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 -