Publications
Found 38 publication(s)
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Raffelsbauer, V.; Pucha-Cofrep, F.; Strobl, S.; Knüsting, J.; Schorsch, M.; Trachte, K.; Scheibe, R.; Bräuning, A.; Windhorst, D.; Bendix, J.; Silva, B. & Beck, E. (2023): Trees with anisohydric behavior as main drivers of nocturnal evapotranspiration in a tropical mountain rainforest. PloS ONE 18(3), 1-1.
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DOI: 10.1371/journal.pone.0282397
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Abstract:
Abstract:
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. Irre-
spective 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 rela-
tively 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 circum-
ference fluctuations. Nighttime transpiration and hydrological type: In contrast to the isohy-
drically performing trees of the Ocotea group, the anisohydric trees showed considerable
water vapour pressure deficit (VPD)-dependent nocturnal transpiration. Therefore, we con-
clude that nighttime ET at the forest level is mainly sourced by the tree species with aniso-
hydric performance.
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Keywords: |
dendrometer |
Evapotranspiration |
Sap flux |
Eddy covariance |
Bendix, J.; Aguirre, N.; Beck, E.; Bräuning, A.; Brandl, R.; Breuer, L.; Boehning-Gaese, K.; Dantas De Paula, M.; Hickler, T.; Homeier, J.; Inclan, D.; Leuschner, C.; Neuschulz, E.; Schleuning, M.; Suarez, J.P.; Trachte, K.; Wilcke, W. & Farwig, N. (2021): A research framework for projecting ecosystem change in highly diverse tropical mountain ecosystems. Oecologia 2021, 1-13.
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DOI: 10.1007/s00442-021-04852-8
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Abstract:
Abstract:
Tropical mountain ecosystems are threatened by climate and land-use changes. Their diversity and complexity make projec-
tions 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 efect 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-efect-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.
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Keywords: |
Biodiversity-Land-Surface-Model |
Knoke, T.; Paul, C.; Rammig, A.; Gosling, E.; Hildebrandt, P.; Härtl, F.; Peters, T.; Richter, M.; Diertl, K.; Castro, L.M.; Calvas, B.; Ochoa Moreno, S.; Valle-Carrión, L.A.; Hamer, U.; Tischer, A.; Potthast, K.; Windhorst, D.; Homeier, J.; Wilcke, W.; Velescu, A.; Gerique, A.; Pohle, P.; Adams, J.; Breuer, L.; Mosandl, R.; Beck, E.; Weber, M.; Stimm, B.; Silva, B.; Verburg, P.H. & Bendix, J. (2020): Accounting for multiple ecosystem services in a simulation of land-use decisions: Does it reduce tropical deforestation?. Global Change Biology 26( ), 1-22.
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DOI: 10.1111/gcb.15003
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Abstract 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.
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Keywords: |
Ecuador |
biodiversity |
ecosystem services |
landscape restoration |
land allocation |
robust optimization |
Beck, E.; Knoke, T.; Farwig, N.; Breuer, L.; Siddons, D. & Bendix, J. 2017: Landscape Restoration, Sustainable Land Use and Cross-scale Monitoring of Biodiversity and Ecosystem Functions. A Science-directed Approach for South Ecuador. (Universität Bayreuth).
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DOI: 10.5678/lcrs/pak823-825.cit.1696
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Abstract:
Abstract:
In 201 3, the “Platform for Biodiversity and Ecosystem
Monitoring and Research in South Ecuador”
(www.TropicalMountainForest.org) was launched as a
knowledge transfer program in the biodiversity
hotspot of the southern Ecuadorian Andes, jointly
funded by the German Research Foundation (DFG)
and Ecuadorian non-university partners. One of the
overall aims of the transdisciplinary program is to
design science-directed recommendations for an
ecologically sustainable, economically profitable and
socially compatible use of the mainly rural land. The
second major goal of the program is the development
of functional indicators that are crucial for the
monitoring of impacts of environmental change on the
ecosystem and its functions. They encompass
abiotic, abiotic-biotic and biotic-biotic interrelations,
and are sensitive - though to different extent - to
subtle changes in the environment. Therefore, it is not
only the interaction per se, which has to be examined.
In addition to that the quantification of the response to
certain environmental stressors is needed.
Representing the fundament of ecosystem functioning,
biodiversity as such or certain functional taxa can
be monitored for an assessment of the ecosystem’s
state. Important further criteria for the selection of an
indicator are general applicability, easiness of
handling and stability against pitfalls.
This book “Landscape Restoration, Sustainable
Use and Cross-scale Monitoring of Biodiversity
and Ecosystem Functions: A Science-directed
Approach for South Ecuador” presents in its first
part a compilation of sustainable land use concepts
that have been proven for application in the Provinces
Loja and Zamora Chinchipe and beyond, given
comparable environmental conditions. The second
part describes functional indicators as well as their
development, monitoring and application.
Both parts start with introductory chapters on the
major aims of the respective transdisciplinary
program, followed by contributions showing how land
use concepts can be used to achieve sustainable
management and ecosystem services, as well as how
functional indicators can be used to assess and
monitor the stability of biodiversity and ecosystem
functions.
It should be stressed that this book has not the aim to
present only a scientific summary of the developed
systems. Instead, it targets on stakeholders as our
non-university partners and beyond which are in
charge of environmental planning and ecosystem
function surveillance in Ecuador. In the manner of a
technical handbook, it gives a comprehensible introduction
to the land use option or the indicator,
followed by hints how to apply, implement and assess
the developed systems. The book is and was
complementing our three pillars of capacity building
which also includes stakeholder workshops on the
developed land use options and indicators, and
demonstration plots in the field.
With this book the authors highly acknowledge the
generous funding of the research by the German
Science Foundation (DFG) and the logistic,
administrative and practical support by the foundation
Naturaleza y Cultura Internacional (Loja and Del
Mar). Such research requires also fruitful
collaboration with local academic institutions, the
Universidad Tecnica Particular de Loja, the
Universidad Nacional de Loja, the Universidad de
Cuenca, the Universidad de Azuay, and the local
weather service INAMHI. These partnerships were a
great experience in capacity building on both sides,
as evidenced by a number of academic degrees
obtained and by numerous joint publications. The
authors are also grateful for the support of our nonuniversity
research partners beyond NCI, namely
ETAPA EP (Empresa Pública Municipal de
Telecomunicaciones, Agua potable, lcantarillado y
Saneamiento de Cuenca- Ecuador), the Gobierno
Municipal de Zamora and the regional water fund
FORAGUA (Fondo Regional del Agua). Further,
sincere thanks are owed to the Ecuadorian Ministry of
the Environment (MAE) for permission to conduct
research in South Ecuador.
The Editors
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Keywords: |
sustainable land use |
Cross-scale Monitoring |
science-directed guidelines |
landscape restoration |
Correa, A.; Windhorst, D.; Tetzlaff, D.; Crespo, P.; Celleri, R.; Feyen, J. & Breuer, L. (2017): Temporal dynamics in dominant runoff sources and flow paths in the Andean Páramo. Water Resources Research 53(8), 5998-6017.
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DOI: 10.1002/2016WR020187
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Abstract:
Abstract:
The relative importance of catchment's water provenance and flow paths varies in space and time, complicating the conceptualization of the rainfall-runoff responses. We assessed the temporal dynamics in source areas, flow paths, and age by End Member Mixing Analysis (EMMA), hydrograph separation, and Inverse Transit Time Proxies (ITTPs) estimation within a headwater catchment in the Ecuadorian Andes. Twenty-two solutes, stable isotopes, pH, and electrical conductivity from a stream and 12 potential sources were analyzed. Four end-members were required to satisfactorily represent the hydrological system, i.e., rainfall, spring water, and water from the bottom layers of Histosols and Andosols. Water from Histosols in and near the riparian zone was the highest source contributor to runoff throughout the year (39% for the drier season, 45% for the wetter season), highlighting the importance of the water that is stored in the riparian zone. Spring water contributions to streamflow tripled during the drier season, as evidenced by geochemical signatures that are consistent with deeper flow paths rather than shallow interflow through Andosols. Rainfall exhibited low seasonal variation in this contribution. Hydrograph separation revealed that 94% and 84% is preevent water in the drier and wetter seasons, respectively. From low-flow to high-flow conditions, all the sources increased their contribution except spring water. The relative age of stream water decreased during wetter periods, when the contributing area of the riparian zone expands. The multimethod and multitracer approach enabled to closely study the interchanging importance of flow processes and water source dynamics from an interannual perspective.
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Keywords: |
hydrochemistry |
Paramo |
hydrological processes |
catchment flow dynamics |
Timbe, E.; Feyen, J.; Windhorst, D.; Breuer, L.; Crespo, P.; Celleri, R. & Frede, H. (2017): Multicriteria assessment of water dynamics reveals subcatchment variability in a seemingly homogeneous tropical cloud forest catchment. Hydrological Processes 31(7), 1456-1468.
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DOI: 10.1002/hyp.11146
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Abstract:
Abstract:
To improve the current knowledge of the rainfall–runoff phenomena of tropical montane catchments, we explored the usefulness of several hydrological indicators on a nested cloud forest catchment (76.9 km2). The used metrics belong to 5 categories: baseflow mean transit time, physicochemical properties of stream water, land cover, topographic, and hydrometric parameters. We applied diverse statistical techniques for data analysis and to contrast findings. Multiple regression analysis showed that mean transit times of base flow could be efficiently predicted by sodium concentrations (higher during baseflows) and temperatures of stream water, indicating a major influence of geomorphology rather than topographic or land cover characteristics. Principal component analysis revealed that no specific subset of catchment indicators could be identified as prevailing descriptors for all catchments. The agglomerative hierarchical clustering analysis provided concomitant results, implying larger levels of dissimilarity between smaller subcatchments than between larger ones. Overall, results point out an intricate interdependence of diverse processes at surface and subsurface level indicating a high level of heterogeneity. Disregarding heterogeneity of nested or paired catchments could lead to incomplete or misleading conclusions, especially in tropical mountain regions where pronounced spatial and temporal gradients are present.
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Keywords: |
tropical cloud forest |
catchment flow dynamics |
catchment heterogeneity |
mean transit times |
multicriteria assessment |
rainfall–runoff processes |
Windhorst, D. (2014): Prediction of hydrological fluxes under global change in a tropical mountainous rainforest ecosystem of South Ecuador University of Giessen - Institute of Landscape Ecology and Resources Management, phd thesis
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The comparatively long research history within the study area allowed to develop well-grounded hypotheses on how the hydrological system within the study area should behave (Bogner et al., 2014; Boy et al., 2008; Bücker et al., 2011, 2010; Crespo et al., 2012, 2011; Fleischbein et al., 2006; Goller et al., 2005). Based on those earlier findings made within the study area and the hydrological research conducted elsewhere in tropical mountain cloud forests (see Bonell and Bruijnzeel, 2004; Bruijnzeel, 2004; Bruijnzeel et al., 2011 for recent overviews) provided the background to shape the research conducted within this dissertation around the focal point of global change impacts on the hydrological cycle inside the study area (see chapter 1.3).Separated into three chapters, each representing a scientific research paper, this thesis will address the issue on how to evaluate effects of land-use change on the hydrological cycle (chapter 2), how stable water isotopes are distributed over space and time within the study area (chapter 3) and how stable water isotopes can be used in hydrological models to assist this analysis of global change impacts in the future (chapter 4). All of the research conducted for this dissertation was performed in the Rio San Francisco catchment within South Ecuador.
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Keywords: |
hydrologic response |
isotope tracers |
Ecuador, Climate Change, Land Use |
Hydrological modelling |
Correa, A.; Windhorst, D.; Crespo, P.; Celleri, R.; Feyen, J. & Breuer, L. (2016): Continuous versus event based sampling: How many samples are required for deriving general hydrological understanding on Ecuador's páramo region?. Hydrological Processes 30(22), 4059-4073.
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DOI: 10.1002/hyp.10975
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Abstract:
As a consequence of the remote location of the Andean páramo is knowledge on their hydrologic functioning limited, notwithstanding this alpine tundra ecosystem act as water towers for a large fraction of the society. Given the harsh environmental conditions in this region is year-round monitoring cumbersome, and it would be beneficially if the monitoring needed for the understanding of the rainfall-runoff response could be limited in time. To identify the hydrological response and the effect of temporal monitoring a nested (n?=?7) hydrological monitoring network was set up in the Zhurucay catchment (7.53?km2), south Ecuador. The research questions were: (1) can event sampling provide similar information in comparison to continuous monitoring, and (2) if so, how many events are needed to achieve a similar degree of information? A subset of 34 rainfall runoff events was compared to monthly values derived from a continuous monitoring scheme from December 2010 to November 2013. Land cover and physiographic characteristics were correlated with eleven hydrological indices. Results show that despite some distinct differences between event and continuous sampling, both datasets reveal similar information; more in particular the monitoring of a single event in the rainy season provides the same information as continuous monitoring, while during the dry season 10 events ought to be monitored.
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Keywords: |
Paramo |
Andes |
hydrologic response |
catchment hydrology |
sampling design |
Mosquera, G.; Segura, C.; Vaché, K.; Windhorst, D.; Breuer, L. & Crespo, P. (2016): Insights into the water mean transit time in a high-elevation tropical ecosystem. Hydrology and Earth System Sciences (HESS) 20(7), 2987-3004.
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DOI: 10.5194/hess-20-2987-2016
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Abstract:
Abstract:
This study focuses on the investigation of the mean transit time (MTT) of water and its spatial variability in a tropical high-elevation ecosystem (wet Andean páramo). The study site is the Zhurucay River Ecohydrological Observatory (7.53?km2) located in southern Ecuador. A lumped parameter model considering five transit time distribution (TTD) functions was used to estimate MTTs under steady-state conditions (i.e., baseflow MTT). We used a unique data set of the ?18O isotopic composition of rainfall and streamflow water samples collected for 3 years (May 2011 to May 2014) in a nested monitoring system of streams. Linear regression between MTT and landscape (soil and vegetation cover, geology, and topography) and hydrometric (runoff coefficient and specific discharge rates) variables was used to explore controls on MTT variability, as well as mean electrical conductivity (MEC) as a possible proxy for MTT. Results revealed that the exponential TTD function best describes the hydrology of the site, indicating a relatively simple transition from rainfall water to the streams through the organic horizon of the wet páramo soils. MTT of the streams is relatively short (0.15–0.73 years, 53–264 days). Regression analysis revealed a negative correlation between the catchment's average slope and MTT (R2?=??0.78, p?<?0.05). MTT showed no significant correlation with hydrometric variables, whereas MEC increases with MTT (R2?=??0.89, p?<?0.001). Overall, we conclude that (1) baseflow MTT confirms that the hydrology of the ecosystem is dominated by shallow subsurface flow; (2) the interplay between the high storage capacity of the wet páramo soils and the slope of the catchments provides the ecosystem with high regulation capacity; and (3) MEC is an efficient predictor of MTT variability in this system of catchments with relatively homogeneous geology.
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Keywords: |
Paramo |
mean transit time |
hydrological processes |
Iniguez, C.; Rausche, S.; Cueva, A.; Sánchez-Rodríguez, A.; Espinosa, C. & Breuer, L. (2016): Shifts in leaf litter breakdown along a forest–pasture–urban gradient in Andean streams. Ecology and Evolution 6(14), 4849-4865.
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DOI: 10.1002/ece3.2257
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Abstract:
Abstract:
Tropical montane ecosystems of the Andes are critically threatened by a rapid land-use change which can potentially affect stream variables, aquatic communities, and ecosystem processes such as leaf litter breakdown. However, these effects have not been sufficiently investigated in the Andean region and at high altitude locations in general. Here, we studied the influence of land use (forest–pasture–urban) on stream physico-chemical variables (e.g., water temperature, nutrient concentration, and pH), aquatic communities (macroinvertebrates and aquatic fungi) and leaf litter breakdown rates in Andean streams (southern Ecuador), and how variation in those stream physico-chemical variables affect macroinvertebrates and fungi related to leaf litter breakdown. We found that pH, water temperature, and nutrient concentration increased along the land-use gradient. Macroinvertebrate communities were significantly different between land uses. Shredder richness and abundance were lower in pasture than forest sites and totally absent in urban sites, and fungal richness and biomass were higher in forest sites than in pasture and urban sites. Leaf litter breakdown rates became slower as riparian land use changed from natural to anthropogenically disturbed conditions and were largely determined by pH, water temperature, phosphate concentration, fungal activity, and single species of leaf-shredding invertebrates. Our findings provide evidence that leaf litter breakdown in Andean streams is sensitive to riparian land-use change, with urban streams being the most affected. In addition, this study highlights the role of fungal biomass and shredder species (Phylloicus; Trichoptera and Anchytarsus; Coleoptera) on leaf litter breakdown in Andean streams and the contribution of aquatic fungi in supporting this ecosystem process when shredders are absent or present low abundance in streams affected by urbanization. Finally, we summarize important implications in terms of managing of native vegetation and riparian buffers to promote ecological integrity and functioning of tropical Andean stream ecosystems.
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Keywords: |
stream water |
decomposition |
Aquatic Pollution |
Knoke, T.; Paul, C.; Hildebrandt, P.; Calvas, B.; Castro, L.M.; Härtl, F.; Döllerer, M.; Hamer, U.; Windhorst, D.; Wiersma, Y.; Curatola Fernández, G.F.; Obermeier, W.A.; Adams, J.; Breuer, L.; Mosandl, R.; Beck, E.; Weber, M.; Stimm, B.; Haber, W.; Fürst, C. & Bendix, J. (2016): Compositional diversity of rehabilitated tropical lands supports multiple ecosystem services and buffers uncertainties. Nature Communications 7, Article number:11877.
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DOI: 10.1038/ncomms11877
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Abstract:
Abstract:
High landscape diversity is assumed to increase the number and level of ecosystem services. However, the interactions between ecosystem service provision, disturbance and landscape composition are poorly understood. Here we present a novel approach to include uncertainty in the optimization of land allocation for improving the provision of multiple ecosystem services. We refer to the rehabilitation of abandoned agricultural lands in Ecuador including two types of both afforestation and pasture rehabilitation, together with a succession option. Our results show that high compositional landscape diversity supports multiple ecosystem services (multifunction effect). This implicitly provides a buffer against uncertainty. Our work shows that active integration of uncertainty is only important when optimizing single or highly correlated ecosystem services and that the multifunction effect on landscape diversity is stronger than the uncertainty effect. This is an important insight to support a land-use planning based on ecosystem services.
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Keywords: |
ecosystem services |
South Ecuador |
sustainable land use |
land use modeling |
restoration |
Timbe, E.; Windhorst, D.; Celleri, R.; Timbe, L.; Crespo, P.; Frede, H.; Feyen, J. & Breuer, L. (2015): Sampling frequency trade-offs in the assessment of mean transit times of tropical montane catchment waters under semi-steady-state conditions. Hydrology and Earth System Sciences 19(3), 1153-1168.
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DOI: 10.5194/hess-19-1153-2015
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Abstract:
Abstract:
Precipitation event samples and weekly based water samples from streams and soils were collected in a tropical montane cloud forest catchment for 2 years and analyzed for stable water isotopes in order to understand the effect of sampling frequency in the performance of three lumped-parameter distribution functions (exponential-piston flow, linear-piston flow and gamma) which were used to estimate mean transit times of waters. Precipitation data, used as input function for the models, were aggregated to daily, weekly, bi-weekly, monthly and bi-monthly sampling resolutions, while analyzed frequencies for outflows went from weekly to bi-monthly. By using different scenarios involving diverse sampling frequencies, this study reveals that the effect of lowering the sampling frequency depends on the water type. For soil waters, with transit times on the order of few weeks, there was a clear trend of over predictions.
In contrast, the trend for stream waters, which have a more damped isotopic signal and mean transit times on the order of 2 to 4 years, was less clear and showed a dependence on the type of model used. The trade-off to coarse data resolutions could potentially lead to misleading conclusions on how water actually moves through the catchment, notwithstanding that these predictions could reach better fitting efficiencies, fewer uncertainties, errors and biases. For both water types an optimal sampling frequency seems to be 1 or at most 2
weeks. The results of our analyses provide information for the planning of future fieldwork in similar Andean or other catchments.
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Keywords: |
hydrology |
isotope tracers |
Exbrayat, J.F.; Buytaert, W.; Timbe, E.; Windhorst, D. & Breuer, L. (2014): Addressing sources of uncertainty in runoff projections for a data scarce catchment in the Ecuadorian Andes. Climatic Change --(--), 1-15.
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DOI: 10.1007/s10584-014-1160-x
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Abstract:
Abstract:
Future climate projections from general circulation models (GCMs) predict an
acceleration of the global hydrological cycle throughout the 21st century in response to human-induced rise in temperatures. However, projections of GCMs are too coarse in resolution to be used in local studies of climate change impacts. To cope with this problem, downscaling methods have been developed that transform climate projections into high resolution datasets to drive impact models such as rainfall-runoff models. Generally, the range of changes simulated by different GCMs is considered to be the major source of variability in the results of such studies. However, the cascade of uncertainty in runoff projections is further elongated by differences between impact models, especially where robust calibration is hampered by the scarcity of data.
Here, we address the relative importance of these different sources of uncertainty in a poorly monitored headwater catchment of the Ecuadorian Andes. Therefore, we force 7 hydrological models with downscaled outputs of 8 GCMs driven by the A1B and A2 emission scenarios over the 21st century. Results indicate a likely increase in annual runoff by 2100 with a large variability between the different combinations of a climate model with a hydrological
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Keywords: |
climate change |
Uncertainty analysis |
hydrological catchment model |
Windhorst, D.; Kraft, P.; Timbe, E.; Frede, H. & Breuer, L. (2014): Stable water isotope tracing through hydrological models for disentangling runoff generation processes at the hillslope scale. Hydrol. Earth Syst. Sci. 18(10), 4113-4127.
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DOI: 10.5194/hess-18-4113-2014
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Abstract:
Abstract:
Hillslopes are the dominant landscape components
where incoming precipitation becomes groundwater, streamflow
or atmospheric water vapor. However, directly observing
flux partitioning in the soil is almost impossible. Hydrological
hillslope models are therefore being used to investigate
the processes involved. Here we report on a modeling
experiment using the Catchment Modeling Framework
(CMF) where measured stable water isotopes in vertical
soil profiles along a tropical mountainous grassland hillslope
transect are traced through the model to resolve potential
mixing processes. CMF simulates advective transport of
stable water isotopes 18O and 2H based on the Richards equation
within a fully distributed 2-D representation of the hillslope.
The model successfully replicates the observed temporal
pattern of soil water isotope profiles (R2 0.84 and Nash–
Sutcliffe efficiency (NSE) 0.42). Predicted flows are in good
agreement with previous studies. We highlight the importance
of groundwater recharge and shallow lateral subsurface
flow, accounting for 50 and 16% of the total flow leaving the
system, respectively. Surface runoff is negligible despite the
steep slopes in the Ecuadorian study region.
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Keywords: |
isotopes |
isotope tracers |
hydrological catchment model |
Knoke, T.; Bendix, J.; Pohle, P.; Hamer, U.; Hildebrandt, P.; Roos, K.; Gerique, A.; Lopez Sandoval, M.F.; Breuer, L.; Tischer, A.; Silva, B.; Calvas, B.; Aguirre, N.; Castro, L.M.; Windhorst, D.; Weber, M.; Stimm, B.; Günter, S.; Palomeque, X.; Mora, J.; Mosandl, R. & Beck, E. (2014): Afforestation or intense pasturing improve the ecological and economic value of abandoned tropical farmlands. Nature Communications 5:5612, 1-50.
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DOI: 10.1038/ncomms6612
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Abstract:
Abstract:
Increasing demands for livelihood resources in tropical rural areas have led to progressive
clearing of biodiverse natural forests. Restoration of abandoned farmlands could counter
this process. However, as aims and modes of restoration differ in their ecological and
socio-economic value, the assessment of achievable ecosystem functions and bene?ts
requires holistic investigation. Here we combine the results from multidisciplinary research
for a unique assessment based on a normalization of 23 ecological, economic and social
indicators for four restoration options in the tropical Andes of Ecuador. A comparison of the
outcomes among afforestation with native alder or exotic pine, pasture restoration with either
low-input or intense management and the abandoned status quo shows that both variants of
afforestation and intense pasture use improve the ecological value, but low-input pasture
does not. Economic indicators favour either afforestation or intense pasturing. Both Mestizo
and indigenous Saraguro settlers are more inclined to opt for afforestation.
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Keywords: |
sustainable land-use |
Iniguez, C.; Leiva Calderón, A.; Breuer, L.; Frede, H. & Hampel, H. (2014): Deforestation and benthic indicators: How much vegetation cover is needed to sustain healthy Andean streams? . PLoS ONE 9(8), e105869.
Timbe, E.; Windhorst, D.; Crespo, P.; Frede, H.; Feyen, J. & Breuer, L. (2014): Understanding uncertainties when inferring mean transit times of water trough tracer-based lumped-parameter models in Andean tropical montane cloud forest catchments. Hydrology and Earth System Sciences 18(4), 1503-1523.
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DOI: 10.5194/hess-18-1503-2014
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Abstract:
Abstract:
Weekly samples from surface waters, springs, soil water and rainfall were collected in a 76.9 km² mountain rain forest catchment and its tributaries in southern Ecuador.Time series of the stable water isotopes (oxygen-18 and deuterium) were used to calculate mean transit times (MTTs) and the transit time distribution functions (TTDs) solving the convolution method for seven lumped-parameter models. For each model setup, the generalized likelihood uncertainty estimation (GLUE) methodology was applied to find the best predictions, behavioral solutions and parameter identifiability. For the study basin, TTDs based on model types such as the linear–piston flow for soil waters and the exponential–piston flow for surface waters and springs performed better than more versatile equations such as the gamma and the two parallel linear reservoirs. Notwithstanding both approaches yielded a better goodness of fit for most sites, but with considerable larger uncertainty shown by GLUE. Among the tested models, corresponding results were obtained for soil waters with short MTTs (ranging from 2 to 9 weeks). For waters with longer MTTs differences were found, suggesting that for those cases the MTT should be based at least on an intercomparison of several models. Under dominant baseflow conditions long MTTs for stream water ? 2 yr were detected, a phenomenon also observed for shallow springs. Short MTTs for water in the top soil layer indicate a rapid exchange of surface waters with deeper soil horizons. Differences in travel times between soils suggest that there is evidence of a land use effect on flow generation.
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Keywords: |
mean transit time |
transit time distribution function |
isotope tracers |
catchment hydrology |
Uncertainty analysis |
Lumped-models |
Windhorst, D.; Waltz, T.; Timbe, E.; Frede, H. & Breuer, L. (2013): Impact of elevation and weather patterns on the isotopic composition of precipitation in a tropical montane rainforest. Hydrol. Earth Syst. Sci. 177, 409-419.
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DOI: 10.5194/hess-17-409-2013
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Abstract:
Abstract:
This study presents the spatial and temporal variability of ?18O and ?2H isotope signatures in precipitation of a south Ecuadorian montane cloud forest catchment (San Francisco catchment). From 2 September to 25 December 2010, event sampling of open rainfall was conducted along an altitudinal transect (1800 to 2800 m a.s.l.) to investigate possible effects of altitude and weather conditions on the isotope signature.
The spatial variability is mainly affected by the altitude effect. The event based ?18O altitude effect for the study area averages ?0.22‰ × 100 m?1 (?2H: ?1.12‰ × 100 m?1). The temporal variability is mostly controlled by prevailing air masses. Precipitation during the times of prevailing southeasterly trade winds is significantly enriched in heavy isotopes compared to precipitation during other weather conditions. In the study area, weather during austral winter is commonly controlled by southeasterly trade winds. Since the Amazon Basin contributes large amounts of recycled moisture to these air masses, trade wind-related precipitation is enriched in heavy isotopes. We used deuterium excess to further evaluate the contribution of recycled moisture to precipitation. Analogously to the ?18O and ?2H values, deuterium excess is significantly higher in trade wind-related precipitation. Consequently, it is assumed that evaporated moisture is responsible for high concentrations of heavy isotopes during austral winter.
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Keywords: |
climate |
rainwater chemistry |
hydrological processes |
isotopes |
Breuer, L. (2012): Simulating ecosystem functioning of tropical mountainous cloud forests in southern Ecuador. Ecological Modelling 239, 1-2.
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DOI: 10.1016/j.ecolmodel.2012.05.027
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Abstract:
Abstract:
Tropical mountainous cloud forests belong to the most diverse ecosystems on earth. If you ask scientists which features characterize these ecosystems, then the answers are as diverse as is the flora and fauna within them: persistent cloud cover, reduced solar radiation due to cloud cover, distinctly structured vegetation forms, suppressed evapotranspiration as a consequence of high relative humidity, stripping of clouds by tree canopies and resulting large amount of throughfall, reduced canopy heights, high rainfall rates, gnarled tree trunks at increasing altitudes, substantial epiphyte biomass, moss-covered stems, organic rich and typically wet soils, and – last but not least – extremely high biodiversity with a paramount endemism (Bruijnzeel et al., 2011).
Crespo, P.; Bücker, A.; Feyen, J.; Frede, H. & Breuer, L. (2012): Preliminary evaluation of the runoff processes in a remote montane cloud forest basin using Mixing Model Analysis and Mean Transit Time. Hydrological Processes -, -.
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DOI: 10.1002/hyp.8382
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Abstract:
Abstract:
In this study, the Mean Transit Time and Mixing Model Analysis methods are combined to unravel the runoff generation process of the San Francisco River basin (73.5 km2) situated on the Amazonian side of the Cordillera Real in the southernmost Andes of Ecuador. The montane basin is covered with cloud forest, sub-páramo, pasture and ferns. Nested sampling was applied for the collection of streamwater samples and discharge measurements in the main tributaries and outlet of the basin, and for the collection of soil and rock water samples. Weekly to biweekly water grab samples were taken at all stations in the period April 2007–November 2008. Hydrometric data, Mean Transit Time and Mixing Model Analysis allowed preliminary evaluation of the processes controlling the runoff in the San Francisco River basin. Results suggest that flow during dry conditions mainly consists of lateral flow through the C-horizon and cracks in the top weathered bedrock layer, and that all subcatchments have an important contribution of this deep water to runoff, no matter whether pristine or deforested. During normal to low precipitation intensities, when antecedent soil moisture conditions favour water infiltration, vertical flow paths to deeper soil horizons with subsequent lateral subsurface flow contribute most to streamflow. Under wet conditions in forested catchments, streamflow is controlled by near surface lateral flow through the organic horizon. Exceptionally, saturation excess overland flow occurs. By absence of the litter layer in pasture, streamflow under wet conditions originates from the A horizon, and overland flow. Copyright © 2011 John Wiley & Sons, Ltd.
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Keywords: |
Ecuador |
mixing model analysis |
mean transit time |
tracer |
hydrological processes |
cloud forest |
Plesca, I.; Timbe, E.; Exbrayat, J.F.; Windhorst, D.; Kraft, P.; Crespo, P.; Vaché, K.; Frede, H. & Breuer, L. (2011): Model intercomparison to explore catchment functioning: Results from a remote montane tropical rainforest. Ecological Modelling in press, 1-11.
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DOI: 10.1016/j.ecolmodel.2011.05.005
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Abstract:
Abstract:
Catchment-scale runoff generation involves a complex interaction of physical and chemical processes operating over a wide distribution of spatial and temporal scales. Understanding runoff generation is challenged by this inherent complexity ? the more uncertain step of predicting the hydrologic response of catchments is that much more challenging. Many different hypotheses have been implemented in hydrological models to capture runoff generation processes and provide hydrologic predictions. These concepts have been developed based on extended field observations. Here we propose inferring water flux understanding and catchment exploring through the application of a variety of available hydrological models as a mechanism to build upon and extend models that have been developed to capture particular hydrological processes. We view this ensemble modeling strategy as particularly appropriate in ungauged catchments. The study is carried out in a tropical montane rainforest catchment in Southern Ecuador. The catchment is 75 km2 and is covered by forest in the south, while the northern slopes have been partly deforested for grazing. Annual rainfall is highly variable, reaching up to 5700 mm per year in the upper parts of the catchment. To explore the dominating runoff processes, an ensemble of 6 hydrological models with different structures applied over different levels of both spatial and temporal detail was developed. The ensemble includes spatially lumped (HBV-light), semi-distributed (HEC-HMS, CHIMP, SWAT, LASCAM) and a fully distributed model (HBV-N-D). The hydro-statistical toolkit WETSPRO was used to characterize simulated and observed hydrographs. Estimated baseflow indices, flow minima and maxima, flow duration curves and cumulative errors were generated and compared among the ensemble of models. This process facilitated the exploration of processes controlling runoff generation, enabled an evaluation of the applicability of the screened models to tropical montane rainforests, and provided the capacity to evaluate and explain where different models failed.
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Keywords: |
Ecuador |
tropical montane forest |
model evaluation |
flow duration |
rainfall-runoff models |
flow minima and maxima |
Crespo, P.; Feyen, J.; Buytaert, W.; Bücker, A.; Breuer, L.; Frede, H. & Ramirez, M. (2011): Identifying controls of the rainfall?runoff response of small catchments in the tropical Andes (Ecuador). Journal of Hydrology 407, 164?174.
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DOI: 10.1016/j.jhydrol.2011.07.021
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Abstract:
Abstract:
Tropical mountain regions are characterized by strong spatial climate gradients which together with the limited amount of data and knowledge of the underlying processes hinder the management of the water resources. Especially for regional-scale prediction it is important to identify the dominant factors controlling the rainfall?runoff response and link those to known spatial patterns of climate, soils, and vegetation. This study analyzes the rainfall?runoff relation of 13 intensively monitored micro-catchments in the Andes of southern Ecuador. The results of this study show that streamflow in the southern cordillera of the Ecuadorian Andes, above 2500 m a.s.l., primarily consists of subsurface flow. The yearly amount of streamflow is controlled by the annual rainfall depth, whereas the temporal distribution is mainly governed by the lateral saturated hydraulic conductivity, the soil water retention and the antecedent soil moisture content. Anthropogenic effects were found insignificant, with the exception in one of the studied micro-catchment. Effect of land use changes in most of the micro-catchments did not reflect in the shape of the flow duration curve because either the spatial extent of human impact was small and/or the overall basin slope was less than 20%.
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Keywords: |
Ecuador |
hydrologic response |
basin properties |
streamflow components |
principal component analysis |
andean mountain range |
Bücker, A.; Crespo, P.; Frede, H. & Breuer, L. (2011): Solute behaviour and export rates in neotropical montane catchments under different land-uses. Journal of Tropical Ecology 27, 305?317.
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DOI: 10.1017/S0266467410000787
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Abstract:
Abstract:
To improve our knowledge of the influence of land-use on solute behaviour and export rates in neotropical
montane catchments we investigated total organic carbon (TOC), Ca, Mg, Na, K, NO3 and SO4 concentrations during April 2007?May 2008 at different flow conditions and over time in six forested and pasture-dominated headwaters (0.7?76 km2) in Ecuador. NO3 and SO4 concentrations decreased during the study period, with a continual decrease in NO3 and an abrupt decrease in February 2008 for SO4. We attribute this to changing weather regimes connected to a weakening La Nina event. Stream Na concentration decreased in all catchments, and Mg and Ca concentration decreased in all but the forested catchments during storm flow. Under all land-uses TOC increased at high flows. The differences in solute behaviour during storm flow might be attributed to largely shallow subsurface and surface flow paths in pasture streams on the one hand, and a predominant origin of storm flow from the organic layer in the forested streams on the other hand. Nutrient export rates in the forested streams were comparable to the values found in literature for tropical streams. They amounted to 6?8 kg ha−1 y−1 for Ca, 7?8 kg ha−1 y−1 for K, 4?5 kg ha−1 y−1 for Mg, 11?14 kg ha−1 y−1 for Na, 19?22 kg ha−1 y−1 for NO3 (i.e. 4.3?5.0 kg ha−1 y−1 NO3-N) and 17 kg ha−1 y−1 for SO4. Our data contradict the assumption that nutrient export increases with the loss of forest cover. For NO3 we observed a positive correlation of export value and percentage forest cover.
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Keywords: |
Ecuador |
nitrate |
nutrient export |
rain forest |
tropical streams |
Bücker, A.; Sondermann, M.; Frede, H. & Breuer, L. (2010): The influence of land-use on macroinvertebrate communities in montane tropical streams - a case study from Ecuador. Fundamental and Applied Limnology 177, 267-282.
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DOI: 10.1127/1863-9135/2010/0177-0267
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Abstract:
Abstract:
Despite the importance of tropical montane cloud forest streams, studies investigating aquatic communities
in these regions are rare and knowledge on the driving factors of community structure is missing. The objectives
of this study therefore were to understand how land-use infl uences habitat structure and macroinvertebrate
communities in cloud forest streams of southern Ecuador. We evaluated these relationships in headwater streams
with variable land cover, using multivariate statistics to identify relationships between key habitat variables and
assemblage structure, and to resolve differences in composition among sites. Results show that shading intensity,
substrate type and pH were the environmental parameters most closely related to variation in community composition
observed among sites. In addition, macroinvertebrate density and partly diversity was lower in forested sites,
possibly because the pH in forested streams lowered to almost 5 during spates. Standard bioindicator metrics were
unable to detect the changes in assemblage structure between disturbed and forested streams. In general, our results
indicate that tropical montane headwater streams are complex and heterogeneous ecosystems with low invertebrate
densities. We also found that some amount of disturbance, i.e. patchy deforestation, can lead at least initially to an
increase in macroinvertebrate taxa richness of these streams.
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Keywords: |
cloud forest |
acroinvertebrates |
land-use |
indicators |
neotropics |
canonical correspondence analysis (CCA) |
non-metric mutidimensional scaling (NMDS) |
Bücker, A.; Crespo, P.; Frede, H.; Vaché, K.; Cisneros, F. & Breuer, L. (2010): Identifying Controls on Water Chemistry of Tropical Cloud Forest Catchments: Combining Descriptive Approaches and Multivariate Analysis. Aquatic Geochemistry 16(1), 127-149.
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DOI: 10.1007/s10498-009-9073-4
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Abstract:
Abstract:
Abstract We investigated controls on the water chemistry of a South Ecuadorian cloud
forest catchment which is partly pristine, and partly converted to extensive pasture. From
April 2007 to May 2008 water samples were taken weekly to biweekly at nine different
subcatchments, and were screened for differences in electric conductivity, pH, anion, as
well as element composition. A principal component analysis was conducted to reduce
dimensionality of the data set and define major factors explaining variation in the data.
Three main factors were isolated by a subset of 10 elements (Ca2?, Ce, Gd, K?, Mg2?,
Na?, Nd, Rb, Sr, Y), explaining around 90% of the data variation. Land-use was the major
factor controlling and changing water chemistry of the subcatchments. A second factor was
associated with the concentration of rare earth elements in water, presumably highlighting
other anthropogenic influences such as gravel excavation or road construction. Around
12% of the variation was explained by the third component, which was defined by the
occurrence of Rb and K and represents the influence of vegetation dynamics on element
accumulation and wash-out. Comparison of base- and fast flow concentrations led to the
assumption that a significant portion of soil water from around 30 cm depth contributes to
storm flow, as revealed by increased rare earth element concentrations in fast flow samples.
Our findings demonstrate the utility of multi-tracer principal component analysis to study
tropical headwater streams, and emphasize the need for effective land management in
cloud forest catchments.
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Keywords: |
Ecuador |
water quality |
land-use change |
rare earth elements |
principal component analysis |
tropical cloud forest |