Refine
Year of publication
Document Type
Way of publication
- Open Access (2)
Keywords
- Diffusive-wave equation (3)
- microtopography (3)
- rainfall variability (3)
- runoff generation (3)
- Runoff generation (2)
- SWIM (2)
- Shallow-water equations (2)
- Surface runoff (2)
- Zero-inertia equation (2)
- deep drainage (2)
Institute
- FG Hydrologie (86)
- Forschungszentrum Landschaftsentwicklung und Bergbaulandschaften (FZLB) (21)
- FG Bodenschutz und Rekultivierung (14)
- FG Geopedologie und Landschaftsentwicklung (3)
- FG Atmosphärische Prozesse (2)
- FG Volkswirtschaftslehre, insbesondere Umweltökonomie (2)
- FG Ökologie (2)
- FG Numerische Strömungs- und Gasdynamik (1)
- Zentrale Analytik der BTU Cottbus-Senftenberg (ZA-BTU) / Zentrales Analytisches Labor (1)
Reactive transport controls on sandy acid sulfate soils and impacts on shallow groundwater quality
(2014)
Disturbance or drainage of potential acid sulfate soils (PASS) can result in the release of acidity and degradation of infrastructure, water resources, and the environment. Soil processes affecting shallow groundwater quality have been investigated using a numerical code that integrates (bio)geochemical processes with water, solute, and gas transport. The patterns of severe and persistent acidification (pH < 4) in the sandy, carbonate-depleted podzols of a coastal plain could be reproduced without calibration, based on oxidation of microcrystalline pyrite after groundwater level decrease and/or residual groundwater acidity, due to slow vertical solute transport rates. The rate of acidification was limited by gas phase diffusion of oxygen and hence was sensitive to soil water retention properties and in some cases also to oxygen con-sumption by organic matter mineralization. Despite diffusion limitation, the rate of oxidation in sandy soils was rapid once pyrite-bearing horizons were exposed, even to a depth of 7.5 m. Groundwater level movement was thus identified as an important control on acidification, as well as the initial pyrite content. Increase in the rate of Fe(II) oxidation lead to slightly lower pH and greater accumulation of Fe(III) phases, but had little effect on the overall amount of pyrite oxidized. Aluminosilicate (kaolinite) dissolution had a small pH-buffering effect but lead to the release of Al and associated acidity. Simulated dewatering scenarios highlighted the potential of the model for risk assessment of (bio)geochemical impacts on soil and groundwater over a range of temporal and spatial scales.
Tagebau(folge)landschaften bieten gute Möglichkeiten den Wandel ökohydrologische Systeme aufgrund veränderter Umweltbedingungen zu untersuchen: Im Zuge des Tagebaubetriebs wird die Vegetation vollständig entfernt, nach dem Tagebau wächst die Vegetation entweder durch aktive Rekultivierung oder natürliche Sukzession wieder auf. Von Interesse ist, ob und wie bzw. wie schnell sich die Tagebauflächen von der Störung erholen und ähnliche Bedingungen wie vor dem Tagebau bzw. auf ungestörten Flächen herrschen. Klimatische,
geomorphologische und ökologische Gegebenheiten sowie die Rekultivierungsstrategie spielen eine große Rolle in der Phase der Rehabilitation und bestimmen die Rate der Wiederbesiedlung
mit Pflanzen bzw. deren Wachstum. Der NDVI (normalisierter differenzierter Vegetationsindex) bietet die Möglichkeit generelle Muster der Vegetation quantitativ zu detektieren, um die Regenerationsrate der Vegetation für verschiedene Klima- und Ökoregionen abzuschätzen. Wir analysierten den MODIS Terra NDVI (achttägliche Werte) für Tagebaulandschaften verschiedener Klimate (äquatoriale, trockene, warm gemäßigte und Schnee-Klimate nach Köppen-Geiger) im Zeitraum 2001 bis 2015. Es wurden Kohletagebaue
betrachtet, da diese gut definierte Chronosequenzen der Störung erzeugen. Bei der Analyse der NDVI-Zeitreihen sollten Charakteristiken der Rehabilitationsphase erfasst werden. Um
die räumliche Heterogenität der Zellen (ca. 250 x 250 m²) der Tagebaulandschaft abzubilden, wurde je Tagebau eine hierarchische Clusteranalyse durchgeführt. Die einzelnen Zeitreihen der Cluster wurden mit einer Methode zur Detektion von Bruchpunkten und zur Zeitreihenzerlegung auf Konsistenz bezüglich Eigenschaften der Zeitreihen (Beginn des Tagebaus, Ende des Tagebaus/Beginn der Rehabilitation, Rate der Rehabilitation) untersucht. Die Clusteranalyse führt zu einer Einordnung der Zellen in vom Tagebau nicht direkt beeinflusste Flächen, aktiven Tagebau und in der Rehabilitation befindliche Fläche verschiedenen Alters
bzw. rehabilitierte Flächen. Das Zeitfenster der Entfernung der Vegetation kann im NDVI-Signal identifiziert werden, es zeigt sich meist in einer abrupten Änderung des NDVI. Die Rehabilitationsphase hingegen verläuft graduell und kann mehrere Jahre bis Jahrzehnte
andauern. Die Zeitreihenzerlegung zeigt auf, dass in der Rehabilitationsphase der Trend dominiert, während mit Voranschreiten der Rehabilitation die Saisonalität im NDVI-Signal vorherrschend wird. Durch die ermittelte Rate der Rehabilitation können die Flächen innerhalb eines Tagebaus miteinander verglichen werden. Die mittlere Rehabilitationsrate der Tagebaue kann in Zusammenhang mit den vorherrschenden hydroklimatischen Bedingungen der Klimazonen und mit Rekultivierungsstrategien gebracht werden. Zudem ist auch eine
Betrachtung hydrometeorologischer Größen zur Erkennung von kurzzeitigen Veränderungen des Pflanzenwachstums im NDVI-Signal möglich.
The artificial Hühnerwasser catchment has experienced a significant and monitored evolution since 2005, changing from a post-mining landscape to an almost fully vegetated ecosystem. The early stages showed a fast rate of ecohydrological evolution with changing dominating processes and feedbacks. The evolution of rill vegetation encroachment is one of such complex co-evolving processes.
We hypothesise that rill vegetation encroachment is driven by the evolution of the hydrologic/hydraulic regime of the rill network, which in turn affects the regime, potentially creating
a stabilising positive feedback. We further hypothesise that rill vegetation occurs later than hillslope vegetation, and follows a particular establishment and encroachment timeline in
response to the changing hydrological/hydraulic regimes. That is, the early runoff-dominated regime results in higher flows, velocities, transport and erosion capacity, thus favouring seed
flushing and seedling uprooting. On the other hand, as the system transitions from a runoffdominated into an infiltration- and ET-dominated system, flow, velocity, transport and erosion
capacity in the rill network are reduced, making seed establishment in the rills more likely. We explore these hypothesis with two complementary approaches: an analysis of the spatiotemporal distribution of vegetation and a process-based numerical modelling study. Firstly, we assess aerial photography of rill vegetation encroachment between 2007 and 2012 in terms of several vegetation types to derive temporal indicators of encroachment. The
analysis reveals that in the initial stages, a rill network developed in the hillslope. Shortly after vegetation first established on hillslopes, the rill network became progressively vegetated. Different pioneering species established heterogeneously, at different times and encroached into the rills at different rates. However, despite the volume of data, it is difficult to assess
which are the governing and limiting processes which respectively drive and constrain how and at which rate vegetation encroaches into the rills. In consequence, a pilot modelling study to identify the relative relevance of rill network geometry, bare soil infiltration, hillslope vegetation heterogeneity and intra-storm variability on the hydraulic response of the rill network and its possible impact on encroachment. The overall results suggest that vegetation
encroachment may be controlled by the rill network hydraulic regime, but such regime is the result of a complex superposition of responses of all the aforementioned factors, of which rill geometry appears to be a dominant one. Furthermore, the simulations showed
that vegetation spatial heterogeneity has an impact on the hydraulic regime coupled to the presence of temporal rainfall variability. Altogether, these results show that the governing coevolving
ecohydrological processes are interacting and are strongly affected by spatial and temporal heterogeneities.
Studien zum Einfluss des zukünftigen Klimawandels auf das Abflussgeschehen fokussieren oft auf die Fortpflanzung von Unsicherheiten in Modellkaskaden, berücksichtigen meist jedoch
die Wasserressourcenbewirtschaftung nur ungenügend. Wir untersuchten den Einfluss der Wasserressourcenbewirtschaftung auf die Abflussvariabilität und die Fortpflanzung von Unsicherheiten von Klimaprojektionen auf Abflusssimulationen in den Einzugsgebieten von
Spree (bis Pegel Große Tränke: 6200 km²) und Schwarzer Elster (5700 km²). Die Einzugsgebiete ähneln sich hinsichtlich Klima, Topographie, Boden und Landnutzung, jedoch ist das Spreeeinzugsgebiet stärker durch den Braunkohletagebau und die damit verbundenen Bewirtschaftung geprägt und durch einen höheren Speicherausbaugrad gekennzeichnet. Um zwischen Bewirtschaftungseinflüssen und meteorologischen Einflüssen zu separieren, wurden für den Zeitraum 1961-2005 beobachtete Abflüsse mit durch das Modell SWIM rekonstruierten natürlichen (d.h. ohne Bewirtschaftungseinfluss) Abflüssen der Vergangenheit verglichen. Mögliche Einflüsse des Klimawandels wurden für den Zeitraum 2018-2052 auf Grundlage von 3 Szenarien des statistischen Regionalmodells STAR (je 100 Realisierungen) mit SWIM (natürliche Abflüsse) und dem Langfristbewirtschaftungsmodell WBalMo (bewirtschaftete Abflüsse) modelliert. Die Analyse erfolgte mit Fokus auf Saisonalität, Oszillation, Verteilung und räumliche Variabilität der Abflüsse. Der Vergleich zwischen beobachteten
und natürlichen Abflüssen der vergangenen Jahrzehnte zeigt, dass die zwischenjährliche Abflussvariabilität im Spreeeinzugsgebiet stärker durch Grubenwassereinleitungen als durch natürliche hydrologische Prozesse bestimmt wurde. Zusätzlich führt der höhere Speicherausbaugrad dazu, dass die kurzzeitliche und saisonale Variabilität im Spreeeinzugsgebiet geringer als im Einzugsgebiet der Schwarzen Elster ist. Simulationen mit Klimaszenarien, welche
steigende Jahresmitteltemperaturen und einen Rückgang der Niederschlagsjahressummen enthalten, führen zu deutlichen Abflussrückgängen. Die Unterschiede der natürlichen Abflüsse
beider Einzugsgebiete sind gering, die Unsicherheiten der Klimaprojektionen werden durch die hydrologische Modellierung verstärkt. Die natürlichen und bewirtschafteten Abflüsse
der Schwarzen Elster unter Klimawandel unterscheiden sich kaum. Im Spreeeinzugsgebiet zeigt sich eine deutliche Verringerung der Variabilität und Unsicherheiten unter Klimawandel von den natürlichen zu den bewirtschafteten Abflüssen. Die Analysen zeigen, dass effektive Wasserressourcenbewirtschaftung die Abflussvariabilität verringern kann und damit auch
dazu beitragen kann, die sich aus Klimawandelprojektionen ergebenden Unsicherheiten zu vermindern. Einzugsgebiete mit einem hohen Ausbaugrad weisen weniger Vulnerabilität bezüglich klimatischer Änderungen auf. Dies unterstreicht die Bedeutung von Wasserresourcenbewirt-schaftungfür die Anpassung an den Klimawandel.
Coevolution of hydrological and vegetation dynamics in semi-arid regions has been widely observed to result in vegetation self-organisation (VSO). Many hypothesis of VSO’s underlying ecohydrological processes and feedbacks have been studied relying on mathematical models, which have been key to evaluate the sensitivity
of ecohydrological systems to environmental factors and drivers. Although this ecohydrological coevolution is essentially multiscale, researchers have continued to be constrained by the simplicity of the models which are unable to cope with the multiscale, process-based complexity of fast-moving surface water over complex
topographies driven by varying rainfall, during decade-to-century long VSO processes. This limitation has not allowed deep exploration of the role and sensitivity of key environmental factors such as topography and rainfall variability, and the lack of proper hydrodynamics still constrains adequate sediment transport modelling and its feedback effects on VSO. We hypothesize that the intra-storm water redistribution by surface runoff at the hillslope scale is strongly controlled by both topography and storm intensity and may control VSO. This requires for these environmental factors to be accurately represented in models and their their hydraulic and hydrological effects properly reflected. This work provides the first systematic study of the effects of topography and intra-annual rainfall distributions on vegetation band formation at the hillslope scale. Simulations were performed with a physically-based
numerical model solving the Zero-Inertia approximation to the shallow water equations for surface flow coupled
to the HilleRisLambers-Rietkerk vegetation model, allowing to explicitly represent arbitrary topography. An idealized study of ecohydrological evolution over 30 years was performed, solving with a temporal resolution in the seconds scale. Plane, convex and convex hillslope topologies with different slopes were used, while forcing
the model with different annual rainfalls along a semi-arid rainfall gradient, with discrete events of different frequencies. We describe results in terms of evolution of total biomass, hydrological water balance, and of the spatial properties of banded vegetation.
Results show that both topography and intra-annual rainfall distribution can play a shaping and governing role in VSO by controlling surface water redistribution and the hydrologic water balance. Increasing slopes favours runoff over infiltration, reducing the available water for vegetation and resulting in different evolutions of vegetation band geometry and band migration. Hillslope topology plays a strong role in the internal water redistribution of the system. Plane and convex surfaces behave similarly, but concave surfaces exhibit a different ecohydrological behaviour, despite the very small topological differences. Different intra-annual rainfall distributions result in different rainfall intensities for the same total annual rainfall which strongly affect
the band formation and evolution process: higher intensities lead to less available water, to which vegetation adapts by spatially clustering in bands with different geometrical properties. The study also shows that it is computationally feasible (a few hours runtime) to perform decade-to-century long simulations of these systems
with physically-based numerical models paving the way to simulate natural systems with arbitrary topography and high-resolution rainfall data, and is a first step in introducing physically-based sediment transport processes and feedbacks in these studies.
The artificial catchment “Hühnerwasser” was built in a post-mining landscape, as a field experiment to observe and monitor early-development ecosystems at hillslope scale. Early on, rain-induced rill and channels formation was observed, followed by vegetation growth in between rills, and later on inside the rills.
In this work, we aim to describe the temporal evolution of the spatial distribution of rill vegetation. In general terms, we hypothesize four different encroachment patterns might occur: (1) The vegetation spreads from the top of the rills downstream. The underlying hypothesis would be a higher establishment probability due to a lower velocity of surface runoff and therefore less transport probability compared to downstream rill segments. (2)
The vegetation starts growing downstream and moves upwards. In this case we can hypothesize that the spatial distribution of the vegetation is dominated by water availability, which is higher or more stable downstream. (3) The vegetation encroaches from the sides into the rills, meaning that inter-rill vegetation governs vegetation encroachment inside the rills. (4) If no patterns are detected it might mean that the encroachment process depends
strongly on very local conditions, or perhaps that the underlying assumption of an initially homogeneous seed distribution is false.
To investigate the rills formation and rill vegetation encroachment processes, rills and vegetation patches inside these rills were identified and digitized from aerial photographs of the catchment from 2007 to 2012. Different vegetation types were identified based on the colour and texture of the patches. The geometrical properties of the rill segments and vegetation patches were used to define how the different vegetation types have distributed in space and how this distribution has changed over time. Rill mapping reveals a large increase of rill area from 2007 to 2008 and only a small rise from 2008 to 2009. Starting in 2010 dense vegetation prevents a precise mapping of the rills in the aerial photographs, so we assume that there is no change in rill area from 2009 to 2012. In 2007 vegetation covered only 1.4% of the rill area. There is only a small increase of this area in 2008 compared to the later years. In 2012 more than 50% of the rill area is covered by plants. Ten different vegetation types have been identified in the aerial photographs, starting with two types in 2007. By 2012 nine types are spotted in
the rills of the catchment. Some of these vegetation types show an encroachment from up- to downstream (e.g. Tussilago farfara), some from down- to upstream like Phragmites australis, whose creeping rhizomes can also promote such spreading. Others reveal no patterns. To better assess and identify the underlying processes leading
to these encroachment processes shown by the different vegetation types further data analysis –e.g. comparison with ground based vegetation mapping– and process-based hydrological modelling is necessary to fully explain these observations and assessing additional competition effects, which may be at play.
The Hühnerwasser catchment is a monitored, early-development constructed catchment within the Lower Lausatia post-mining landscape in Germany. Observations have shown that a sequence of landscape-forming processes occurred, including the initial vegetation establishment stages, which are the main interest of this study. In the initial stages of geomorphic development a surface drainage network of rills was formed as vegetation started to
appear on the hillslopes and subsequently inside the rill network. Observations and analysis of the rill vegetation establishment suggest that different vegetation types encroach into the rill network at different times, rates and form different directions. We hypothesize that these encroachment processes may respond to the runoff properties of the catchment at such time: velocity distribution in the rills might play a significant role in flushing seeds in high-velocity reaches of the rill network, thus favouring the appearance of vegetation in low-velocity regions.
Consequently, the goal of this study is to assess the magnitudes and spatiotemporal behaviour of velocity in the rill network, to assess its possible impact on seed flushing and rill vegetation encroachment. One rill subcatchment of Hühnerwasser was selected to perform an explorative study of rill hydrodynamics and their impact on vegetation establishment. Two vegetation states were simulated: bare hillslopes and vegetated hillslopes. The vegetated cover polygons were obtained from digitized aerial photography, and stochastically dissagregated 10-minute resolution precipitation data were used, selecting events with early, middle and late peak
storm intensities. A 2D explicit finite volume scheme solving the Zero-Inertia approximation to the shallow water
equations was used to simulate surface flow in the subcatchment.
The preliminary modelling results suggest that that there is no clear overall velocity gradient in the downstream
direction along the rills. In fact, velocity in the rills may increase or decrease along the rill following local topography and rill geometry. Consequently, no global trend for the probability of seeds being transported can be established. The results also shows that varying rainfall intensity and rainfall intrastorm distribution –in the absence of hillslope vegetation– does not affect the rill locations of maximum velocities, but mostly affect the magnitude of velocity. In the presence of hillslope vegetation –and thus heterogeneous infiltration conditions in the hillslopes– the spatial distribution of velocity is strongly affected, and can be in fact governed not by topography or rill geometry, but by the spatial heterogeneity of infiltration capacity. Furthermore, the time at which maximum discharge and velocities occur may not match that of maximum intensity. That is, emerging temporal dynamics arise due to the introduction of spatial heterogeneity, which also manifests in the fact that outflow from the subcatchment exhibits a intensity-thresholded behaviour.
Convergent biomass, divergent patterns: Can initial conditions govern vegetation self-organisation?
(2018)
Vegetation self-organisation in water-limited ecosystems in semi-arid climates has been extensively studied by means of numerical simulation using a set of different reaction-diffusion-equations. Most of such models and studies have been concerned with the long-term steady ecohydrological states on domains with periodic
boundaries and forced by steady rainfall, whilst little interest has been given to the transient states which lead to them as well as the spatiotemporal multiscale nature of the feedback processes.
It is generally accepted that alternative random initial biomass distributions do not significantly affect the resulting steady state vegetation patterns. However, the role of the initial hydrological conditions –initial surface and subsurface water– has not been explored, mainly due to the interest in the long-term steady state. Nonetheless, vegetation patterns are directly linked to the water distribution occurring at much shorter time scales than
vegetation growth, and because they have been shown to be sensitive to annual rainfall, it is reasonable that the initially available water will also play a role. We therefore hypothesize that the initially available water will play a role in the transient process leading to a steady ecohydrological state, and that the steady vegetation patterns will differ in response to the water availability in time during the entire process. In this contribution we explore the role of initial hydrological conditions on both the transient and longterm steady ecohydrological state. A simulation study was performed using the HilleRisLambers-Rietkerk ecohydrological model on a flatland varying the initial available water whilst also spanning the rainfall gradient (90 – 360 mm/year) . The results were assessed in terms of the evolution and steady state of total biomass yield and hydrological water balance, as well as a quantitative assessment of both transient and steady vegetation
patterns. The results show that the initially available water does play a role, not only in the early transient state, but in the long-term steady state, and indeed in the geometry of the converged vegetation pattern. Furthermore, although the steady state biomass yield may be the same for varying initial conditions, the final patterns still differ, e.g., a reduction to one-fourth initial water availability results in more but smaller vegetation patches, while
a reduction to one-eigth initial water results in less, but larger patches, and a reduction to one-sixteenth results in a completely new pattern, although total biomass is the same for all. This suggests that long-term average rainfall may govern the total biomass but the initial conditions may play a relevant shaping role in the long term spatial distributions of steady ecohydrological states of water-limited ecohydrosystems. This is relevant, among
other reasons, because the resilience of the system is associated to the vegetation patterns. It also suggests that neither the temporal distribution of rainfall nor the system’s evolution cannot be neglected to understand the environmental factors which lead to a steady ecohydrological state, since multiple paths may be possible. This warrants further developments from the ecohydrological modelling community and further study of transient states through process-based models.
In landscapes with heterogeneous vegetation structure, interception and throughfall patterns produce spatiotemporal
variability of soil moisture. This variability is important for eco-hydrological processes, in particular on
small spatial scales up to the catchment scale. Throughfall depends on vegetation structure, whereas vegetation
development is presumably co-determined by the spatio-temporal distribution of throughfall itself. In addition
to vegetation structure, meteorological factors like wind speed and rainfall intensity also have an impact on
throughfall.
The objective of this study is to quantify the influence of vegetation structure and meteorological variables
on spatial (and in the long run the temporal) variability of throughfall. For that purpose, we developed an
approach combining field methods, image analysis and multivariate statistics. The 6-ha constructed catchment
‚Hühnerwasser‘ (aka Chicken Creek, southern Brandenburg, Germany) offers ideal conditions for the investigation
of eco-hydrological feedback processes. After more than 10 years of development, vegetation structure on the
catchment is spatially heterogeneous and evolves through natural succession. Furthermore, complementary
meteorological data are available on-site.
Throughfall was measured using 50 tipping-bucket rain gauges, which are aligned along two transects in 0.5
and 1 m heights, covering the dominating vegetation types on the catchment (e.g., robinia, sallow thorn, reed,
reedgrass, herbs). The spatial distribution of vegetation structures around each measurement site was recorded
with hemispheric photographs, which were subsequently analyzed using image processing techniques. Two
weather stations provide reference values for precipitation and relevant meteorological variables for wind speed
and direction, air humidity, temperature and irradiation.
The amount and distribution of precipitation measured in scarcely vegetated areas of the catchment widely
correspond with values from the reference weather stations. Under dense vegetation, very heterogeneous values
were recorded, which can be explained by i) canopy interception, and ii) fetching effects. The results of this study
can serve as basis for interception models and may also contribute to complex eco-hydrological models.