祁连山疏勒河上游多年冻土区高寒草甸土壤CO2通量特征

研究青藏高原多年冻土区高寒草甸土壤CO₂通量有助于准确估算该区域的土壤CO₂排放, 对认识高原土壤碳循环及其对全球气候变化的响应具有重要意义. 利用静态箱-气相色谱法和LI-8100土壤CO₂通量自动测量系统对疏勒河上游多年冻土区高寒草甸土壤CO₂通量进行了定期观测, 结合气象和土壤环境因子进行了分析. 结果表明: 整个观测期高寒草甸土壤表现为CO₂的源, 土壤CO₂通量的日变化范围为2.52～532.81 mg·m^-2·h^-1. 土壤CO₂年排放总量为1 429.88 g·m^-2, 年均通量为163.23 mg·m^-2·h^-1; 其中, CO₂通量与空气温度和相对湿度、活动层表层2 cm、10 cm、20 cm、30 cm 土壤温度、含水量和盐分均显著相关. 2 cm土壤温度、空气温度和总辐射、空气温度、2 cm土壤盐分分别是影响活动层表层2 cm土壤完全融化期、冻结过程期、完全冻结期、融化过程期土壤CO₂通量的最重要因子. 在完全融化期、冻结过程期和整个观测期, 拟合最佳的温度因子变化分别能够解释土壤CO₂通量变化的72.0%、82.0%和38.0%, 对应的Q₁₀值分别为1.93、6.62和2.09. 冻融期(含融化过程期和冻结过程期)和完全冻结期的土壤CO₂排放量分别占年排放总量的15.35%和11.04%, 在年排放总量估算中不容忽视.     

The emergence of braided magnetic fields

We study the emergence of braided magnetic fields from the top of the solar interior through to the corona. It is widely believed that emerging regions smaller than active regions are formed in the upper convection zone near the photosphere. Here, bundles of braided, rather than twisted, magnetic field can be formed, which then rise upward to emerge into the atmosphere. To test this theory, we investigate the behaviour of braided magnetic fields as they emerge into the solar atmosphere. We compare and contrast our models to previous studies of twisted flux tube emergence and discuss results that can be tested observationally. Although this is just an initial study, our results suggest that the underlying magnetic field structure of small emerging regions need not be twisted and that braided field, formed in the convection zone, could suffice.     

Effects of soil compaction,rain exposure and their interaction on soil carbon dioxide emission

Soils release more carbon, primarily as carbon dioxide (CO₂), per annum than current global anthropogenic emissions. Soils emit CO₂ through mineralization and decomposition of organic matter and respiration of roots and soil organisms. Given this, the evaluation of the effects of abiotic factors on microbial activity is of major importance when considering the mitigation of greenhouse gases emissions. Previous studies demonstrate that soil CO₂ emission is significantly affected by temperature and soil water content. A limited number of studies have illustrated the importance of bulk density and soil surface characteristics as a result of exposure to rain on CO₂ emission, however, none examine their relative importance. Therefore, this study investigated the effects of soil compaction and exposure of the soil surface to rainfall and their interaction on CO₂ release. We conducted a factorial laboratory experiment with three soil types after sieving (clay, silt and sand soil), three different bulk densities (1·1 g cm^–3, 1·3 g cm^–3, 1·5 g cm^–3) and three different exposures to rainfall (no rain, 30 minutes and 90 minutes of rainfall). The results demonstrated CO₂ release varied significantly with bulk density, exposure to rain and time. The relationship between rain exposure and CO₂ is positive: CO₂ emission was 53% and 42% greater for the 90 minutes and 30 minutes rainfall exposure, respectively, compared to those not exposed to rain. Bulk density exhibited a negative relationship with CO₂ emission: soil compacted to a bulk density of 1·1 g cm^–3 emitted 32% more CO₂ than soil compacted to 1·5 g cm^–3. Furthermore we found that the magnitude of CO₂ effluxes depended on the interaction of these two abiotic factors. Given these results, understanding the influence of soil compaction and raindrop impact on CO₂ emission could lead to modified soil management practices which promote carbon sequestration. Copyright © 2012 John Wiley & Sons, Ltd.     

Diagnosis of river basins as CO2 sources or sinks subject to sediment movement

Sediment movement during erosion, transport and deposition greatly affects the ecosystem of river basins. However, there is presently no consensus as to whether particular river basins act as carbon dioxide (CO₂) sources or sinks related to these processes. This paper introduces a rule‐of‐thumb coordinate system based on sediment delivery ratio (SDR) and soil humin content (SHC) in order to evaluate the net effect of soil erosion, sediment transport and deposition on CO₂ flux in river basins. The SDR–SHC system delineates CO₂ source and sink areas, and further divides the sink into strong and weak areas according to the world‐average line. The Yellow River Basin, most severely suffering soil erosion in the world, only appears to be a weak erosion‐induced CO₂ sink in this system. The average annual CO₂ sequestration is ~0·235 Mt from 1960 to 2008, a relatively small value considering its 3·1% contribution to the World's sediment discharge. The temporal analysis shows that the Yellow River Basin was once a source in the 1960s, but changed its role to become a weak sink in the past 40 years due to both anthropogenic and climatic influences. The spatial analysis identifies the middle sub‐basin as the main source region, and the lower as the main sink. For comparison, sediment‐movement‐related CO₂ fluxes of eight other major basins in four continents are examined. It is found that the six basins considered in the Northern Hemisphere appear to be sinks, while the other two in the Southern Hemisphere act as sources. Copyright © 2012 John Wiley & Sons, Ltd.     

Performance of a flux splitting scheme when solving the single-phase pressure equation discretized by MPFA

In this article we present a series of tests to study how well suited the TPFA coefficient matrix is as a preconditioner for the MPFA discrete system of equations in an iterative solver, using a flux splitting method. These tests have been conducted for single-phase flow for a wide range of anisotropy, heterogeneity, and grid skewness (mainly parallelogram grids). We use the K-orthogonal part of the MPFA transmissibilities for a parallelogram grid to govern the TPFA transmissibilities. The convergence of the flux splitting method is for each test case measured by the spectral radius of the iteration matrix.     

Using climate to relate water discharge and area in modern and ancient catchments

Models relating sediment supply to catchment properties are important in order to use the geological record to deduce landscape evolution and interplay between tectonics and climate. Water discharge (Q _w) is an important factor in the widely used ‘BQART ’ model, which relates sediment load to a set of measurable catchment parameters. Although many of the factors in this equation may be independently estimated with some degree of certainty in ancient systems, water discharge (Q _w) certainly cannot. An analysis of a world database of modern catchments with 1255 entries shows that the commonly applied equation relating catchment area (A ) to water discharge (Q _w = 0·075A^0·8) does not predict water discharge from catchment area well in many cases (R ² = 0·5 and an error spanning about three orders of magnitude). This is because the method does not incorporate the effect of arid and wet climate on river water discharge. The inclusion of climate data into such estimations is an opportunity to refine these estimates, because generalized estimates of palaeoclimate can often be deduced on the basis of sedimentological data such as palaeosol types, mineralogy and palaeohydraulics. This paper investigates how the relationship between catchment area and river discharge varies with four runoff categories (arid, semi‐arid, humid and wet), which are recognizable in the geological record, and modifies the coefficient and exponent of the above‐mentioned equation according to these classes. This modified model yields improved results in relating discharge to catchment area (R ² = 0·95 and error spanning one order of magnitude) when core, outcrop or regional palaeoclimate reconstruction data are available in non‐arid systems. Arid systems have an inherently variable water discharge, and catchment area is less important as a control due to downstream losses. The model here is sufficient for many geological applications and makes it possible to include variations in catchment humidity in mass‐flux estimates in ancient settings.     

DNDC模型对我国旱地N2O释放的拟合对比分析

本文根据贵州省玉米－油菜轮作田、休耕地和大豆－冬小麦轮作田的N2O释放通量及其影响因子季节变化的是观测结果，对比分析了DNDC模型计算与三试验田田间观测在N2O释放通量及其主要影响因子季节变化上的拟合程度。结果表明，对N2O释放通量、土壤NO3^-和NH4^ 含量、土壤湿度和土温，模型计算结果与田间观测具有相似的季节变化模式和相近的数值，模型较好地反映了上述参数的动态变化过程。据此，推算出贵州省农业土壤N2O年释放量，并分析了气候变化和农业活动对释放量的潜在影响。     

煤田火区碳排放量计算模型和关键参数研究

完善碳排放清单,是进行减排工作的基础,为了查明煤田火区对大气碳排放的贡献量,以煤氧复合作用学说为理论基础,从不同的研究思路出发,提出了烧失煤量法和排放通量法两种火区碳排放量计算模型。在明确模型中关键参数“释放因子”“排放系数α”“排放通量”“排放系数β”的具体含义的基础上,重点对各参数所对应的获取途径进行了研究论述：(1)释放因子通过在室内进行煤自燃模拟实验得出;(2)排放系数α通过煤岩吸附实验结合火区实地勘测得出;(3)排放通量通过对火区现场煤自燃气体排放及环境因素的实时监测得出;(4)排放系数β通过对遥感图像裂隙信息的提取得到。上述两种计算模型在我国乌达实验区进行了实际应用,并对其可实现性进行了检验。     

非均匀月壤介质的被动微波辐射传输模拟

基于非均匀月壤物理模型和辐射传输方程,模拟月壤介质中的微波辐射传输特性,探讨频率、月壤厚度等与月表亮温的关系。结果表明:在低频段,月壤微波辐射亮温的动态变化范围较大,可探测的月壤厚度大,3 GHz时的最大可探测月壤厚度达12.4 m;在高频段对应的可探测月壤厚度较小,特别是从50GHz往后的频率段内,最大可探测月壤厚度均小于2 m。不同频率的亮温-厚度变化曲线没有交叉点,且频率越高,所能探测的月壤厚度越小。根据模拟结果,建立了月壤厚度与亮温的查找表。基于查找表,利用单个波段的亮温数据即可得到月壤厚度信息。     

Application of membrane technology for water treatment： Ultrasound-associated cleaning of fouled microfiltration membranes

The use of membranes is a widely employed, versatile, and effective separation process. One of the limiting aspects in applying microfiltration （MF） for wastewater treatment is that of problems with membrane fouling and consequent flux reduction. Membrane fouling occurs by the irreversible deposition of retained particles, colloids, macromolecules, salts, etc. at the membrane surface and/or inside the membrane. The predominant fouling mechanisms observed with MF membranes are classified as three categories： the build-up of a cake layer on the membrane surface, blocking of membrane pores, and adsorption of fouling material on the membrane surface or in the pore walls. Although many techniques have been developed to overcome fouling, studies on membrane cleaning still seem to be insufficient for practical membrane filtration systems. Current membrane cleaning technologies include hydraulic, chemical, and mechanical methods. Ultrasound （US） has been widely used as a method of cleaning materials because of the cavitation phenomenon. In this study, US cleaning technique was applied to removing the fouling of polyvinglidenefluoride （PVDF） MF membrane, which was used to treat yeast cell and isolated soybean protein （ISP） solution, respectively. The US employed 40 kHz frequency and the output power of 1.43-2.85 W/cm^2. The evolution of the cleaning effect is followed by the measurements of the flux recovery rate （FRstat） and the cleaning time cycle. Results showed that the membrane property, which was fouled by yeast cell solution, could be recovered by water cleaning with US irradiation. And the cleaning time with the same FRstat decreased with the increase of US intensity.