Pulse Effect of Precipitation: Spatial Patterns and Mechanisms of Soil Carbon Emissions

The rapid and strong release of CO2 caused by precipitation (known as the pulse effect) is a common phenomenon that significantly affects ecosystem C cycling. However, the degree to which the pulse effect occurs overlarge regional scales remains unclear. In this study, we conducted continuous and high-frequency measurements of soil CO2 release rates (Rs) for 48 h after simulated precipitation, along a precipitation gradient of different grassland types (i.e., meadow, typical, and desert) in Inner Mongolia, China. Pulse effects were assessed using the maximum Rs (Rsoil–max) and accumulated CO2 emissions (ARs–soil). Strong precipitation pulse effects were found in all sites; however, the effects differed among grassland types. In addition, an apparent decrease in both Rsoil–max and ARs–soil was observed from the east to west, i.e., along the decreasing precipitation gradient. ARs–soil values followed the order: temperate meadow grassland (0.097 mg C g–1 soil) > typical temperate grassland (0.081 mg C g–1 soil) > temperate desert grassland (0.040 mg C g–1 soil). Furthermore, Rsoil–max and ARs–soil were significantly positively correlated with soil quality (SOC, POC, and N, etc.; P < 0.01). ARs–soil (P < 0.05) and ARs–SOC (P < 0.01) were significantly affected. ARs–soil and ARs–SOC were also positively correlated with soil microbial biomass significantly (P < 0.05). Rsoil–max and ARs–soil had similar spatial variations and controlling mechanisms. These results greatly support the substrate supply hypothesis for the effects of precipitation pulses, and provide valuable information for predicting CO2 emissions. Our findings also verified the significant effect of soil CO2 release from precipitation pulses on the grasslands of arid and semi-arid regions. Our data provide a scientific basis for model simulations to better predict the responses of ecosystem carbon cycles in arid and semi-arid regions under predicted climate change scenarios.

Performance of Moment Resisting RC Frames under Repeated Earthquakes Containing Fling-Step Effect

The ground motion record from near-field earthquake may have forward and backward directivity effects. The first has pulse and fling-step signatures in its velocity and displacement motions, respectively. It is well recognized that the ground motion with pulse and fling-step effects amplified the building drift larger than the ground motion with no pulse and fling-step effects. The building damage also occurs due to earthquakes that are not singly exhibited. This includes the ground motion with fling-step, which is not many studied so far, especially in comparison with ground motion with pulse effect. Therefore, the goals of this study are to find out the effect of repeated earthquakes containing fling-step on the reinforced concrete (RC) moment resisting frames (MRF) in form of interstory drift ratio (IDR) and collapse probability. The 5-, 10-, and 15-story RC frames are taking into account as special, moderate and ordinary MRF, which is based on the R-factor of R = 8, R = 5, and R = 3. Based on the result of incremental dynamic analysis, the cumulative distribution function is statistically developed to define the fragility function. This function is treated as the probability of collapse of RC frames. The result shows that the performance of RC frames induced by single ground motion containing fling-step is at least 2 times larger than the single ground motion with pulse effect. The repeated earthquakes containing fling-step effect propagate the drift of 1.32 and 1.50 times larger than single earthquake with fling-effect. These motions cause the 10- and 15-story RC frames with R = 8 to have 100% of probability of collapse.