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.     

空基下视时序影像瞬时成像模型研究

物方空间的物体随着时间的推移进行着绝对运动,运动导致了相对位置的变化,时间序列影像记录了物方三维空间的动态变化。本文基于下视时间序列影像的动态特性,在共线方程中引入时间元素,提出了空基下视时间序列影像瞬时成像模型,描述了动态“物像”间的瞬时投影关系;针对地表不同类型动态物体,构建了“由像到物”的应用模型,实现了从像方动态特征计算地表物体特征的目的。通过仿真和真实航空下视序列影像的试验与分析,验证了序列影像瞬时成像模型能够定量计算像地动态特征。     

横断山区垂直带谱的分布模式与坡向效应

根据收集到的横断山区山地垂直带谱数据,对山地垂直带的坡向效应和空间分布规律进行了分析和研究.结果表明:1)主要的垂直带和垂直带界线如林线、暗针叶林带、雪线等的纬度和经度地带性分布规律明显并且分布模式都相似,纬向上呈开口向下的二次曲线分布模式,经向上呈开口向上的二次曲线分布模式,两者共同形成"双曲抛物面"分布模式,充分反映了横断山区的环境与生态的复杂性和独特性,也进一步丰富和发展了山地垂直带谱的二次曲线假说; 2)横断山区山地垂直带谱表现出明显的基于水分驱动的坡向效应,主要表现为同一山体的东、西坡往往具有不同的基带和带谱结构,相同类型的带谱出现的海拔和分布范围不同,迎风坡表现出较为湿润的类型和带谱结构,而背风坡则表现出更为干旱的类型和组成结构;横断山区的坡向效应主要是由于山体对当地盛行季风的影响,造成迎风坡和背风坡水热条件相差很大,从而发育不同的山地垂直带谱类型.从横断山区山地垂直带谱的空间分布规律来看, 28°～29°N、98°～101°E范围内,即大致在澜沧江以东-雅砻江以西,山地垂直带谱普遍表现出干热的特点,为横断山区干热气候的核心地带.但如何定量分析山地的坡向效应尚有待于进一步的研究和讨论.此外、数据质量和数据误差也对分析的结果,尤其是空间分布模式的数学模拟结果产生一定的影响,在以后的研究中尚需进一步完善.     

LATE PLEISTOCENE—HOLOCENE RAPID UPLIFT AND EROSION IN TIBET: CONSTRAINTS FROM COSMOGENIC EXPOSURE AGE DATA

LATE PLEISTOCENE—HOLOCENE RAPID UPLIFT AND EROSION IN TIBET: CONSTRAINTS FROM COSMOGENIC EXPOSURE AGE DATA1　CopelandP ,HarrisonTM ,KiddWSF ,etal.RapidearlyMioceneaccelerationofupliftintheGangdeseBelt,Xizang(southernTibet) ,anditsbearingonaccommodationmechanismsoftheIndian Asiacollision[J].EarthPlanetSciLett,1987,86 :2 40～ 2 5 2 . 2　FieldingEJ .Tibetupliftanderosion[J].Tectonophysics,1994,2 6 0 :5 5～ 84. 3　HarrisonTM ,CopelandP ,Ki…     

Concentrations of PAHs (polycyclic aromatic hydrocarbons) in various marine organisms in relation to those in sediments and to trophic level

Sediments and marine organisms such as mussels (Mytilus galloprovincialis), fish (Mullus barbatus, Serranus scriba), crabs (Polybius henslowi) and shrimp-like crustaceans (mysids, euphausiids) were sampled on European coasts, France, Spain) and analysed for their PAH content by gas chromatography/mass spectrometry (GC-MS). The PAH concentrations determined in the organisms were significantly negatively correlated with logK_ow values, but to different extents according to the species. This was explained by the greater exposure of the organisms to the lower molecular weight compounds with differences resulting from different feeding habits, habitat, and biotransformation capacities of the organisms in relation to trophic levels. The influence of these observations on the use of different sentinel species in biomonitoring programmes is discussed.     

Health risk assessment for typical and abandoned chromium-contaminated sites

Chromium pollution were investigated by sampling the abandoned chromium contaminated sites in Chongqing. Its health risk was assessed following the procedures made by USEPA. The results showed that the most seriously polluted land was found at the former production area （G4） with average Cr（VI） concentration of 3369.2 mg kg-1 on the surface soil. The assessment indicated that there was high risk of non-carcinogens for children. The assessed risk of the first layer of office area （G1） for children, chromium slag transition （G2）, drainage pipeline chromium slag transition （G3） and production area （G4） for both children and adults were not acceptable （〉1.00× 106）. It was strongly suggested that the accessible measures of remediation should be taken for a portion of contaminated sites before the reuse of abandoned lands.     

Hydraulics of overland flow influenced by litter incorporation under extreme rainfall

Water erosion on hillslopes is a worldwide environmental problem, which is a rainfall‐induced process, especially extreme rainfall. The great intensity of extreme rainfall strongly enhances the power of overland flow to detach soil and transport sediment. Plant litter is one of the most important constituents of ecosystems that often covers the soil surface and can be incorporated into topsoil. However, little attention has been paid to its effect on flow hydraulics owing to the veiled nature. This study aimed to examine the effects of incorporated litter on the hydraulic properties under extreme rainfall condition. To reach this goal, six litter rates of 0, 0.05, 0.10, 0.20, 0.35, and 0.50 kg m^?2 and four litter types collected from deciduous trees, coniferous trees, shrubs, and herbs were incorporated into topsoil. Then, simulated rainfall experiments were performed on five slope gradients (5°, 10°, 15°, 20°, and 25°) with an extreme rainfall intensity of 80 mm h^?1. The results showed that Froude number and flow velocity of the overland flow decreased, whereas flow resistance increased exponentially with litter incorporation rate. Litter type had an influence on flow hydraulics, which can mainly be attributed to the variations in surface coverage of the exposed litter and the litter morphology. Flow velocity and Darcy–Weisbach coefficient increased markedly with slope gradient. However, the variation of slope gradient did not modify the relationships between flow hydraulics and incorporated litter rate. The random roughness, resulting from heterogeneous erosion due to the uneven protection of surface exposed litter, increased linearly with litter incorporated rate. As rainfall proceeded, flow hydraulics varied with incorporated litter rate and slope gradient complicatedly due to the increases in flow rate and coverage of the exposed litter and the modification of soil surface roughness.     

COSMOGENIC 10BE-AGES FROM THE STORE KOLDEWEY ISLAND, NE GREENLAND

Earlier work in northeast Greenland has suggested a limited advance of the Greenland Ice Sheet during the Last Glacial Maximum (LGM). However, this concept has recently been challenged by marine geological studies, indicating grounded ice on the continental shelf at this time. New ¹⁰Be‐ages from the Store Koldewey island, northeast Greenland, suggest that unscoured mountain plateaus at the outer coast were covered at least partly by cold‐based ice during the LGM. It is, however, still inconclusive whether this ice was dynamically connected to the Greenland Ice Sheet or not. Regardless of the LGM ice sheet extent, the ¹⁰Be results from Store Koldewey add to a growing body of evidence suggesting considerable antiquity of crystalline unscoured terrain near present and Pleistocene ice sheet margins.