TY - JOUR A1 - Barthold, Frauke Katrin A1 - Turner, Benjamin L. A1 - Elsenbeer, Helmut A1 - Zimmermann, Alexander T1 - A hydrochemical approach to quantify the role of return flow in a surface flow-dominated catchment JF - Hydrological processes N2 - Stormflow generation in headwater catchments dominated by subsurface flow has been studied extensively, yet catchments dominated by surface flow have received less attention. We addressed this by testing whether stormflow chemistry is controlled by either (a) the event-water signature of overland flow, or (b) the pre-event water signature of return flow. We used a high-resolution hydrochemical data set of stormflow and end-members of multiple storms in an end-member mixing analysis to determine the number of end-members needed to explain stormflow, characterize and identify potential end-members, calculate their contributions to stormflow, and develop a conceptual model of stormflow. The arrangement and relative positioning of end-members in stormflow mixing space suggest that saturation excess overland flow (26-48%) and return flow from two different subsurface storage pools (17-53%) are both similarly important for stormflow. These results suggest that pipes and fractures are important flow paths to rapidly release stored water and highlight the value of within-event resolution hydrochemical data to assess the full range and dynamics of flow paths. KW - EMMA KW - hydrochemistry KW - overland flow KW - return flow KW - stormflow generation Y1 - 2016 U6 - https://doi.org/10.1002/hyp.11083 SN - 0885-6087 SN - 1099-1085 VL - 31 IS - 5 SP - 1018 EP - 1033 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Schmidt, Lena Katharina A1 - Zimmermann, Alexander A1 - Elsenbeer, Helmut T1 - Ant mounds as a source of sediment in a tropical rainforest? JF - Hydrological processes N2 - In Lutzito catchment on Barro Colorado Island, Panama, extraordinarily high suspended-sediment yields of 1-2Mgha-1year-1 were generated despite the dense forest cover coinciding with erosion-resistant soils. We hypothesized that ant mounding activity is an important zoogeomorphological mechanism in this area, providing relevant quantities of easily transportable material at the soil surface. To test this hypothesis, all ant mound material was collected collected for dry mass determination from thirty 4m2 plots installed in the study area every 1-3days during the 39-day sampling period. Additionally, three ground-nesting ant species responsible for mounds in the study area, Ectatomma ruidum, Trachymyrmex cornetzi and Strumigenys marginiventris, were identified. On the basis of the total of 1.38kg of material collected in the wet season of 2011, the estimate for the whole 8months wet season amounts to 725kgha-1. As this value is in the same order of magnitude as sediment output, it shows that ants may act as important ecosystem engineers and contribute to sediment production here by providing large quantities of fine-grained, readily erodible material at the soil surface for subsequent transport to the streambed. Copyright (c) 2014 John Wiley & Sons, Ltd. KW - ant mounds KW - soil erosion KW - sediment output KW - zoogeomorphology Y1 - 2014 U6 - https://doi.org/10.1002/hyp.10222 SN - 0885-6087 SN - 1099-1085 VL - 28 IS - 13 SP - 4156 EP - 4160 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Zimmermann, B. A1 - Zimmermann, Alexander A1 - Scheckenbach, H. L. A1 - Schmid, T. A1 - Hall, Jefferson. S. A1 - van Breugel, Michiel T1 - Changes in rainfall interception along a secondary forest succession gradient in lowland Panama JF - Hydrology and earth system sciences : HESS N2 - Secondary forests are rapidly expanding in tropical regions. Yet, despite the importance of understanding the hydrological consequences of land-cover dynamics, the relationship between forest succession and canopy interception is poorly understood. This lack of knowledge is unfortunate because rainfall interception plays an important role in regional water cycles and needs to be quantified for many modeling purposes. To help close this knowledge gap, we designed a throughfall monitoring study along a secondary succession gradient in a tropical forest region of Panama. The investigated gradient comprised 20 forest patches 3 to 130 yr old. We sampled each patch with a minimum of 20 funnel-type throughfall collectors over a continuous 2month period that had nearly 900 mm of rain. During the same period, we acquired forest inventory data and derived several forest structural attributes. We then applied simple and multiple regression models (Bayesian model averaging, BMA) and identified those vegetation parameters that had the strongest influence on the variation of canopy interception. Our analyses yielded three main findings. First, canopy interception changed rapidly during forest succession. After only a decade, throughfall volumes approached levels that are typical for mature forests. Second, a parsimonious (simple linear regression) model based on the ratio of the basal area of small stems to the total basal area outperformed more complex multivariate models (BMA approach). Third, based on complementary forest inventory data, we show that the influence of young secondary forests on interception in realworld fragmented landscapes might be detectable only in regions with a substantial fraction of young forests. Our re-sults suggest that where entire catchments undergo forest regrowth, initial stages of succession may be associated with a substantial decrease of streamflow generation. Our results further highlight the need to study hydrological processes in all forest succession stages, including early ones. Y1 - 2013 U6 - https://doi.org/10.5194/hess-17-4659-2013 SN - 1027-5606 SN - 1607-7938 VL - 17 IS - 11 SP - 4659 EP - 4670 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Zimmermann, Beate A1 - Zimmermann, Alexander A1 - Turner, Benjamin L. A1 - Francke, Till A1 - Elsenbeer, Helmut T1 - Connectivity of overland flow by drainage network expansion in a rain forest catchment JF - Water resources research N2 - Soils in various places of the Panama Canal Watershed feature a low saturated hydraulic conductivity (K-s) at shallow depth, which promotes overland-flow generation and associated flashy catchment responses. In undisturbed forests of these areas, overland flow is concentrated in flow lines that extend the channel network and provide hydrological connectivity between hillslopes and streams. To understand the dynamics of overland-flow connectivity, as well as the impact of connectivity on catchment response, we studied an undisturbed headwater catchment by monitoring overland-flow occurrence in all flow lines and discharge, suspended sediment, and total phosphorus at the catchment outlet. We find that connectivity is strongly influenced by seasonal variation in antecedent wetness and can develop even under light rainfall conditions. Connectivity increased rapidly as rainfall frequency increased, eventually leading to full connectivity and surficial drainage of entire hillslopes. Connectivity was nonlinearly related to catchment response. However, additional information on factors such as overland-flow volume would be required to constrain relationships between connectivity, stormflow, and the export of suspended sediment and phosphorus. The effort to monitor those factors would be substantial, so we advocate applying the established links between rain event characteristics, drainage network expansion by flow lines, and catchment response for predictive modeling and catchment classification in forests of the Panama Canal Watershed and in similar regions elsewhere. KW - connectivity KW - overland flow KW - stormflow KW - suspended sediment KW - phosphorus KW - drainage network expansion Y1 - 2014 U6 - https://doi.org/10.1002/2012WR012660 SN - 0043-1397 SN - 1944-7973 VL - 50 IS - 2 SP - 1457 EP - 1473 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Voss, Sebastian A1 - Zimmermann, Beate A1 - Zimmermann, Alexander T1 - Detecting spatial structures in throughfall data: The effect of extent, sample size, sampling design, and variogram estimation method JF - Journal of hydrology N2 - In the last decades, an increasing number of studies analyzed spatial patterns in throughfall by means of variograms. The estimation of the variogram from sample data requires an appropriate sampling scheme: most importantly, a large sample and a layout of sampling locations that often has to serve both variogram estimation and geostatistical prediction. While some recommendations on these aspects exist, they focus on Gaussian data and high ratios of the variogram range to the extent of the study area. However, many hydrological data, and throughfall data in particular, do not follow a Gaussian distribution. In this study, we examined the effect of extent, sample size, sampling design, and calculation method on variogram estimation of throughfall data. For our investigation, we first generated non Gaussian random fields based on throughfall data with large outliers. Subsequently, we sampled the fields with three extents (plots with edge lengths of 25 m, 50 m, and 100 m), four common sampling designs (two grid-based layouts, transect and random sampling) and five sample sizes (50, 100, 150, 200, 400). We then estimated the variogram parameters by method-of-moments (non-robust and robust estimators) and residual maximum likelihood. Our key findings are threefold. First, the choice of the extent has a substantial influence on the estimation of the variogram. A comparatively small ratio of the extent to the correlation length is beneficial for variogram estimation. Second, a combination of a minimum sample size of 150, a design that ensures the sampling of small distances and variogram estimation by residual maximum likelihood offers a good compromise between accuracy and efficiency. Third, studies relying on method-of-moments based variogram estimation may have to employ at least 200 sampling points for reliable variogram estimates. These suggested sample sizes exceed the number recommended by studies dealing with Gaussian data by up to 100 %. Given that most previous through fall studies relied on method-of-moments variogram estimation and sample sizes <<200, currently available data are prone to large uncertainties. (C) 2016 Elsevier B.V. All rights reserved. KW - Throughfall KW - Geostatistics KW - Sampling KW - variogram KW - Residual maximum likelihood Y1 - 2016 U6 - https://doi.org/10.1016/j.jhydrol.2016.06.042 SN - 0022-1694 SN - 1879-2707 VL - 540 SP - 527 EP - 537 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Germer, Sonja A1 - Zimmermann, Alexander A1 - Neill, Christopher A1 - Krusche, Alex V. A1 - Elsenbeer, Helmut T1 - Disproportionate single-species contribution to canopy-soil nutrient flux in an Amazonian rainforest JF - Forest ecology and management N2 - Rainfall, throughfall and stemflow were monitored on an event basis in an undisturbed open tropical rainforest with a large number of palm trees located in the southwestern Amazon basin of Brazil. Stemflow samples were collected from 24 trees with a diameter at breast height (DBH) > 5 cm, as well as eight young and four full-grown babassu palms (Attalea speciosa Mart.) for 5 weeks during the peak of the wet season. We calculated rainfall, throughfall and stemflow concentrations and fluxes of Na+, K+, Ca2+, Mg2+,, Cl-, SO42-, NO3- and H+ and stemflow volume-weighted mean concentrations and fluxes for three size classes of broadleaf trees and three size classes of palms. The concentrations of most solutes were higher in stemflow than in rainfall and increased with increasing tree and palm size. Concentration enrichments from rainfall to stemflow and throughfall were particularly high (81-fold) for NO3-. Stemflow fluxes of NO3- and H+ exceeded throughfall fluxes but stemflow fluxes of other solutes were less than throughfall fluxes. Stemflow solute fluxes to the forest soil were dominated by fluxes on babassu palms, which represented only 4% of total stem number and 10% of total basal area. For NO3-, stemflow contributed 51% of the total mass of nitrogen delivered to the forest floor (stemflow + throughfall) and represented more than a 2000-fold increase in NO3- flux compared what would have been delivered by rainfall alone on the equivalent area. Because these highly localized fluxes of both water and NO3- persist in time and space, they have the potential to affect patterns of soil moisture, microbial populations and other features of soil biogeochemistry conducive to the creation of hotspots for nitrogen leaching and denitrification, which could amount to an important fraction of total ecosystem fluxes. Because these hotspots occur over very small areas, they have likely gone undetected in previous studies and need to be considered as an important feature of the biogeochemistry of palm-rich tropical forest. KW - Stemflow KW - Throughfall KW - DBH KW - Open tropical rain forest KW - Babassu palm (Attalea speciosa Mart. synonym: Orbignya phalerata Mart.) KW - Amazonia Y1 - 2012 U6 - https://doi.org/10.1016/j.foreco.2011.11.041 SN - 0378-1127 VL - 267 IS - 2 SP - 40 EP - 49 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Fathizadeh, O. A1 - Hosseini, Seyed Mehrdad A1 - Zimmermann, Alexander A1 - Keim, R. F. A1 - Boloorani, A. Darvishi T1 - Estimating linkages between forest structural variables and rainfall interception parameters in semi-arid deciduous oak forest stands JF - The science of the total environment : an international journal for scientific research into the environment and its relationship with man N2 - An understanding of the relationship between canopy structure and the water balance is needed for predicting how forest structure changes affect rainfall partitioning and, consequently, water resources. The objective of this study was to predict rainfall interception (I) and canopy storage capacity (S) using canopy structure variables and to investigate how seasonal changes influence their relationship. The study was conducted in twelve 50 m x 50 m plots in the Zagros forest in the western Iranian state of Ilam, protected forests of Dalab region. Average cumulative I was 84.2mm, accounting for 10.2% of cumulative gross precipitation (GP) over a 1-year period. Using a regression based method, S averaged similar to 1 mm and 0.1 mm in the leafed and leafless periods, respectively. There were no relationships between tree density and I: GP or S, but I: GP and S increased with leaf area index, canopy cover fraction, basal area, tree height, and diameter at breast height in the leafed period. In addition, wood area index and canopy cover fraction were related to I: GP or S in the leafless period. (C) 2017 Elsevier B.V. All rights reserved. KW - Canopy storage capacity KW - Canopy structure KW - Rainfall interception KW - Quercus brantii KW - Zagros forests Y1 - 2017 U6 - https://doi.org/10.1016/j.scitotenv.2017.05.233 SN - 0048-9697 SN - 1879-1026 VL - 601 SP - 1824 EP - 1837 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Zimmermann, Alexander A1 - Voss, Sebastian A1 - Metzger, Johanna Clara A1 - Hildebrandt, Anke A1 - Zimmermann, Beate T1 - estimating mean throughfall JF - Journal of hydrology N2 - The selection of an appropriate spatial extent of a sampling plot is one among several important decisions involved in planning a throughfall sampling scheme. In fact, the choice of the extent may determine whether or not a study can adequately characterize the hydrological fluxes of the studied ecosystem. Previous attempts to optimize throughfall sampling schemes focused on the selection of an appropriate sample size, support, and sampling design, while comparatively little attention has been given to the role of the extent. In this contribution, we investigated the influence of the extent on the representativeness of mean throughfall estimates for three forest ecosystems of varying stand structure. Our study is based on virtual sampling of simulated throughfall fields. We derived these fields from throughfall data sampled in a simply structured forest (young tropical forest) and two heterogeneous forests (old tropical forest, unmanaged mixed European beech forest). We then sampled the simulated throughfall fields with three common extents and various sample sizes for a range of events and for accumulated data. Our findings suggest that the size of the study area should be carefully adapted to the complexity of the system under study and to the required temporal resolution of the throughfall data (i.e. event-based versus accumulated). Generally, event-based sampling in complex structured forests (conditions that favor comparatively long autocorrelations in throughfall) requires the largest extents. For event-based sampling, the choice of an appropriate extent can be as important as using an adequate sample size. (C) 2016 Elsevier B.V. All rights reserved. KW - Throughfall KW - Sampling KW - Extent KW - Hydrological monitoring KW - Tropical forest KW - European beech forest Y1 - 2016 U6 - https://doi.org/10.1016/j.jhydrol.2016.09.047 SN - 0022-1694 SN - 1879-2707 VL - 542 SP - 781 EP - 789 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Zimmermann, Alexander A1 - Francke, Till A1 - Elsenbeer, Helmut T1 - Forests and erosion: Insights from a study of suspended-sediment dynamics in an overland flow-prone rainforest catchment JF - Journal of hydrology N2 - Forests seem to represent low-erosion systems, according to most, but not all, studies of suspended-sediment yield. We surmised that this impression reflects an accidental bias in the selection of monitoring sites towards those with prevailing vertical hydrological flowpaths, rather than a tight causal link between vegetation cover and erosion alone. To evaluate this conjecture, we monitored, over a 2-year period, a 3.3 ha old-growth rainforest catchment prone to frequent and widespread overland flow. We sampled stream flow at two and overland flow at three sites in a nested arrangement on a within-event basis, and monitored the spatial and temporal frequency of overland flow. Suspended-sediment concentrations were modeled with Random Forest and Quantile Regression Forest to be able to estimate the annual yields for the 2 years, which amounted to 1 t ha(-1) and 2 t ha(-1) in a year with below-average and with average precipitation, respectively. These estimates place our monitoring site near the high end of reported suspended-sediment yields and lend credence to the notion that low yields reflect primarily the dominance of vertical flowpaths and not necessarily and exclusively the kind of vegetative cover. Undisturbed forest and surface erosion are certainly no contradiction in terms even in the absence of mass movements. KW - Rainforest KW - Overland flow KW - Erosion KW - Suspended-sediment yield KW - Quantile Regression Forest model KW - Panama Canal watershed Y1 - 2012 U6 - https://doi.org/10.1016/j.jhydrol.2012.01.039 SN - 0022-1694 VL - 428 IS - 7 SP - 170 EP - 181 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Zimmermann, Alexander A1 - Uber, Magdalena A1 - Zimmermann, Beate A1 - Levia, Delphis F. T1 - Predictability of stemflow in a species-rich tropical forest JF - Hydrological processes N2 - Numerous studies investigated the influence of abiotic (meteorological conditions) and biotic factors (tree characteristics) on stemflow generation. Although these studies identified the variables that influence stemflow volumes in simply structured forests, the combination of tree characteristics that allows a robust prediction of stemflow volumes in species-rich forests is not well known. Many hydrological applications, however, require at least a rough estimate of stemflow volumes based on the characteristics of a forest stand. The need for robust predictions of stemflow motivated us to investigate the relationships between tree characteristics and stemflow volumes in a species-rich tropical forest located in central Panama. Based on a sampling setup consisting of ten rainfall collectors, 300 throughfall samplers and 60 stemflow collectors and cumulated data comprising 26 rain events, we derive three main findings. Firstly, stemflow represents a minor hydrological component in the studied 1-ha forest patch (1.0% of cumulated rainfall). Secondly, in the studied species-rich forest, single tree characteristics are only weakly related to stemflow volumes. The influence of multiple tree parameters (e.g. crown diameter, presence of large epiphytes and inclination of branches) and the dependencies among these parameters require a multivariate approach to understand the generation of stemflow. Thirdly, predicting stemflow in species-rich forests based on tree parameters is a difficult task. Although our best model can capture the variation in stemflow to some degree, a critical validation reveals that the model cannot provide robust predictions of stemflow. A reanalysis of data from previous studies in species-rich forests corroborates this finding. Based on these results and considering that for most hydrological applications, stemflow is only one parameter among others to estimate, we advocate using the base model, i.e. the mean of the stemflow data, to quantify stemflow volumes for a given study area. Studies in species-rich forests that wish to obtain predictions of stemflow based on tree parameters probably need to conduct a much more extensive sampling than currently implemented by most studies. Copyright (c) 2015 John Wiley & Sons, Ltd. KW - stemflow KW - rainfall partitioning KW - multivariate regression KW - tropical lowland rainforest KW - ecohydrology Y1 - 2015 U6 - https://doi.org/10.1002/hyp.10554 SN - 0885-6087 SN - 1099-1085 VL - 29 IS - 23 SP - 4947 EP - 4956 PB - Wiley-Blackwell CY - Hoboken ER -