TY - JOUR A1 - Zehe, E. A1 - Ehret, U. A1 - Pfister, L. A1 - Blume, Theresa A1 - Schroeder, Boris A1 - Westhoff, M. A1 - Jackisch, C. A1 - Schymanski, Stanislauv J. A1 - Weiler, M. A1 - Schulz, K. A1 - Allroggen, Niklas A1 - Tronicke, Jens A1 - van Schaik, Loes A1 - Dietrich, Peter A1 - Scherer, U. A1 - Eccard, Jana A1 - Wulfmeyer, Volker A1 - Kleidon, Axel T1 - HESS Opinions: From response units to functional units: a thermodynamic reinterpretation of the HRU concept to link spatial organization and functioning of intermediate scale catchments JF - Hydrology and earth system sciences : HESS N2 - According to Dooge (1986) intermediate-scale catchments are systems of organized complexity, being too organized and yet too small to be characterized on a statistical/conceptual basis, but too large and too heterogeneous to be characterized in a deterministic manner. A key requirement for building structurally adequate models precisely for this intermediate scale is a better understanding of how different forms of spatial organization affect storage and release of water and energy. Here, we propose that a combination of the concept of hydrological response units (HRUs) and thermodynamics offers several helpful and partly novel perspectives for gaining this improved understanding. Our key idea is to define functional similarity based on similarity of the terrestrial controls of gradients and resistance terms controlling the land surface energy balance, rainfall runoff transformation, and groundwater storage and release. This might imply that functional similarity with respect to these specific forms of water release emerges at different scales, namely the small field scale, the hillslope, and the catchment scale. We thus propose three different types of "functional units" - specialized HRUs, so to speak - which behave similarly with respect to one specific form of water release and with a characteristic extent equal to one of those three scale levels. We furthermore discuss an experimental strategy based on exemplary learning and replicate experiments to identify and delineate these functional units, and as a promising strategy for characterizing the interplay and organization of water and energy fluxes across scales. We believe the thermodynamic perspective to be well suited to unmask equifinality as inherent in the equations governing water, momentum, and energy fluxes: this is because several combinations of gradients and resistance terms yield the same mass or energy flux and the terrestrial controls of gradients and resistance terms are largely independent. We propose that structurally adequate models at this scale should consequently disentangle driving gradients and resistance terms, because this optionally allow sequifinality to be partly reduced by including available observations, e. g., on driving gradients. Most importantly, the thermodynamic perspective yields an energy-centered perspective on rainfall-runoff transformation and evapotranspiration, including fundamental limits for energy fluxes associated with these processes. This might additionally reduce equifinality and opens up opportunities for testing thermodynamic optimality principles within independent predictions of rainfall-runoff or land surface energy exchange. This is pivotal to finding out whether or not spatial organization in catchments is in accordance with a fundamental organizing principle. Y1 - 2014 U6 - https://doi.org/10.5194/hess-18-4635-2014 SN - 1027-5606 SN - 1607-7938 VL - 18 IS - 11 SP - 4635 EP - 4655 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - van Schaik, Loes A1 - Palm, Juliane A1 - Klaus, Julian A1 - Zehe, Erwin A1 - Schroeder, Boris T1 - Linking spatial earthworm distribution to macropore numbers and hydrological effectiveness JF - Ecohydrology : ecosystems, land and water process interactions, ecohydrogeomorphology N2 - Due to its high spatial and temporal variability, preferential flow is difficult to measure and quantify. Earthworms create macropores that provide common pathways for preferential flow. Therefore in this article, we link earthworm abundance to macropore numbers and hydrological effectiveness, with the future aim to use species distribution models of earthworms for the spatial parameterization of preferential flow. Earthworms are generally categorized into three ecological types with varying burrowing behaviour, resulting in a different impact on soil hydrological processes. Therefore, we studied the relationships between the abundance of the earthworm ecological types and macropores of different size classes and in different soil depths. The abundance and biomass of earthworms were well correlated to different sizes of macropores in different soil depths. This is mainly the case for the larger, vertically oriented macropores (>6mm diameter), which are generally connected to the soil surface and hydrologically most effective. The correlation of total earthworm biomass and macropores ranges from 072 to 089 for different soil depths. Although there is quite some variation in infiltration patterns, infiltration from macropores into the matrix is profile-specific, as it varies strongly between profiles, but not within one profile. Macropore coating seems to have a larger effect on this macropore matrix interaction than the soil physical properties of the matrix. Although the amount of macropores and their effectiveness are clearly related to the earthworm distribution, the variation in infiltration from macropores to soil matrix should be further studied. KW - macropores KW - spatial parameterization KW - earthworm ecological types KW - infiltration patterns KW - preferential flow Y1 - 2014 U6 - https://doi.org/10.1002/eco.1358 SN - 1936-0584 SN - 1936-0592 VL - 7 IS - 2 SP - 401 EP - 408 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - van Schaik, Loes A1 - Palm, Juliane A1 - Klaus, Julian A1 - Zehe, Erwin A1 - Schroeder, Boris T1 - Potential effects of tillage and field borders on within-field spatial distribution patterns of earthworms JF - Biological chemistry N2 - Earthworms play a key role in regulating soil ecosystem functions and services. The small scale variability in earthworm abundance is often found to be very high, which is a problem for representative sampling of earthworm abundance at larger scales. In agricultural fields, soil tillage may influence both the average earthworm abundance as well as the spatial distribution of earthworms. Therefore we studied the abundance and spatial pattern of the different ecological earthworm types, i.e. endogeic, epigeic and anecic earthworms, in four agricultural fields differing in soil tillage (two fields with regular tillage and two fields with conservation tillage) and surrounding land use (other cropped fields or apple orchard and forest). To this aim we sampled earthworms on a total number of 430 plots (50 x 50 cm(2)) using a combination of extraction with mustard solution and hand sorting. The results exhibit large differences in average earthworm abundance between the four fields. Only one of the two fields with conservation tillage had a comparatively very high overall abundance of earthworms. Furthermore, we found a high spatial variability of earthworms within the field scale often exhibiting a patchy distribution. We detected a trend of decreasing earthworm abundances from the field border into the field for different earthworm groups on each of the fields. In three fields with low total earthworm abundance (and only very few epigeic earthworms) there was a short scale autocorrelation with ranges varying strongly for the endogeic earthworms (37.9 m, 62.6 m, and 85.2 m) compared to anecic earthworms (19.8 m, 22.8 m, and 27.4 m). In the field with high abundance, after trend removal, the variogram models for anecic and endogeic earthworms were rejected based on their negative explained variances. On this field, we found only a short scale autocorrelation for the epigeic earthworms with a range of 143 m. Based on these results it seems that ploughing alone cannot explain the differences in abundance and range of autocorrelation found on the four fields. The trend of strongly decreasing earthworm abundance from the field border into the field in the one field with high abundance does indicate that the field border or surrounding land use may also influence the recolonization of fields, but more research is required to provide further evidence for this hypothesis. Due to the very different patterns of earthworm distributions in the fields it remains difficult to recommend an optimal number and distance of samples to obtain a representative earthworm abundance for the field scale. (C) 2016 Elsevier B.V. All rights reserved. KW - Earthworms KW - Spatial distribution KW - Autocorrelation KW - Agricultural fields KW - Soil tillage Y1 - 2016 U6 - https://doi.org/10.1016/j.agee.2016.05.015 SN - 0167-8809 SN - 1873-2305 VL - 228 SP - 82 EP - 90 PB - De Gruyter CY - Berlin ER - TY - JOUR A1 - Müller, Eva Nora A1 - van Schaik, Loes A1 - Blume, Theresa A1 - Bronstert, Axel A1 - Carus, Jana A1 - Fleckenstein, Jan H. A1 - Fohrer, Nicola A1 - Geissler, Katja A1 - Gerke, Horst H. A1 - Gräff, Thomas A1 - Hesse, Cornelia A1 - Hildebrandt, Anke A1 - Hölker, Franz A1 - Hunke, Philip A1 - Körner, Katrin A1 - Lewandowski, Jörg A1 - Lohmann, Dirk A1 - Meinikmann, Karin A1 - Schibalski, Anett A1 - Schmalz, Britta A1 - Schröder-Esselbach, Boris A1 - Tietjen, Britta T1 - Scales, key aspects, feedbacks and challenges of ecohydrological research in Germany JF - Hydrologie und Wasserbewirtschaftung N2 - Ecohydrology analyses the interactions of biotic and abiotic aspects of our ecosystems and landscapes. It is a highly diverse discipline in terms of its thematic and methodical research foci. This article gives an overview of current German ecohydrological research approaches within plant-animal-soil-systems, meso-scale catchments and their river networks, lake systems, coastal areas and tidal rivers. It discusses their relevant spatial and temporal process scales and different types of interactions and feedback dynamics between hydrological and biotic processes and patterns. The following topics are considered key challenges: innovative analysis of the interdisciplinary scale continuum, development of dynamically coupled model systems, integrated monitoring of coupled processes at the interface and transition from basic to applied ecohydrological science to develop sustainable water and land resource management strategies under regional and global change. KW - Coastal regions KW - drylands KW - ecohydrological modelling KW - feedback KW - hyporheic zone KW - meso-scale ecosystems KW - plant-animal-soil-system KW - river networks Y1 - 2014 U6 - https://doi.org/10.5675/HyWa_2014,4_2 SN - 1439-1783 VL - 58 IS - 4 SP - 221 EP - 240 PB - Bundesanst. für Gewässerkunde CY - Koblenz ER - TY - JOUR A1 - Loritz, Ralf A1 - Hassler, Sibylle K. A1 - Jackisch, Conrad A1 - Allroggen, Niklas A1 - van Schaik, Loes A1 - Wienhöfer, Jan A1 - Zehe, Erwin T1 - Picturing and modeling catchments by representative hillslopes JF - Hydrology and earth system sciences : HESS N2 - This study explores the suitability of a single hillslope as a parsimonious representation of a catchment in a physically based model. We test this hypothesis by picturing two distinctly different catchments in perceptual models and translating these pictures into parametric setups of 2-D physically based hillslope models. The model parametrizations are based on a comprehensive field data set, expert knowledge and process-based reasoning. Evaluation against streamflow data highlights that both models predicted the annual pattern of streamflow generation as well as the hydrographs acceptably. However, a look beyond performance measures revealed deficiencies in streamflow simulations during the summer season and during individual rainfall-runoff events as well as a mismatch between observed and simulated soil water dynamics. Some of these shortcomings can be related to our perception of the systems and to the chosen hydrological model, while others point to limitations of the representative hillslope concept itself. Nevertheless, our results confirm that representative hillslope models are a suitable tool to assess the importance of different data sources as well as to challenge our perception of the dominant hydrological processes we want to represent therein. Consequently, these models are a promising step forward in the search for the optimal representation of catchments in physically based models. Y1 - 2017 U6 - https://doi.org/10.5194/hess-21-1225-2017 SN - 1027-5606 SN - 1607-7938 VL - 21 IS - 2 SP - 1225 EP - 1249 PB - Copernicus CY - Göttingen ER - TY - GEN A1 - Loritz, Ralf A1 - Hassler, Sibylle K. A1 - Jackisch, Conrad A1 - Allroggen, Niklas A1 - van Schaik, Loes A1 - Wienhöfer, Jan A1 - Zehe, Erwin T1 - Picturing and modeling catchments by representative hillslopes T2 - Postprints der Universität Potsdam : Mathematisch Naturwissenschaftliche Reihe N2 - This study explores the suitability of a single hillslope as a parsimonious representation of a catchment in a physically based model. We test this hypothesis by picturing two distinctly different catchments in perceptual models and translating these pictures into parametric setups of 2-D physically based hillslope models. The model parametrizations are based on a comprehensive field data set, expert knowledge and process-based reasoning. Evaluation against streamflow data highlights that both models predicted the annual pattern of streamflow generation as well as the hydrographs acceptably. However, a look beyond performance measures revealed deficiencies in streamflow simulations during the summer season and during individual rainfall-runoff events as well as a mismatch between observed and simulated soil water dynamics. Some of these shortcomings can be related to our perception of the systems and to the chosen hydrological model, while others point to limitations of the representative hillslope concept itself. Nevertheless, our results confirm that representative hillslope models are a suitable tool to assess the importance of different data sources as well as to challenge our perception of the dominant hydrological processes we want to represent therein. Consequently, these models are a promising step forward in the search for the optimal representation of catchments in physically based models. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 635 KW - soil-moisture dynamics KW - hydrologic-response simulation KW - rainfall-runoff response KW - preferential flow KW - subsurface stormflow KW - water-uptake KW - field-scale KW - transport KW - system KW - basin Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-419082 IS - 635 SP - 1225 EP - 1249 ER - TY - JOUR A1 - Klaus, Julian A1 - Zehe, Erwin A1 - Elsner, Martin A1 - Palm, Juliane A1 - Schneider, Dorothee A1 - Schroeder, Boris A1 - Steinbeiss, Sibylle A1 - van Schaik, Loes A1 - West, Stephanie T1 - Controls of event-based pesticide leaching in natural soils: A systematic study based on replicated field scale irrigation experiments JF - Journal of hydrology N2 - Tile drains strongly influence the water cycle in agricultural catchment in terms of water quantity and quality. The connectivity of preferential flow to tile drains can create shortcuts for rapid transport of solutes into surface waters. The leaching of pesticides can be linked to a set of main factors including, rainfall characteristics, soil moisture, chemical properties of the pesticides, soil properties, and preferential flow paths. The connectivity of the macropore system to the tile drain is crucial for pesticide leaching. Concurring influences of the main factors, threshold responses and the role of flow paths are still poorly understood. The objective of this study is to investigate these influences by a replica series of three irrigation experiments on a tile drain field site using natural and artificial tracers together with applied pesticides. We found a clear threshold behavior in the initialization of pesticide transport that was different between the replica experiments. Pre-event soil water contributed significantly to the tile drain flow, and creates a flow path for stored pesticides from the soil matrix to the tile drain. This threshold is controlled by antecedent soil moisture and precipitation characteristics, and the interaction between the soil matrix and preferential flow system. Fast transport of pesticides without retardation and the remobilization could be attributed to this threshold and the interaction between the soil matrix and the preferential flow system. Thus, understanding of the detailed preferential flow processes clearly enhances the understanding of pesticide leaching on event and long term scale, and can further improve risk assessment and modeling approaches. (C) 2014 Elsevier B.V. All rights reserved. KW - Irrigation experiment KW - Preferential flow KW - Threshold KW - Pesticide transport Y1 - 2014 U6 - https://doi.org/10.1016/j.jhydrol.2014.03.020 SN - 0022-1694 SN - 1879-2707 VL - 512 SP - 528 EP - 539 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Keesstra, Saskia Deborah A1 - Geissen, Violetta A1 - Mosse, K. A1 - Piiranen, S. A1 - Scudiero, E. A1 - Leistra, M. A1 - van Schaik, Loes T1 - Soil as a filter for groundwater quality JF - Current opinion in environmental sustainability N2 - The filtering function of soil is an important ecosystem service for groundwater and surface water protection. The efficiency of soils as a filter depends on the behaviour of pollutants in the soil and the hydrological transport processes. This paper aims to identify knowledge gaps in processes influencing pollutant behaviour in soils and their potential transport to groundwater. Currently most soil-filter function research is approached from two disciplines, one originating from agronomical/environmental sciences; one from more fundamental hydrological process research. Combining insights and approaches from both disciplines through collaboration could lead to better understanding of this complex system and enhance assessments of management strategy changes, both over the long term as well as in different climatic settings. Y1 - 2012 U6 - https://doi.org/10.1016/j.cosust.2012.10.007 SN - 1877-3435 SN - 1877-3443 VL - 4 IS - 5 SP - 507 EP - 516 PB - Elsevier CY - Oxford ER -