Li, L.; Wu, L.; Wang, X., and Cui, Z., 2015. Seismic response of underground structures in saturated soil based on the fluid-solid coupling dynamic formulation.In this paper, the seismic response of the underground structures in the saturated soil is studied by ABAQUS, with the saturated soil being simulated by the pore pressure element based on the fluid-solid coupling dynamic formulation of fluid-saturated porous media. It is illustrated that by the end of the earthquake input, the value of Mises stress is maximal on the two bottom corners of the structure. The value of pore pressure and vertical displacement is large in the bottom area near the structure, and the value of pore pressure and vertical displacement is equal on two sides of the structure. The vertical displacement of the soil decreases with the increase of depth. The maximal seismic response occurs when the acceleration of the earthquake input is maximal. ADDITIONAL INDEX WORDS:Underground structure, seismic response, saturated soil, fluid-solid coupling dynamic formulation, pore pressure element, UEL in ABAQUS.

Bacteria play a critical role in the material and energy-cycling processes of lake ecosystems. To understand the characteristics of the bacterial community in Wuliangsuhai Lake in spring, we explored the influence of environmental factors on the community structure of particle-attached bacteria (PA) and free-living bacteria (FL) in the water column of Wuliangsuhai Lake. In this study, we analyzed the bacterial community characteristics of 10 sampling sites in Wuliangsuhai Lake in April 2019 based on the high-throughput sequencing of 16S rRNA genes. Redundancy analysis (RDA) was used to analyze the influence of environmental factors on bacterial communities in lake water. The results showed the following: (1) The relative abundance of bacteria in Wuliangsuhai Lake did not significantly differ among the 10 sampling sites, and the dominant bacterial phyla were Actinobacteria, Proteobacteria, and Bacteroidetes. In addition, the community diversity of particle-attached (PA) was higher than that of free-living (FL). (2) The relative abundance of Bacteroidetes in PA (28.83%~54.67%) was significantly higher than that of FL (10.56%~28.44%), the relative abundance of Actinobacteria in the number of PA (20.02%~61.61%) was lower than that of FL (8.18%~16.71%), and the relative abundance of Verrucomicrobia in the PA (0.55%~13.11%) was higher than that of FL (0.05%~6.31%). (3) The redundancy analysis (RDA) showed that transparency, total nitrogen, total phosphorus, and NH4+-N were the main factors influencing the dominant bacterial communities in Wuliangsuhai Lake. This study provides the basis for further research on bacterial communities in freshwater lakes and may help local governments in the management of the water resources of Wuliangsuhai Lake.

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Ecological pollution caused by heavy metals released by sediments is a worldwide concern. However, the effect of changes in sediment speciation on their release of heavy metals has not been adequately reported. This study analysed changes in the sediment speciation of Pb and Cr before and after a release experiment by varying the temperature, pH, and salinity of the water column. The results show that the release of Pb and Cr from sediments increases with increasing water temperature, mainly due to the conversion of the residual fraction of Pb to the Fe-Mn oxide fraction and Cr converting more residual fraction to the organic matter and sulfide fraction. The release of sediment Pb and Cr decreased with increasing pH, with Pb converting more acid extractable fraction to the residual fraction and Cr converting more organic matter and sulfide fraction to the residual fraction. In contrast, the release of Pb and Cr increased and then decreased with increasing salinity, with the acid extractable and residual fractions of Pb interconverting, and the organic matter and sulfide fraction and the residual fraction of Cr showing higher interconversion. For Pb, the acid extractable fraction was more susceptible to conversion to the residual fraction by environmental influences, whereas for Cr, the organic matter and sulfide fraction was susceptible to conversion to the residual fraction. This study highlights the influence of environmental factors on the sediment speciation of heavy metals, which can help reveal the transport and transformation of heavy metals in cold and arid lake sediments.

Nitrogen is one of the most important elements involved in ecosystem biogeochemical cycling. However, little is known about the characteristics of nitrogen cycling during the ice-covered period in seasonally frozen lakes. In this study, shotgun metagenomic sequencing of subglacial water and sediment from Lake Ulansuhai was performed to identify and compare nitrogen metabolism pathways and microbes involved in these pathways. In total, ammonia assimilation was the most prominent nitrogen transformation pathway, and Bacteria and Proteobacteria (at the domain and phylum levels, respectively) were the most abundant portion of microorganisms involved in nitrogen metabolism. Gene sequences devoted to nitrogen fixation, nitrification, denitrification, dissimilatory nitrate reduction to ammonium, and ammonia assimilation were significantly higher in sediment than in surface and subsurface water. In addition, 15 biomarkers of nitrogen-converting microorganisms, such as Ciliophora and Synergistetes, showed significant variation between sampling levels. The findings of the present study improve our understanding of the nitrogen cycle in seasonally frozen lakes.