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 - Neill, Christopher A1 - Jankowski, KathiJo A1 - Brando, Paulo M. A1 - Coe, Michael T. A1 - Deegan, Linda A. A1 - Macedo, Marcia N. A1 - Riskin, Shelby H. A1 - Porder, Stephen A1 - Elsenbeer, Helmut A1 - Krusche, Alex V. T1 - Surprisingly Modest Water Quality Impacts From Expansion and Intensification of Large-Sscale Commercial Agriculture in the Brazilian Amazon-Cerrado Region JF - Tropical conservation science N2 - Large-scale commercial cropping of soybeans expanded in the tropical Amazon and Cerrado biomes of Brazil after 1990. More recently, cropping intensified from single-cropping of soybeans to double-cropping of soybeans with corn or cotton. Cropland expansion and intensification, and the accompanying use of mineral fertilizers, raise concerns about whether nutrient runoff and impacts to surface waters will be similar to those experienced in commercial cropland regions at temperate latitudes. We quantified water infiltration through soils, water yield, and streamwater chemistry in watersheds draining native tropical forest and single-and double-cropped areas on the level, deep, highly weathered soils where cropland expansion and intensification typically occurs. Although water yield increased four-fold from croplands, streamwater chemistry remained largely unchanged. Soil characteristics exerted important control over the movement of nitrogen (N) and phosphorus (P) into streams. High soil infiltration rates prevented surface erosion and movement of particulate P, while P fixation in surface soils restricted P movement to deeper soil layers. Nitrogen retention in deep soils, likely by anion exchange, also appeared to limit N leaching and export in streamwater from both single-and double-cropped watersheds that received nitrogen fertilizer. These mechanisms led to lower streamwater P and N concentrations and lower watershed N and P export than would be expected, based on studies from temperate croplands with similar cropping and fertilizer application practices. KW - water KW - quality KW - agriculture KW - intensification KW - impact Y1 - 2017 U6 - https://doi.org/10.1177/1940082917720669 SN - 1940-0829 VL - 10 PB - Sage Publ. CY - Thousand Oaks 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 - Messmer, Tobias A1 - Elsenbeer, Helmut A1 - Wilcke, Wolfgang T1 - High exchangeable calcium concentrations in soils on Barro Colorado Island, Panama JF - Geoderma : an international journal of soil science N2 - The soils on four lithologies (basaltic conglomerates, Bohio; Andesite; volcanoclastic sediments with basaltic agglomerates, Caimito volcanic; foraminiferal limestone, Caimito marine) on Barro Colorado Island (BCI have high exchangeable Ca concentrations and cation-exchange capacities (CEC) compared to other tropical soils on similar parent material. In the 0-10 cm layer of 24 mineral soils, pH values ranged from 5.7 (Caimito volcanic and Andesite) to 6.5 (Caimito marine), concentrations of exchangeable Ca from 134 mmol(c) kg(-1) (Caimito volcanic) to 585 mmolc kg-1 (Caimito marine), and cation exchange capacities from 317 mmol(c) kg(-1) (Caimito volcanic) to 933 mmol(c) kg(-1) (Caimito marine). X-ray diffractometry of the fraction <2 mu m revealed that smectites dominated the clay mineral assemblage in soil except on Caimito volcanic, where kaolinite was the dominant clay mineral. Exchangeable Ca concentrations decreased with increasing soil depth except on Caimito marine. The weathering indices Chemical Index of Alteration (CIA), Plagioclase Index of Alteration (PIA) and Weathering Index of Parker (WIP) determined for five soils on all geological formations, suggested that in contrast to expectation the topsoil (0-10 cm) appeared to be the least and the subsoil (50-70 cm) and saprolite (isomorphically weathered rock in the soil matrix) the most weathered. Additionally, the weathering indices indicated depletion of base cations and enrichment of Al-(hydr)oxides throughout the soil profile. Tree species did not have an effect on soil properties. Impeded leaching and the related occurrence of overland flow seem to be important in determining clay mineralogy. Our results suggest that (i) edaphic conditions favor the formation of smectites on most lithologies resulting in high CEC and thus high retention capacity for Ca and (ii) that there is an external source such as dust or sea spray deposition supplying Ca to the soils. KW - Panama KW - Cation-exchange capacity KW - Exchangeable Ca KW - Clay mineralogy KW - Weathering indices Y1 - 2014 U6 - https://doi.org/10.1016/j.geoderma.2013.10.021 SN - 0016-7061 SN - 1872-6259 VL - 217 SP - 212 EP - 224 PB - Elsevier CY - Amsterdam 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 - Aich, Valentin A1 - Zimmermann, Alexander A1 - Elsenbeer, Helmut T1 - Quantification and interpretation of suspended-sediment discharge hysteresis patterns: How much data do we need? JF - Catena : an interdisciplinary journal of soil science, hydrology, geomorphology focusing on geoecology and landscape evolution N2 - Sediment-discharge hysteresis loops are frequently analyzed to facilitate the understanding of sediment transport processes. Hysteresis patterns, however, are often complex and their interpretation can be complicated. Particularly, quantifying hysteresis patterns remains a problematic issue. Moreover, it is currently unknown how much data is required for analyzing sediment-discharge hysteresis loops in a given area. These open questions and challenges motivated us to develop a new method for quantifying suspended-sediment hysteresis. Subsequently, we applied the new hysteresis index to three suspended-sediment and discharge datasets from a small tropical rainforest catchment. The datasets comprised a different number of events and sampling sites. Our analyses show three main findings: (1) datasets restricted to only few events, which is typical for rapid assessment surveys, were always sufficient to identify the dominating hysteresis pattern in our research area. Furthermore, some of these small datasets contained multiple-peak events that allowed identifying intra-event exhaustion effects and hence, limitations in sediment supply. (2) Datasets comprising complete hydrological years were particularly useful for analyzing seasonal dynamics of hysteresis. These analyses revealed an exhaustion of hysteresis on the inter-event scale which also points to a limited sediment supply. (3) Datasets comprising measurements from two consecutive gauges installed at the catchment outlet and on a slope within that catchment allowed analyzing the change of hysteresis patterns along the flowpath. On the slope, multiple-peak events showed a stronger intra-event exhaustion of hysteresis than at the catchment outlet. Furthermore, exhaustion of hysteresis on the inter-event scale was not evident on the slope but occurred at the catchment outlet. Our results indicate that even small sediment datasets can provide valuable insights into sediment transport processes of small catchments. Furthermore, our results may serve as a first guideline on what to expect from an analysis of hysteresis patterns for datasets of varying quality and quantity. (c) 2014 Elsevier B.V. All rights reserved. KW - Suspended sediment KW - Hysteresis index KW - Sediment monitoring KW - Overland flow KW - Tropical forest Y1 - 2014 U6 - https://doi.org/10.1016/j.catena.2014.06.020 SN - 0341-8162 SN - 1872-6887 VL - 122 SP - 120 EP - 129 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Haßler, Sibylle Kathrin A1 - Lark, R. M. A1 - Zimmermann, Beate A1 - Elsenbeer, Helmut T1 - Which sampling design to monitor saturated hydraulic conductivity? JF - European journal of soil science N2 - Soil in a changing world is subject to both anthropogenic and environmental stresses. Soil monitoring is essential to assess the magnitude of changes in soil variables and how they affect ecosystem processes and human livelihoods. However, we cannot always be sure which sampling design is best for a given monitoring task. We employed a rotational stratified simple random sampling (rotStRS) for the estimation of temporal changes in the spatial mean of saturated hydraulic conductivity (K-s) at three sites in central Panama in 2009, 2010 and 2011. To assess this design's efficiency we compared the resulting estimates of the spatial mean and variance for 2009 with those gained from stratified simple random sampling (StRS), which was effectively the data obtained on the first sampling time, and with an equivalent unexecuted simple random sampling (SRS). The poor performance of geometrical stratification and the weak predictive relationship between measurements of successive years yielded no advantage of sampling designs more complex than SRS. The failure of stratification may be attributed to the small large-scale variability of K-s. Revisiting previously sampled locations was not beneficial because of the large small-scale variability in combination with destructive sampling, resulting in poor consistency between revisited samples. We conclude that for our K-s monitoring scheme, repeated SRS is equally effective as rotStRS. Some problems of small-scale variability might be overcome by collecting several samples at close range to reduce the effect of small-scale variation. Finally, we give recommendations on the key factors to consider when deciding whether to use stratification and rotation in a soil monitoring scheme. Y1 - 2014 U6 - https://doi.org/10.1111/ejss.12174 SN - 1351-0754 SN - 1365-2389 VL - 65 IS - 6 SP - 792 EP - 802 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Hayhoe, Shelby J. A1 - Neill, Christopher A1 - Porder, Stephen A1 - McHorney, Richard A1 - Lefebvre, Paul A1 - Coe, Michael T. A1 - Elsenbeer, Helmut A1 - Krusche, Alex V. T1 - Conversion to soy on the Amazonian agricultural frontier increases streamflow without affecting stormflow dynamics JF - Global change biology N2 - Large-scale soy agriculture in the southern Brazilian Amazon now rivals deforestation for pasture as the region's predominant form of land use change. Such landscape-level change can have substantial consequences for local and regional hydrology, but these effects remain relatively unstudied in this ecologically and economically important region. We examined how the conversion to soy agriculture influences water balances and stormflows using stream discharge (water yields) and the timing of discharge (stream hydrographs) in small (2.5-13.5 km2) forested and soy headwater watersheds in the Upper Xingu Watershed in the state of Mato Grosso, Brazil. We monitored water yield for 1 year in three forested and four soy watersheds. Mean daily water yields were approximately four times higher in soy than forested watersheds, and soy watersheds showed greater seasonal variability in discharge. The contribution of stormflows to annual streamflow in all streams was low (< 13% of annual streamflow), and the contribution of stormflow to streamflow did not differ between land uses. If the increases in water yield observed in this study are typical, landscape-scale conversion to soy substantially alters water-balance, potentially altering the regional hydrology over large areas of the southern Amazon. KW - Amazon KW - baseflow KW - hydrology KW - land use change KW - soybean cultivation KW - water yield Y1 - 2011 U6 - https://doi.org/10.1111/j.1365-2486.2011.02392.x SN - 1354-1013 VL - 17 IS - 5 SP - 1821 EP - 1833 PB - Wiley-Blackwell CY - Malden ER - TY - JOUR A1 - Haßler, Sibylle Kathrin A1 - Zimmermann, Beate A1 - van Breugel, Michiel A1 - Hall, Jefferson S. A1 - Elsenbeer, Helmut T1 - Recovery of saturated hydraulic conductivity under secondary succession on former pasture in the humid tropics JF - Forest ecology and management N2 - Landscapes in the humid tropics are undergoing a continuous change in land use. Deforestation is still taking its toll on forested areas, but at the same time more and more secondary forests emerge where formerly agricultural lands and pastures are being abandoned. Regarding soil hydrology, the extent to which secondary succession can recover soil hydrological properties disturbed by antecedent deforestation and pasture use is yet poorly understood. We investigated the effect of secondary succession on saturated hydraulic conductivity (Ks) at two soil depths (0-6 and 6-12 cm) using a space-for-time approach in a landscape mosaic in central Panama. The following four land-use classes were studied: pasture (P), secondary forest of 5-8 years of age (SF5), secondary forest of 12-15 years of age (SF12) and secondary forest of more than 100 years of age (SF100), each replicated altogether four times in different micro-catchments across the study region. The hydrological implications of differences in Ks in response to land-use change with land use, especially regarding overland flow generation, were assessed via comparisons with rainfall intensities. Recovery of Ks could be detected in the 0-6 cm depth after 12 years of secondary succession: P and SF5 held similar Ks values, but differed significantly (alpha = 0.05) from SF12 and SF100 which in turn were indistinguishable. Variability within the land cover classes was large but, due to sufficient replication in the study, Ks recovery could be detected nonetheless. Ks in the 6-12 cm depth did not show any differences between the land cover classes; only Ks of the uppermost soil layer was affected by land-use changes. Overland flow - as inferred from comparisons of Ks with rainfall intensities - is more likely on P and SF5 sites compared to SF12 and 5E100 for the upper sample depth; however, generally low values at the 6-12 cm depth are likely to impede vertical percolation during high rainfall intensities regardless of land use. We conclude that Ks can recover from pasture use under secondary succession up to pre-pasture levels, but the process may take more than 8 years. In order to gain comprehensive understanding of Ks change with land use and its hydrological implications, more studies with detailed land-use histories and combined measurements of Ks, overland flow, precipitation and throughfall are essential. KW - Land cover change KW - Forest KW - Land use KW - Overland flow KW - Soil hydrology KW - Ecosystem services Y1 - 2011 U6 - https://doi.org/10.1016/j.foreco.2010.06.031 SN - 0378-1127 SN - 1872-7042 VL - 261 IS - 10 SP - 1634 EP - 1642 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Neumann-Cosel, Luisa A1 - Zimmermann, Beate A1 - Hall, Jefferson S. A1 - van Breugel, Michiel A1 - Elsenbeer, Helmut T1 - Soil carbon dynamics under young tropical secondary forests on former pastures-A case study from Panama JF - Forest ecology and management N2 - Secondary forests are gaining increased importance in tropical landscapes and have recently been reported to act as potential belowground carbon sinks. While economic interest in the management of secondary forests to mitigate carbon emissions is rising, the dynamics of soil carbon stocks under these ecosystems remain poorly understood. Recent studies report conflicting results concerning soil carbon trends as well as multiple confounding factors (e.g. soil type, topography and land-use history) affecting these trends. In this study, organic carbon stocks were measured in the mineral soil up to 20 cm depth of at 24 active pastures, 5-8-year-old, and 12-15-year-old secondary forest sites on former pastures. Additionally, we estimated carbon stocks under a 100-year-old secondary forest and compared them to those of nearby mature forests. Abiotic conditions in the study area were homogenous, enabling us to isolate the effect of land-use change on soil organic carbon stocks. Contrary to our expectations, soil carbon stocks in the top 10 cm did not change with young secondary forest development. Pasture soils stored 24.8 +/- 2.9 Mg ha(-1) carbon (mean +/- standard error) in the top 10 cm, and no accumulation of soil carbon was apparent during the first 15 years of secondary succession. Soil carbon stocks under 100-year-old secondary forests, averaging 43.0 +/- 7.9 Mg ha(-1) (mean +/- standard error), were clearly higher than those recorded at younger sites and approached levels of soil carbon stocks under mature forests. These data indicate that soil carbon stocks in this region of Panama are not affected by the land-use transition from pasture to young secondary regrowth. However, an increase of soil carbon storage might be possible over a longer period of time. Our results support trends observed in other tropical areas and highlight the importance of environmental conditions such as soil properties rather than land-use transitions on soil carbon dynamics. While our understanding of organic carbon dynamics in tropical soils remains limited, these results underscore the challenges of undertaking short-term reforestation projects with the expectation of increasing soil carbon sequestration. KW - Soil carbon KW - Secondary forest KW - Pasture KW - Land-use change KW - C sequestration KW - Panama Y1 - 2011 U6 - https://doi.org/10.1016/j.foreco.2010.07.023 SN - 0378-1127 VL - 261 IS - 10 SP - 1625 EP - 1633 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Neill, Christopher A1 - Chaves, Joaquín E. A1 - Biggs, Trent A1 - Deegan, Linda A. A1 - Elsenbeer, Helmut A1 - Figueiredo, Ricardo O. A1 - Germer, Sonja A1 - Johnson, Mark S. A1 - Lehmann, Johannes A1 - Markewitz, Daniel A1 - Piccolo, Marisa C. T1 - Runoff sources and land cover change in the Amazon an end-member mixing analysis from small watersheds JF - Biogeochemistry N2 - The flowpaths by which water moves from watersheds to streams has important consequences for the runoff dynamics and biogeochemistry of surface waters in the Amazon Basin. The clearing of Amazon forest to cattle pasture has the potential to change runoff sources to streams by shifting runoff to more surficial flow pathways. We applied end-member mixing analysis (EMMA) to 10 small watersheds throughout the Amazon in which solute composition of streamwater and groundwater, overland flow, soil solution, throughfall and rainwater were measured, largely as part of the Large-Scale Biosphere-Atmosphere Experiment in Amazonia. We found a range in the extent to which streamwater samples fell within the mixing space determined by potential flowpath end-members, suggesting that some water sources to streams were not sampled. The contribution of overland flow as a source of stream flow was greater in pasture watersheds than in forest watersheds of comparable size. Increases in overland flow contribution to pasture streams ranged in some cases from 0% in forest to 27-28% in pasture and were broadly consistent with results from hydrometric sampling of Amazon forest and pasture watersheds that indicate 17- to 18-fold increase in the overland flow contribution to stream flow in pastures. In forest, overland flow was an important contribution to stream flow (45-57%) in ephemeral streams where flows were dominated by stormflow. Overland flow contribution to stream flow decreased in importance with increasing watershed area, from 21 to 57% in forest and 60-89% in pasture watersheds of less than 10 ha to 0% in forest and 27-28% in pastures in watersheds greater than 100 ha. Soil solution contributions to stream flow were similar across watershed area and groundwater inputs generally increased in proportion to decreases in overland flow. Application of EMMA across multiple watersheds indicated patterns across gradients of stream size and land cover that were consistent with patterns determined by detailed hydrometric sampling. KW - Cattle pasture KW - Deforestation KW - Flowpaths KW - Principal components analysis KW - Overland flow KW - Soil solution Y1 - 2011 U6 - https://doi.org/10.1007/s10533-011-9597-8 SN - 0168-2563 VL - 105 IS - 1-3 SP - 7 EP - 18 PB - Springer CY - Dordrecht ER - TY - JOUR A1 - Loos, Martin A1 - Elsenbeer, Helmut T1 - Topographic controls on overland flow generation in a forest - An ensemble tree approach JF - Journal of hydrology N2 - Overland flow is an important hydrological pathway in many forests of the humid tropics. Its generation is subject to topographic controls at differing spatial scales. Our objective was to identify such controls on the occurrence of overland flow in a lowland tropical rainforest. To this end, we installed 95 overland flow detectors (OFDs) in four nested subcatchments of the Lutzito catchment on Barro Colorado Island, Panama, and monitored the frequency of overland flow occurrence during 18 rainfall events at each OFD location temporal frequency. For each such location, we derived three non-digital terrain attributes and 17 digital ones, of which 15 were based on Digital Elevation Models (DEMs) of three different resolutions. These attributes then served as input into a Random Forest ensemble tree model to elucidate the importance and partial and joint dependencies of topographic controls for overland flow occurrence. Lutzito features a high median temporal frequency in overland flow occurrence of 0.421 among OFD locations. However, spatial temporal frequencies of overland flow occurrence vary strongly among these locations and the subcatchments of Lutzito catchment. This variability is best explained by (1) microtopography, (2) coarse terrain sloping and (3) various measures of distance-to-channel, with the contribution of all other terrain attributes being small. Microtopographic features such as concentrated flowlines and wash areas produce highest temporal frequencies, whereas the occurrence of overland flow drops sharply for flow distances and terrain sloping beyond certain threshold values. Our study contributes to understanding both the spatial controls on overland flow generation and the limitations of terrain attributes for the spatially explicit prediction of overland flow frequencies. KW - Overland Bow KW - Tropical rainforest KW - Random Forest KW - Spatial scale KW - Digital Elevation Model KW - Topography Y1 - 2011 U6 - https://doi.org/10.1016/j.jhydrol.2011.08.002 SN - 0022-1694 VL - 409 IS - 1-2 SP - 94 EP - 103 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Scheffler, Raphael A1 - Neill, Christopher A1 - Krusche, Alex V. A1 - Elsenbeer, Helmut T1 - Soil hydraulic response to land-use change associated with the recent soybean expansion at the Amazon agricultural frontier JF - Agriculture, ecosystems & environment : an international journal for scientific research on the relationship of agriculture and food production to the biosphere N2 - Clearing for large-scale soy production and the displacement of cattle-breeding by soybeans are major features of land-use change in the lowland Amazon that can alter hydrologic properties of soils and the runoff generation over large areas. We measured infiltrability and saturated hydraulic conductivity (Ksat) under natural forest, pasture, and soybeans on Oxisols in a region of rapid soybean expansion in Mato Grosso, Brazil. The forest-pasture conversion reduced infiltrability from 1258 to 100 mm/h and Ksat at all depths. The pasture-soy conversion increased infiltrability from 100 to 469 mm/h (attributed to shallow disking), did not affect Ksat at 12.5 cm, but decreased Ksat at 30 cm from 122 to 80 mm/h, suggesting that soybean cultivation enhances subsoil compaction. Permeability decreased markedly with depth under forest, did not change under pasture, and averaged out at one fourth the forest value under soybeans with a similar pattern of anisotropy. Comparisons of permeability with rainfall intensities indicated that land-use change did not alter the predominantly vertical water movement within the soil. We conclude that this landscape is well buffered against land-use changes regarding near-surface hydrology, even though short-lived ponding and perched water tables may occur locally during high-intensity rainfall on pastures and under soybeans. KW - Land-cover change KW - Tropical forest KW - Pasture KW - Infiltrability KW - Saturated hydraulic conductivity KW - Ksat KW - Hydrological flowpaths Y1 - 2011 U6 - https://doi.org/10.1016/j.agee.2011.08.016 SN - 0167-8809 VL - 144 IS - 1 SP - 281 EP - 289 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Haßler, Sibylle Kathrin A1 - Lark, Richard M. A1 - Milne, A. E. A1 - Elsenbeer, Helmut T1 - Exploring the variation in soil saturated hydraulic conductivity under a tropical rainforest using the wavelet transform JF - European journal of soil science N2 - Saturated hydraulic conductivity (Ks) of the soil is a key variable in the water cycle. For the humid tropics, information about spatial scales of Ks and their relation to soil types deduced from soil map units is of interest, as soil maps are often the only available data source for modelling. We examined the influence of soil map units on the mean and variation in Ks along a transect in a tropical rainforest using undisturbed soil cores at 06 and 612 cm depth. The Ks means were estimated with a linear mixed model fitted by residual maximum likelihood (REML), and the spatial variation in Ks was investigated with the maximum overlap discrete wavelet packet transform (MODWPT). The mean values of Ks did not differ between soil map units. The best wavelet packet basis for Ks at 06 cm showed stationarity at high frequencies, suggesting uniform small-scale influences such as bioturbation. There were substantial contributions to wavelet packet variance over the range of spatial frequencies and a pronounced low frequency peak corresponding approximately to the scale of soil map units. However, in the relevant frequency intervals no significant changes in wavelet packet variance were detected. We conclude that near-surface Ks is not dominated by static, soil-inherent properties for the examined range of soils. Several indicators from the wavelet packet analysis hint at the more dominant dynamic influence of biotic processes, which should be kept in mind when modelling soil hydraulic properties on the basis of soil maps. Y1 - 2011 U6 - https://doi.org/10.1111/j.1365-2389.2011.01400.x SN - 1351-0754 VL - 62 IS - 6 SP - 891 EP - 901 PB - Wiley-Blackwell CY - Malden 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 - 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 - Vorpahl, Peter A1 - Elsenbeer, Helmut A1 - Märker, Michael A1 - Schröder-Esselbach, Boris T1 - How can statistical models help to determine driving factors of landslides? JF - Ecological modelling : international journal on ecological modelling and engineering and systems ecolog N2 - Landslides are a hazard for humans and artificial structures. From an ecological point of view, they represent an important ecosystem disturbance, especially in tropical montane forests. Here, shallow translational landslides are a frequent natural phenomenon and one local determinant of high levels of biodiversity. In this paper, we apply weighted ensembles of advanced phenomenological models from statistics and machine learning to analyze the driving factors of natural landslides in a tropical montane forest in South Ecuador. We exclusively interpret terrain attributes, derived from a digital elevation model, as proxies to several driving factors of landslides and use them as predictors in our models which are trained on a set of five historical landslide inventories. We check the model generality by transferring them in time and use three common performance criteria (i.e. AUC, explained deviance and slope of model calibration curve) to, on the one hand, compare several state-of-the-art model approaches and on the other hand, to create weighted model ensembles. Our results suggest that it is important to consider more than one single performance criterion. Approaching our main question, we compare responses of weighted model ensembles that were trained on distinct functional units of landslides (i.e. initiation, transport and deposition zones). This way, we are able to show that it is quite possible to deduce driving factors of landslides, if the consistency between the training data and the processes is maintained. Opening the 'black box' of statistical models by interpreting univariate model response curves and relative importance of single predictors regarding their plausibility, we provide a means to verify this consistency. With the exception of classification tree analysis, all techniques performed comparably well in our case study while being outperformed by weighted model ensembles. Univariate response curves of models trained on distinct functional units of landslides exposed different shapes following our expectations. Our results indicate the occurrence of landslides to be mainly controlled by factors related to the general position along a slope (i.e. ridge, open slope or valley) while landslide initiation seems to be favored by small scale convexities on otherwise plain open slopes. KW - Landslides KW - Tropical montane forests KW - Statistical modeling KW - Model comparison KW - Artificial neuronal network KW - Classification trees KW - Random forests KW - Boosted regression trees KW - Generalized linear models KW - Multivariate adaptive regression splines KW - Maximum entropy method KW - Weighted model ensembles Y1 - 2012 U6 - https://doi.org/10.1016/j.ecolmodel.2011.12.007 SN - 0304-3800 SN - 1872-7026 VL - 239 IS - 7 SP - 27 EP - 39 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Bäse, Frank A1 - Elsenbeer, Helmut A1 - Neill, Christopher A1 - Krusche, Alex V. T1 - Differences in throughfall and net precipitation between soybean and transitional tropical forest in the southern Amazon, Brazil JF - Agriculture, ecosystems & environment : an international journal for scientific research on the relationship of agriculture and food production to the biosphere N2 - The expansion of soybean cultivation into the Amazon in Brazil has potential hydrological effects at local to regional scales. To determine the impacts of soybean agriculture on hydrology, a comparison of net precipitation (throughfall, stemflow) in undisturbed tropical forest and soybean fields on the southern edge of the Amazon Basin in the state of Mato Grosso is needed. This study measured throughfall with troughs and stemflow with collar collectors during two rainy seasons. The results showed that in forest 91.6% of rainfall was collected as throughfall and 0.3% as stemflow, while in soybean fields with two-month old plants, 46.2% of rainfall was collected as throughfall and 9.0% as stemflow. Hence, interception of precipitation in soybean fields was far greater than in intact forests. Differences in throughfall, stemflow and net precipitation were found to be mainly associated with differences in plant structure and stem density in transitional forest and soybean cropland. Because rainfall interception in soybean fields is higher than previously believed and because both the area of cropland and the frequency of crop cycles (double cropping) are increasing rapidly, interception needs to be reconsidered in regional water balance models when consequences of land cover changes are analyzed in the Amazon soybean frontier region. Based on the continued expansion of soybean fields across the landscape and the finding that net precipitation is lower in soy agriculture, a reduction in water availability in the long term can be assumed. KW - Throughfall KW - Net precipitation KW - Stemflow KW - Soybean KW - Tropical forest Y1 - 2012 U6 - https://doi.org/10.1016/j.agee.2012.06.013 SN - 0167-8809 VL - 159 SP - 19 EP - 28 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Vorpahl, Peter A1 - Dislich, Claudia A1 - Elsenbeer, Helmut A1 - Märker, Michael A1 - Schröder-Esselbach, Boris T1 - Biotic controls on shallow translational landslides JF - Earth surface processes and landforms : the journal of the British Geomorphological Research Group N2 - In undisturbed tropical montane rainforests massive organic layers accommodate the majority of roots and only a small fraction of roots penetrate the mineral soil. We investigated the contribution of vegetation to slope stability in such environments by modifying a standard model for slope stability to include an organic layer with distinct mechanical properties. The importance of individual model parameters was evaluated using detailed measurements of soil and vegetation properties to reproduce the observed depth of 11 shallow landslides in the Andes of southern Ecuador. By distinguishing mineral soil, organic layer and above-ground biomass, it is shown that in this environment vegetation provides a destabilizing effect mainly due to its contribution to the mass of the organic layer (up to 973 t ha-1 under wet conditions). Sensitivity analysis shows that the destabilizing effect of the mass of soil and vegetation can only be effective on slopes steeper than 37.9 degrees. This situation applies to 36% of the study area. Thus, on the steep slopes of this megadiverse ecosystem, the mass of the growing forest promotes landsliding, which in turn promotes a new cycle of succession. This feedback mechanism is worth consideration in further investigations of the impact of landslides on plant diversity in similar environments. KW - shallow translational landslides KW - tropical montane forest KW - biomass KW - organic layer Y1 - 2013 U6 - https://doi.org/10.1002/esp.3320 SN - 0197-9337 VL - 38 IS - 2 SP - 198 EP - 212 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Zimmermann, Alexander A1 - Schinn, Dustin S. A1 - Francke, Till A1 - Elsenbeer, Helmut A1 - Zimmermann, Beate T1 - Uncovering patterns of near-surface saturated hydraulic conductivity in an overland flow-controlled landscape JF - Geoderma : an international journal of soil science N2 - Saturated hydraulic conductivity (K-s) is an important soil characteristic affecting soil water storage, runoff generation and erosion processes. In some areas where high-intensity rainfall coincides with low K-s values at shallow soil depths, frequent overland flow entails dense drainage networks. Consequently, linear structures such as flowlines alternate with inter-flowline areas. So far, investigations of the spatial variability of K-s mainly relied on isotropic covariance models which are unsuitable to reveal patterns resulting from linear structures. In the present study, we applied two sampling approaches so as to adequately characterize K-s spatial variability in a tropical forest catchment that features a high density of flowlines: A classical nested sampling survey and a purposive sampling strategy adapted to the presence of flowlines. The nested sampling approach revealed the dominance of small-scale variability, which is in line with previous findings. Our purposive sampling, however, detected a strong spatial gradient: surface K-s increased substantially as a function of distance to flowline; 10 m off flowlines, values were similar to the spatial mean of K-s. This deterministic trend can be included as a fixed effect in a linear mixed modeling framework to obtain realistic spatial fields of K-s. In a next step we used probability maps based on those fields and prevailing rainfall intensities to assess the hydrological relevance of the detected pattern. This approach suggests a particularly good agreement between the probability statements of K-s exceedance and observed overland flow occurrence during wet stages of the rainy season. KW - Soil hydrology KW - Saturated hydraulic conductivity KW - Overland flow generation KW - Spatial patterns KW - Drainage network Y1 - 2013 U6 - https://doi.org/10.1016/j.geoderma.2012.11.002 SN - 0016-7061 VL - 195 IS - 169 SP - 1 EP - 11 PB - Elsevier CY - Amsterdam ER -