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  • ddc:551.48  (6)
  • 631.4  (4)
  • 03. Hydrosphere::03.04. Chemical and biological::03.04.05. Gases
  • Blackwell Publishing Ltd  (7)
  • Chichester, UK  (5)
  • American Physical Society
  • 1
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    Hydrodynamic modeling of ephemeral flow in the Iishana channel systems of the Cuvelai Basin—Northern Namibia (2023)
    John Wiley & Sons, Ltd. | Chichester, UK
    Details
    Publication Date: 2024-04-19
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉The transboundary region of the Iishana system in the western Cuvelai Basin, between southern Angola and northern Namibia, is frequently affected by floods at irregular intervals. As a result, the predominantly rural, subsistence farming population has experienced crop failures, human, and economic losses. To date, very little is known about the generation of floods, flood concentration, and stormwater drainage dynamics in this region. In this study, 2D‐hydrodynamic modeling was applied to reconstruct one of the latest major flood events during the rainy season from November 2008 to March 2009 in order to study the runoff behavior and interconnectivity of the Iishana system. The model focused on the eastern part of the Iishana system, which was most affected by floods and flood damage due to the high population density in and around Oshakati, the regional capital. Two main streams were identified noteworthy because they merge and subsequently affect Oshakati. Regarding the simulated flood event water depths vary from 0.1 m to 14 m, with an average of 0.2 m, while water depths above 5 m were attributed to borrow pits. The inundation area ranged up to 1860 km〈sup〉2〈/sup〉 and the amount of water left after the rainy season on March 25th, 2009, was determined between 0.116 and 0.547 km〈sup〉3〈/sup〉, depending on the amount of evapotranspiration considered in the model. Thus, in the Angolan part of the Iishana system, significantly larger quantities of water are available for longer periods of time during the subsequent dry season, whereas the system in Namibia stores less water, resulting in a shorter water retention period.〈/p〉
    Description: Deutsche Hydrologische Gesellschaft (DHG)
    Description: Freie Universität Berlin http://dx.doi.org/10.13039/501100007537
    Description: https://dx.doi.org/10.17169/refubium-35737
    Keywords: ddc:551.48 ; flood ; FloodArea11 ; SCS‐CN ; TanDEM‐X ; TRMM
    Language: English
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  • 2
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    Toward an adequate level of detail in flood risk assessments (2023)
    Blackwell Publishing Ltd | Oxford, UK
    Details
    Publication Date: 2024-01-24
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉Flood risk assessments require different disciplines to understand and model the underlying components hazard, exposure, and vulnerability. Many methods and data sets have been refined considerably to cover more details of spatial, temporal, or process information. We compile case studies indicating that refined methods and data have a considerable effect on the overall assessment of flood risk. But are these improvements worth the effort? The adequate level of detail is typically unknown and prioritization of improvements in a specific component is hampered by the lack of an overarching view on flood risk. Consequently, creating the dilemma of potentially being too greedy or too wasteful with the resources available for a risk assessment. A “sweet spot” between those two would use methods and data sets that cover all relevant known processes without using resources inefficiently. We provide three key questions as a qualitative guidance toward this “sweet spot.” For quantitative decision support, more overarching case studies in various contexts are needed to reveal the sensitivity of the overall flood risk to individual components. This could also support the anticipation of unforeseen events like the flood event in Germany and Belgium in 2021 and increase the reliability of flood risk assessments.〈/p〉
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: BMBF http://dx.doi.org/10.13039/501100002347
    Description: Federal Environment Agency http://dx.doi.org/10.13039/501100010809
    Description: http://howas21.gfz-potsdam.de/howas21/
    Description: https://www.umwelt.niedersachsen.de/startseite/themen/wasser/hochwasser_amp_kustenschutz/hochwasserrisikomanagement_richtlinie/hochwassergefahren_und_hochwasserrisikokarten/hochwasserkarten-121920.html
    Description: https://download.geofabrik.de/europe/germany.html
    Description: https://emergency.copernicus.eu/mapping/list-of-components/EMSN024
    Description: https://data.jrc.ec.europa.eu/collection/id-0054
    Description: https://oasishub.co/dataset/surface-water-flooding-footprinthurricane-harvey-august-2017-jba
    Description: https://www.wasser.sachsen.de/hochwassergefahrenkarte-11915.html
    Keywords: ddc:551.48 ; decision support ; extreme events ; integrated flood risk management ; risk assessment
    Language: English
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  • 3
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    Using hydro‐morphological assessment parameters to estimate the flood‐induced vulnerability of watercourses ‐ a methodological approach across three spatial scales in Germany and the Czech Republic (2022)
    John Wiley & Sons, Ltd. | Chichester, UK
    Details
    Publication Date: 2024-01-22
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉In addition to their ecological importance, rivers and streams have always been used in diverse ways by humans, resulting in the development of settlements and their connected built environments along many of the world's watercourses. During heavy rainfall, buildings, traffic infrastructure and water‐related infrastructure are exposed to potential hazards in the form of (flash) floods. In contrast to near‐natural watercourses, anthropogenically modified channels in urban areas are particularly susceptible to damage by flooding. Previous damage assessments have highlighted the need to forecast such damage to watercourses in order to identify critical areas and justify the selection and expansion of adaptation measures. Within the scope of the current study, we have developed a method based on the hydro‐morphological properties of watercourses to make transferable estimates of the economic damage potential based on ecologically‐relevant parameters. Using a scale‐specific cause‐effect analysis, we have identified characteristics of the watercourse type and adjacent structures as well as construction‐related properties of reinforcements that can increase the damage potential during flooding. In this way, we are able to show that several influencing factors determine the vulnerability of watercourses: in addition to the specific longitudinal gradient and size (macroscale) of various watercourse types, damage‐relevant boundary conditions in watercourse sections (mesoscale) and the resistance of typical bed and bank constructions are also important, reflecting the specific structural conditions. Taking rivers in Germany and the Czech Republic as case studies, in the following, we review the local identification of critical areas and describe the necessary data management. The presented “Hydro‐morphological based Vulnerability Assessment‐Concept (HyVAC)” can contribute to the flood damage prevention at watercourses by utilizing existing basic data to the greatest possible extent and thus is suitable for preliminary investigations according to the EC Flood Risk Management Directive.〈/p〉
    Description: STRIMA II
    Description: EU‐funded research project
    Keywords: ddc:551.48 ; assessment parameters ; flood risk management ; hydro‐morphology ; vulnerability ; watercourses
    Language: English
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  • 4
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    Importance of catchment hydrological processes and calibration of hydrological‐hydrodynamic rainfall‐runoff models in small rural catchments (2023)
    Blackwell Publishing Ltd | Oxford, UK
    Details
    Publication Date: 2024-01-19
    Description: 〈title xmlns:mml="http://www.w3.org/1998/Math/MathML"〉Abstract〈/title〉〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉In recent years, many two‐dimensional (2D) hydrodynamic models have been extended to include the direct rainfall method (DRM). This allows their application as a hydrological‐hydrodynamic model for the determination of floodplains in one model system. In previous studies on DRM, the role of catchment hydrological processes (CaHyPro) and its interaction with the calibration process was not investigated in detail. In the present, case‐oriented study, the influence of the spatiotemporal distribution of the processes precipitation and runoff formation in combination with the 2D model HEC‐RAS is investigated. In a further step, a conceptual approach for event‐based interflow is integrated. The study is performed on the basis of a single storm event in a small rural catchment (low mountain range, 38 km〈sup〉2〈/sup〉) in Hesse (Germany). The model results are evaluated against six quality criteria and compared to a simplified baseline model. Finally, the calibrated improved model is contrasted with a calibrated baseline model. The results show the enhancement of the model results due to the integration of the CaHyPro and highlight its interplay with the calibrated model parameters.〈/p〉
    Keywords: ddc:551.48 ; 2D hydrodynamic modeling ; calibration ; direct rainfall modeling ; hydrological processes ; radar data ; runoff formation
    Language: English
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  • 5
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    The HydroEcoSedimentary tool: An integrated approach to characterise interstitial hydro‐sedimentary and associated ecological processes (2021)
    John Wiley & Sons, Ltd. | Chichester, UK
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    Publication Date: 2022-04-01
    Description: Increased deposition of fine sediments in rivers and streams affects a range of key ecosystem processes across the sediment–water interface, and it is a critical aspect of river habitat degradation and restoration. Understanding the mechanisms leading to fine sediment accumulation along and across streambeds and their effect on ecological processes is essential for comprehending human impacts on river ecosystems and informing river restoration. Here, we introduce the HydroEcoSedimentary tool (HEST) as an integrated approach to assess hydro‐sedimentary and ecologically relevant processes together. The HEST integrates the estimation of sedimentary processes in the interstitial zone, as well as hydraulic, geochemical and ecological assessments, with a focus on brown trout early life stages. Compared to other methods, the HEST expands the possibilities to monitor and quantify fine sediment deposition in streambeds by differentiating between vertical, lateral and longitudinal infiltration pathways, and distinguishing between the depth (upper vs. lower layers) at which interstitial processes occur within the sediment column. By testing the method in two rivers with different degrees of morphological degradation, we detail the possible measurements and uses of the HEST, demonstrate its feasibility and discuss its reliability.
    Description: Alexander von Humboldt‐Stiftung http://dx.doi.org/10.13039/100005156
    Description: Bavarian State Ministry of Science and Arts (Bayerisches Staatsministerium für Wissenschaft und Kunst)
    Keywords: ddc:551.48 ; ddc:550.724
    Language: English
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  • 6
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    The effect of stream shading on the inflow characteristics in a downstream reservoir (2021)
    John Wiley & Sons, Ltd. | Chichester, UK
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    Publication Date: 2022-04-01
    Description: In thermally stratified reservoirs, inflows form density currents according to the interplay between inflow temperature and reservoir stratification. The temperature of inflowing water is affected by catchment properties, including shading by riparian vegetation. We hypothesize that the degree of shading in the catchment can affect the inflow dynamics in downstream reservoirs by changing inflow temperature and consequently the nature of the density current. We test it for a subtropical drinking water reservoir by combining catchment‐scale hydrological and stream temperature modeling with observations of reservoir stratification. We analyze the formation of density currents, defined as under, inter and overflow, for scenarios with contrasting shading conditions in the catchment. Inflow temperatures were simulated with the distributed water‐balance model LARSIM‐WT, which integrates heat‐balance and water temperature. River temperature measurements and simulations are in good agreement with a RMSE of 0.58°C. In simulations using the present state of shading, underflows are the most frequent flow path, 63% of the annual period. During the remaining time, river intrusion form interflows. In a scenario without stream shading, average inflow temperature increased by 2.2°C. Thus, interflows were the most frequent flow path (51%), followed by underflows (34%) and overflows (15%). With this change, we would expect a degradation of reservoir water quality, as overflows promote longer periods of anoxia and nutrient loads would be delivered to the photic zone, a potential trigger for algae blooms. This study revealed a potentially important, yet unexplored aspect of catchment management for controlling reservoir water quality.
    Description: Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347
    Description: https://doi.org/10.5281/zenodo.4746288
    Keywords: ddc:628.1 ; ddc:551.48
    Language: English
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  • 7
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    Tillage erosion as an important driver of in‐field biomass patterns in an intensively used hummocky landscape (2021)
    John Wiley & Sons, Ltd. | Chichester, UK
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    Publication Date: 2021-10-06
    Description: Tillage erosion causes substantial soil redistribution that can exceed water erosion especially in hummocky landscapes under highly mechanized large field agriculture. Consequently, truncated soil profiles can be found on hill shoulders and top slopes, whereas colluvial material is accumulated at footslopes, in depressions, and along downslope field borders. We tested the hypothesis that soil erosion substantially affects in‐field patterns of the enhanced vegetation index (EVI) of different crop types on landscape scale. The interrelation between the EVI (RAPIDEYE satellite data; 5 m spatial resolution) as a proxy for crop biomass and modeled total soil erosion (tillage and water erosion modeled using SPEROS‐C) was analyzed for the Quillow catchment (size: 196 km2) in Northeast Germany in a wet versus normal year for four crop types (winter wheat, maize, winter rapeseed, winter barley). Our findings clearly indicate that eroded areas had the lowest EVI values, while the highest EVI values were found in depositional areas. The differences in the EVI between erosional and depositional sites are more pronounced in the analyzed normal year. The net effect of total erosion on the EVI compared to areas without pronounced erosion or deposition ranged from −10.2% for maize in the normal year to +3.7% for winter barley in the wet year. Tillage erosion has been identified as an important driver of soil degradation affecting in‐field crop biomass patterns in a hummocky ground moraine landscape. While soil erosion estimates are to be made, more attention should be given toward tillage erosion.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Keywords: 631.4 ; agroscapelab Quillow ; crop biomass patterns ; EVI ; remote sensing ; tillage erosion
    Type: map
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  • 8
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    The potential of ryegrass as cover crop to reduce soil N2O emissions and increase the population size of denitrifying bacteria (2021)
    Blackwell Publishing Ltd | Oxford, UK
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    Publication Date: 2021-07-05
    Description: Nitrogen (N) fertilization is the major contributor to nitrous oxide (N2O) emissions from agricultural soil, especially in post‐harvest seasons. This study was carried out to investigate whether ryegrass serving as cover crop affects soil N2O emissions and denitrifier community size. A microcosm experiment was conducted with soil planted with perennial ryegrass (Lolium perenne L.) and bare soil, each with four levels of N fertilizer (0, 5, 10 and 20 g N m−2; applied as calcium ammonium nitrate). The closed‐chamber approach was used to measure soil N2O fluxes. Real‐time PCR was used to estimate the biomass of bacteria and fungi and the abundance of genes involved in denitrification in soil. The results showed that the presence of ryegrass decreased the nitrate content in soil. Cumulative N2O emissions of soil with grass were lower than in bare soil at 5 and 10 g N m−2. Fertilization levels did not affect the abundance of soil bacteria and fungi. Soil with grass showed greater abundances of bacteria and fungi, as well as microorganisms carrying narG, napA, nirK, nirS and nosZ clade I genes. It is concluded that ryegrass serving as a cover crop holds the potential to mitigate soil N2O emissions in soils with moderate or high NO3− concentrations. This highlights the importance of cover crops for the reduction of N2O emissions from soil, particularly following N fertilization. Future research should explore the full potential of ryegrass to reduce soil N2O emissions under field conditions as well as in different soils. Highlights This study was to investigate whether ryegrass serving as cover crop affects soil N2O emissions and denitrifier community size; Plant reduced soil N substrates on one side, but their root exudates stimulated denitrification on the other side; N2O emissions were lower in soil with grass than bare soil at medium fertilizer levels, and growing grass stimulated the proliferation of almost all the denitrifying bacteria except nosZ clade II; Ryegrass serving as a cover crop holds the potential to mitigate soil N2O emissions.
    Description: China Scholarship Council http://dx.doi.org/10.13039/501100004543
    Description: The National Science Project for University of Anhui Province
    Keywords: 551.9 ; 631.4 ; denitrification ; perennial ryegrass (Lolium perenne L.) ; soil bacteria ; soil CO2 emissions ; soil N2O emissions
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  • 9
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    Synthetic resampling strategies and machine learning for digital soil mapping in Iran (2021)
    Blackwell Publishing Ltd | Oxford, UK
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    Publication Date: 2021-07-04
    Description: Most common machine learning (ML) algorithms usually work well on balanced training sets, that is, datasets in which all classes are approximately represented equally. Otherwise, the accuracy estimates may be unreliable and classes with only a few values are often misclassified or neglected. This is known as a class imbalance problem in machine learning and datasets that do not meet this criterion are referred to as imbalanced data. Most datasets of soil classes are, therefore, imbalanced data. One of our main objectives is to compare eight resampling strategies that have been developed to counteract the imbalanced data problem. We compared the performance of five of the most common ML algorithms with the resampling approaches. The highest increase in prediction accuracy was achieved with SMOTE (the synthetic minority oversampling technique). In comparison to the baseline prediction on the original dataset, we achieved an increase of about 10, 20 and 10% in the overall accuracy, kappa index and F‐score, respectively. Regarding the ML approaches, random forest (RF) showed the best performance with an overall accuracy, kappa index and F‐score of 66, 60 and 57%, respectively. Moreover, the combination of RF and SMOTE improved the accuracy of the individual soil classes, compared to RF trained on the original dataset and allowed better prediction of soil classes with a low number of samples in the corresponding soil profile database, in our case for Chernozems. Our results show that balancing existing soil legacy data using synthetic sampling strategies can significantly improve the prediction accuracy in digital soil mapping (DSM). Highlights Spatial distribution of soil classes in Iran can be predicted using machine learning (ML) algorithms. The synthetic minority oversampling technique overcomes the drawback of imbalanced and highly biased soil legacy data. When combining a random forest model with synthetic sampling strategies the prediction accuracy of the soil model improves significantly. The resulting new soil map of Iran has a much higher spatial resolution compared to existing maps and displays new soil classes that have not yet been mapped in Iran.
    Description: Alexander von Humboldt‐Stiftung http://dx.doi.org/10.13039/100005156
    Description: German Research Foundation http://dx.doi.org/10.13039/501100001659
    Description: Soil and Water Research Institute, Agricultural Research, Education and Extension Organization, Karaj, Iran
    Keywords: 631.4 ; covariates ; imbalanced data ; machine learning ; random forest ; soil legacy data
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  • 10
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    Impact of biochar on nutrient supply, crop yield and microbial respiration on sandy soils of northern Germany (2021)
    Blackwell Publishing Ltd | Oxford, UK
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    Publication Date: 2021-06-16
    Description: The application of biochar to agricultural soils to increase nutrient availability, crop production and carbon sequestration has gained increasing interest but data from field experiments on temperate, marginal soils are still under‐represented. In the current study, biochar, produced from organic residues (digestates) from a biogas plant, was applied with and without digestates at low (3.4 t ha−1) and intermediate (17.1 t ha−1) rates to two acidic and sandy soils in northern Germany that are used for corn (Zea mays L.) production. Soil nutrient availability, crop yields, microbial biomass and carbon dioxide (CO2) emissions from heterotrophic respiration were measured over two consecutive years. The effects of biochar application depended on the intrinsic properties of the two tested soils and the biochar application rates. Although the soils at the fallow site, with initially low nutrient concentrations, showed a significant increase in pH, soil nutrients and crop yield after low biochar application rates, a similar response was found at the cornfield site only after application of substantially larger amounts of biochar. The effect of a single dose of biochar at the beginning of the experiment diminished over time but was still detectable after 2 years. Whereas plant available nutrient concentrations increased after biochar application, the availability of potentially phytotoxic trace elements (Zn, Pb, Cd, Cr) decreased significantly, and although slight increases in microbial biomass carbon and heterotrophic CO2 fluxes were observed after biochar application, they were mostly not significant. The results indicate that the application of relatively small amounts of biochar could have positive effects on plant available nutrients and crop yields of marginal arable soils and may decrease the need for mineral fertilizers while simultaneously increasing the sequestration of soil organic carbon. Highlights A low rate of biochar increased plant available nutrients and crop yield on marginal soils. Biochar application reduced the availability of potentially harmful trace elements. Heterotrophic respiration showed no clear response to biochar application. Biochar application may reduce fertilizer need and increase carbon sequestration on marginal soils.
    Description: German Academic Exchange Service http://dx.doi.org/10.13039/501100001655
    Description: Institute Strategic Programme grants, “Soils to Nutrition”
    Keywords: 631.4 ; black carbon ; carbon sequestration ; corn ; digestate ; heterotrophic respiration ; marginal soils ; microbial biomass
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