黄河流域:天水城市空间营造

该文是个案研究系列之黄河流域天水城市空间营造研究,对天水城市族群的更替叠累及城市空间营造进行了分析研究。

Revision of P-wave Velocity and Thickness of Hydrate Layer in Shenhu Area, South China Sea

To revise P-wave velocity and thickness of the hydrate layer in the Shenhu area of the South China Sea, acoustic and resistivity logging curves are reanalyzed. The waterlogging phenomenon is found in the shallow sediments of five drilling wells, which causes P-wave velocity to approximate the propagation velocity of sea water(about 1500 m s-1). This also affects the identification of the hydrate layer and results in the underestimate of its thickness. In addition, because there could be about a 5 m thick velocity ramp above or below the hydrate layer as interpreted by acoustic and resistivity logging curves, the recalibrated thickness of this layer is less than the original estimated thickness. The recalibrated P-wave velocity of the hydrate layer is also higher than the original estimated velocity. For the drilling well with a relatively thin hydrate layer, the velocity ramp plays a more important role in identifying and determining the thickness of the layer.

Analysis of the Synoptic Situation Field on the Red Tide Occurred in Yangtze River Estuary Water Area

The occurrence of the red tide is an extremely complex process, which is considered as the comprehensive result of various factors. The Yangtze River estuary water area is always in high incidence area of red tide. In this paper, according to the events of red tide and meteorologic and hydrologic data in Yangtze River estuary water area from 2000 to 2010, by using mathematical statistics methods, we analyze the relevance between the occurrence of the red tide and the synoptic situation field, and probe into the regular patterns.

Controlling factors for gas hydrate occurrence in Shenhu area on the northern slope of the South China Sea

Temperature and pressure on seafloor of the northern slope in the South China Sea are suitable for gas hydrate formation, but bottom simulation reflector (BSR), an indication of gas hydrate occurrence, only occurred in limited areas of the slope. Drillings in the BSR-distributed area (the District S) on the northern slope of the South China Sea suggested that gas hydrate only occurred at Sites SH2, SH3, and SH7 with high saturation (up to 20%-40%), and there is no hydrate at Sites SH1 and SH5 although the distance between SH1 to SH3 is only 500m. In this paper, we investigated seafloor gradient, fault development, temperature, and pressure in the District S on the northern slope of the South China Sea to understand the possible factors con- trolling BSR distribution and gas hydrate occurrence. The District S is a structurally fractured continental slope zone and its seafloor gradient varied greatly. The BSR-occurred areas have an average gradient of 19.89×10 2 whereas the BSR-free zone has the average gradient of 10.57×10 2 . The calculated relative structural intensities from fault densities and displacements show that the BSR-distributed areas tend to occur in the areas with a moderately high structural intensity, where faults frequently developed close to the seafloor that are possibly favored for lateral migration of gases. On the basis of temperatures and pressures at drilling sites, hydrate-occurred Sites SH2, SH3, and SH7 are located within the thermodynamically stable area for methane hydrate, and hydrate-absent Sites SH1 and SH5 are out of the thermodynamically stable area for methane hydrate formation, suggesting that both BSR and the thermodynamic stability are necessary for hydrate occurrence in the subsurface.

Effect of thermal stimulation on gas production from hydrate deposits in Shenhu area of the South China Sea

The Shenhu area on the northern continental slope of the South China Sea （SCS） is one of the promising fields for gas hydrate exploitation. The hydrate-bearing layer at drilling site SH2 is overlain and underlain by permeable zones of mobile water. In this study a vertical well was configured with a perforated Interval I for producing gas and a coiled Interval II for heating sed- iment, The hydrate is dissociated by a small depressurization at Interval Ⅰ and a thermal stimulation at Interval Ⅱ. The numeri- cal simulations indicate that the thermal stimulation has a significant effect on gas release from the hydrates in the production duration and improves the gas production in the late period. The gas released by thermal stimulation cannot be produced as quickly as the production gets operated because of the hard pathway for fluids to flow in the sediments. The gas production is enhanced due to the heating for 7242 m3 in the whole production. Increasing heating temperature at Interval Ⅱcan improve gas production and restrain water output, and advance the arrival time of the gas flow from the zone at Interval Ⅱ. The absolute criterion and relative criterion suggest that the thermal stimulation in the production schemes is pronounced for releasing gas from the hydrate deposit, but the production efficiency of gas is limited by the sediment of low permeability. The study pro- vides an insight into the production potential of the hydrate accumulations by thermal stimulation with depressurization in two wells, and a basis for analyzing economic feasibility of gas production from the area.

Study of atmospheric CO2 and CH4 at Longfengshan WMO/GAW regional station： The variations, trends, influence of local sources/sinks, and transport

Atmospheric CO_2 and CH_4 have been continuously measured since 2009 at Longfengshan WMO/GAW station(LFS) in China. Variations of the mole fractions, influence of long-distance transport, effects of local sources/sinks and the characteristics of synoptic scale variations have been studied based on the records from 2009 to 2013. Both the CO_2 and CH_4 mole fractions display increasing trends in the last five years, with growth rates of 3.1±0.02 ppm yr.1 for CO_2 and 8±0.04 ppb yr.1(standard error, 1-σ)for CH_4. In summer, the regional CO_2 mole fractions are apparently lower than the Marine Boundary Layer reference, with the lowest value of.13.6±0.7 ppm in July, while the CH_4 values are higher than the MBL reference, with the maximum of 139±6 ppb.From 9 to 17(Local time, LT) in summer, the atmospheric CO_2 mole fractions at 10 m a.g.l. are always lower than at 80 m, with a mean difference of.1.1±0.2 ppm, indicating that the flask sampling approach deployed may underestimate the background mole fractions in summer. In winter, anthropogenic emissions dominate the regional CO_2 and CH_4 mole fractions. Cluster analysis of backward trajectories shows that atmospheric CO_2 and CH_4 at LFS are influenced by anthropogenic emissions from the southwest(Changchun and Jilin city) all year. The synoptic scale variations indicate that the northeastern China plain acts as an important source of atmospheric CO_2 and CH_4 in winter.

Efficiency of a Grass Buffer Strip for Limiting Diuron Losses from an Uphill Vineyard Towards Surface and Subsurface Waters

Grass buffer strips limit the transfer of pesticides from cultivated fields to rivers. These solutions are generally efficient at reducing polluted surface flows, mainly by infiltration of the soil, raising the question of the fate of the infiltrated pollutants. An environmental evaluation was conducted on the efficiency of a grass strip receiving diuron-contaminated water from an uphill vineyard in France. During two runoff events, the following measurements were taken: surface inflow and outflow with Venturi flumes, vertical percolated flow below the root layer (0-50 cm), and variations in water and solute content of the root layer. One runoff event occurred under natural rainfall conditions, while the other runoff event was artificially provoked with water doped by diuron and bromide. For the natural runoff event, representative of medium intensity events, 94% of the diuron was retained in the root layer, whereas 2% left the grass strip by surface runoff and 4% left the grass strip in the water percolating under the root zone. For the artificial event, representative of intense runoff events, more than half of the incoming diuron was retained by the grass strip, whereas 24% and 18% of it were transferred by surface runoff and percolation, respectively. These results showed that the capacity of the root layer to retain diuron was highly significant despite a large percolation flux. However, for large runoff events, surface and subsurface losses can still be considerable, up to 40% of the pesticide load entering the strip.