To test hypotheses about catchment processes inferred from hydrological and hydrochemical patterns observed at the outlet, measurements are needed at a high temporal frequency from multiple water sources distributed in space. Here we present the Water Analysis Trailer for Environmental Research (WATER), a trailer-based mobile sampling platform capable of autonomously measuring stable water isotopes, nitrate, electrical conductivity, pH and temperature for 72 samples per day, collected from up to 11 sources. As a proof of concept, the WATER was deployed to the Schwingbach Environmental Observatory (1.03 km2) in Hesse, Germany, where six water sources were analysed (2 × stream water, 3 × groundwater, 1 × precipitation) for a period of six months. The multi-source, high-frequency data offered new insights into catchment functioning that had not been revealed by previous, lower-resolution sampling campaigns. For example, rapid vertical movement of incoming precipitation into the soil and a strong linkage between shallow sub-surface flow paths and the stream became apparent during events. In addition, streamflow generation and water quality at the catchment outlet showed likely signs of influence from nearby water sources and arable farming practices. Simulating the reduced sampling frequency associated with connecting additional sources to the WATER indicated that key features of the collected data would likely be preserved if sampling occurred over a period of several months. Overall, the WATER provides a mobile and scalable approach for moving from pattern-based inference to process understanding through multi-source, high-temporal-frequency measurements.

In complex hydrological systems, flow path dynamics, water storage and mixing, and biogeochemical processing vary in space and may change rapidly during events. Understanding source areas, connectivity and short-term dynamics in stream water quality therefore requires high-temporal-frequency, multi-source observations both within and across catchments. Revolutions in field-deployable analysers and sensors, together with advancement in automation techniques, now make such observations feasible via true “labs-in-the-field”. This paper details the technical realisation and proof-of-concept for the Water Analysis Trailer for Environmental Research (WATER). The WATER is a mobile, trailer-based platform for environmental sensing and automated, high-temporal-frequency sampling and analysis of water from multiple (currently up to 11) sources. It offers two analytical pathways – a Throughflow Pathway for measurement devices using a flow cell and a 5 µm-filtered Reservoir Pathway for devices requiring filtered water – and is currently equipped to measure stable water isotopes, nitrate, electrical conductivity, pH and temperature. Integration of additional measurement devices in the future is supported by the modular design of the WATER. A field test in the 1.03 km2 Schwingbach Environmental Observatory, Germany, demonstrated the ability of the system to successfully and autonomously collect and analyse samples from six water sources (2× stream water, 3× groundwater, 1× precipitation) over a period of six months, with collected data offering potential for new understanding of catchment functioning. Insights were also gained into the practical considerations necessary when deploying the WATER for an extended period of time, such as ensuring an adequate self-sufficient power supply and scheduling routine maintenance visits. Simulation of the reduced sampling frequency that would result from extending the WATER to sample at its full capacity of 11 sources also indicated that, over multi-month periods, key distributional characteristics of the collected data would likely be maintained. Overall, the WATER provides a mobile and scalable solution for high-temporal-frequency, multi-source hydrological and hydrochemical monitoring that can be (re-)deployed in different locations with relative ease.

The woody plant life forms in a tropical dry forest differ largely in their diurnal and seasonal patterns of root water uptake and the related atmospheric and edaphic drivers. As a consequence of global climate change, the frequency and intensity of drought events in tropical forest ecosystems is expected to increase. Woody species in tropical dry forests (TDFs) exhibit diverse strategies to withstand drought such as leaf-shedding or stem succulence that have mainly been studied from an aboveground perspective. Much less is known about the functioning of small and fine roots during the dry season and their response to soil re-wetting. We measured sap flux in small-diameter roots (2–6 mm) of four woody Ecuadorian TDF species using calibrated miniature sap flow gauges based on the heat-ratio method to unravel seasonal and diurnal patterns in root water uptake in dependence on phenology, soil moisture, and climatic drivers. Continuous data from 17 months showed that water uptake in the deciduous trees Eriotheca ruizii, Ceiba trischistandra, and Vachellia macracantha was closely linked to leaf phenology, soil moisture, and, in wet soil, vapor pressure deficit (VPD), while the tall, stem-succulent cactus Armatocereus laetus revealed a highly opportunistic water uptake pattern with rapid responses to small rainfall amounts in the dry season and decoupling from atmospheric drivers. While root sap flux density was on average highest in C. trischistandra with largest foliage area, the cactus roots were able to absorb water all day round without daytime dormancy and thus outperformed the other two species even during wetter periods. Deeper insights into small-root functionality across seasons is essential for a more mechanistic understanding of the water relations of TDF perennials with different drought response strategies.

Mean Transit Time (MTT) and Transit time distribution (TTD) functions are crucial for understanding the temporal dynamics of water flow through a catchment system, particularly in the context of rainfall-runoff processes that govern the solute storage and transport. Traditionally, these insights have been assessed using lumped TTD functions through models based on quasi-linearity and steady-state conditions. In contrast, the Ensemble Hydrograph Separation technique (EHS) presents a promising alternative for estimating TTD through multiple linear equations representing the relation between tracer fluctuations. This approach is advantageous, eliminating the need for continuous time series data of tracer measures and avoiding constraints related to the shape of transit distributions or system stationarity. However, EHS faces a sensitivity challenge in its regularization process, governed by a parameter denoted as "v," making the technique susceptible to either under-smoothing or over-smoothing the TTD function. Consequently, the judicious estimation of the regularization parameter within EHS becomes imperative.This study aims to investigate how both the traditional lumped TTD approach and the innovative EHS method contribute to our understanding of catchment hydrology. The present investigation was conducted using stable water isotope data of stream and soil water collected in a typical Andean tropical mountain cloud forest catchment. The sampling was conducted at six sites along two altitudinal transects (at elevations of 3000 m, 2000 m, and 1000 m), encompassing two distinct land covers (forest and pasture). At each site, soil water samples were collected at three different depths (0.10, 0.25, and 0.40 m below ground). The main objective is to assess the feasibility of substituting one method with the alternative by comparing their performance using different evaluation criteria such as the Nash-Sutcliffe coefficient (NSE), mean absolute error (MAE), and coefficient of determination (R2).Through Monte-Carlo simulations, we calibrated the “v” parameter and conducted a comprehensive comparison of both approaches. At 75% of the monitoring points, we observed NSE and R2 coefficients exceeding 0.65. These results align with previous studies, emphasizing the feasibility of assuming stationary conditions in humid tropical ecosystems. The study systematically examined the concordance between the Lumped TTD approach and Ensemble Hydrograph Separation (EHS) findings when utilizing similar TTDs. Furthermore, it provided a detailed analysis of the strengths and limitations of EHS implementation with actual real data. The insights gained from this research can be extrapolated to identify situations where each approach may be more suitable, offering valuable recommendations for their future application in various catchments.

Understanding the partitioning of downward shortwave radiation into direct and diffuse components is essential for modeling ecosystem energy fluxes. Accurate partitioning functions are critical for land surface models (LSMs) coupled with climate models, yet these functions often depend on regional cloud and aerosol conditions. While data for developing semi-empirical partitioning functions are abundant in mid-latitudes, their performance in tropical regions, particularly in the high Andes, remains poorly understood due to scarce ground-based measurements. This study analyzed a unique dataset of shortwave radiation components from a tropical mountain rainforest (MRF) in southern Ecuador, developing and testing a locally adapted partitioning function using Random Forest Regression. The model achieved high accuracy in predicting the percentage of diffuse radiation (%Dif; R2=0.95, RMSE = 5.33, MAE = 3.74) and absolute diffuse radiation (R2=0.99, RMSE = 5.30, MAE = 14). When applied to simulate upward shortwave radiation, the model outperformed commonly used partitioning functions achieving the lowest RMSE (8.62) and MAE (5.82) while matching the highest R2 (0.97). These results underscore the importance of regionally adapted radiation partitioning functions for improving LSM performance, particularly in complex tropical environments. The adapted LSM will be further utilized for studies on heat fluxes and carbon sequestration.

Latent heat flux is a central element of land-atmosphere interactions under climate change. Knowledge is particularly poor in the biodiversity hotspot of the Andes, where heat flux measurements using eddy covariance stations are scarce and land surface models (LSMs) often oversimplify the complexity of the ecosystems. The main objective of this study is to perform latent heat flux simulations for the tropical South Eastern (SE) Ecuadorian Andes using a coupled LSM framework, and to test the performance with heat flux and soil moisture data collected from a tropical high-altitude pasture. Prior to testing, we applied multi-criteria model calibration of sensitive model parameters, focusing on improving simulated soil water conditions and radiation fluxes as a prerequisite for proper heat flux simulations. The most sensitive parameters to improve soil moisture and radiation flux simulations were soil porosity, saturated hydraulic conductivity, leaf area index, soil colour and NIR (Near Infrared) leaf optical properties. The best calibrated model run showed a very good performance for half-hourly latent heat flux simulations with an R2 of 0.8 and an RMSE of 34.0 W m-2, outperforming simulations with uncalibrated and uncoupled LSM simulations in comparable areas. The slight overall overestimation in the simulated latent heat flux can be related to (i) simulation uncertainties in the canopy heat budget, (ii) an imbalance in the observed flux data and (iii) slight overestimations in the simulated soil moisture. Although our study focuses on latent heat fluxes and their relation to simulated radiation fluxes and soil moisture, model outputs of sensible heat fluxes were also discussed. The systematic overestimation of sensible heat flux in the model seems to be mainly a result of overestimated canopy temperatures. The improved simulation for latent heat flux has a high translational potential to support land use strategies in the tropical Andes under climate change.

Study regions: This study examined preferential flow occurrence and patterns in eight ecosystem types on the southern slopes of Mount Kilimanjaro in Tanzania. Study focus: We analyzed continuous soil moisture content measured in three soil depths and rainfall data at 1-h resolution from January 2022 to August 2023. After a separation and clustering of rainfall events we assessed the dynamics of soil moisture responses. The sequence and timing of soil moisture changes informed about the occurrence of preferential versus sequential (matrix) flow. New hydrological insights for the region: The results showed that the frequency of occurrence of preferential flow events were notably high in Erica forest (81.6 %), montane forest (26.4 %), and Ocotea forest (30.1 %), highlighting rapid subsurface water movement and potential for groundwater recharge. Other land covers such as disturbed Ocotea forest, grassland and maize indicated more uniform flow dynamics, which may favor surface runoff and increased soil erosion. We found that rainfall depth, duration and intensity are important factors that influence preferential flow. Additionally, the level of initial soil moisture also played a role in preferential flow occurrence, with optimal initial soil moisture levels between 35 % and 45 %. Both, very dry and very wet soil conditions were less favorable for preferential flow occurrence. These findings have important implications for understanding subsurface water movements and managing water resources in both natural and disturbed ecosystems.

This study addresses transpiration in a tropical evergreen mountain forest in the Ecuadorian Andes from the leaf to the stand level, with emphasis on nocturnal plant-water relations. The stand level: Evapotranspiration (ET) measured over 12 months with the Eddy-Covariance (ECov) technique proved as the major share (79%) of water received from precipitation. Irrespective of the humid climate, the vegetation transpired day and night. On average, 15.3% of the total daily ET were due to nocturnal transpiration. Short spells of drought increased daily ET, mainly by enhanced nighttime transpiration. Following leaf transpiration rather than air temperature and atmospheric water vapor deficit, ET showed its maximum already in the morning hours. The tree level: Due to the humid climate, the total water consumption of trees was generally low. Nevertheless, xylem sap flux measurements separated the investigated tree species into a group showing relatively high and another one with low sap flux rates. The leaf level: Transpiration rates of Tapirira guianensis, a member of the high-flux-rate group, were more than twice those of Ocotea aciphylla, a representative of the group showing low sap flux rates. Representatives of the Tapirira group operated at a relatively high leaf water potential but with a considerable diurnal amplitude, while the leaves of the Ocotea group showed low water potential and small diurnal fluctuations. Overall, the Tapirira group performed anisohydrically and the Ocotea group isohydrically. Grouping of the tree species by their water relations complied with the extents of the diurnal stem circumference fluctuations. Nighttime transpiration and hydrological type: In contrast to the isohydrically performing trees of the Ocotea group, the anisohydric trees showed considerable water vapour pressure deficit (VPD)-dependent nocturnal transpiration. Therefore, we conclude that nighttime ET at the forest level is mainly sourced by the tree species with anisohydric performance.

The megadiverse Andean mountain rain forests in southern Ecuador are threatened by climate and land use change, which are expected to alter biodiversity and thus functional traits impacting ecosystem processes. However, the high biodiversity of tropical mountain forests is still poorly represented in Land Surface Models (LSMs). We developed a biodversity-informed LSM entitled HUMBOL-TD (Hydroatmo Unified Model of Biotic interactions and Local Trait Diversity) to analzye the impact of climate and land-use change on carbon- and water fluxes. HUMBOL-TD consists of three coupled submodels specialized to represent different processes at the land surface. As such, energy- and water fluxes between land surface and atmosphere (LSMatmo) are simulated by the Community Land Model (CLM), vegetation dynamics including C, N and P cycling (LSMbio) are simulated by the Lund-Potsdam-Jena General Ecosystem Simulator (LPJ-GUESS), while the soil hydrology (LSMhydro) is represented by the Catchment Modeling Framework (CMF). A first test towards the simulation of the mountain forests and their replacement systems is conducted for a pasture site at 2000 m elevation. The model is parameterized and validated using a year of local site data. The first runs of the model enable the investigation of the differences in accuracy of modeled changes in the carbon- and water fluxes between coupled, partially coupled (LSMatmo – LSMbio, LSMatmo – LSMhydro, LSMbio – LSMhydro) and the fully coupled model (LSMatmo – LSMbio – LSMhydro).

Tropical mountain ecosystems are threatened by climate and land-use changes. Their diversity and complexity make projections how they respond to environmental changes challenging. A suitable way are trait-based approaches, by distinguishing between response traits that determine the resistance of species to environmental changes and effect traits that are relevant for species' interactions, biotic processes, and ecosystem functions. The combination of those approaches with land surface models (LSM) linking the functional community composition to ecosystem functions provides new ways to project the response of ecosystems to environmental changes. With the interdisciplinary project RESPECT, we propose a research framework that uses a trait-based response-effect-framework (REF) to quantify relationships between abiotic conditions, the diversity of functional traits in communities, and associated biotic processes, informing a biodiversity-LSM. We apply the framework to a megadiverse tropical mountain forest. We use a plot design along an elevation and a land-use gradient to collect data on abiotic drivers, functional traits, and biotic processes. We integrate these data to build the biodiversity-LSM and illustrate how to test the model. REF results show that aboveground biomass production is not directly related to changing climatic conditions, but indirectly through associated changes in functional traits. Herbivory is directly related to changing abiotic conditions. The biodiversity-LSM informed by local functional trait and soil data improved the simulation of biomass production substantially. We conclude that local data, also derived from previous projects (platform Ecuador), are key elements of the research framework. We specify essential datasets to apply this framework to other mountain ecosystems.

Accurate determination of the water retention curve (WRC) of a soil is essential for the understanding and modelling of the subsurface hydrological, ecological, and biogeochemical processes. Volcanic ash soils with andic properties (Andosols) are recognized as important providers of ecological and hydrological services in mountainous regions worldwide due to their outstanding water holding capacity. Previous comparative analyses of in situ (field) and standard laboratory (hydrostatic equilibrium based) methods for the determination of the WRC of Andosols showed contrasting results. Based on an extensive analysis of laboratory, experimental, and field measured WRCs of Andosols in combination with data extracted from the published literature we show that standard laboratory methods using small soil sample volumes (≤300 cm3) mimic the WRC of these soils only partially. The results obtained by the latter resemble only a small portion of the wet range of the Andosols’ WRC (from saturation up to -5 kPa, or pF 1.7), but overestimate substantially their water content for higher matric potentials. The disagreement limits our capacity to infer correctly subsurface hydrological behavior, as illustrated through the analysis of long-term soil moisture and matric potential data from an experimental site in the tropical Andes. These findings imply that results reported in past research should be used with caution and that future research should focus on determining laboratory methods that allow obtaining a correct characterization of the WRC of Andosols.

Ecohydrological processes in tropical rainforests are insufficiently understood, and existing studies yield contradictory results. We investigated relative contributions of different soil depths to tree water uptake of 83 trees and possible species‐specific differences in a 50 × 50 m forest plot at four dates in a tropical montane forest in Kenya using stable water isotopes and the Bayesian mixing model framework MixSIAR. We found distinct individual tree differences (e.g. Drypetes gerrardii taking 75% of its water from <0.5 m, or a rather large shift in uptake patterns based on the climatic conditions, that is the fourth sampling date), but no consistent species‐specific or small‐scale spatiotemporal patterns in water uptake and depth contributions. Soil water δ 18 O showed a lateral variation of up to 6‰, which was accounted for by a spatial interpolation of soil water isotopes and enabled us to improve allocations of water uptake sources to individual trees. Our results show that ignoring the lateral variability of water isotope signatures in soils complicates the applicability of a mixing model in this context and might be a widespread constraint reducing the validity and comparability of mixing model results. Further research on underlying processes of water fluxes in forest ecosystems is urgently needed and we point out the need for considering large individual differences in water uptake patterns and small‐scale variability of soil water isotopic composition despite homogeneous soil characteristics.

Conversion of tropical forests is among the primary causes of global environmental change. The loss of their important environmental services has prompted calls to integrate ecosystem services (ES) in addition to socio-economic objectives in decision-making. To test the effect of accounting for both ES and socio-economic objectives in land-use decisions, we develop a new dynamic approach to model deforestation scenarios for tropical mountain forests. We integrate multi-objective optimization of land allocation with an innovative approach to consider uncertainty spaces for each objective. These uncertainty spaces account for potential variability among decision-makers, who may have different expectations about the future. When optimizing only socio-economic objectives, the model continues the past trend in deforestation (1975-2015) in the projected land-use allocation (2015-2070). Based on indicators for biomass production, carbon storage, climate and water regulation, and soil quality, we show that considering multiple ES in addition to the socio-economic objectives has heterogeneous effects on land-use allocation. It saves some natural forest if the natural forest share is below 38%, and can stop deforestation once the natural forest share drops below 10%. For landscapes with high shares of forest (38%-80% in our study), accounting for multiple ES under high uncertainty of their indicators may, however, accelerate deforestation. For such multifunctional landscapes, two main effects prevail: (a) accelerated expansion of diversified non-natural areas to elevate the levels of the indicators and (b) increased landscape diversification to maintain multiple ES, reducing the proportion of natural forest. Only when accounting for vascular plant species richness as an explicit objective in the optimization, deforestation was consistently reduced. Aiming for multifunctional landscapes may therefore conflict with the aim of reducing deforestation, which we can quantify here for the first time. Our findings are relevant for identifying types of landscapes where this conflict may arise and to better align respective policies.

High temporal resolution (20-min intervals) measurements of stable isotopes from groundwater, stream water and precipitation were investigated to understand the hydrological response behavior and control of precipitation and antecedent wetness conditions on runoff generation. Data of 20 precipitation events were collected by a self-sufficient mobile system for in situ measurements over four months in the Schwingbach Environmental Observatory (SEO, temperate climate), Germany. Isotopic hydrograph separation indicated that more than 79% of the runoff consisted of pre-event water. Short response times of maximum event water fractions in stream water and groundwater revealed that shallow subsurface flow pathways rapidly delivered water to the stream. Macropore and soil pipe networks along relatively flat areas in stream banks were likely relevant pathways for the rapid transmission of water. Event water contribution increased with increasing precipitation amount. Pre-event water contribution was moderately affected by precipitation, whereas, the antecedent wetness conditions were not strong enough to influence pre-event water contribution. The response time was controlled by mean precipitation intensity. A two-phase system was identified, at which the response times of stream water and groundwater decreased after reaching a threshold of mean precipitation intensity of 0.5 mm h−1. Our results suggest that high temporal resolution measurements of stable isotopes of multiple water sources combined with hydrometrics improve the understanding of the hydrological response behavior and runoff generation mechanisms.

Hydrological responses to precipitation events in headwater catchments often vary in space and time. Understanding of such patterns leads to constrain runoff generation mechanisms and flow pathways. The use of stable isotopes of water combined with classical hydrometrics have increased in recent years to elucidate the response behavior of runoff components and their drivers in runoff generation. However, most of the previous studies dealing with investigation of catchment responses were limited to daily to monthly data, at which potential fine-scale variations could not be captured. Recently, few studies applied high-temporal resolution sampling of stable isotopes of water to investigate isotopic response variation within precipitation events. Sampling sources were mostly limited to streamflow and precipitation. An important, yet poorly known mechanism is the response of shallow groundwater to precipitation.In this study, we used an automated in-situ mobile laboratory to continuously sample stable istopes of multiple sources, including stream water, groundwater and precipitation every 20 mintutes. The study was realized in the Schwingbach Environmetal Observatory (SEO) in Hesse, Germany. Hydrograph seperation technique was applied to quantify the share of event and pre-event water contribution to the stream and to estimate response times of maximum event water fractions in the stream water and the groundwater for 20 events in the dry year 2018. We investigated the control of precipitation and antecedent wetness hydrometrics on response characteristics using Spearman rank correlation analysis.High-temporal resolution sampling of multiple sources captured the fine-scale variation of isotope concentrations in stream water and groundwater sources during the precipitation events indicating that the Schwingbach is a highly responsive, pre-event water dominated creek. More than 79% of the runoff consisted of pre-event water. Short response times combined with soil moisture variations of different depths revealed the linkage between shallow groundwater in near-stream zones and the stream itself. As a response of the dry conditions in 2018, an extended crack network developed that acted like adrainage system causing rapid delivering of water to the stream network. Event water contribution increased with increasing precipitation amount. Pre-event water contribution was moderately affected by precipitation amount, while antecedent wetness did not influence the runoff generation. The response time of stream water and groundwater was controlled by mean precipitation intensity. A two-phase system was identified, at which the response times of stream water and groundwater started to decrease after reaching a threshold of mean precipitation intensity (0.5 mm h1).

Hillslope soils developed on volcanic ash (Andosols) provide key hydrological services such as water storage and streamflow regulation in montane environments. Yet, little is known about how they influence subsurface water flow paths and flow transport and mixing dynamics. To fill this knowledge gap, we analyzed a unique 3-year dataset of hourly precipitation, soil moisture, and groundwater level and weekly precipitation and soil water stable isotope data collected along a steep hillslope transect underlain by Andosols. In combination with a detailed characterization of soil properties, we investigated how these soils influence water transport and tracer mixing in the subsurface. Our results indicate that the high organic matter (33-42%) and clay (29-31%) content of the soils’ organic horizon and an abrupt change in hydraulic conductivity between the highly conductive rooted soil layer and a low conductive underlying layer results in a perched water layer that remains near saturated year-round. Despite the formation of the latter, our isotope-based water age estimations depict that water resides within the organic horizon of the soils for short periods (2-4 weeks). The dynamics of soil moisture suggest a fast transfer of hydraulic potentials (few hours) along the entire soil profile in response to rainfall events. This hydraulic response is explained by the exponential shape of the soils’ water retention curves that facilitate a rapid vertical mobilization of water through the porous soil matrix. These findings indicate that the hydrological behavior of volcanic ash soils resemble that of a “layered sponge” in which vertical flow paths are dominant despite the formation of a perched water layer.

High‐elevation tropical grassland systems, called Páramo, provide essential ecosystem services such as water storage and supply for surrounding and lowland areas. Páramo systems are threatened by climate and land use changes. Rainfall generation processes and moisture transport pathways influencing precipitation in the Páramo are poorly understood but needed to estimate the impact of these changes, particularly during El Niño conditions, which largely affect hydrometeorological conditions in tropical regions. To fill this knowledge gap, we present a stable isotope analysis of rainfall samples collected on a daily to weekly basis between January 2015 and May 2016 during the strongest El Niño event recorded in history (2014–2016) in two Páramo regions of Central America (Chirripó, Costa Rica) and the northern Andes (Cajas, south Ecuador). Isotopic compositions were used to identify how rainfall generation processes (convective and orographic) change seasonally at each study site. Hybrid Single Particle Lagrangian Integrated Trajectory model (HYSPLIT) air mass back trajectory analysis was used to identify preferential moisture transport pathways to each Páramo site. Our results show the strong influence of north‐east trade winds to transport moisture from the Caribbean Sea to Chirripó and the South American low‐level jet to transport moisture from the Amazon forest to Cajas. These moisture contributions were also related to the formation of convective rainfall associated with the passage of the Intertropical Convergence Zone over Costa Rica and Ecuador during the wetter seasons and to orographic precipitation during the transition and drier seasons. Our findings provide essential baseline information for further research applications of water stable isotopes as tracers of rainfall generation processes and transport in the Páramo and other montane ecosystems in the tropics.

We demonstrated the great value of spatially distributed and temporally high-resolution hydro-chemical data to enhance knowledge about the intra-catchment variability of flow processes and the runoff composition of individual storms in a tropical alpine (Paramo) ecosystem. In this study, water sources (rainfall, spring water, and water from soil layers of Histosols and Andosols) and nested streams were sampled bi-weekly (2013-2014), including three storm high-resolution events (5-240 min). Water samples were analyzed for 14 tracers including electrical conductivity (EC) and rare earth trace elements and used as input to perform End-Member Mixing Analysis (EMMA). End-members identified for the outlet could explain the hydrological behavior of four out of the five tributaries, indicating similar hydro-geochemical processes and geomorphic features within the catchments. The runoff source contributions of the individual sub-catchments varied among (e.g. Andosols similar to 40% in tributaries and similar to 25% at the outlet) and within storm events (e.g. Histosols 15% higher in small peak discharge event), indicating a time-variable composition of streamflows. The latter was also reflected by the interaction of different sources and the chronology of flow paths in EMMA-space, evidencing a faster connectivity with hillslopes in the upper sub-catchments compared to the lower sub-catchments. We found counter-clockwise hysteresis patterns of storms in the lower catchments and clockwise hysteresis loops in the upper catchments. The latter bi-directionality can be related to lower slopes, wider riparian areas and the higher proportion of Histosols in the lower catchments compared to the upper sites. (c) 2018 Elsevier B.V. All rights reserved.