Abstract. The effect of high atmospheric CO 2 concentrations on the dynamics of mineral nutrient is not well documented, especially for subtropical China. We used model forest ecosystems in open-top chambers to study the effects of CO 2 enrichment alone and together with N addition on the dynamics of soil cations and anions. Two years of exposure to a 700 ppm CO 2 atmospheric concentration resulted in increased annual nutrient losses by leaching below 70 cm soil profile. Compared to the control, net Mg 2+ losses increased by 385%, K + by 223%, Ca 2+ by 167% and NO − 3 -N by 108%, respectively. Increased losses following exposure to elevated CO 2 were related to both faster weathering of minerals/organic matter decomposition and greater amounts of leaching water. Net annual nutrient losses in the high CO 2 concentration chambers reached 22.2 kg ha −1 year −1 for K + , 171.3 kg ha −1 year −1 for Ca 2+ , 8.2 kg ha −1 year −1 for Mg 2+ and about 2 kg ha −1 year −1 for NO − 3 -N. The N addition alone had no significant effect on the mineral nutrient leaching losses. However, addition of N together with the high CO 2 treatment significantly reduced mineral nutrient losses.We hypothesize that forests in subtropical China might suffer from nutrient limitation and reduction in plant biomass under elevated CO 2 concentration due to mineral leaching losses in the future.
Concrete is heterogeneous and usually described as a three-phase material, where matrix, aggregate and interface are distinguished. To take this heterogeneity into consideration, the Generalized Beam (GB) lattice model is adopted. The GB lattice model is much more computationally efficient than the beam lattice model. Numerical procedures of both quasi-static method and dynamic method are developed to simulate fracture processes in uniaxial tensile tests conducted on a concrete panel. Cases of different loading rates are compared with the quasi-static case. It is found that the inertia effect due to load increasing becomes less important and can be ignored with the loading rate decreasing, but the inertia effect due to unstable crack propagation remains considerable no matter how low the loading rate is. Therefore, an unrealistic result will be obtained if a fracture process including unstable cracking is simulated by the quasi-static procedure.
Using a low-cost infrared light source and a selection of narrowband filters, the non-resonant photoacoustic device is able to detect CO, SO2 and CF4 in SF6 down to a few ppm.
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