Redistribution process of precipitation in ecological restoration activity of Pinus sylvestris var. mongolica in Mu Us Sandy Land, China

Precipitation was the most important water resource in semi-arid regions of China. The redistribution of precipitation among atmospheric water, soil water and groundwater are related to the land surface ecological system sustainability. The study took widely replanted Pinus sylvestris var. mongolica (PSM) in Mu Us Sandy Land (MUSL) as a research object and monitored precipitation, soil moisture, sap flow, and deep soil recharge (DSR) to find out moisture distribution in shallow soil layer. Results showed that the restoration process of PSM in MUSL changed the distribution of precipitation. Precipitation was intercepted in shallow soil, evapotranspiration increased, and DSR significantly decreased, resulting in up to 466.94 mm of precipitation returning to the atmosphere through evapotranspiration in 2016. Vegetation increased soil water storage (SWS) capacity, with maximum SWS in PSM plot and bare sandy land (BSL) being 260 mm and 197 mm per unit horizontal area, respectively in 2016. DSR decreased from 54.03 % of precipitation in BSL to 0.2 % of precipitation in PSM in 2016. Infiltration was not only intercepted by PSM ecosystem, resulting in a time lag, but was also affected by soil temperature, and the infiltration rate in the BSL plot was 11 times of that in the PSM plot from August to September in an annual base. SWS decreased 16 mm and 7.58 mm per unit horizontal area over a one-year period (from March to October) in 2017 and 2019, respectively. The PSM annual sap flow was maintained at a relatively constant level of 153.98 mm/yr. This study helps understand the role of precipitation-induced groundwater recharge in the process of vegetation restoration in semi-arid regions and explains the possible causes of PSM forest degradation. It is necessary to reduce PSM density to allow adaptation to extreme drought in the future.

Shale Compaction Kinetics

The grain-to-grain stress vertically in sediments is given by the overburden less the pore fluid pressure, σ, divided by the fraction of the horizontal area which is the supporting matrix , (1 − φ), where φ is the porosity. It is proposed that the fractional reduction of this ratio, Λ, with time is given by the product of φ 4m/3 , (1 − φ) 4n/3 , and one or more Arrhenius functions A exp(−E/RT ) with m and n close to 1. This proposal is tested for shale sections in six wells from around the world for which porosity-depth data are available. Good agreement is obtained above 30-40 C and porosities less than 0.5. Single activation energies for each well are obtained in the range 15-33 kJ/mole, close to pressure solution of quartz, 24 kJ/mol. Values of m and n are in the range 1 to 0.8, indicating nearly fractal pore-matrix spaces and water-wet interfaces. Results are independent of over- or under-pressure of pore water. This model explains shale compaction quantitatively. Given porosity-depth data and accurate activation energy, E, one can infer paleo-geothermal-gradient and from that organic maturity, thus avoiding unnecessary drilling.

Operational Stability of a Hydropower Plant with a Pipe-Shaped Air-Cushion Surge Chamber

This paper theoretically analyzed the design and operating parameters of a pipe-shaped air-cushion surge chamber (PS-ACSC). A mathematical model for a small load disturbance in a hydropower plant containing the PS-ACSC was established to analyze the effects of the sensitivity of its initial horizontal area and the air-water volume ratio on the operational stability of the plant. The results showed that the PS-ACSC should occupy a critical horizontal area, and its initial water level and the initial air-water volume ratio should be within a certain range to ensure its own stable operation as well as that of the turbine units. The results of a case study showed that a hydropower plant containing the PS-ACSC is most stable when the initial air-water volume ratio ranges from 2.90:1 to 6.68:1. In addition, a hydropower plant containing the PS-ACSC delivers better performance than a horseshoe-shaped air-cushion surge chamber under the same conditions. This study contributes to the design and operational control of hydropower plants containing the PS-ACSC.

Shale Compaction Kinetics

1 Abstract The grain-to-grain stress vertically in sediments is given by the overburden less the pore fluid pressure, σ, divided by the fraction of the horizontal area which is the supporting matrix , (1 − φ), φ being the porosity. It is proposed that the fractional reduction of this ratio, Λ, with time is given by the product of φ 4m/3) , (1 − φ) 4n/3 , and one or more Arrhenius functions A exp(−E/RT ) with m and n close to 1. This proposal is tested for shale sections in six wells from around the world for which porosity-depth data are available. Good agreement is obtained above 30-40 C. A single activation energy of 23+-5 kJ/mole, indicating pressure solution of quartz, 24 kJ/mol, was obtained. The average value of m is 1, indicating fractal pore-matrix spaces and water-wet interfaces. Grain-to -grain interfaces may be fractal with m close to 1, but can have lower values suggesting smooth surfaces and even grain-to-grain welding. Results are independent of over- or under-pressure of pore water. This model explains shale compaction quantitatively.

Initiation of Deep Convection over an Idealized Mesoscale Convergence Line

This study performs cloud-resolving simulations of cumulus convection over an idealized surface-based convergence zone to investigate the mechanisms and sensitivities of deep convection initiation forced by mesoscale ascent. The surface convergence forms in response to a localized diurnal heating anomaly over an otherwise homogeneous and unheated surface, producing a strong boundary layer updraft over the center of the heat source. This updraft gives rise to a line of cumuli that gradually deepen and, in some cases, transition into deep convection. To statistically investigate the factors controlling this transition, a new thermal-tracking algorithm is developed to follow incipient cumulus cores as they ascend through the troposphere. This tool is used to isolate the impacts of key environmental parameters (cloud-layer lapse rate, midlevel humidity, etc.) and initial core parameters near cloud base (horizontal area, vertical velocity, etc.) on the ultimate cloud-top height. In general, the initial core size determines which thermals in a given cloud field will undergo the deepest ascent, and the sensitivity of cloud depth to initial core parameters increases in environments that are more hostile to deep convection. Diurnal midlevel moistening from detraining cumuli above the convergence line produces a small but robust enhancement in cloud-top height, particularly for smaller cores.