TY - JOUR A1 - Zibulski, Romy A1 - Herzschuh, Ulrike A1 - Pestryakova, Luidmila Agafyevna T1 - Vegetation patterns along micro-relief and vegetation type transects in polygonal landscapes of the Siberian Arctic JF - Journal of vegetation science N2 - QuestionHow important is the effect of micro-relief and vegetation type on the characteristics of vascular plants and bryophytes in low-centred polygons? LocationSiberian Arctic, Russia. MethodsEight low-centred polygons in northern Siberia were surveyed for vegetation along transects running from the rim to the pond via the rim-pond transition of each polygon and across a vegetation type gradient from open forest to tundra. ResultsThe cover of vascular plants and bryophytes displays no significant differences between the rim and rim-pond transition but is significantly lower in the pond section of the polygons. Alpha-diversity of vascular plants decreases strongly from rim to pond, whereas bryophyte diversity in pond plots is significantly distinct from the rim and the rim-pond transition. There is no clear trend in cover for either plant group along the vegetation type transect and only a weak trend in -diversity. However, both gradients are reflected in the compositional turnover. The applied indicator species analysis identified taxa characteristic of certain environmental conditions. Among others, we found vascular plants primarily characteristic of the rim and bryophyte taxa characteristic of each micro-relief level and vegetation type. ConclusionsThe observed gradual pattern in -diversity and composition of polygonal vegetation suggests that micro-relief is the main driver of changes in the vegetation composition, while vegetation type and the related forest cover change are of subordinate importance for polygonal vegetation patterns along the Siberian tree line. KW - Bryophytes KW - Indicator species KW - Low-centred polygon KW - NMDS KW - Russia KW - Tree line KW - Tundra KW - Vascular plants Y1 - 2016 U6 - https://doi.org/10.1111/jvs.12356 SN - 1100-9233 SN - 1654-1103 VL - 27 SP - 377 EP - 386 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Carus, Jana A1 - Paul, Maike A1 - Schroeder, Boris T1 - Vegetation as self-adaptive coastal protection: Reduction of current velocity and morphologic plasticity of a brackish marsh pioneer JF - Ecology and evolution N2 - By reducing current velocity, tidal marsh vegetation can diminish storm surges and storm waves. Conversely, currents often exert high mechanical stresses onto the plants and hence affect vegetation structure and plant characteristics. In our study, we aim at analysing this interaction from both angles. On the one hand, we quantify the reduction of current velocity by Bolboschoenus maritimus, and on the other hand, we identify functional traits of B. maritimus’ ramets along environmental gradients. Our results show that tidal marsh vegetation is able to buffer a large proportion of the flow velocity at currents under normal conditions. Cross-shore current velocity decreased with distance from the marsh edge and was reduced by more than 50% after 15 m of vegetation. We were furthermore able to show that plants growing at the marsh edge had a significantly larger diameter than plants from inside the vegetation. We found a positive correlation between plant thickness and cross-shore current which could provide an adaptive value in habitats with high mechanical stress. With the adapted morphology of plants growing at the highly exposed marsh edge, the entire vegetation belt is able to better resist the mechanical stress of high current velocities. This self-adaptive effect thus increases the ability of B. maritimus to grow and persist in the pioneer zone and may hence better contribute to ecosystem-based coastal protection by reducing current velocity. KW - Adaptive value KW - Bolboschoenus maritimus KW - brackish marsh KW - flow velocity KW - mechanical pressure KW - morphological adaptation KW - phenotypic plasticity KW - pioneer zone Y1 - 2016 U6 - https://doi.org/10.1002/ece3.1904 SN - 2045-7758 VL - 6 SP - 1579 EP - 1589 PB - Wiley CY - Hoboken ER - TY - THES A1 - Olen, Stephanie M. T1 - Understanding Himalayan denudation at the catchment and orogen scale T1 - Verständnis von Denudation auf regionalem und orogenem Maßstab im Himalaja N2 - Understanding the rates and processes of denudation is key to unraveling the dynamic processes that shape active orogens. This includes decoding the roles of tectonic and climate-driven processes in the long-term evolution of high- mountain landscapes in regions with pronounced tectonic activity and steep climatic and surface-process gradients. Well-constrained denudation rates can be used to address a wide range of geologic problems. In steady-state landscapes, denudation rates are argued to be proportional to tectonic or isostatic uplift rates and provide valuable insight into the tectonic regimes underlying surface denudation. The use of denudation rates based on terrestrial cosmogenic nuclide (TCN) such as 10Beryllium has become a widely-used method to quantify catchment-mean denudation rates. Because such measurements are averaged over timescales of 102 to 105 years, they are not as susceptible to stochastic changes as shorter-term denudation rate estimates (e.g., from suspended sediment measurements) and are therefore considered more reliable for a comparison to long-term processes that operate on geologic timescales. However, the impact of various climatic, biotic, and surface processes on 10Be concentrations and the resultant denudation rates remains unclear and is subject to ongoing discussion. In this thesis, I explore the interaction of climate, the biosphere, topography, and geology in forcing and modulating denudation rates on catchment to orogen scales. There are many processes in highly dynamic active orogens that may effect 10Be concentrations in modern river sands and therefore impact 10Be-derived denudation rates. The calculation of denudation rates from 10Be concentrations, however, requires a suite of simplifying assumptions that may not be valid or applicable in many orogens. I investigate how these processes affect 10Be concentrations in the Arun Valley of Eastern Nepal using 34 new 10Be measurements from the main stem Arun River and its tributaries. The Arun Valley is characterized by steep gradients in climate and topography, with elevations ranging from <100 m asl in the foreland basin to >8,000 asl in the high sectors to the north. This is coupled with a five-fold increase in mean annual rainfall across strike of the orogen. Denudation rates from tributary samples increase toward the core of the orogen, from <0.2 to >5 mm/yr from the Lesser to Higher Himalaya. Very high denudation rates (>2 mm/yr), however, are likely the result of 10Be TCN dilution by surface and climatic processes, such as large landsliding and glaciation, and thus may not be representative of long-term denudation rates. Mainstem Arun denudation rates increase downstream from ~0.2 mm/yr at the border with Tibet to 0.91 mm/yr at its outlet into the Sapt Kosi. However, the downstream 10Be concentrations may not be representative of the entire upstream catchment. Instead, I document evidence for downstream fining of grains from the Tibetan Plateau, resulting in an order-of-magnitude apparent decrease in the measured 10Be concentration. In the Arun Valley and across the Himalaya, topography, climate, and vegetation are strongly interrelated. The observed increase in denudation rates at the transition from the Lesser to Higher Himalaya corresponds to abrupt increases in elevation, hillslope gradient, and mean annual rainfall. Thus, across strike (N-S), it is difficult to decipher the potential impacts of climate and vegetation cover on denudation rates. To further evaluate these relationships I instead took advantage of an along-strike west-to-east increase of mean annual rainfall and vegetation density in the Himalaya. An analysis of 136 published 10Be denudation rates from along strike of the revealed that median denudation rates do not vary considerably along strike of the Himalaya, ~1500 km E-W. However, the range of denudation rates generally decreases from west to east, with more variable denudation rates in the northwestern regions of the orogen than in the eastern regions. This denudation rate variability decreases as vegetation density increases (R=- 0.90), and increases proportionately to the annual seasonality of vegetation (R=0.99). Moreover, rainfall and vegetation modulate the relationship between topographic steepness and denudation rates such that in the wet, densely vegetated regions of the Himalaya, topography responds more linearly to changes in denudation rates than in dry, sparsely vegetated regions, where the response of topographic steepness to denudation rates is highly nonlinear. Understanding the relationships between denudation rates, topography, and climate is also critical for interpreting sedimentary archives. However, there is a lack of understanding of how terrestrial organic matter is transported out of orogens and into sedimentary archives. Plant wax lipid biomarkers derived from terrestrial and marine sedimentary records are commonly used as paleo- hydrologic proxy to help elucidate these problems. I address the issue of how to interpret the biomarker record by using the plant wax isotopic composition of modern suspended and riverbank organic matter to identify and quantify organic matter source regions in the Arun Valley. Topographic and geomorphic analysis, provided by the 10Be catchment-mean denudation rates, reveals that a combination of topographic steepness (as a proxy for denudation) and vegetation density is required to capture organic matter sourcing in the Arun River. My studies highlight the importance of a rigorous and careful interpretation of denudation rates in tectonically active orogens that are furthermore characterized by strong climatic and biotic gradients. Unambiguous information about these issues is critical for correctly decoding and interpreting the possible tectonic and climatic forces that drive erosion and denudation, and the manifestation of the erosion products in sedimentary archives. N2 - Schlüssel im Verständnis der dynamischen Prozesse in aktiven Orogenen ist die Kenntnis der Abtragungsraten und -prozesse. Eine breite Auswahl geologischer Fragen können mit well-constrained Abtragungsraten erörtert werden. Sind Landschaften im Gleichgewicht so sind die Denudationsraten proportional zu den tektonischen und isostatischen Hebungsraten und geben somit wichtige Hinweise über die tektonischen Eigenschaften der Region. Eine weit verbreitete und etablierte Methode zur Bestimmung mittlerer Denudationsraten eines bestimmten Einzugsgebietes ist Beryllium-10, ein terrestrisches kosmogenes Nuklid (10Be TCN). 10Be TCN Messungen stellen durchschnittliche Abtragungsraten über einen Zeitraum von 10^2 – 10^5 Jahren dar und sind daher weniger verletzlich gegenüber stochastischen Änderungen wie Erosionsraten, die über einen kurzen Zeitraum ermittelt werden z.B. in Suspension. Sie sind daher zuverlässig einsetzbar um langfristige Prozesse zu vergleichen. Allerdings ist unklar welche Einfluss verschiedene klimatische, biologische oder erdoberflächen Prozesse auf die 10Be Konzentration ausüben und somit auch auf die resultierenden Abtragungsraten. In dieser Doktorarbeit, setze ich mich mit dem Zwischenspiel von Klima, Biosphäre, Topographie und Geologie auseinander und dem Einfluss, den sie auf Abtragungsraten ausüben sowohl auf regionalem wie auch auf orogenem Maßstab. In hoch dynamischen aktiven Gebirgen gibt es viele Prozesse, welche die 10Be Konzentration in heutigen Flusssanden beeinflussen und damit auch die, mittels 10Be berechneten, Abtragungsraten. Um diese Raten mittels 10Be Konzentrationen zu berechnen benötigen wir einige vereinfachende Annahmen, die möglicherweise in anderen Regionen keine Gültigkeit haben. Ich untersuche den Einfluss dieser Prozesse auf die 10Be Konzentration. Dazu haben wir im Arun Tal im Osten Nepals 34 neue 10Be Konzentrationen des Arun Flusses und seinen Zuflüssen untersucht. Charakteristisch für das Arun Tal sind die steilen Gradienten im Klima mit einem fünffachen Anstieg des mittleren jährlichen Regenfalls über das Orogens, und in der Topographie mit Höhen von weniger als 100 m über Meer im Vorlandbecken bis über 8000 m über Meer im Gebirge. Die Abtragungsraten der Proben der Zuflüsse nehmen gegen das Zentrum des Gebirges von weniger <0.2 zu mehr als >5 mm/yr zu d.h. ansteigend vom Lesser zum Higher Himalaya. Sehr hohe Denudationsraten (> 2mm/yr) können durch erdoberflächen und klimatische Prozesse verwässert werden z. B. grosse Erdrutsche und Vergletscherungen, und sind daher nicht unbedingt repräsentativ für langzeitliche Abtragungsraten. Im Arun nehmen die Raten des Hauptflusses flussabwärts von 0.2 mm/yr im Bereich der Grenze zu Tibet auf 0.91 mm/yr am Ausfluss in Sapt Kosi zu. Es ist möglich, dass diese 10Be Konzentrationen nicht das vollständige flussauswärtsliegende Einzugsgebiet repräsentieren. Stattdessen lege ich dar wie sich die Korngrösse ab dem tibetischen Plateau verfeinert und dazu führt, dass die 10Be Konzentrationen offenkundig im Bereich einer Grössenordnung abnehmen. Im Arun Tal und sowie über den ganzen Himalaja sind Topographie, Klima und Vegetation sehr stark miteinander verbunden. Das Ansteigen der Denudationsraten im Übergang vom Lesser zum Higher Himalaya stimmt mit dem abrupten Ansteigen der Höhe, des Hangneigungsgradienten und des mittleren jährlichen Regenfalles überein. Es ist schwierig die möglichen Einflüssen von Klima und der Vegetationsdichte auf die Abtragungsraten über das Orogen hinweg (N-S) zu entziffern. Stattdessen, nutzen wir den Vorteil der, von West nach Ost, parallel zum Himalaja verlaufenden, Zunahme des mittleren jährlichen Regenfalles und der Vegetationsdichte. Eine Analyse 136 publizierter 10Be TCN Abtragungsraten entlang des Gebirges, zeigt dass die im Streichen liegenden mittleren Denudationsraten (ca. 1500 km Ost-West) nicht deutlich variieren. Generell sinkt die Wertebereich der Denudationsraten vom Westen gegen Osten, wobei in den nordwestlichen Regionen des Himalajas variablere Abtragungsraten vorherrschen als in den östlichen Regionen. Diese Vielfalt in den Denudationsraten sinkt mit steigender Vegetationsdichte (R=-0.90) und steigt proportional zur (jährlichen) Saisonalität der Vegetation (R=0.99). Vielmehr noch wird das Verhältnis zwischen der topographischen Steilheit und den Abtragungsraten durch Regen und Vegetation beeinflusst z. B. in feuchten Gebieten mit starker Vegetation reagiert die Topographie linearer auf Wechsel in den Abtragungsraten als in trockenen, kaum bewachsenen Regionen, wo die Reaktion der topographischen Steilheit auf die Denudationsraten äusserst nicht-linear ist. Das Verständnis der Beziehung zwischen Erosion, Topographie und Klima ist auch entscheidend für die Interpretation von Sedimentarchiven. Unser Wissen über die Repräsentativität von terrestrisches organisches Material, abgelagert in z.B. Flussdeltas, für die Einzugsgebiete der entsprechenden Flüsse, ist nach wie vor nur vage. Dennoch sind Blattwachse höherer Landpflanzen, extrahiert aus terrestrischen und marinen Sedimenten, ein häufig verwendeter paläohydrologischer Proxy. Im Rahmen dieser Arbeit nutzen wir die Isotopenzusammensetzung von Pflanzenwachsen aus Suspensionsmaterial und aus Flusssedimenten als Herkunftsmarker und zur Quantifizierung des organischen Materials im Arun Tal. Die Analyse von Vegetationsdichte und Regenverteilung in Kombination mit Abtragungsraten des Einzugsgebietes, welche durch die mittleren 10Be-Erosionsraten gestützt werden, zeigen, dass das Vorhandensein dichter Vegetation ein zwar notwendiges, aber nicht hinreichendes Kriterium für hohen OM-Export ist. Vielmehr können wir zeigen, dass nur eine Kombination aus dichter Vegetationsdecke und Erosion zu hohem OM-Export führt. Für die Interpretation entspechender Archive bedeutet das, dass sie im Wesentlichen jene Bereiche des Einzugsgebietes repräsentieren, welche durch hohe Pflanzendichte und starke Erosion charakterisiert sind. Diese Studien belegen wie wichtig es ist die Abtragungsraten in aktiven Gebirgen umfassend zu verstehen. Für die Interpretation kann dieses Verständnis der möglichen tektonischen und klimatischen Gewalten, welche Erosion und Abtragung steuern, und auch das Verständnis der Sedimentarchive aus den Gebirgen stammend, entscheidend sein. KW - geology KW - geomorphology KW - Himalaya KW - Geologie KW - Geomorphologie KW - Himalaja Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-91423 ER - TY - GEN A1 - Schwanghart, Wolfgang A1 - Worni, Raphael A1 - Huggel, Christian A1 - Stoffel, Markus A1 - Korup, Oliver T1 - Uncertainty in the Himalayan energy–water nexus BT - estimating regional exposure to glacial lake outburst floods N2 - Himalayan water resources attract a rapidly growing number of hydroelectric power projects (HPP) to satisfy Asia's soaring energy demands. Yet HPP operating or planned in steep, glacier-fed mountain rivers face hazards of glacial lake outburst floods (GLOFs) that can damage hydropower infrastructure, alter water and sediment yields, and compromise livelihoods downstream. Detailed appraisals of such GLOF hazards are limited to case studies, however, and a more comprehensive, systematic analysis remains elusive. To this end we estimate the regional exposure of 257 Himalayan HPP to GLOFs, using a flood-wave propagation model fed by Monte Carlo-derived outburst volumes of >2300 glacial lakes. We interpret the spread of thus modeled peak discharges as a predictive uncertainty that arises mainly from outburst volumes and dam-breach rates that are difficult to assess before dams fail. With 66% of sampled HPP are on potential GLOF tracks, up to one third of these HPP could experience GLOF discharges well above local design floods, as hydropower development continues to seek higher sites closer to glacial lakes. We compute that this systematic push of HPP into headwaters effectively doubles the uncertainty about GLOF peak discharge in these locations. Peak discharges farther downstream, in contrast, are easier to predict because GLOF waves attenuate rapidly. Considering this systematic pattern of regional GLOF exposure might aid the site selection of future Himalayan HPP. Our method can augment, and help to regularly update, current hazard assessments, given that global warming is likely changing the number and size of Himalayan meltwater lakes. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 266 KW - hydropower KW - water resources KW - glacial hazards KW - glacial lake outburst floods KW - Himalayas Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-97136 ER - TY - JOUR A1 - Schwanghart, Wolfgang A1 - Worni, Raphael A1 - Huggel, Christian A1 - Stoffel, Markus A1 - Korup, Oliver T1 - Uncertainty in the Himalayan energy–water nexus BT - estimating regional exposure to glacial lake outburst floods JF - Environmental research letters : ERL N2 - Himalayan water resources attract a rapidly growing number of hydroelectric power projects (HPP) to satisfy Asia's soaring energy demands. Yet HPP operating or planned in steep, glacier-fed mountain rivers face hazards of glacial lake outburst floods (GLOFs) that can damage hydropower infrastructure, alter water and sediment yields, and compromise livelihoods downstream. Detailed appraisals of such GLOF hazards are limited to case studies, however, and a more comprehensive, systematic analysis remains elusive. To this end we estimate the regional exposure of 257 Himalayan HPP to GLOFs, using a flood-wave propagation model fed by Monte Carlo-derived outburst volumes of >2300 glacial lakes. We interpret the spread of thus modeled peak discharges as a predictive uncertainty that arises mainly from outburst volumes and dam-breach rates that are difficult to assess before dams fail. With 66% of sampled HPP are on potential GLOF tracks, up to one third of these HPP could experience GLOF discharges well above local design floods, as hydropower development continues to seek higher sites closer to glacial lakes. We compute that this systematic push of HPP into headwaters effectively doubles the uncertainty about GLOF peak discharge in these locations. Peak discharges farther downstream, in contrast, are easier to predict because GLOF waves attenuate rapidly. Considering this systematic pattern of regional GLOF exposure might aid the site selection of future Himalayan HPP. Our method can augment, and help to regularly update, current hazard assessments, given that global warming is likely changing the number and size of Himalayan meltwater lakes. KW - Himalayas KW - glacial hazards KW - glacial lake outburst floods KW - hydropower KW - water resources Y1 - 2016 U6 - https://doi.org/10.1088/1748-9326/11/7/074005 SN - 1748-9326 VL - 11 PB - IOP Publ. CY - Bristol ER - TY - JOUR A1 - Schwanghart, Wolfgang A1 - Worni, Raphael A1 - Huggel, Christian A1 - Stoffel, Markus A1 - Korup, Oliver T1 - Uncertainty in the Himalayan energy-water nexus: estimating regional exposure to glacial lake outburst floods JF - Environmental research letters N2 - Himalayan water resources attract a rapidly growing number of hydroelectric power projects (HPP) to satisfy Asia's soaring energy demands. Yet HPP operating or planned in steep, glacier-fed mountain rivers face hazards of glacial lake outburst floods (GLOFs) that can damage hydropower infrastructure, alter water and sediment yields, and compromise livelihoods downstream. Detailed appraisals of such GLOF hazards are limited to case studies, however, and a more comprehensive, systematic analysis remains elusive. To this end we estimate the regional exposure of 257 Himalayan HPP to GLOFs, using a flood-wave propagation model fed by Monte Carlo-derived outburst volumes of >2300 glacial lakes. We interpret the spread of thus modeled peak discharges as a predictive uncertainty that arises mainly from outburst volumes and dam-breach rates that are difficult to assess before dams fail. With 66% of sampled HPP are on potential GLOF tracks, up to one third of these HPP could experience GLOF discharges well above local design floods, as hydropower development continues to seek higher sites closer to glacial lakes. We compute that this systematic push of HPP into headwaters effectively doubles the uncertainty about GLOF peak discharge in these locations. Peak discharges farther downstream, in contrast, are easier to predict because GLOF waves attenuate rapidly. Considering this systematic pattern of regional GLOF exposure might aid the site selection of future Himalayan HPP. Our method can augment, and help to regularly update, current hazard assessments, given that global warming is likely changing the number and size of Himalayan meltwater lakes. KW - hydropower KW - water resources KW - glacial hazards KW - glacial lake outburst floods KW - Himalayas Y1 - 2016 U6 - https://doi.org/10.1088/1748-9326/11/7/074005 SN - 1748-9326 VL - 11 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Wehrhan, Marc A1 - Rauneker, Philipp A1 - Sommer, Michael T1 - UAV-Based Estimation of Carbon Exports from Heterogeneous Soil Landscapes-A Case Study from the CarboZALF Experimental Area JF - SENSORS N2 - The advantages of remote sensing using Unmanned Aerial Vehicles (UAVs) are a high spatial resolution of images, temporal flexibility and narrow-band spectral data from different wavelengths domains. This enables the detection of spatio-temporal dynamics of environmental variables, like plant-related carbon dynamics in agricultural landscapes. In this paper, we quantify spatial patterns of fresh phytomass and related carbon (C) export using imagery captured by a 12-band multispectral camera mounted on the fixed wing UAV Carolo P360. The study was performed in 2014 at the experimental area CarboZALF-D in NE Germany. From radiometrically corrected and calibrated images of lucerne (Medicago sativa), the performance of four commonly used vegetation indices (VIs) was tested using band combinations of six near-infrared bands. The highest correlation between ground-based measurements of fresh phytomass of lucerne and VIs was obtained for the Enhanced Vegetation Index (EVI) using near-infrared band b(899). The resulting map was transformed into dry phytomass and finally upscaled to total C export by harvest. The observed spatial variability at field- and plot-scale could be attributed to small-scale soil heterogeneity in part. KW - VI KW - soil landscape KW - carbon export KW - agriculture KW - multispectral KW - UAV Y1 - 2016 U6 - https://doi.org/10.3390/s16020255 SN - 1424-8220 VL - 16 PB - MDPI CY - Basel ER - TY - GEN A1 - Wehrhan, Marc A1 - Rauneker, Philipp A1 - Sommer, Michael T1 - UAV-Based estimation of carbon exports from heterogeneous soil landscapes BT - a case study from the CarboZALF experimental area T2 - Sensors N2 - The advantages of remote sensing using Unmanned Aerial Vehicles (UAVs) are a high spatial resolution of images, temporal flexibility and narrow-band spectral data from different wavelengths domains. This enables the detection of spatio-temporal dynamics of environmental variables, like plant-related carbon dynamics in agricultural landscapes. In this paper, we quantify spatial patterns of fresh phytomass and related carbon (C) export using imagery captured by a 12-band multispectral camera mounted on the fixed wing UAV Carolo P360. The study was performed in 2014 at the experimental area CarboZALF-D in NE Germany. From radiometrically corrected and calibrated images of lucerne (Medicago sativa), the performance of four commonly used vegetation indices (VIs) was tested using band combinations of six near-infrared bands. The highest correlation between ground-based measurements of fresh phytomass of lucerne and VIs was obtained for the Enhanced Vegetation Index (EVI) using near-infrared band b(899). The resulting map was transformed into dry phytomass and finally upscaled to total C export by harvest. The observed spatial variability at field- and plot-scale could be attributed to small-scale soil heterogeneity in part. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 451 KW - VI KW - soil landscape KW - carbon export KW - agriculture KW - multispectral KW - UAV Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-407706 ER - TY - THES A1 - Hohenbrink, Tobias Ludwig T1 - Turning a problem into a solution: heterogeneities in soil hydrology T1 - Ein Problem zur Lösung machen: Heterogenitäten in der Bodenhydrologie N2 - It is commonly recognized that soil moisture exhibits spatial heterogeneities occurring in a wide range of scales. These heterogeneities are caused by different factors ranging from soil structure at the plot scale to land use at the landscape scale. There is an urgent need for effi-cient approaches to deal with soil moisture heterogeneity at large scales, where manage-ment decisions are usually made. The aim of this dissertation was to test innovative ap-proaches for making efficient use of standard soil hydrological data in order to assess seep-age rates and main controls on observed hydrological behavior, including the role of soil het-erogeneities. As a first step, the applicability of a simplified Buckingham-Darcy method to estimate deep seepage fluxes from point information of soil moisture dynamics was assessed. This was done in a numerical experiment considering a broad range of soil textures and textural het-erogeneities. The method performed well for most soil texture classes. However, in pure sand where seepage fluxes were dominated by heterogeneous flow fields it turned out to be not applicable, because it simply neglects the effect of water flow heterogeneity. In this study a need for new efficient approaches to handle heterogeneities in one-dimensional water flux models was identified. As a further step, an approach to turn the problem of soil moisture heterogeneity into a solu-tion was presented: Principal component analysis was applied to make use of the variability among soil moisture time series for analyzing apparently complex soil hydrological systems. It can be used for identifying the main controls on the hydrological behavior, quantifying their relevance, and describing their particular effects by functional averaged time series. The ap-proach was firstly tested with soil moisture time series simulated for different texture classes in homogeneous and heterogeneous model domains. Afterwards, it was applied to 57 mois-ture time series measured in a multifactorial long term field experiment in Northeast Germa-ny. The dimensionality of both data sets was rather low, because more than 85 % of the total moisture variance could already be explained by the hydrological input signal and by signal transformation with soil depth. The perspective of signal transformation, i.e. analyzing how hydrological input signals (e.g., rainfall, snow melt) propagate through the vadose zone, turned out to be a valuable supplement to the common mass flux considerations. Neither different textures nor spatial heterogeneities affected the general kind of signal transfor-mation showing that complex spatial structures do not necessarily evoke a complex hydro-logical behavior. In case of the field measured data another 3.6% of the total variance was unambiguously explained by different cropping systems. Additionally, it was shown that dif-ferent soil tillage practices did not affect the soil moisture dynamics at all. The presented approach does not require a priori assumptions about the nature of physical processes, and it is not restricted to specific scales. Thus, it opens various possibilities to in-corporate the key information from monitoring data sets into the modeling exercise and thereby reduce model uncertainties. N2 - Es ist allgemein anerkannt, dass Bodenfeuchte auf verschiedenen Raumskalen räumliche Heterogenitäten aufweist. Diese Heterogenitäten werden durch verschiedene Faktoren verursacht, die auf den unterschiedlichen Skalen wirken. Dies können z.B. die Bodenstruktur auf Plotskala oder die Landnutzung auf Landschaftsskala sein. Es werden dringend effiziente Ansätze benötigt, um mit den Heterogenitäten der Bodenfeuchte umzugehen. Dies gilt be-sonders für große Skalen, auf denen in der Regel weitreichende Managemententscheidun-gen getroffen werden. Das Ziel dieser Dissertation war es, effiziente Methoden zu testen, die es ermöglichen auf Basis bodenhydrologischer Daten sowohl Sickerwasserraten als auch die Haupteinflussfaktoren der Bodenfeuchtedynamik zu bestimmen. Dies bezieht Effekte von Bodenheterogenitäten mit ein. In einem ersten Schritt wurde die Eignung einer vereinfachten Buckingham-Darcy Methode zur Abschätzung von Sickerwasserflüssen auf Grundlage punktuell gemessener Zeitreihen der Bodenfeuchte untersucht. Hierzu wurde eine Simulationsstudie durchgeführt, in der ein breites Spektrum an Bodentexturen und Texturheterogenitäten berücksichtigt wurde. Die Methode lieferte gute Ergebnisse für die meisten Texturklassen. In reinem Sand jedoch stell-te sie sich als nicht anwendbar heraus, da hier Sickerwasserflüsse von heterogenen Fließfel-dern dominiert wurden. In dieser Studie wurde ein Bedarf an neuen effizienten Ansätzen für den Umgang mit Heterogenitäten in eindimensionalen Wasserflussmodellen identifiziert. In einem weiteren Schritt wurde ein Ansatz vorgestellt, um aus dem Problem der Boden-feuchteheterogenität eine Lösung zu machen: In einer Hauptkomponentenanalyse wurde die Variabilität zwischen Bodenfeuchtezeitreihen genutzt, um die wahre Komplexität bo-denhydrologischer Systeme zu analysieren. Auf diesem Weg ist es möglich die Haupteinfluss-faktoren des hydrologischen Verhaltens zu identifizieren, ihre Relevanz zu quantifizieren und ihre jeweiligen Effekte als funktional gemittelte Zeitreihen zu beschreiben. Der Ansatz wurde zunächst mit simulierten Bodenfeuchtezeitreihen für unterschiedliche Texturklassen im ho-mogenen und heterogenen Fall getestet. Anschließend wurde die Methode auf 57 Boden-feuchtezeitreihen angewendet, die in einem Langzeitfeldexperiment in Nordostdeutschland gemessen wurden. Die Dimensionalität beider Datensätze war gering, da mehr als 85 % der gesamten Boden-feuchtevarianz bereits durch das hydrologische Eingangssignal und die Transformation dieses Signals mit zunehmender Bodentiefe erklärt werden konnten. Analysen der Signaltransfor-mation haben sich als wertvolle Ergänzung zu den weit verbreiteten Massenflussbetrachtun-gen herausgestellt. Hierbei wird untersucht, wie sich hydrologische Eingangssignale (z.B. Nie-derschlag oder Schneeschmelze) in der vadosen Zone fortpflanzen. Die generellen Muster der Signaltransformation wurden weder durch verschiedene Bodentexturen noch durch räumliche Heterogeneitäten beeinfluss. Dies zeigt, dass komplexe räumliche Strukturen nicht zwangsläufig ein komplexes hydrologisches Verhalten hervorrufen. Im Fall der Felddaten wurden weitere 3,6 % der Gesamtvarianz durch verschiedene Fruchtfolgen erklärt. Darüber hinaus konnte gezeigt werden, dass die Bodenbearbeitung keinen Einfluss auf die Boden-feuchtedynamik hatte. Der vorgestellte Ansatz erfordert keine Vorannahmen über physikalische Prozesse und ist nicht auf eine bestimmte Skala begrenzt. Dadurch ergeben sich viele Möglichkeiten, wichtige Informationen aus Monitoringdatensätzen in die Modellbildung einzubeziehen und damit Modell-unsicherheiten zu verringern. KW - soil hydrology KW - soil heterogeneity KW - soil moisture KW - deep seepage KW - time series analysis KW - transformation of hydrological signals KW - Bodenhydrologie KW - Bodenheterogenität KW - Bodenfeuchte KW - Tiefenversickerung KW - Zeitreihenanalyse KW - Transformation hydrologischer Signale Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-101485 ER - TY - JOUR A1 - Kruse, Stefan A1 - Wieczorek, Mareike A1 - Jeltsch, Florian A1 - Herzschuh, Ulrike T1 - Treeline dynamics in Siberia under changing climates as inferred from an individual-based model for Larix JF - Ecological modelling : international journal on ecological modelling and engineering and systems ecolog KW - Forest change KW - IBM KW - ODD model description KW - Larix gmelinii KW - Permafrost ecosystem KW - Time-lag effects Y1 - 2016 U6 - https://doi.org/10.1016/j.ecolmodel.2016.08.003 SN - 0304-3800 SN - 1872-7026 VL - 338 SP - 101 EP - 121 PB - Elsevier CY - Amsterdam ER -