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SSS8.8

Ecosystems, their abiotic and biotic compartments as well as their internal processes and interactions can be interpreted as the result of numerous evolutionary steps during system development. Understanding ecosystem development can be regarded, therefore, as crucial for understanding ecosystem functioning.
Most of these basic ecosystem processes are not directly accessible and several of them become apparent only after disturbance (e.g. drought, heat waves) or anthropogenic system modifications when single ecosystem processes produce distinct signals. Thus, experiments are widely used for elucidating Critical Zone development, function and its links to ecosystem processes. In this part of the session we aim at creating an overview on experimental ecosystem development research infrastructures and model natural systems. Besides insights into flagship sites this session provides interdisciplinary contributions dealing with exemplary concepts of experimental ecosystem infrastructures and landscape observatories in Critical Zone research, concepts for monitoring Critical Zone processes in experimental landscape observatories, results of experiments and monitoring studies, as well as modelling approaches for explaining process linking Critical zone and ecosystem processes in responses to global changes.
The second part of the session focuses on spatial patterns of vegetation, soils and landforms which are recognized as sources of valuable information for inferring the state and function of ecosystems. This part of the session will focus on ecogeomorphological and ecohydrological aspects of landscapes, conservation of soil resources, and the restoration of ecosystem functions. Contributions will deal with theoretical, modelling and empirical studies addressing the organization of vegetation and coevolving soils and landforms, and particularly, the soil erosion-vegetation relationships that rule the formation of landscape-level spatial patterns. In addition, studies describing the implications of these spatial patterns of soils and vegetation for the resilience and stability of ecosystems under the pressure of climate change and/or human disturbances will be presented.
The conveners are happy to announce a solicited talk on "Dynamics and patterns of plant development in restored mining areas - practical examples" given by Carolina Martínez-Ruis from the University Institute of Research in Sustainable Forestry at the University of Valladolid (Spain).

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Convener: Werner Gerwin | Co-conveners: Jose Rodriguez, Shayli Dor-Haim, Jan Frouz, Mariano Moreno de las Heras, Patricia Saco, Omer Yetemen
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| Thu, 07 May, 16:15–18:00 (CEST)

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Chat time: Thursday, 7 May 2020, 16:15–18:00

D2152 |
EGU2020-4209
| solicited
Carolina Martínez-Ruiz

Opencast mining has altered large areas in many countries, generating major environmental impacts, whose restoration is an urgent need. The effective restoration of opencast mines is a complex process, hampered primarily by the total elimination of vegetation and soil. In the absence of plant cover, these areas may be subject to wind and water erosion, or leaching, polluting rivers, streams, aquifers, and arable lands, as well as being unsightly. Although revegetation of mine wastes can occur naturally, if given time, the process could be extremely slow due to the toxicity, and physical and nutritional shortcomings that wastes often present. Several revegetation approaches have been undertaken worldwide to promote faster vegetation development. However, the results have often been discouraging by a lack of knowledge of the ecological principles involved; the soil is one of the most important limiting factors for vegetation establishment in mine lands.

Topsoil addition over coal-mine wastes in northern Spain favours the establishment of native vegetation by improving physico-chemical and biological soil properties. Without topsoil, vegetation establishment is extremely slow resulting in very unstable plant communities even 40 years after the stop of mining. The addition of herbaceous plant seeds by hydroseeding is frequently used to compensate for the seeds scarcity in the added topsoil. However, hydroseeding is not always successful because of the use of commercial mixtures of non-native seeds. In any case, the installed grassland is being colonized by woody species from the surrounding forest. The structure of the new plant community varies not only in time (succession) but also in space (distance to the seed source), and the process is strongly determined by interactions between the forest edge and the initial grassland patch. The colonization pattern of woody species is affected by fine-scale variations in abiotic factors, including soil properties, which change from the forest to the mine. The native shrubs that colonize the mines (Genista florida and Cytisus scoparius) facilitate the establishment of native oaks (Quercus pyrenaica and Q. petraea) and thus the natural forest expansion. One of the mechanisms driving this facilitation shrub-tree process is the soil improvement mediated by native shrubs. Also, hillside topography, common in mines located in the mountains, has certain peculiarities regarding revegetation in flat areas since there is a segregation of vegetation along the slope with grasslands occupying the upper parts and shrublands of legumes the lower parts.

In order to improve the decision-making during restoration management, it is necessary to be based on the knowledge of the mechanisms that condition the establishment of vegetation and the underlying succession processes. The long-term monitoring of existing experimental devices and their extension to other areas and restoration objectives are essential to establish a protocol of performance to adjust decisions to the particular circumstances of each area to be restored and thus reconcile environmental restoration with the economic activity of the area.

D2153 |
EGU2020-12770
C. Jason Williams, Frederick B. Pierson, Patrick R. Kormos, Osama Z. Al-Hamdan, Sayjro K. Nouwakpo, Viktor O. Polyakov, and Justin C. Johnson

Mitigating and reversing negative ecohydrologic impacts of woody plant encroachment is of global concern. Current knowledge on the ramifications of woody plant encroachment and landscape responses to management is largely based on short-term or point-in-time field studies. The limited longevity of these studies is often dictated by the short-term nature of funding sources and associated infrastructure. Short-term studies advance process-based ecohydrologic knowledge of natural systems and yield valuable insight on treatment effects for various practices to mitigate woody plant encroachment. However, scientists, public and private land owners, and policy makers require knowledge of long-term effectiveness of treatment practices and associated conceptual and quantitative tools to successfully target land management expenditures and actions. This presentation highlights science-based knowledge and ecohydrologic model advancements in management of woody plant encroachment over a nearly 15 yr study period associated with ecohydrologic research at multiple sites in the sagebrush biome within the Great Basin Region of the western United States (the SageSTEP study, www.sagestep.org). The sagebrush biome is considered one of the most ecologically important and imperiled rangeland domains in the United States. A primary driver of degradation to the sagebrush biome is encroachment by pinyon and juniper conifers. These encroaching trees can outcompete sagebrush vegetation for soil and water resources and ultimately propagate and perpetuate pinyon and juniper woodland conditions with extensive bare ground and amplified runoff and soil loss. This study evaluated the ecohydrologic impacts of pinyon and juniper encroachment on sagebrush steppe and the long-term effectiveness of various tree-removal practices to restore sagebrush steppe vegetation and associated ecohydrologic function. Experiments in the study include assessment of vegetation, ground cover, soils, and infiltration, runoff, and erosion processes spanning point to hillslope spatial scales prior to tree removal treatments and at time periods 1 yr, 2 yr, 9 yr, and 13 yr after tree removal. Research products include: 1) advances in conceptual and quantitative understanding of linkages in vegetation and hydrology and erosion processes for the sagebrush steppe ecosystem, 2) enhancements to various conceptual ecological models and the Rangeland Hydrology and Erosion Model (RHEM) tool, 3) advanced understanding of the effectiveness of various tree-removal practices across diverse conditions in the sagebrush biome, and 4) delivery of an extensive publicly-available dataset for developing, enhancing, and/or evaluating other conceptual and quantitative ecohydrologic and erosion models. Lastly, the collective advances in science-based knowledge and modeling tools from the study demonstrate the utility and value of funding and conducting long-term ecohydrological research, particularly for ecologically important biomes around the world.   

 

D2154 |
EGU2020-13190
Vladimir Belyaev, Ilya Shorkunov, Ekaterina Garankina, Evgeniy Konstantinov, Alexey Rusakov, Yulia Shishkina, Pavel Andreev, and Tatiana Verlova

For the landscape and climatic conditions of the Eastern European Plain fluvial processes are considered to be the leading geomorphic force during the Holocene. Different hierarchical levels of fluvial landforms from individual hillslopes through gully network to river systems are characterized by various degrees of resilience and relaxation times in response to external impacts of different duration, magnitude and frequency. These characteristics of fluvial systems largely depend on their spatial scale, effective discharges and morphodynamics. Particularly important is understanding of hydrological and geomorphic connectivity at various scales, rates and patterns of hydrological and sedimentary signals propagation and variable sources-pathways-sinks structure of geomorphic cascades under changing climate and land use conditions. It is generally accepted that landscapes of the European plains have experienced alternating periods of relative stability and significant shifts in climate, soil and geomorphological development over the Holocene. A number of studies has been devoted to the Holocene soil and gully erosion processes in Russia and other European countries. Available sources of information on the past erosion and deposition cycles in small catchments include truncated soils, completely or partially infilled gullies, colluvial deposits and lake or reservoir sediments. The highest temporal resolution may be derived from lacustrine sediments. Such geoarchives are characterized by continuous records and often store signals of landscape changes, surface dynamics and vegetation variability (including land use patterns for the historical period) in decadal to seasonal resolution. However, because of the problem of variable fluvial connectivity and associated limited sediment delivery in cascade fluvial systems, quantification of small catchment sediment budget can be a very difficult task requiring thorough consideration of colluvial deposits storages and remobilization.
This study presents the new results of multidisciplinary reconstruction of interaction of geomorphic and soil-forming processes, landscape changes and stabilization phases during the Holocene for the Puzbol gully catchment (about 7.95 km2) draining the Borisoglebsk Upland northeastern slope towards the Nero Lake (Yaroslavl Region, central European Russia). The study is based on complex geomorphic, lithostratigraphic and soil surveys by means of detailed field description, photo-fixation, sampling and laboratory analysis of materials from >40 natural or artificial exposures, cores and soil sections. Observed absence of the early Holocene deposits can be explained by generally negative sediment budget of the catchment. It was more likely caused by high-magnitude low-frequency runoff events associated with climatic extremes rather than by dominance of continuous moderate erosion. A series of the middle Holocene 14C dates obtained by analyzing total organic carbon from humic layers of buried soils, lake gyttja and peats provides strong evidence of the synchronous phase of landscape stabilization in both upper and lower parts of the Puzhbol catchment accompanied by active infilling of smaller tributary gullies along its banks at middle part. The upper part of the Puzhbol Gully fan sediment shows clear evidence of synchronous accumulation of agrogenic colluvium and gully alluvium since XIIth Century on top of the Nero Lake terrace deposits.
The study is supported by the Russian Science Foundation (Project No. 19-77-10061).

D2155 |
EGU2020-15168
Andrea Román-Sánchez and Pavel Samonil

Soil formation is a complex process that depends on topography, biota, bedrock, climate, and time. Despite of the great effort dedicated to explore soil evolution, little is known about the role of stochastic phenomena such as soil disturbance in spatial pedocomplexity formation in old-growth temperate forests. Within this study we aim to (i) reveal spatial pattern of chemical soil properties, (ii) explain differences in spatial pedocomplexity formation in A and B soil horizons.

The issue was studied in Zofinsky Primeval Forest Reserve (hereinafter Zofin) in SW Czech Republic. The Zofin has been strictly protected since 1838 and it represented the 4th oldest forest reserve in Europe. Zofin belongs to the global network of forest research plots ForestGeo (www.forestgeo.si.edu/) as the first site in continental Europe. We sampled 309 soil profiles on an area of 74 ha. In total 34 chemical soil properties were analysed in A and B horizons, particularly those, which affect soil evolution and tree growth. We analysed concentrations of Al, Fe, Mn, Ca, Na, Sr, Si fractions, characteristics of sorption complex (CEC, EA, base content), pH etc. 

We used descriptive statistics and geostatistics to spatial pedocomplexity study. The experimental variograms were modelled to fit them to the best theoretical distribution. From the theoretical distribution we calculated the spatial properties in each soil elements as the range, sill and nugget. Then, using AIC estimator, we selected the same best model for both horizons to compare the spatial parameters through parametric or not parametric statistical test depending on the normalization of the data.

The results indicate, for the first time, significantly longer ranges of spatial autocorrelation of soil properties in A horizon with comparison to B horizon, which is not common in geostatistical studies. It is most likely associated with rejuvenation of soil after tree uprooting. Neoformation of A horizon after soil disturbance proceeds quite rapidly and therefore some formerly disturbed A horizons are matured above immature B horizons. The range in both horizons for all chemical soil properties is independent (p-value <0.05), indicating that the driving factors for disturbance in horizon A and B are different. However, for rather biogenic soil properties as Mg, Ca, Na, EA, K there is dependence for horizon A and B (p-value>0.05), indicating similar effect of these elements in both horizons.

D2156 |
EGU2020-4952
Jose Schreckinger, Aline Frossard, Linda Gerull, Mark O. Gessner, and Michael Mutz

Large-scale resource exploitation by open-cast mining severely alters landscapes and impairs key ecosystem properties such as soil and sediment structure and function. Understanding the ecological recovery processes starting from an initially bare landscape generated by destructive land-use is extremely limited. Here we took advantage of a 6-ha experimental catchment to assess microbial community structure and function in soils and stream sediments after 3 and 13 years of catchment succession. The catchment (Chicken Creek) was created in 2005 by depositing quaternary sands from a lignite mine forefield in northeastern Germany and has since been left to develop under undisturbed conditions. In the initial stage, 3 years after catchment construction, rills and small streams had formed and the sparse vegetation cover mainly consisted of forbs. Over the next 10 years, the geomorphology, hydrology, and vegetation structure underwent a major transformation. A nearly full vegetation cover established, including various tree, shrub and grass species. Increased evaporation lowered the shallow groundwater table and led to stream intermittency. These changes were accompanied by large modifications in the structure and function of the microbial communities in sediments and soils. Initially, microbial structure and function were strikingly disconnected, whereas linkages had established 10 years later, although some functions still remained disconnected. Potential enzymatic activities increased vastly over the course of 10 years and also became much less variable across seasons. Cyanobacteria, predominant in soils and sediments during the early successional stage, declined to become a minor component of the microbial community. Moreover, despite distinct flow intermittency of the streams, microbial structure and function distinctly differed between sediments and adjacent soils. These results demonstrate a rapid succession of microbial communities during a decade of ecosystem development, suggesting that undisturbed succession is a feasible catchment restoration strategy.

D2157 |
EGU2020-8650
Joana Sauze, Jacques Roy, Clément Piel, Damien Landais, Emmanuel S Gritti, Olivier Ravel, Hélène Lemoine, Abdelaziz Faez, Sébastien Devidal, and Alexandru Milcu

The sustainability of agricultural, forested and other managed or natural ecosystems is critical for the future of mankind. However, the services provided by these ecosystems are under threat due to climate change, loss of biodiversity, and land use changes. In order to face the challenges of preserving or improving ecosystems services and securing food supply we need to understand and forecast how ecosystems will respond to current and future changes. To help answer those questions Ecotrons facilities are born. Such infrastructures provide sets of confinement units for the manipulation of environmental conditions and real-time measurement of ecological processes under controlled and reproduceable conditions, bridging the gap between the complexity of in natura studies and the simplicity of laboratory experiments.

The European Ecotron of Montpellier (www.ecotron.cnrs.fr) is an experimental research infrastructure for the study of the impact of climate change on ecosystem functioning and biodiversity. This infrastructure offers, through calls open to the international community, three experimental platforms at different scales. The Macrocosms platform is composed of twelve 40 m3 units, each able to host 2-12 t lysimeters, with a 2-5 m² canopy area and a soil depth of up to 2 m. The Mesocosms one has eighteen 2-4 m3 units, each able to host lysimeters of 0.4-1 m depth and 0.4-1 m² area. The Microcosms platform consists of growth chambers (1 m height, 1 m² area) in which smaller units (with photosynthetic plants, soils, insects, etc.) can be installed. Each experimental unit of each platform allows to confine terrestrial ecosystems. This way, environmental parameters such as temperature (-10 to +50 °C), relative humidity (20-80 %), precipitation (sprinkler or drip) and atmospheric CO2 concentration (200-1000 ppm) are strictly and continuously controlled and recorded. But the uniqueness of the European Ecotron of Montpellier lies on its ability to also continuously measure, in each unit, net gas exchange (evapotranspiration, CO2 / CH4 / N2O net fluxes) that occur in between the ecosystem studied and the atmosphere, as well as CO2, H2O, N2O and O2 isotopologues. Those tools are powerful and remarkable to access additional information about processus involved in ecosystem functioning.

The aim of this presentation is to describe the Macrocosms and the Mesocosms platforms through examples of international projects recently run in these platforms.

D2158 |
EGU2020-10460
Hans De Boeck, Simon Reynaert, Ivan Nijs, Karel Klem, Klaus Steenberg Larsen, Marcelo Sternberg, and Michel Boer

Human activities are directly and indirectly generating major environmental pressures on ecosystems worldwide through climate change, pollution and other global changes. Altogether, these changes result in a rapid erosion of biodiversity and a perturbation of ecological and agricultural systems and services, prompting urgent societal questions on how to retain or promote sustainable ecosystem services in a global change context. Understanding the responses of ecosystems to such pressures and perturbations, and developing adaptation strategies critically requires state-of-the-art experimental facilities that are able to simulate multiple global change factors. AnaEE (Analysis and Experimentation on Ecosystems) brings together such facilities in a European-wide infrastructure for experimental research on managed and unmanaged terrestrial and aquatic ecosystems. It assists and integrates four types of national platforms (Open-air, Enclosed, Analytical, and Modelling) and provides support to scientists who wish to engage in research projects using these platforms or the data they generate. These services are organised through the Central Hub and three Service Centres (Technology, Data and Modelling, Interface and Synthesis). This integrated approach improves the quality and availability of data and projections on ecosystem responses to global changes, enabling policy makers and stakeholders to make fact-based  decisions on how to sustainably manage ecosystem services. As an example, we shortly discuss the new open air FATI-platform (UAntwerp) in which ecosystems can be exposed to various combinations of precipitation change and warming, and present first results of a study on the impacts of precipitation regime changes on temperate grassland.

D2159 |
EGU2020-1415
Wolfgang Schaaf

Besides biodiversity, geodiversity is an important constituent of complex ecosystems. We define geodiversity here mainly as substrate and surface properties and topography.

Especially during initial stages of young ecosystems, the geodiversity of a site or landscape may have a lasting impact on dominating abiotic feedback mechanisms that set the stage for further ecological development.

The Chicken Creek catchment was constructed in the Lusatian mining area as a research platform to study initial ecosystem development at the landscape scale. The 6 ha site was formed as a hillslope with 2 to 3.5 % inclination. Up to 3.5 m of Pleistocene sands were dumped as an aquifer on top of a 1-2 m clay layer. The construction process using large-scale mining machinery resulted in slight differences in substrate properties in different parts of the catchment reflecting the natural variation in overburden material that was used for aquifer construction.

After completion of the construction in 2005, a cross-disciplinary long-term monitoring program was initiated to record major environmental parameters adapted to the development of the site. No amelioration, fertilization or planting was carried out to allow for primary succession.

Time series of environmental data recorded since 2005 revealed that the geodiversity of the initial site affected a number of both abiotic and biotic processes (e.g. surface runoff and erosion intensity, top soil development, colonization by plant functional traits, soil moisture and groundwater patterns, formation of biological soil crusts).

During its first 15 years, the Chicken Creek experimental catchment showed a very dynamic development. Whereas the abiotic geosystem of the first 2-3 years was characterized by heavy erosion and sediment transport, primary succession by invading vegetation and the unexpected formation of soil crusts within only a few years resulted in biotic-abiotic feedbacks that controlled catchment hydrology.

Our data indicate that even minor variations in initial substrate characteristics (e.g. texture) and stochastic single events like thunderstorms can have lasting impacts on the geomorphological, hydrological and biological development of the catchment.

D2160 |
EGU2020-7216
Werner Gerwin and Wolfgang Schaaf

15 years of initial ecosystem development have been observed in the artificial Chicken Creek Catchment in Eastern Germany (State of Brandenburg). The 6 ha site was constructed in 2004/05 as a watershed within a post-mining landscape and was left for an unmanaged primary succession. The number of plant species increased quickly during the first years parallel to an increasing groundwater table within the catchment. In 2014 a total of about 180 vascular plants were identified in this young ecosystem.

During its development vegetation differentiated according to morphological and soil related conditions. The semiaquatic part around a small pond developed differently compared to the upper, terrestrial part. In this terrestrial part Robinia pseudoacacia L. early occurred as a pioneer tree species. Large surface areas, however, remained open land areas without tree or shrub vegetation. Robinia as a N-fixing tree species accumulates nitrogen in its litter layer at the soil surface which influences the further vegetation development in these parts of the catchment.

Furthermore, Robinia together with other tree species contributed obviously to a significant groundwater lowering in the constructed catchment area. This decrease of the groundwater tables in the study area was intensified by two extremely dry summer seasons (2018 and 2019). As a result, the overall composition of the vegetation in the terrestrial part of the catchment changed slightly indicating dryer conditions particularly for herbaceous plants.

Initial abiotic site conditions (geomorphology and soil conditions) in combination with external abiotic drivers (amount of precipitation) shaped the development of plant communities. Vice versa, the occurrence of plant species with specific functionality (N-fixation and high water consumption) contributes to a further spatial differentiation of the vegetation composition. The constructed Chicken Creek catchment as an artificial landscape unit allows for detailed insights into these ecological differentiation processes of the initial developmental ecosystem phase.

D2161 |
EGU2020-13522
Pedro Rojas, Daniel Caviedes-Voullième, and Christoph Hinz

The artificial Hühnerwasser catchment was built in a post-mining landscape (Brandenburg, Germany) as a field experiment to observe and monitor early-development ecosystems at first catchment scale. Given that the spatial distribution and temporal dynamics of vegetation affects water redistribution across scales, quantifying changes in vegetation distributions is an obvious indicator for state transitions, especially in the context of early ecosystem development.

 

In this work, we present a semi-automatic image analysis algorithm designed to identify vegetation patches during the early ecosystem development of the Hühnerwasser catchment (throughout 10 years) from aerial photography. Furthermore, the algorithm also allows to characterise vegetation cover, describe spatial structures and their temporal evolution. The earliest stages are especially of interest. The structure is therefore characterized by the area of the catchment covered by vegetation, the number of vegetation patches, the mean and maximum patch size and a form factor (area of patch divided by its perimeter). Base data are aerial images with a resolution at the centimeter scale. Because the imagery was obtained under very different lighting conditions and under different stages of plant growth, a luminance correction was applied in order to normalise colors, and thus be able of consistently binarise the images into vegetated-non vegetated maps. Binary maps were generated by setting thresholds for red, green and blue channels to differentiate between vegetation cover and bare soil. Additionally, bare soil areas were also identified using a similar procedure. To evaluate the consistency of the binary images of each channel these images were stacked and compared. For validation, the binary maps were compared to manually digitised vegetation patches for a subset of the data. The performance of the method was tested by using a set of combinations of thresholds and a comparison with manual mapping of vegetation cover at an image subset was made.

 

The blue channel seems to be very sensitive to detect vegetation and a better differentiation of vegetation and dark/wet soil can be achieved by setting the thresholds of the channels in a specific order. The structures derived by the classification into vegetated and bare soil are more important in the early years of ecosystem development. In those years (2007 to 2011) the largest changes took place. As time advances vegetation became less patchy, and a mix of different vegetation spawns. By comparing the areas identified as (green) vegetation and those areas identified as bare soil, it is also possible to discriminate non-green vegetation, such as dry grasses, and thus achieve a minimal level of decomposition of the imagery into plant functional types.

 

D2162 |
EGU2020-2652
Annika Badorreck and Davood Moghadas

The Chicken Creek catchment (Brandenburg, Germany) was built 2005 in a post-mining landscape in Eastern Germany and was left for an unmanaged primary ecosystem succession. During the following years this artificially created system was subject to a series of fast changes with regard to morphology, hydrology or vegetation cover. Soil water content plays a major role since it mediates the water and energy exchange between the surface and atmosphere. In this respect, time‐lapse electrical resistivity tomography measurements were carried out along a transect in the Chicken Creek catchment.

Electrical and electromagnetic geophysical techniques have been widely used to estimate soil electrical conductivity (σ) and soil moisture (θ). However, obtaining the relationship is not straightforward due to the non‐linearity and also dependency on many different soil and environmental properties. To ensure proper retrieval of the σ and θ, reference values were measured near the beginning of the transect via an excavated pit using 5TE capacitance sensors installed at different depths.

The purpose of this contribution is to determine if artificial neural network is an appropriate machine learning technique for relating electrical conductivity to soil water content. We explored robustness and pertinence of the artificial neural network approach in comparison with Rhoades model (as a commonly used petrophysical relationship) to convert the inversely estimated σ from electrical resistivity tomography to the θ. The proposed approach was successfully validated and benchmarked by comparing the estimated values with the reference data. This study showed the superiority of the artificial neural network approach to the Rhoades model to obtain relationship. In particular, artificial neural network allowed for more accurate estimation of the temporal wetting front than the petrophysical model. The proposed methodology thus offers a great promise for deriving spatiotemporal soil moisture patterns from geophysical data and obtaining the in situ relationship, taking into account the non‐linear variations of the soil moisture.

D2163 |
EGU2020-2664
Davood Moghadas and Annika Badorreck

Exploring hydrological and ecological processes plays a key role in understanding ecosystem developments. In this respect, the constructed catchment, Chicken Creek (Brandenburg, Germany), has been established for fundamental and interdisciplinary scientific research. The main components of the site include a base soil which is followed by a Tertiary clay layer (aquiclude) and sand layer (aquifer) on the top of the domain. In general, the soil mediates many of the processes that govern water resources and quality, such as the partition of precipitation into infiltration and runoff, groundwater recharge, contaminant transport, plant growth, evaporation and energy exchanges between the Earth’s surface and its atmosphere. In this respect, characterization of the soil electrical conductivity (EC) is important, since it is highly correlated with different chemical and physical soil properties.

Low frequency loop-loop electromagnetic induction (EMI) techniques have found widespread application for non-invasive delineation of the subsurface EC structures at different spatial scales. However, successful inversion of EMI data has been a major challenge for decades, due to the non-linearity, non-uniqueness and dimensionality of the inverse problem. Here, a novel approach based on deep learning inversion via convolutional neural networks is proposed to instantaneously estimate subsurface EC layering from EMI data. In this respect, a fully convolutional network was trained on a large synthetic data set generated based on one-dimensional EMI forward model. The trained network was used to find subsurface electromagnetic conductivity images from EMI data measured along two transect from Chicken Creek catchment. Dipole-dipole electrical resistivity tomography data were measured as well to obtain reference subsurface EC distributions down to a 6 m depth. The inversely estimated models were juxtaposed and compared with their counterparts obtained from a spatially constrained deterministic algorithm as a standard code. Application of the deep learning inversion for subsurface imaging from Chicken Creek catchment manifested the accuracy and robustness of the proposed approach for EMI inversion. This approach returns subsurface EC distribution directly from EMI data in a single step without any iterations. The proposed strategy simplifies considerably EMI inversion and allows for rapid and accurate estimation of subsurface electromagnetic conductivity images from multi-configuration EMI data.

D2164 |
EGU2020-18217
Martin Bartiška and Jan Frouz

Subsurface processes are often omitted in catchment studies here we presented artificial catchment as a new tool to study and budget these processes on catchment level.

Falcon is and artificial  catchment that build in Sokolov post mining sites Catchment consist from four separate micro catchments (pools) each ) 0.25ha in area and 2m in depth which are hydrologically isolated  and filled by post mining overburden. Two fields were levelled while in two was wave like surface was produced to mimic situation after heaping.  Leveled micro catchments were planted by alder (Alnus glutinosa).

Catchment allow to study meteorological variables, surface and subsurface runoff,  and other key ecosystem parameters (water table depth chemical composition of pore water, soil respiration, gas exchange between ecosystem and surrounding atmosphere using eddy tower etc.). First result show large erosion on waves then on levelled sites however large proportion of material eroded from flat site leave the site while in wave like surface most of it is trapped in depression between waves. Subsurface runoff form large proportion of total runoff in wavy sites than in flat sites. Stable water table established quickly in both types of catchments} few months after catchment establishment. Flat sites show higher initial diversity of plants.

D2165 |
EGU2020-1947
Aimin Liao, Jiufu Liu, Hongwei Liu, Haixia Zhang, Niu Wang, and Weizu Gu

To obtain new hydrologic data and reveal new hydrologic mechanisms, it is key to perform high-resolution observation of hydrologic dynamics in experimental catchments. Supported by Chuzhou Hydrology Laboratory, this study conducted experimental investigation of hydrologic dynamics in Nandadish experimental catchment during 2015-2019. Nandadish with an area of 7897 m2 is a natural experimental catchment covered by forest whose dominant tree species are B. papyrifera and Q. acutissima. The surface surrounding boundary was sealed by concrete so that Nadadish forms an excellent critical zone experimental block (CZEB). Four rain gauges were installed over the towers to measure the rain over the trees (inferred as P); 144 rain gauges were used to measure the rain under the trees (i.e. throughfall); and 31 trees were equipped to collect stem flow. A separate runoff observation system was constructed to measure the runoffs in different layers: the uppermost trough collects throughfall; the next lower trough collects surface runoff (RS); the two lower troughs collect subsurface flow from soil layers with the depths of 0–50, and 50–100 cm (inferred as R50 and R100). Soil moisture was observed by 31 profile-type sensors with 9, 12 or 15 sensor points with a depth spacing of 10 cm. An array of 30 galvanized tube wells intersected through the soil till the bed rock. Water table measurement was performed with pressure-type sensors at the bottom of each well. According experimental results, conclusions are determined as following: (1) Throughfall variability during the leafed period was slightly higher than that during the leafless period inferred from the coefficient of variation of throughfall amounts, with 13.2-40.9% and 18.7-31.9%, respectively. The multiple regression model analysis suggested that the controlling factors of throughfall variability were significant differently in different periods. (2) B. papyrifera required less precipitation amount (4.3 to 5.8 mm) to initially trigger stemflow than Q. acutissima (5.4 to 6.0 mm). (3) Under the condition of P≥25 mm, the proportion of RS, R50 and R100 was 46.3%, 15.2% and 38.5%, and thus the subsurface runoff dominated the runoff. The synthetic runoff coefficient of total runoff was 0.33; the synthetic runoff coefficients of Rs, R50 and R100 were 0.15, 0.05 and 0.13, respectively. (4) The depths of soil distinction layers were located at the range of 80-90 cm based on the data of profile soil moisture. (5) Saturated overland flow occurred in the area where the gentle slope with soil depth of less than 1 m was located at the mid-downstream through analyzing the water table dynamics. This investigation can enhance the in-depth understanding of hydrologic dynamics in the small forest headwater catchments.

D2166 |
EGU2020-4048
Hongwei Liu, Jiufu Liu, Jin Lin, Wenzhong Wang, Xing Min, Hao Zheng, and Niu Wang

The glacier recession and the runoff variation on the Qinghai-Tibet plateau conducted by the global warming is changing the regional hydrological and ecological processes. Although there is great need for the knowledge of the runoff evolution and biogenic substances migration and transformation for developing strategies for adaptive utilization of runoff, progress in study on these hydrological questions lags behind because of lack of observation dataset under harsh plateau cold conditions.

In order to understand the critical zone ecohydrological dynamics and evaluate the runoff components in the Qinghai-Tibet Plateau, a series of observation and research were carried out in the Niyang River watershed, a tributary of the Yarlung Zangbo River. Four basins embed in a larger basin (1500 km2) were monitored and sampled at altitudes between 3667 to 6140 m. More than 500 samples from rain, snow, river water, spring water, glacier ice, vegetation stem, and soil were collected, with which theδ2H, δ18O, K, Ca, Na, Mg, Sr, Si, F, Cl, N, and S in the water are examined. 5 automatic hydrometric stations were established, and the water level data was sent back by Beidou satellite. The 3D laser scanning and RTK technologies were used to obtain detailed geomorphological information near the 5 current measurement section, based on which a hydrodynamic model is able to be calibrated for the discharge estimation.

The δ2H and δ18O of the precipitation proposed a local meteoric water isotope line, which is parallel to the WMWL but higher in the δD~δ18O graph. The river water isotopes suggest its source is the precipitation, which are similar to the spring ground water (but the geochemical elements are quite different between the surface and ground water). The vegetation stems water and soil water (by cryogenic vacuum extraction) isotope values suggest the attribute of the river/precipitation sources, but a few observation data appear different implying using water formed by the multiple precipitation events or supplied by the higher place under a significant evaporation influence.

The time series of the runoff and the snow cover and glacier variation results show that the base flow is varied obviously relate to the temperature which influence the melting processes of the glacier and frozen earth from March to August, and the rain runoff events control the flood peek. It suggests that the concentration time should be less than 10 days in the interested watershed.

The tempo-spatial variation characteristics of the geochemical elements are analyzed and mapped in the interested area, which suggested relative steady water components signals contributing to the runoff. Based on which, a set of overdetermined equations are established to evaluate the quantities of different runoff components.

This study could help to evaluate runoff components quantitively in Tibet where lack of data. Monitoring and studing is still going on, which is included in the 2nd comprehensive scientific investigation into Qinghai-Tibet Plateau since 2019.

Funded by the NSFC project 91647111 and 91647203 included in the Runoff Change and its Adaptive Management in the Major Rivers in Southwestern China Major Research Plan.

D2167 |
EGU2020-12330
Tao Ma, Hongwei Liu, Hao Zheng, Xing Min, Aimin Liao, and Wenzhong Wang

In this study, the characteristics of hydrogen and oxygen isotopes as well as four kind of ions(K+、Na+、Ca2+、Mg2+ )in rainfall-runoff processes are analyzed through designing an extensible soil water sampler. It is a kind of multipoint sampling installation with the characteristics of synchronous, in-situ and long-term in sampling. The sampling schemes were summarized, including site layout ways, capacities and materials selection, sample pretreatment and storage methods, and valid date. A series of experiments were carried out such as hydrogen and oxygen isotopes memory effects tests, repeatability test and dilution errors analysis. After recognizing the possible error sources in hydrogen and oxygen isotopes as well as the four kind of ions test, the solution on how to improve accuracy and precision were proposed. Moreover, the spatial-temporal evolution laws of the isotopes and cations was discussed by drawing the contour maps of hydrogen and oxygen isotopes as well as the four kind of ions in soil water and underground water. At last, the possibility and applicability of these substances as tracers in hydrological cycles were explored. These work were quite important for researches on coupling mechanism of hydrological and solute transport processes in critical zone.

D2168 |
EGU2020-6290
Cai Zhao, Liu Jiufu, Liu Hongwei, Liao Aimin, and Liao Minhan

The double-tipping bucket rain gauge (SL3-1) is widely used in meteorological stations to minimize the systematic errors by the influence of rainfall intensity on TBRs in China. With two tipping buckets, the upper tipping bucket turns over and injects rainwater into the converging funnel, and the lower tipping bucket can record the rainfall. In this study, CFD (computational fluid dynamic) simulations and experiments were performed to investigate the function of the double tipping bucket for TBRs in different rainfall intensity. In simulation, the volume-of-fluid model and Reynolds-averaged Navier–Stokes realizable k-ε model and dynamic mesh method were used. In experiments, electric balances, with accuracy of 0.001 g, were used to determine the water volume of the upper tipping bucket outflow. It shows that, with a converging funnel, natural precipitation is uniformed at a certain intensity around 1.9mm/min to control the rainwater outflow into blow tipping bucket to measure rainfall and reduce systematic errors caused by different precipitation intensities. Experimental results demonstrate that the outflow curve of the upper tipping bucket has high correspond with simulation results in tipping process. These results can provide knowledge of advantages of double tipping bucket rain gauge in rainfall measurement and improve the structure designs of double tipping bucket for TBRs and obtain more accurate rainfall data.

D2169 |
EGU2020-6509
Guangxu Jiang, Jiufu Liu, Xuegang Li, Hongwei Liu, and Aimin Liao

The observation accuracy of rainfall processes affects every aspects of the meteorological and hydrological affairs, which is widely monitored by various types of tipping bucket rain gauges(TBRs)because of the simple structure and reliable performance. The study of the measurement errors of TBRs is quite valuable and necessary for improving the rainfall data quality and evaluating the uncertainty of the research based on the dataset.

In this study, an artificial rainfall and monitor experiment system is designed with peristaltic pump, balances, recorder and controller for the accurate rainfall and the TBRs instrumental values record, based on which the error distribution and instrument stability were analyzed. Eight types of TBRs are chose for the error evaluation experiment, including five single-layer TBRs, three double-layer TBRs. For each TBRs, we observe its performance under 6 rain intensity (0.1-4mm/min) in turn. With regard to each rain intensity, when the simulated total rainfall reaches 10 mm, the experiment stops and records the data, then repeats the same experiment 6 times.

The result shows that the single-layer TBRs have a good linear relationship between the rainfall and the measurement error, and the double-layer TBRs has a significant regulating effect on the continuous heavy rain intensity, which can make the rain flow steadily down to the lower tipping bucket (metering tipping bucket) with a stable rain intensity to avoid the rain intensity variation influence on the measurement error. However, due to its high resolution of 0.1mm, it is greatly affected by the residual water volume of the tipper bucket.

According to the results, the single-layer TBRs can correct the actual rainfall measurement process according to the error ~ rainfall intensity curve. The double-layer TBRs can play an important role in the rainy day record, but the randomness of the residual in the tipping bucket needs to be further estimated. Because the proportion of the light rainfall intensity in most of the rainfall events are quite high according to the statistics, it is necessary to have lower measurement error under the light rainfall in the TBRs chosen and calibration process. It's a good idea to choose a combination of rain gauges(0.1mm&0.5mm) to improve the accuracy of rainfall and rainy day.

D2170 |
EGU2020-619
Eliana Jorquera, Angelo Breda, Steven Sandi Rojas, Jose Fernando Rodriguez, and Patricia Saco

Pacific Islands are one of the regions in the world most vulnerable to climate change, mainly due to sea level rise (SLR) and tropical cyclones (TC). Coastal wetlands play a crucial role as a buffer between the ocean and the inland areas. Recent research has shown that accretion and adaptation capacity to SLR of coastal wetlands is intrinsically related to the sediment supply from the upstream catchments and the tidal regime, which is also affected by the hydrodynamic and the vegetation of the system. Modelling the feedback among these systems and their evolution is still challenging.

In this work, we present the case of a coastal wetland at the mouth of Dreketi River catchment, located in Vanua Levu, Fiji. This area belongs to the Great Sea Reef, and it was declared as Ramsar site in 2018. The framework proposed includes the modelling of hydro-sedimentological behaviour of the upstream catchment and its validation using remotely sensed images; and the hydrodynamic-sediment transport model of the tides. These outputs are linked with an ecogeomorphological model (EGM) of the mangrove wetlands used to predict wetland evolution. We have evaluated the catchment response under current scenarios assessing the impact of TC in the last 45 years; and under future scenarios of land use, TC and SLR. We have analysed the same scenarios on the tidal system to then run the EGM incorporating the changes in sediment supply from both the catchments and the tides due to SLR and TC projected by the end of the century.  Our approach combining modelling and remote sensing can be extended to other coastal areas in the region and has enormous potential to assess the evolution of wetlands under climate change throughout the Pacific islands.

D2171 |
EGU2020-1843
Tingzhang Zhou, Pei Xin, and Jirka Jirka Šimůnek

The occurrence of macropores in salt marsh sediments is a natural and ubiquitous phenomenon. Although they are widely assumed to significantly affect water flow in salt marshes, the effects are not well understood. We conducted physical laboratory experiments and numerical simulations to examine the impact of macropores on soil evaporation. Soil columns packed with either sand or clay and with or without macropores were set up with water tables in the columns set at different levels. A high potential evaporation rate was induced by infrared light and a fan. The results showed that in the soil with a low saturated hydraulic conductivity (and thus a low transport capacity), macropores behaved as preferential flow paths, delivering water from the groundwater towards the soil surface and maintaining a high evaporation rate in comparison with the soil without macropores. This effect was more pronounced for sediments with lower hydraulic conductivities and shallower groundwater tables. These results not only improve our understanding of water flow and soil conditions in salt marshes but also shed light on soil evaporation in other hydrological systems.

D2172 |
EGU2020-5398
Nikul Kumari, Omer Yetemen, Ankur Srivastava, Jose F. Rodriguez, and Patricia M. Saco

Aspect-controlled vegetation over opposing hillslopes are driven by non-uniform distribution of incoming solar radiation in semi-arid ecosystems. This leads to variation in soil and vegetation characteristics. In mid- to high-latitudes where available soil moisture is a limiting factor for vegetation growth, poleward-facing slopes develop denser vegetation cover providing greater erosion protection than the equatorward-facing hillslopes. The variation in erosion rates across opposing hillslopes leads to the development of topographic asymmetry of hillslopes over long timescales. This asymmetry is quantified by the hillslope asymmetry index (HAI), a metric given as the ratio of the median slope angles of opposite hillslopes. We present a combined approach of modelling and observed data analysis to investigate the relationships of HAI with climatological, geomorphic, and ecologic variables at a global scale. We analysed these relationships using digital elevation topographic data to compute observed HAI for 80 different catchments across the world, where aspect-controlled vegetation has been reported in the literature. Further, we used the CHILD landscape evolution model (LEM), which uses the continuity equation for water, sediment, and biomass, to investigate the control of climatological, geomorphic, and ecologic variables on the development of hillslope asymmetry through a modelling approach,. The outcomes of the study highlights that latitude and mean topographic gradient are the two dominant factors affecting hillslope asymmetry due to their vital role in controlling vegetation density through the modulation of incoming solar radiation. These results improve our understanding on how different climatic variables and geographic properties affect the magnitude of hillslope asymmetry and their implications on landform evolution modelling.

D2173 |
EGU2020-5280
Ankur Srivastava, Omer Yetemen, Nikul Kumari, and Patricia M. Saco

Topography plays an important role in controlling the amount and the spatial distribution of precipitation due to orographic lift mechanisms. Thus, it affects the existing climate and vegetation distribution. Recent landscape modelling efforts show how the orographic effects on precipitation result in the development of asymmetric topography. However, these modelling efforts do not include vegetation dynamics that inhibits sediment transport. Here, we use the CHILD landscape evolution model (LEM) coupled with a vegetation dynamics component that explicitly tracks above- and below-ground biomass. We ran the model under three scenarios. A spatially‑uniform precipitation scenario, a scenario with increasing rainfall as a function of elevation, and another one that includes rain shadow effects in which leeward hillslopes receive less rainfall than windward ones. Preliminary results of the model show that competition between increased shear stress due to increased runoff and vegetation protection affects the shape of the catchment. Hillslope asymmetry between polar- and equator-facing hillslopes is enhanced (diminished) when rainfall coincides with a windward (leeward) side of the mountain range. It acts to push the divide (i.e., the boundary between leeward and windward flanks) and leads to basin reorganization through reach capture. Our findings suggest that there exists a strong coupling between climate and landform evolution processes, and that orographic precipitation can imprint its influence on landforms in semi-arid ecosystems.  

D2174 |
EGU2020-13238
Claudia Schütt, Daniel Caviedes-Voullième, and Christoph Hinz

Vegetation self-organisation in water-limited ecosystems in semi-arid climates has been studied by means of numerical simulation using a set of reaction-diffusion-equations. The predominant approach in such studies, in particular relating to banded vegetation on slopes, has been to study the long-term steady ecohydrological tates on periodic domains forced by steady rainfall. This default modelling setup does not account for the fact that on a hillslope a net runoff loss may exist at the outlet. Moreover, such runoff loss is modulated by rainfall intensity, i.e., increasing rainfall intensity is likely to favour runoff over infiltration, and therefore affect the banded vegetation formation. Additionally, different inter-storm dry periods prompt different responses from the vegetation. One of the properties of semi-arid climates is a highly intermittent and variable precipitation regime, quite often with a few intense events and a larger number of very mild events. Additionally ecohydrological theory recognises that dryland ecosystems are in a quasi-permanent transient condition, exhibiting non-linear and far-from equilibrium responses to boundary conditions and forcings. The mismatch between the default modelling approach and the properties of rainfall in such systems calls for further complexity in the models and in the forcing.

 

We explore the possible effects that particular rainfall properties can have in banded vegetation dynamics. We solve the well-known Rietkerk model together with a zero-inertia approximation of the shallow-water equations for surface flow. A non-periodic domain with an outlet, i.e., a 2D hillslope with a constant slope is used. We perform simulations forced by a set of variations of idealised temporal distributions of rainfall throughout a year. The reference distribution is a periodic signal of constant intensity storms of a single day, separated by dryspells of equal duration. The total annual rainfall was selected as 270 mm, in the range of semi-arid climates. This annual signal is repeated during the entire simulation. Non-periodic rainfall signals were generated by randomising a single rainfall property but ensuring the same annual rainfall. Randomisations of the inter-storm dryspell duration, the storm duration, and the storm intensity were explored. Although this results also in idealised rainfall signals, it allows for systematic analysis of each property.

 

The banded patterns are assessed both in terms of global signatures (biomass, vegetation cover), spatial properties (number of bands, wavelength and bandwidth), and dynamics (migration velocity of the bands). Our results clearly show qualitatively and quantitatively that the simulated banded vegetation has a strong response to rainfall variability. Moreover, the results also show a high sensitivity to the particular succession of events, e.g., a succession of longer than average dryspells can throw the system away from equilibrium. High sensitivity is also observed to the timing of certain individual events. The system responds differently to events which happen early on in the development, or later, when the system is near equilibrium. The simulated response of the system are arguably too volatile, suggesting that improvements in the vegetation model parametrisation and formulation are warranted to better represent dynamics and allow for stability and resilience studies.

D2175 |
EGU2020-1209
Juan Pablo Quijano Baron, Patricia Saco, Dominik Jaskierniak, and Jose Rodriguez

Arid and semiarid environments accounts approximately 30% of the Earth’s continental surface and are especially sensitive to degradation or loss of their ecosystem functionality. In these ecosystems, vegetation patterns (e.g. banded vegetation) can be found as the adaptive response of the system to resource redistribution (runoff and sediments) and limitation (soil moisture and nutrients). The patterns consist on alternating densely vegetated bands (or ‘groves’) and bare areas (or ‘intergroves’), and can be found in large regions of Africa, Asia, Australia and North America. Understanding the mechanism that regulate banded vegetation ecosystems is critical in order to identify the dynamic behaviour and maintain their functionality. In this work, we model the spatial distribution of soil moisture and soil organic carbon, in order to analyse how differences on the availability of resources can explain the functionality of the banded vegetation systems. We are studying a catchment in Bond Springs, 25 km north of Alice Springs, characterized by the presence of Acacia Aneura trees (Mulga) aligned in bands along the terrain. We use a new model: COPLAS, a tool that couples a Landform Evolution Model with dynamic vegetation and carbon pools modules. It tracks the carbon from the photosynthesis until it becomes soil carbon and the mobilization/redistribution due soil erosion. Results of the model were compared with fieldwork conducted in fifty-three soil samples and terrain surveying with unmanned aerial vehicle. Our results indicate good agreement between the model and the measurements. We found that soil moisture uphill the bands is around 33% more than downhill, and close to 120% more than in bare soil. This result could be explained because a portion of the runoff, generated from bare intercanopy patches, is redistributed downslope and infiltrated uphill the vegetated areas. Moreover, soil carbon is 20% more downhill than uphill the bands because of deposited alluvium and litter downhill and possible less microbial respiration and decomposition due smaller soil moisture content. Additionally, we found a tendency of higher soil carbon concentrations going downhill the catchment. Overall, these findings show the heterogeneous distribution of resources in the area that could explain the ecosystem functionality and highlight the importance of modelling and measuring arid and semiarid ecosystems in order to understand their dynamic behaviour.

D2176 |
EGU2020-21331
Katharina Ramskogler, Svenja Müller, Bettina Knoflach, Johann Stötter, Clemens Geitner, and Brigitta Erschbamer

Glacier forelands are perfect for analysing the development of plant communities from zero onward. According to Matthews (1992), the chronosequence can act as a spatial representation of the temporal sequence. Therefore, it is ideal to analyse changes in landscape and land cover in time slices. Development of plant communities does not only depend on the age of the deposits, but also on topography, microclimate, soil development, and geomorphological processes as well as on biotic interactions. In the long term, permanent plots represent an adequate method to follow the colonisation on differently aged terrain throughout time.

The main research question of the study is: Do cryospheric changes influence plant community development in time and space? During the first study year we were focused on the following questions: i) How fast does a plant community evolve? ii) How many species do occur on different moraine stages? iii) How do soil parameters correlate with primary succession stages?

The study site is located in the southern part of the Central European Alps, Martell Valley (South Tyrol, Italy). We established 12 permanent plot clusters of 2 x 5 m on areas deglaciated between 1985 and 2018, two per retreat area. In each square meter of these clusters, species composition, cover, and number of individuals were sampled. On the ground moraines of the glacier stages 1911 and approximately 1850 we recorded species composition and cover on 10 x 10 m plots (four plots in total). In all plot clusters and plots on the old moraines, soil temperature and soil water potential as well as relevant soil parameters were measured.

We found up to two vascular plant species per square meter on areas ice free for one year and up to 16 vascular plant species per square meter on areas ice free since 1985.

On the moraines of 1911 were up to 39 vascular plant species per plot with a mean cover of 52.5 %. On the moraines of 1850 we found up to 43 vascular plant species with a mean cover of 40 %.

In the next step we will analyse the effects of pioneer, early and late successional species on morphodynamic processes and their response to these processes using functional traits.

Matthews, J.A. (1992): The ecology of recently-deglaciated terrain: a geoecological approach to glacier forelands and primary succession. Cambridge University Press, Cambridge.

D2177 |
EGU2020-9838
Felice Sartori, Donato Loddo, Ilaria Piccoli, and Antonio Berti

Despite conservation agriculture and, overall, the reduction of soil disturbance are considered soil improving cropping systems, these practices could conflict with weed control. Indeed, reduced tillage is usually linked to increased weed species richness and abundance and, thus, it could increase the dependence on chemical treatments. Weed management is one of the reasons behind the distrust of European farmers in the conservation agriculture, that is still not widespread, despites European subsidies. In fact, conservation agriculture is implemented only in the 2.8% of European cropland.

The aim of this study is to evaluate the effect of different tillage intensities on spring-summer weeds richness and abundance in a maize monoculture, during the transition phase from conventional to conservation agriculture.

The weed survey was conducted in June 2019 on an experiment comparing three levels of tillage management: conventional agriculture (CT), which represents the most common choice in Veneto region, involving deep ploughing and harrowing in spring; minimum tillage (MT), consisting only in harrowing at 20 cm; and no tillage (NT), namely sod seeding. The experiment started in 2018, at Padova University experimental farm, in a sub-humid area, with a silty clay loam soil. The survey was conducted with a set of random throws of a 30×30 cm square frame in each plot (ca. 3300 m2).  Weed plants found within the frame were classified and counted. Subsequently, data analysis assessed which botanical families were promoted by each treatment.

The NT resulted the treatment with the highest weed density (915 plant/m2): 6% higher than MT (823 plant/m2) and four-fold more than CT (209 plant/m2). The latter showed to be the treatment with higher diversity, according to both Shannon and Simpson indices. The survey evidenced higher weed species richness in MT, where both annual and perennial species were identified, while the lowest number of species were detected in NT. Plantago major and Chenopodium album were the species with the highest density in CT (>32 plant/m2) while they are negligible in NT and MT (7 plant/m2, on average). Digitaria sanguinalis was instead the dominant species in MT and NT (>600 plant/m2) while a lower density was observed in CT (11 plant/m2). Low levels of Asteraceae weeds were measured in all treatments. These results shows that the actual flora rapidly changes depending on tillage intensity, with an increase of both dominance and number of species in MT. Differently, only a limited number of adapted species germinated in NT, despite higher infestations if compared with the other treatments.

It should be expected that other species more adapted to conservation agriculture (namely Asteraceae), still marginally present in the seed bank, will spread in the next years. This stresses the importance of a continuous monitoring and effective control of weeds to avoid uncontrolled evolutions of the weed flora and increase of seed bank in the transition phase from conventional to conservation agriculture.

D2178 |
EGU2020-12021
Susana Bautista, Francisco Fornieles, David Fuentes, Anna M Urgeghe, Diana Turrión, and Angeles G Mayor

A variety of theoretical and observational works indicate that drylands may experience sudden shifts from functional to degraded states in response to gradual increases in human and climatic pressures. However, there is little experimental testing of the factors and processes that control sudden shifts in drylands. Adopting a combination of mesocosms and manipulative experimental approach, we assessed the occurrence of sudden transitions towards degraded states in response to increasing pressure, and investigated the mechanisms underlying the observed dynamics. We mimicked a gradually increasing pressure of grazing and wood gathering by removing increasing amounts of vegetation on a series of experimental plots and mesocosms. We then monitored the impact of such gradient of pressure on runoff and sediment yield, vegetation dynamics, bare-soil connectivity and soil-surface condition over a 7-year period.  Overall, our results support that decreasing plant cover nonlinearly increases the loss of resources from the system and may trigger a change to a degraded state. Within the range from 40% to 30 % vegetation cover, a small change in the cover percentage resulted in a turning point in both the vegetation and the hydrological dynamics, driving the system to a new state that exhibited lower capacity for resource conservation all over the study period.

D2179 |
EGU2020-20715
Lizeth Karina Vásconez Navas, Alexander Gröngröft, Joscha N. Becker, and Annette Eschenbach

Understanding the influence of habitat properties on the dynamics of terrestrial ecosystems is a fundamental part of ecosystem research under climate change, especially in areas of high environmental heterogeneity, such as floodplains. The present research is part of the collaborative and interdisciplinary MediAN project (Mechanisms of ecosystem services in hardwood floodplain forests: Scientific analysis and optimization of conservation management), where topics regarding carbon storage of soils and tree biomass, as well as tree vitality and the diversity of herbaceous vegetation are investigated. Thus, in this study we aim to understand and characterize the causes and effects of biotic interactions in relation to the edaphic site properties - in particular between the soil water balance and hardwood forests.

In this context, we identified the spatiotemporal variability of soil hydro-physical properties in six active and former hardwood floodplain forest sites in the Middle Elbe River, Germany. The study sites represent the floodplain geomorphology, therefore varying in elevation (high and low sites), soil texture and hydrological properties, as well as in forest age. We opened three soil profiles per site and installed soil sensors to monitor the variation of volumetric water content (VWC), and water tension at 10 cm, 30 cm, 60 cm, 100 cm and 160 cm depth. Additionally, we installed one groundwater diver and one meteorological station per site. Undisturbed samples were taken per horizon to define the grain size distribution, bulk density and to evaluate soil moisture retention curves.

Preliminary results, from the year 2019 with an unusual dry summer season, show a clear interrelation of soil moisture retention and soil water tension with groundwater level and soil texture. For instance, a predominantly sandy site, located in the high active floodplain, displayed VWC values below 8% throughout the vegetation period and at all depths. Water tension showed higher variation at 10 and 30 cm (2-3.25 pF) compared to deeper soil, which is directly related to precipitation events. These initial observations imply local water stress for the floodplain vegetation; therefore, physiological stress on woody species is expected. In a next step, the dynamics of soil drying will be related to xylem sap flow velocity to estimate effects on the vitality of typical hardwood forest species, such as oaks (Quercus robur L.) and elms (Ulmus laevis) at the representative study sites.

D2180 |
EGU2020-13969
Eileen Eckmeier, Simon Kübler, Akida Meya, and Stephen Mathai Rucina

The East African Serengeti ecosystem hosts a great range of mammals and one of the world’s largest seasonal ungulate movements, with over 1.3 wildebeest and several hundreds of thousands of zebras and antelopes migrating through the region in a regular pattern. While climatic and biological drivers for this migration have been studied in great detail, the role of rock chemistry, weathering and resulting soil diversity as a source for nutrient provision has so far been largely neglected and needs detailed and systematic study.

Geological processes provide important controls on long-term ecosystem dynamics. Volcanic eruptions, earthquakes, and rock weathering influence soil edaphic properties, which represent the ability of soils to provide vital plant-available nutrients, which therefore control grazing patterns of herbivores, particularly during birthing and lactating seasons. Studying the geological role in providing and distributing essential nutrients is critical to understand long-term drivers and stability of animal migrations in dynamic ecosystems. We have carried out a field reconnaissance study in the Serengeti National Park, with the aim to study variations in nutrient variability in soils and vegetation in relation to the chemical composition of soil parent material, i.e. volcanic or metamorphic rocks and sediments derived from those rock units, and under consideration of climatic variations. First results show that the Serengeti ecosystem can be subdivided into three geo-edaphic subregions that correlate with seasonal wildebeest grazing habitats.

(1) The southeastern Serengeti (wet-season grazing), is characterized by soils developed on volcanic ash derived from recent eruptions of the Ol Doinjo Lengai carbonatite volcano. Here, we have identified deeper organic-rich soils with andic and vitric properties and varying amounts of carbonate concretions or near-surface calcrete horizons. High Na, K, and Ca levels of volcanic ashes suggest high levels of those elements in soils and vegetation in this region, also because the precipitation is lowest in this area.

(2) In the central Serengeti (short-term transitional grazing), soils develop on Archean basement rocks including granitic gneisses, phyllites and banded iron formations. Geochemical signatures of these rock types suggest that soils in this region have lower levels in Ca, Mg, and plant available P, compared to the SE Serengeti, which is supported by the transitional nature of this grazing habitat.

(3) Soils in the Northern Serengeti (dry-season grazing) develop on a diverse patchwork of Archean basement rocks as well as basaltic lavas and thick fluvial deposits. North of Mara river, the Insuria fault – a large normal fault of the East African Rift  - creates a wide sedimentary basin dominated by soils developed on basaltic sediments. Here, higher precipitation leads to stronger weathering and leaching of nutrient elements.

Our preliminary results suggests that geochemical variations together with continuous (syngenetic) pedogenesis through active volcanism or tectonic faulting and related fault scarp erosion created regions of high edaphic quality in the north and southeast of the Serengeti ecosystem, and that the patchy nature of soil edaphics is important to understand the underlying drivers of large scale migration of grazing animals in this region.