全球变化条件下的土壤呼吸效应

土壤呼吸是陆地植物固定CO₂尔后又释放CO₂返回大气的主要途径，是与全球变化有关的一个重要过程。综述了全球变化下CO₂浓度上升、全球增温、耕作方式的改变及氮沉降增加的土壤呼吸效应。大气CO₂浓度的上升将增加土壤中CO₂的释放通量，同时将促进土壤的碳吸存；在全球增温的情形下，土壤可能向大气中释放更多的CO₂，传统的土地利用方式可能是引发温室气体CO₂产生的重要原因，所有这些全球变化对土壤呼吸的作用具有不确定性。认为土壤碳库的碳储量增加并不能减缓21世纪大气CO₂浓度的上升。据此讨论了该问题的对策并提出了今后土壤呼吸的一些研究方向。其中强调，尽管森林土壤碳固定能力有限，但植树造林、森林保护是一项缓解大气CO₂上升的可行性对策；基于现有田间尺度CO₂通量测定在不确定性方面的进展，今后应继续朝大尺度田间和模拟程序方面努力；着重回答全球变化条件下的土壤呼吸过程机理；区分土壤呼吸的不同来源以及弄清土壤呼吸黑箱系统中土壤微生物及土壤动物的功能。当然，土壤呼吸的测定方法尚有待改善。     

地球物理测井在天然气水合物勘探中的应用

天然气水合物是一种潜在的巨大能源。美国、日本、俄罗斯等发达国家在该领域已经进行了大量的研究工作，试图从各个角度去探测天然气水合物的存在并评价其蕴藏量。地球物理测井在天然气水合物探测与储量评价领域发挥了重要作用并且随着以勘探天然气水合物为目的的钻井的增多，日益受到重视。基于国内在该领域研究较少的现状，综述了国外地球物理测井技术在天然气水合物勘探中的应用，详细介绍了常规测井方法定性识别和定量评价天然气水合物储层的孔隙度、饱和度方法和技术，基于含天然气水合物储层的碳氧比能谱测井解释模型以及成像测井在含天然气水合物井段的测井响应。并在此基础上分析了我国在该领域的研究思路。     

Comparison of two different equations of state for application of carbon dioxide sequestration

We suggest that different equations of state (EOS) algorithms can and frequently will provide very different predictions of CO₂ migration following injection for sequestration. Rather than carry out an exhaustive examination of all EOS algorithms available, we elected to evaluate this general hypothesis by making detailed comparisons of simulation results of two very common EOS algorithms. We simulated and compared CO₂ migration patterns using two fundamentally different EOS algorithms – Modified Redlich-Kwong EOS (MRKEOS) and Span and Wagner EOS (SWEOS). In general, the predictions of thermophysical properties for both algorithms are close, except for a contrast in the predicted fugacity coefficient of CO₂, which subsequently propagates to a contrast in predicted solubility in water/brine. Typically, MRKEOS underestimates solubility of CO₂ compared to both SWEOS and experimental solubility data. In simulations of CO₂ migration, dissolution rates of separate-phase CO₂ predicted from the two EOS algorithms were significantly different, even for small contrasts in predicted fluid properties from EOS algorithms, resulting in markedly different migration patterns.     

Changes in material fluxes from the Changjiang River and their implications on the adjoining continental shelf ecosystem

This study aims to examine the changing patterns of Changjiang material fluxes, which are influenced by anthropogenic activities, and the resultant modifications to the coastal and shelf oceanographic conditions, and to propose future research about the effect of these changes on the estuarine and shelf ecosystem. Within the catchment basin of the Changjiang River, the construction of more than 48,000 dams has caused significant sediment discharge reduction, together with modifications to the timing of seasonal freshwater discharge. In the future, the mean freshwater discharge will decrease following the completion of the water-diverting project for water supply to northern China. At the same time, the riverine nutrient loadings (N and P) have increased due to the extensive use of chemical fertilizers and the large discharge of industrial wastewater and domestic sewage. These changes are modifying the oceanographic conditions of the estuarine and shelf waters. The flushing time for the river water becomes longer in wet seasons but shorter in dry seasons. An increase in salinity can be expected after the completion of the water-diverting project. Nutrient concentrations will be enhanced in the shelf waters. In contrast to the decrease in the suspended sediment concentration of the river water, field measurements have not shown well-defined patterns of changes within the estuary; nevertheless, net sediment accumulation and carbon burial rates would be reduced in the deltaic areas because of the reduced sediment discharge. Finally, increase in the nutrient input appears to enhance the primary production in the East China Sea region, which, in turn, may enhance the fishery catch.     

Comparison of hypoxia among four river-dominated ocean margins: The Changjiang (Yangtze), Mississippi,Pearl, and Rhône rivers

We examined the occurrence of seasonal hypoxia (O₂<2 mg l⁻¹) in the bottom waters of four river-dominated ocean margins (off the Changjiang, Mississippi, Pearl and Rhône Rivers) and compared the processes leading to the depletion of oxygen. Consumption of oxygen in bottom waters is linked to biological oxygen demand fueled by organic matter from primary production in the nutrient-rich river plume and perhaps terrigenous inputs. Hypoxia occurs when this consumption exceeds replenishment by diffusion, turbulent mixing or lateral advection of oxygenated water. The margins off the Mississippi and Changjiang are affected the most by summer hypoxia, while the margins off the Rhône and the Pearl rivers systems are less affected, although nutrient concentrations in the river water are very similar in the four systems. Spring and summer primary production is high overall for the shelves adjacent to the Mississippi, Changjiang and Pearl (1–10 g C m⁻² d⁻¹), and lower off the Rhône River (<1 g C m⁻² d⁻¹), which could be one of the reasons of the absence of hypoxia on the Rhône shelf. The residence time of the bottom water is also related to the occurrence of hypoxia, with the Mississippi margin showing a long residence time and frequent occurrences of hypoxia during summer over very large spatial scales, whereas the East China Sea (ECS)/Changjiang displays hypoxia less regularly due to a shorter residence time of the bottom water. Physical stratification plays an important role with both the Changjiang and Mississippi shelf showing strong thermohaline stratification during summer over extended periods of time, whereas summer stratification is less prominent for the Pearl and Rhône partly due to the wind effect on mixing. The shape of the shelf is the last important factor since hypoxia occurs at intermediate depths (between 5 and 50 m) on broad shelves (Gulf of Mexico and ECS). Shallow estuaries with low residence time such as the Pearl River estuary during the summer wet season when mixing and flushing are dominant features, or deeper shelves, such as the Gulf of Lion off the Rhône show little or no hypoxia.     

Productivity,carbon assimilation and intra-annual change in tropical reef platform seagrass communities of the Torres Strait,north-eastern Australia

Detailed data on seagrass distribution, abundance, growth rates and community structure information were collected at Orman Reefs in March 2004 to estimate the above-ground productivity and carbon assimilated by seagrass meadows. Seagrass meadows were re-examined in November 2004 for comparison at the seasonal extremes of seagrass abundance. Ten seagrass species were identified in the meadows on Orman Reefs. Extensive seagrass coverage was found in March (18,700 ha) and November (21,600 ha), with seagrass covering the majority of the intertidal reef-top areas and a large proportion of the subtidal areas examined. There were marked differences in seagrass above-ground biomass, distribution and species composition between the two surveys. Major changes between March and November included a substantial decline in biomass for intertidal meadows and an expansion in area of subtidal meadows. Changes were most likely a result of greater tidal exposure of intertidal meadows prior to November leading to desiccation and temperature-related stress.     

The oxygen minimum zone (OMZ) off Chile as intense source of CO2 and N2O

The oxygen minimum zones (OMZs) are recognized as intense sources of N₂O greenhouse gas (GHG) and could also be potential sources of CO₂, the most important GHG for the present climate change. This study evaluates, for one of the most intense and shallow OMZ, the Chilean East South Pacific OMZ, the simultaneous N₂O and CO₂ fluxes at the air–sea interface. Four cruises (2000–2002) and 1 year of monitoring (21°–30°–36°S) off Chile allowed the determination of the CO₂ and N₂O concentrations at the sea surface and the analysis of fluxes variations associated with different OMZ configurations. The Chilean OMZ area can be an intense GHG oceanic local source of both N₂O and CO₂. The mean N₂O fluxes are 5–10 times higher than the maximal previous historical source in an OMZ open area as in the Pacific and Indian Oceans. For CO₂, the mean fluxes are also positive and correspond to very high oceanic sources. Even if different coupling and decoupling between N₂O and CO₂ are observed along the Chilean OMZ, 65% of the situations represent high CO₂ and/or N₂O sources. The high GHG sources are associated with coastal upwelling transport of OMZ waters rich in N₂O and probably also in CO₂, located at a shallow depth. The integrated OMZ role on GHG should be better considered to improve our understanding of the past and future atmospheric CO₂ and N₂O evolutions.     

Electro‐Catalytic Degradation of Phenol Organics with SnO2‐Sb2O3/Ti Electrodes

The effect of extraordinary degradation of phenol organics on the SnO₂‐Sb₂O₃/Ti electrode is investigated through experimental research and theoretical analysis. The phenol organics contained 4‐chloro‐phenol, 4‐bromo‐phenol, and 2‐iodo‐phenol. At a current density of 4 mA cm^–2 and an electrolysis time of 12 h, the degradation efficiency of the phenols was over 98% with a relatively short degradation time, whereas the degradation time of the PbO₂/Ti electrode surpassed 40 h while delivering 100% disposal efficiency. Therefore, the effectiveness of electrochemical (EC) oxidation by the SnO₂‐Sb₂O₃/Ti was superior to that of the PbO₂/Ti electrode. At the same time, the SnO₂‐Sb₂O₃/Ti had higher oxygen generation potential and lower electron consumption than the other electrodes. This was mainly due to the effect of the middle Sb₂O₃ layer, which due to its high porosity and good catalytic effect, contributed to a better catalysis than the SnO₂ part.     

Removal of Selenium by Adsorption onto Granular Activated Carbon (GAC) and Powdered Activated Carbon (PAC)

The present work involves the study of Se(IV) adsorption onto granular activated carbon (GAC) and powdered activated carbon (PAC). The adsorbents are coated with ferric chloride solution for the effective removal of selenium. The physico-chemical characterization of the adsorbents is carried out using standard methods, e. g., proximate analysis, scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR), thermo-gravimetric (TGA) and differential thermal analysis (DTA), etc. The FTIR spectra of the GAC and PAC indicate the presence of various types of functional groups, e. g., free and hydrogen bonded OH groups, silanol groups (Si-OH), alkenes, and CO group stretching from aldehydes and ketones on the surface of adsorbents. Batch experiments are carried out to determine the effect of various factors such as adsorbent dose (w), initial pH, contact time (t), and temperature (T) on the adsorption process. The optimum GAC and PAC dosage is found to be 10 g/L and 8 g/L, respectively, for Se(IV) removal with C₀ = 100 mg/L. The percent removal of Se(IV) increases with increasing adsorbent concentration, while removal per unit weight of adsorbent increases with decreasing adsorbent concentration. Se(IV) adsorption onto both the GAC and PAC adsorbents is high at low pH values, and decreases with increased initial pH. The results obtained are analyzed by various kinetic models. The parameters of pseudo-first order, pseudo-second order kinetics, and Weber-Morris intra particle kinetics are determined. It is seen that the sorption kinetics of Se(IV) onto GAC and PAC can be best represented by the pseudo-second order kinetic model.