profundos se detectó una mayor concentración de hidrocarburos y ácidos grasos de cadena corta (característicos de microalgas)

Se comparan, a través de registros sedimentarios, palinológicos y diatomológicos, dos momentos de la historia ambiental del sistema lacustre de San Pedro. El primero, corresponde al periodo prehispánico, representando a las condiciones prístinas o línea base del sistema. El segundo periodo, el más reciente, representa aproximadamente a los últimos diez años de intervención antrópica. Para lograr lo anterior, se recolectaron muestras verticales de sedimento del fondo en los dos lagos del sistema lacustre de San Pedro (Lagunas Grande y Chica). Se realizaron análisis cronológicos (C14), palinológicos y diatomológicos de los estratos superiores e inferiores de la columna sedimentaria. Los resultados indican que el sistema lacustre de San Pedro ha experimentado drásticos cambios desde la llegada de los españoles, evolucionando desde una cobertura vegetacional natural, predominantemente nativa, a una fuerte presión de uso forestal. Del mismo modo, el estado cualitativo del agua presenta una variación en sus características tróficas, reconociéndose una evolución desde aguas oligotróficas a eutróficas, en Laguna Grande, y de oligotrofía a mesotrofía en Laguna Chica. Finalmente, se propone la incorporación del análisis de los registros sedimentarios en los estudios ambientales y planes de manejo de los sistemas lacustres. De esta forma será posible conocer la línea base (condiciones prehispánicas) y la respuesta del ecosistema acuático a las influencias antrópicasTwo moments of the environmental history of San Pedro lacustrine system are compared through sedimentary, pollen and diatom records. The first one corresponds to the pre-Hispanic period, representing the pristine conditions or background of the system. The second period, more recently, represents the human disturbance conditions during the late ten years. To achieve the above mentioned, sediment cores were collected from the bottom of two lakes that conform the San Pedro lacustrine system (Laguna Grande and Chica). Chronological (C14), pollen and diatom analysis of superior and inferior layers of the cores were carried out. The results indicate that the San Pedro lacustrine system has undergone drastic changes since Spanish settlement. Evolving from a natural vegetation, predominantly native, to an intense pressure of forestry use. In the same way, the qualitative water state presents a variation in its trophic features, showing a evolution from oligotrophic to eutrophic waters in Laguna Grande and from oligotrophic to mesotrophic in Laguna Chica. Finally, it is suggested the incorporation of sedimentary records analysis in the study of environmental impact and management of lakes. In this way, it will be possible to know the background (the existing pre-Hispanic conditions) and the response of aquatic ecosystem to the human influences

En esta investigación se estudian, mediante geocronología radioisotópica (Pb210), las variaciones históricas en el proceso de erosión-sedimentación en Laguna Chica de San Pedro, VIII Región. Las estimaciones cronológicas indican que, durante los últimos 100 años, el aporte de sedimentos desde la cuenca de drenaje osciló drásticamente en un orden de magnitud. Se concluye que las variaciones son producto de los cambios históricos en el uso del suelo. Finalmente, se proponen tres períodos históricos que habrían provocado el aumento de la erosión de los suelos en la cuenca. In this study, the historical variations in the erosional-sedimentation process in the "Laguna Chica de San Pedro" (VIII Region), are studied using lead210 geochronology. The results indicate that over the last century, the sediment supply from the drainage basin fluctuated drastically in an order of magnitude. It is concluded that this variations are the result of the historical changes in the land use. Finally, three historic periods are proposed which would have caused an increase in the erosion in the basin soils.

En este artículo se analizan los principales efectos ambientales de la costanera del río Bío-Bío, proyectada para ser construida en el sector ribereño comprendido entre el Puente Viejo (Comuna de Concepción) y La Leonera (Comuna de Chiguayante). Los antecedentes que se presentan forman parte del Estudio de Impacto Ambiental (EIA) del proyecto Defensas Fluviales y vía troncal en ribera norte del río Bío-Bío, desarrollado por el Centro EULA de la Universidad de Concepción, por encargo del Ministerio de Obras Públicas, para cumplir con los requerimientos establecidos por la ley del Medio Ambiente y proporcionar nuevos elementos de análisis, fundados en criterios ambientales, para orientar las decisiones relacionadas con el proyecto.