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Natural abundance sediment δ15N as a proxy for long-term gross N-turnover processes, GHG emissions, and denitrification hotspots within fluvial ecosystems
No full textNitrogen-rich agricultural headwater streams are known hotspots for fluvial
greenhouse gas (GHG) emissions and denitrification, yet the underlying processes driving
these elevated rates are not fully understood. In this study, we examined these mechanisms by
combining measurements of gross nitrogen turnover processes, open-channel GHG and N2
saturation (%) and fluxes, and δ15N isotopic analysis of stream sediment and water at nine
headwater stream sites with varying levels of agricultural land use. To assess seasonal
patterns, data were collected across two transitional periods: spring–summer and winter–
spring. Catchment land use emerged as an important environmental driver of variability, as
open channel GHG emissions and denitrification rates were up to 11 times higher in fertilized
grasslands and croplands compared to those in forested areas. In-vitro nitrogen turnover rates
followed a similar trend and were mainly positively related to both GHG and N2
oversaturation. This finding suggests that the excess nitrogen inputs in agricultural streams
promote enhanced nitrogen turnover and gaseous carbon and nitrogen losses. We also
observed a proportional increase in CO2, CH4, and N2 saturation in the water column with
sediment δ15N enrichment, a known indicator of long-term nitrogen turnover processes.
Because the highest GHG emissions and denitrification N2 losses occurred within streams in
fertilized areas, our findings highlight the potential of using sediment δ15N as an indicator of
long-term anthropogenic hotspots of fluvial GHG emissions and denitrification rates
Klimafreundliche Wohnbauten: Erprobung und Weiterentwicklung von Grundlagen der Ökobilanzierung
No full text
The obligation to long-term governance: a philosophical analysis
No full textBackground
Many of the problems currently facing our societies are long-term. Long-term problems are complex, often large-scale, and may require considerable planning and resources to avert undesirable outcomes in the (far) future. Consider issues such as climate change, nuclear waste disposal, and the sustainable management of ecosystems. The ability of a society to adequately address the most relevant problems depends on appropriate long-term governance, i.e., strategic, consistent, and coherent governance over an extended period of time.
Main text
Serious obstacles are inherent in long-term governance. These include short election cycles, intergenerational trade-offs, and the uncertainties involved in long-term decision-making. Liberal democracies appear to encounter difficulties in providing adequate responses to pertinent long-term issues, such as climate change, due to the institutions’ current design, which primarily focuses on safeguarding the interests of the present generation.
Conclusions
This paper introduces long-term governance as a distinct philosophical topic by defining it in relation to a novel perspective on long-term challenges. The paper defends an obligation to engage in long-term governance based on the basic rights of those who do not yet vote. This includes, in particular, an obligation to engage in research into long-term governance institutions
The Risk Perception Paradox—Implications for Governance and Communication of Natural Hazards
No full textGEMS-GER: a machine learning benchmark dataset of long-term groundwater levels in Germany with meteorological forcings and site-specific environmental features
No full textMicrostructural and mechanical investigations regarding the formability of glass fiber reinforced thermoplastic pultruded profiles
No full textThermoplastic fiber reinforced composites have crucial benefits over thermoset composite materials regarding sustainability and reusability, as well as in post-processing, like welding or forming. In this study in-situ pultruded unidirectional reinforced glass fiber reinforced anionic polyamide composites are investigated for their formability, to be used as local stiffening elements in light weight over molded polymer matrix composites. A forming setup was designed and manufactured and a systematic study on forming parameters was carried out in a bending radius ranging from 10 to 30 mm, pre-heating temperature from 180 to 235°C and a fiber volume content from 60 to 70 vol -%. The formed profiles were investigated regarding their stiffness in a bridged apex flexure test and a cantilever flexure test and the microstructure of the composite with microscopy and computed tomography. The ideal forming parameters were found to be 20 mm bending radius, 70 vol.-% glass fiber content and 215°C pre-heating temperature of the profiles, for the forming setup used. For forming with lower radius and temperatures, the profiles showed fiber buckling, undulations and folded fiber bundles up to fiber breakage in the inner of the formed radius. For higher temperatures, degradation on the profile surface got visible and squeeze out effects, reducing the profile shape quality. This led to lower mechanical properties and higher scatter of values. The findings give insights to process optimization for forming thermoplastic pultrusion profiles and help to prevent pre-damage during manufacturing. With this, the study participates in making fiber reinforced polymer matrix composites more sustainable and in the green transformation of structural light-weight materials
Manufacturability and microstructure of AlSi10Mg/SiC composites with different volume fractions of SiC using laser powder bed fusion
No full textIn the present study commercially available AlSi10Mg and SiC powders were mixed in a tumble mixer with resulting compositions of 5, 15 and 25 vol% SiC and processed using laser powder bed fusion. Different process parameters were used to manufacture samples which were characterized by various properties, such as porosity, microstructure and occurring phases to evaluate the manufacturability of the powder mixtures. The samples showed increasing porosity with lowered volumetric energy density and increasing SiC content. Relative densities of about 93.0% (25 vol% SiC), 94.5% (15 vol% SiC) and 98.5% (5 vol% SiC) respectively could be achieved. In addition, the correlation between the used energy density and the retained SiC particles in the samples was investigated. The quantity of retained SiC particles correlates negatively with the achievable density for all compositions, making compromises between these two properties necessary depending on the desired application. It is shown that SiC can get dissolved due to the high absorption of the laser energy resulting in the formation of primary silicon crystals as well as AlC and AlSiC phases. Microstructure characterizations using AFM revealed the influence of the SiC fraction on the eutectic structure and the formation of the new phases. Finally, EDS and TOF-SIMS analysis showed that the formed AlC phase can react with the humidity of ambient air at the surface, leading to localized cracks due to AlOOH formation
