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In this paper we compare the outputs of neural network metamodels with numerical solutions of differential equation models in modeling cesium-137 transportation in sand. Convolutional neural networks (CNNs) were trained with differential equation simulation results. Training sets of various sizes (from 5120 to 163,840) were used. First order and total order Sobol methods were applied to both models in order to test the feasibility of neural network metamodels for sensitivity analysis of a radionuclide transport model. Convolutional neural networks were found to be capable of emulating the differential equation models with high accuracy when the training set size was 40,960 or higher. Neural network metamodels also gave similar results compared with the numerical solutions of the partial differential equation model in sensitivity analysis. [ABSTRACT FROM AUTHOR]

In recent years, there has been an intense public debate about whether and, if so, to what extent investments in nuclear energy should be part of strategies to mitigate climate change. Here, we address this question from an ethical perspective, evaluating different strategies of energy system development in terms of three ethical criteria, which will differentially appeal to proponents of different normative ethical frameworks. Starting from a standard analysis of climate change as arising from an intergenerational collective action problem, we evaluate whether contributions from nuclear energy will, on expectation, increase the likelihood of successfully phasing out fossil fuels in time to avert dangerous global warming. For many socio-economic and geographic contexts, our review of the energy system modeling literature suggests the answer to this question is “yes.” We conclude that, from the point of view of climate change mitigation, investments in nuclear energy as part of a broader energy portfolio will be ethically required to minimize the risks of decarbonization failure, and thus the tail risks of catastrophic global warming. Finally, using a sensitivity analysis, we consider which other aspects of nuclear energy deployment, apart from climate change, have the potential to overturn the ultimate ethical verdict on investments in nuclear energy. Out of several potential considerations (e.g., nuclear waste, accidents, safety), we suggest that its potential interplay — whether beneficial or adverse — with the proliferation of nuclear weapons is the most plausible candidate. [ABSTRACT FROM AUTHOR]

As bacteria and archaea are key components in the ecosystem, information on their dynamics in soil profiles is important for understanding the biogeochemical cycles in peatlands. However, little is known about the vertical distribution patterns of bacteria and archaea in the Bitahai peatland, or about their relationships with soil chemical properties. Here, bacterial and archaeal abundance, diversity, and composition of the Bitahai peatlands at 0-100 cm soil depths were analyzed by sequencing of 16S rRNA genes (Illumina, MiSeq). Soil pH, total C, N, and P concentrations and stoichiometric ratios were also estimated. The results revealed that total C and total N contents, as well as C:P and N:P ratios, significantly increased with increasing peatland soil depths, while total P decreased. The top three dominant phyla were Proteobacteria (39.64%), Acidobacteria (12.93%), and Chloroflexi (12.81%) in bacterial communities, and were Crenarchaeota (58.67%), Thaumarchaeota (14.34%), and Euryarchaeota (10.82%) in archaeal communities in the Bitahai peatland, respectively. The total relative abundance of methanogenic groups and ammonia-oxidizing microorganisms all significantly decreased with soil depth. Both bacterial and archaeal diversities were significantly affected by the soil depth. Soil C, N, and P concentrations and stoichiometric ratios markedly impacted the community structure and diversity in archaea, but not in bacteria. Therefore, these results highlighted that the microbial community structure and diversity depended on soil depth for the Bitahai peatlands, and the factors affecting bacteria and archaea in the Bitahai peatlands were different. [ABSTRACT FROM AUTHOR]

The buffer material in deep geological repositories for disposing high-level radioactive nuclear waste must have sufficient thermal conductivity to dissipate the decay heat. The graphite is a potential addictive to improve the thermal conductivity of bentonite buffer material, thus the thermal-hydro-mechanical performance was experimentally investigated. A series of tests including the free swelling index, grain size distribution, swelling pressure, saturated hydraulic conductivity and thermal conductivity measurements were performed on compacted graphite–bentonite mixtures (GB) at various graphite ratios (5%, 10%, 15%, 20%, 30%, 40%) and meshes (50, 100, 200, and 325 mesh), indicating that adding graphite could significantly influence the properties of GB, depending on the water content and dry density as well. It was also found that the optimal graphite ratio was approximately 15–20% by weight, and that the proper graphite should have a grain size ranging from 100 to 200 mesh. Meanwhile, the pore size distribution (PSD) curves of compacted GB showed that graphite particles graded as too large or too small were prone to forming macropores by point-edge mode contact with the generally smaller bentonite particles or agglomerates. Moreover, as graphite is hydrophobic, water can easily pass through the surface of the graphite sheets, even when the bentonite expands after hydration. [ABSTRACT FROM AUTHOR]

To predict the effects of nitrogen deposition on nitrogen-mineralizing enzyme activity and soil microbial community structure in artificial temperate forests in northern China, we studied the soil properties, nitrogen-mineralizing enzyme activity, and microbial community structure in the soil of a Korean pine plantation in which different concentrations (0, 20, 40, 80 kg N ha−1 year−1) of ammonium nitrate were applied for 5 consecutive years. The results showed that nitrogen addition at different concentrations did not significantly affect the soil pH. High nitrogen addition (80 kg N ha−1 year−1) significantly increased the soil organic matter, ammonium nitrogen, and nitrate nitrogen content in the Korean pine plantation, and ammonium nitrogen was the key factor that influenced the soil fungal community structure. The urease activity under the moderate nitrogen addition treatment (40 kg N ha−1 year−1) was significantly lower than that under the control (0 kg N ha−1 year−1), and the protease activity in the three treatments was also significantly lower than that in the control. There was no significant correlation between microbial community structure and the four mineralizing enzymes. After nitrogen addition at different concentrations, the Simpson and Shannon indexes of soil bacteria decreased significantly under low nitrogen addition (20 kg N ha−1 year−1), but the α-diversity index of soil fungi did not show significant differences under nitrogen addition. The microbial community composition was significantly changed by the different treatments. PLS-DA analysis showed that Tardiphaga was an important genus that made the greatest contribution to the differences in bacterial community composition among treatments, as was Taeniolella for fungal community composition. The low level of nitrogen addition inhibited nitrogen mineralization in the Korean pine plantation by reducing the relative abundances of Nitrosomonadaceae and Betaproteobacteriales and by reducing the abundances of symbiotrophic fungi. Berkelbacteria and Polyporales were bacteria and fungi, respectively, that changed significantly under the high nitrogen addition treatment (80 kg N ha−1 year−1). This study provides more data to support predictions of the changes in nitrogen-mineralizing enzyme activity and microbial community structure in artificial temperate forest soils in response to increased nitrogen deposition. [ABSTRACT FROM AUTHOR]

Globally, wetlands are in decline due to anthropogenic modification and climate change. Knowledge about the spatial distribution of biodiversity and biological processes within wetlands provides essential baseline data for predicting and mitigating the effects of present and future environmental change on these critical ecosystems. To explore the potential for environmental DNA (eDNA) to provide such insights, we used 16S rRNA metabarcoding to characterise prokaryote communities and predict the distribution of prokaryote metabolic pathways in peats and sediments up to 4m below the surface across seven New Zealand wetlands. Our results reveal distinct vertical structuring of prokaryote communities and metabolic pathways in these wetlands. We also find evidence for differences in the relative abundance of certain metabolic pathways that may correspond to the degree of anthropogenic modification the wetlands have experienced. These patterns, specifically those for pathways related to aerobic respiration and the carbon cycle, can be explained predominantly by the expected effects of wetland drainage. Our study demonstrates that eDNA has the potential to be an important new tool for the assessment and monitoring of wetland health. [ABSTRACT FROM AUTHOR]

Copyright of Ecoscience (Ecoscience) is the property of Taylor & Francis Ltd and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Pacific coastal temperate rainforest (PCTR) is a global hot-spot for carbon cycling and export. Yet the influence of microorganisms on carbon cycling processes in PCTR soil is poorly characterized. We developed and tested a conceptual model of seasonal microbial carbon cycling in PCTR soil through integration of geochemistry, micro-meteorology, and eukaryotic and prokaryotic ribosomal amplicon (rRNA) sequencing from 216 soil DNA and RNA libraries. Soil moisture and pH increased during the wet season, with significant correlation to net CO2 flux in peat bog and net CH4 flux in bog forest soil. Fungal succession in these sites was characterized by the apparent turnover of Archaeorhizomycetes phylotypes accounting for 41% of ITS libraries. Anaerobic prokaryotes, including Syntrophobacteraceae and Methanomicrobia increased in rRNA libraries during the wet season. Putatively active populations of these phylotypes and their biogeochemical marker genes for sulfate and CH4 cycling, respectively, were positively correlated following rRNA and metatranscriptomic network analysis. The latter phylotype was positively correlated to CH4 fluxes (r = 0.46, p < 0.0001). Phylotype functional assignments were supported by metatranscriptomic analysis. We propose that active microbial populations respond primarily to changes in hydrology, pH, and nutrient availability. The increased microbial carbon export observed over winter may have ramifications for climate-soil feedbacks in the PCTR. [ABSTRACT FROM AUTHOR]

The through-diffusion method and batch sorption experiments were used to explore the influence of pH on the diffusion behavior of 75Se(IV) in matrix Beishan granite (BsG). In the pH range of 2.0-8.5, the De values of 75Se(IV) in BsG decreased first and then increased with pH increasing, while the changing trend of Kd was nearly opposite. It was speculated that the influence of pH on the diffusion of 75Se(IV) in BsG was due to the joint effects of different species distribution of Se, change in surface charge of BsG and change in ionic strength at various pH values. [ABSTRACT FROM AUTHOR]

The Gahai Lake wetland natural conservation area in northwestern China includes peatland that has been accumulating over hundreds of years and is seldom disturbed by industry. Bacteria and archaea in peat soil, which is a reservoir for carbon and water, may influence its ecological function. The objective of this study was to obtain a clearer understanding of peat microbial ecology and its relationship to the environmental conditions of this area. Hence, the microbial community of the peatland ecosystem was investigated by sequencing bacterial and archaeal DNA extracted from samples collected at different peat depths. Results showed that in all samples the dominant bacterial phyla were Proteobacteria (relative abundance 0.39 ± 0.12) and Chloroflexi (0.16 ± 0.09), while the dominant archaeal phyla were Miscellaneous Crenarchaeotic Group (MCG) (0.62 ± 0.21) and Euryarchaeota (0.27 ± 0.16). The diversity and microbial community structure at deeper depths (90 and 120 cm below the peat surface) significantly differ from that at shallower depths (10, 30 and 50 cm deep). In contrast to the shallow layers, the deeper layers became more abundant in the bacterial phyla Chloroflexi, Bacteroidetes, Atribacteria, Aminicenantes, Chlorobi, TA06, Caldiserica and Spirochaetae; and in the archaeal phyla MCG and Miscellaneous Euryarchaeotic Group (MEG). This study revealed a significant shift in microbial community in peat between 50 cm and 90 cm deep, as probably influenced by the oxygen supply at different depths. Furthermore, new insights into the microbial taxa were obtained, thus providing a baseline for future studies of this peat ecosystem. [ABSTRACT FROM AUTHOR]

The sorption of inorganic radiocarbon on goethite, hematite and magnetite was studied as a function of carbon concentration, pH and ionic strength. It was discovered that the sorption of radiocarbon on magnetite was negligible in all studied conditions. The distribution coefficients of radiocarbon on hematite and goethite decreased with increasing pH whereas the ionic strength had only a slight decreasing effect on radiocarbon sorption. The sorption on goethite and hematite was modelled with PhreeqC using a generalized double-layer surface complexation model. [ABSTRACT FROM AUTHOR]

The speciation and sorption of iodine was studied on humus and mineral soil samples in the initial chemical forms of iodide and iodate. Iodate was reduced to iodide in significant amounts especially in anaerobic soil conditions and in low pH. An unidentified, possible organo-iodine species was detected in humus samples and in aerobic mineral soil at incubation times of 1-21 days and in low pH (4-5). The overall retention of iodide and iodate on Olkiluoto mineral soil was very weak and organic matter proved to be the main sorbent for iodine. [ABSTRACT FROM AUTHOR]

As part of the long-term diffusion project a 780 days long in situ diffusion experiment was performed at the Grimsel Test Site where several radionuclides and inactive iodine were circulated in the packered interval in granodiorite. This paper presents in situ diffusion profiles for tritiated water and iodine acquired from overcored sections of the circulation interval by out-leaching. [ABSTRACT FROM AUTHOR]

The sorption of cesium was studied using humus and mineral soil samples. The effect of grain size, soil depth, organic matter and mineralogy were evaluated. The smallest grain size showed the highest sorption whilst it was rather equal for larger grains sizes. The sorption of cesium increased with soil depth being the lowest in the humus. Among the mineral soil layers the highest retention was found in the layer enriched with clay fraction. Muscovite retained cesium fairly well in pure water and model soil solution. Quartz showed the poorest sorption in both solutions. [ABSTRACT FROM AUTHOR]

Cesium sorption on Olkiluoto mineral soil samples was studied in batch experiments. The effect of incubation time, incubation conditions, pH and competing cations were investigated. The retention of cesium increased with increasing time. In anaerobic conditions the sorption of cesium was lower than in aerobic ones, possibly caused by the formation of NH. Increase in pH promoted the sorption of cesium. Stable cesium reduced the sorption of Cs the most, and the overall sorption hindering effectivity of cations decreased in the order of stable Cs > NH > K » Ca > Na. [ABSTRACT FROM AUTHOR]

This study aims to analyse the combined impacts of future discharges and sea levels on erosion-sedimentation potential, and its seasonal changes, in a ~43-km-long coastal river reach of South-west Finland. To our knowledge, this kind of combined study has not been performed before. In addition to surveying the present erosion-sedimentation conditions, the daily erosion-sedimentation potential is simulated with a one-dimensional hydrodynamic model for the 1971-2000 and 2070-2099 periods by applying four discharge scenarios. Different sea level stages are also employed in the simulations. All scenarios forecast increasing autumn and winter discharges, but diminishing summer discharges. This indicates increasing river channel erosion, particularly during winters and autumns. Although discharge changes have altogether a greater influence on erosion-sedimentation potential, the importance of sea level changes on sedimentation is noticeable in the estuary. The rising sea level scenarios increase the sedimentation potential. In total, by 2070-2099, the erosion potential may increase in most parts of the study area. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The need to address radiological impacts from radiocarbon released to the biosphere has been recognized for some time. In 2011, the Swedish Radiation Safety Authority (SSM) commissioned a study to develop a 14C model of the soilplant- atmosphere system that would provide them with an independently developed assessment capability. This paper summarizes that study, which comprised a review of contemporary models, the development of a new conceptual model, SSPAM14C, and the application of SSPAM14C to a set of experimental data relating to the atmospheric exposure of cabbages. [ABSTRACT FROM AUTHOR]

Copyright of Hydrogeology Journal is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)