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1.
水气混合洞塞泄流溶解氧输移扩散的数值计算 总被引：1，自引：0，他引：1
为研究水气二相混合洞塞泄流欠饱和溶解氧输移扩散行为特性,揭示气体体积分数、进口溶解氧浓度、雷诺数等流动特征参数和洞塞尺寸等几何参数对溶解氧浓度恢复的影响规律,开展了水气二相混合洞塞泄流溶解氧输移扩散的室内模型试验,观测流速、压力和溶解氧浓度分布。建立了水气二相混合洞塞泄流溶解氧输移扩散数学模型,并利用物理模型试验数据对数学模型进行了验证。利用验证后的数学模型,分别计算不同进口气体体积分数、溶解氧浓度、雷诺数、洞塞长度和洞塞直径条件下水气二相混合洞塞泄流溶解氧浓度恢复情况。结果发现:气体体积分数越大,进口溶解氧浓度与饱和溶解氧浓度差值越大,雷诺数越小,溶解氧浓度增量越大;洞塞长度越长,洞塞直径越小,溶解氧浓度增量越大。 相似文献
2.
The goal of this study was to demonstrate how the extent of denitrification, which is indirectly related to dissolved organ carbon and directly related to oxygen concentrations, can also be linked to unsaturated-zone thickness, a mappable aquifer property. Groundwater from public supply and monitoring wells in Northport on Long Island, New York state (USA), were analyzed for denitrification reaction progress using dissolved N2/Ar concentrations by membrane inlet mass spectrometry. This technique allows for discernment of small amounts of excess N2, attributable to denitrification. Results show an average 15 % of total nitrogen in the system was denitrified, significantly lower than model predictions of 35 % denitrification. The minimal denitrification is due to low dissolved organic carbon (29.3–41.1 μmol L?1) and high dissolved oxygen concentrations (58–100 % oxygen saturation) in glacial sediments with minimal solid-phase electron donors to drive denitrification. A mechanism is proposed that combines two known processes for aquifer re-aeration in unconsolidated sands with thick (>10 m) unsaturated zones. First, advective flux provides 50 % freshening of pore space oxygen in the upper 2 m due to barometric pressure changes. Then, oxygen diffusion across the water-table boundary occurs due to high volumetric air content in the unsaturated-zone catchment area. 相似文献
3.
Gianni Cortecci 《Geochimica et cosmochimica acta》1973,37(6):1531-1542
The results obtained by measuring the sulfate content and its ratios through time in some volcanic, tectonic and dam Italian lakes are reported here. The variations with time of the oxygen isotopic composition of the lake waters are also reported. The measurements refer mainly to surface water; however, a few deep samples were also studied.In the case of all the lakes examined, the variations with time of the oxygen isotopic composition and of the concentration of the dissolved sulfate cannot be explained in terms of the addition and of seasonal variations of the O18 content of rainwater sulfate. Biological redox processes involving bacterial reduction of sulfate and sulfide oxidation can reasonably account for the results obtained.According to Lloyd (1967), when sulfate is formed by bacterial sulfide oxidation, 68 per cent of the sulfate oxygen is water oxygen, while 32 per cent is dissolved molecular oxygen. The isotopic enrichment of the dissolved molecular oxygen in the lake waters relative to the isotope content of the atmospheric oxygen is mainly related to the biological activity in the waters.Assuming that a stagnation period takes place during summer and fall while a period of strong bio-respiratory activity takes place during winter and spring, it follows that a small isotope fractionation effect on molecular dissolved oxygen can be expected during stagnation while a high isotope fractionation can be expected during winter and spring. The O18 content of the sulfate dissolved in volcanic and tectonic lakes varies according to this hypothesis. The fact that similar O18 contents of the dissolved sulfate are or are not found in the same period of different years is probably related to similarities or differences in the climatic conditions.The bio-physical behaviour of the Corbara dam lake is different from that of other lakes. However, because of the continuous feeding by the Tiber River, variations of the sulfate concentration and its oxygen isotopic composition can be caused by the contribution of polluted water. 相似文献
4.
古海洋溶解氧研究方法综述 总被引：15，自引：0，他引：15
介绍了国内外在古海洋溶解氧研究领域内的主要方法和动态，并分别对沉积构造法、沉积硫法、同位素法、微量元素法、稀土元素法、有机地球化学法及古生态法等研究方法进行了全面的分析和评论，指出,古海洋溶解氧含量重建对于理解大洋循环、古气候、生物绝灭、地质事件以及有机质演化具有十分重要的科学意义，它有赖于溶解氧含量的替代性指标的建立、富氧问题研究的进一步深入以及综合分析气圈、水圈、沉积圈、生物圈等各子系统内部及它们之间氧的物质输送和转化。 相似文献
5.
M. H. Abdullah M. B. Mokhtar S. H. J. Tahir A. B. T. Awaluddin 《Environmental Geology》1997,29(1-2):112-117
Sipadan Island is a small oceanic island with limited storage of fresh groundwater. A study was carried out to determine
the effect of tidal change on the groundwater quality of such an island using temperature, dissolved oxygen content, conductivity,
salinity, and pH values as indicators. Overall, the results indicated that the groundwater quality changes with tides, but
the trends of fluctuation differs between the observed parameters. It was found that the percentages of changes during the
period of study were 0.8% (temperature), 53% (dissolved oxygen), 61% (conductivity), 58% (salinity), and 1.7% (pH) at the
centre of the island; and 0.9% (temperature), 33% (dissolved oxygen), 40% (conductivity), 42% (salinity), and 9% (pH) at a
station 120 m from the coast, based on 2.9-m and 2.8-m tidal ranges at each station.
Received: 5 July 1995 · Accepted: 6 November 1995 相似文献
6.
三种方法测试岩溶水样氢氧同位素的对比研究 总被引：1，自引：0，他引：1
通过高温热转换元素-同位素比值质谱法（TC/EA-IRMS）、多用途气体制备仪-同位素比值质谱法（GasbenchⅡ-IRMS）以及激光光谱法对岩溶水样进行对比检测,其结果显示:对于氢同位素,TC/EA-IRMS的精密度达到0.3 ‰,激光光谱法的精密度达到0.1 ‰,均优于GasbenchⅡ-IRMS的精密度1.4 ‰;对于氧同位素,GasbenchⅡ-IRMS的精密度达到0.02 ‰,激光光谱法的精密度达到0.04 ‰,优于TC/EA-IRMS的精密度0.16 ‰。使用激光光谱法测定岩溶水样的氢氧同位素,所需要的样品量少,精密度高,能够满足岩溶区样品的高精度测试要求。 相似文献
7.
Dissolved oxygen concentration below 5 mg 1−1 has characterized the lower tidal portion of the San Joaquin River downstream of Stockton, California, during the summer
and fall for the past four decades. Intensive field research in 2000 and 2001 indicated low dissolved oxygen concentration
was restricted to the first 14 km of the river, which was deepened to 12 m for shipping, downstream of Stockton. The persistent
low dissolved oxygen concentration in the shipping channel was not caused by physical stratification that prevented aeration
from vertical mixing or respiration associated wigh high phytoplankton biomass. The low dissolved oxygen concentration was
primarily caused bynitrification that produced up to 81% of the total oxygen demand. Stepwise multiple regression analysis
isolated dissolved ammonia concentration and carbonaceous oxygen demand as the water quality variables most closely associated
with the variation in oxygen demand. Between these two sources, dissolved ammonia concentration accounted for 60% of the total
variation in oxygen demand compared with a maximum of 30% for carbonceous oxygen demand. The Stockton wastewater treatment
plant and nonpoint sources upstream were direct sources of dissolved ammonia in the channel. A large portion of the dissolved
ammonia in the channel was also produced by oxidation of the organic nitrogen load from upstream. The phytoplankton biomass
load from upstream primarily produced the carbonaceous oxygen demand. Mass balance models suggested the relative contribution
of the wastewater and nonpoint upstream load to the ammonia concentration in the shipping channel at various residence times
was dependent on the cumulative effect of ammonification, composition of the upstream load, and net downstream transport of
the daily load. 相似文献
8.
Seasonal dynamics of dissolved trace metals (Cd, Co, Cu, Ni and Zn) and its relationship with redox conditions and phytoplankton
activity has been studied in the Scheldt estuary, during nine surveys carried out between May 1995 and June 1996. Seasonal
profiles of dissolved trace metals and general estuarine water quality variables are compared, to identify the geochemical
and biological processes responsible for the observed trace metal distributions. In keeping with previous studies, the behavior
of dissolved Cd, Cu, and Zn can be explained by the presence of anoxic headwaters and the restoration of dissolved oxygen
within the estuary. In the river water, the concentration of dissolved Cu and Zn is generally low, except during winter when
dissolved oxygen is present in the water column, although highly undersaturated. Mobilization of particle-bound Cd, Cu, and
Zn occurs as dissolved oxygen increases with increasing salinity, possibly because of oxidation of metal sulfides in the suspended
matter. The geochemistry of dissolved Co is also related to the redox conditions but in an opposite way. Dissolved Co is mobilized
in the anoxic upper estuary, along with the reduction in Mn (hydro) oxides, and subsequently coprecipitated with Mn (hydro)
oxides when dissolved oxygen is restored. Conservative behavior is observed for dissolved Ni within the estuary. In the middle
estuary, Cd and Zn are readsorbed during phytoplankton blooms, as suggested by the low concentrations of these metals during
the most productive periods in spring and early summer. The removal may be caused by direct biological uptake and/or increased
adsorption to suspended matter because of the pH increase associated with algae blooms. In the lower estuary, chemical gradients
are much weaker and dilution with seawater is the dominant process. 相似文献
9.
Influence of dissolved oxygen concentration and aeration time on nitrite accumulation in partial nitrification process 总被引：1，自引：1，他引：0
X. Guo Ph. D. J. H. Kim Ph.D. S. K. Behera Ph.D. H. S. Park Ph.D. 《International Journal of Environmental Science and Technology》2008,5(4):527-534
This study investigated the influence of dissolved oxygen concentration and aeration time on nitrification and nitrite accumulation in an attempt to optimize the recently developed biological-partial-nitritation process for the treatment of strong nitrogen wastewaters. Investigation of dissolved oxygen concentration on ammonium and nitrite oxidation was carried out in a batch reactor. The dissolved oxygen concentration of 0.5 mg O2/L inhibited both ammonium as well as nitrite oxidation, while increase of dissolved oxygen concentration to ～1 mg O2/L increased the ammonium oxidation rate and was comparable to that at higher dissolved oxygen concentrations. Experiments were carried out in a sequencing batch reactor for more than 100 days to investigate the influence of aeration time on nitrite accumulation. The dissolved oxygen concentration was controlled at ～1.0 mg O2/L (in the range of 0.8–1.5 mg/L) during the aeration stage, and volatile suspended solid was maintained at 2.0 g/L while temperature and pH were 30±1°C and 8.3±0.1, respectively. In a typical cycle, complete nitrification occurred at aeration time longer than 6 h. When the aeration time was reduced to 4 h., ～80 % of partial nitritation was achieved. With a further reduction in aeration time to 3 h., nearly 1:1 nitrite/ammonium ratio was yielded. This result revealed that for the reactor design, aeration time determined by feasibility experiments must be considered based on the nitrogen strength in wastewater and biomass concentration in the reactor with dissolved oxygen concentration of ～1.0 mg O2/L for satisfactory partial nitrification with subsequent processes such as anaerobic ammonium oxidation. 相似文献
10.
11.
A preliminary mass balance model of primary productivity and dissolved oxygen in the Mississippi River Plume/Inner Gulf Shelf Region 总被引：1，自引：0，他引：1
Victor J. Bierman Scott C. Hinz Dong-Wei Zhu William J. Wiseman Nancy N. Rabalais R. Eugene Turner 《Estuaries and Coasts》1994,17(4):886-899
A deterministic, mass balance model for phytoplankton, nutrients, and dissolved oxygen was applied to the Mississippi River Plume/Inner Gulf Shelf (MRP/IGS) region. The model was calibrated to a comprehensive set of field data collected during July 1990 at over 200 sampling stations in the northern Gulf of Mexico. The spatial domain of the model is represented by a three-dimensional, 21-segment water-column grid extending from the Mississippi River Delta west to the Louisiana-Texas border, and from the shoreline seaward to the 30–60 m bathymetric contours. Diagnostic analyses and numerical experiments were conducted with the calibrated model to better understand the environmental processes controlling primary productivity and dissolved oxygen dynamics in the MRP/IGS region. Underwater light attenuation appears relatively more important than nutrient limitation in controlling rates of primary productivity. Chemical-biological processes appear relatively more important than advective-dispersive transport processes in controlling bottom-water dissolved oxygen dynamics. Oxidation of carbonaceous material in the water column, phytoplankton respiration, and sediment oxygen demand all appear to contribute significantly to total oxygen depletion rates in bottom waters. The estimated contribution of sediment oxygen demand to total oxygen-depletion rates in bottom waters ranges from 22% to 30%. Primary productivity appears to be an important source of dissolved oxygen to bottom waters in the region of the Atchafalaya River discharge and further west along the Louisiana Inner Shelf. Dissolved oxygen concentrations appear very sensitive to changes in underwater light attenuation due to strong coupling between dissolved oxygen and primary productivity in bottom waters. The Louisiana Inner Shelf in the area of the Atchafalaya River discharge and further west to the Texas border appears to be characterized by significantly different light attenuation-depth-primary productivity relationships than the area immediately west of the Mississippi Delta. Nutrient remineralization in the water column appears to contribute significantly to maintaining chlorophyll concentrations on the Louisiana Inner Shelf. 相似文献
12.
生物磷灰石壳体的磷酸根氧同位素组成是重建古温度理想指标之一,在古环境研究中具有重要意义.针对牙形石等磷灰石量极少的情况,稳定可靠的前处理方法是分析其δ18OPO4的重要保障,目前仅有少数国外实验室已建立了相关提取分析方法.结合这些方法的优缺点对分析步骤进行改进优化,建立了微量磷灰石的磷酸根氧同位素分析方法,通过硝酸消解磷灰石并除去非磷酸根氧,利用KF溶液沉淀法分离Ca2+,采用氨缓冲溶液形式调节pH,并加入AgNO3溶液以氨挥发法将PO43-转化成Ag3PO4结晶分离,气体稳定同位素质谱仪在线测定Ag3PO4氧同位素组成.结果表明,方法全流程未产生明显的氧同位素分馏,样品最低仅需0.2 mg,标准偏差小于0.2‰（1σ）,与目前国际报道的分析精度一致. 相似文献
13.
Managed aquifer recharge is one of the most popular methods for dealing with local water shortage issues, and the bacterial community could be a vital factor influencing groundwater quality during this process. In this study, analysis of variations in groundwater components during artificial recharge revealed three stages at a text site in China. During stage I, total iron and dissolved organic carbon levels are stable basically, dissolved oxygen and SO4 2? levels have rising trends, NO3 ? curve varied not obviously. Variation curves show increases in dissolved oxygen, NO3 ?, SO4 2? and stabilization in dissolved organic carbon and total iron at stage II. During stage III, dissolved oxygen and NO3 ? have rising trends, dissolved organic carbon, total iron, and SO4 2? keep stable. At 25 and 70 days the Simpson and Shannon–Wiener indices show that microbial community richness and population diversity underwent a gradual dynamic change after recharge water arrived. Correlation analysis shows that the Simpson index was mainly affected by dissolved oxygen and NO3 ?. PCR-DGGE confirmed these findings. Overall, the results revealed that the main bacterial communities reduce total nitrogen, total phosphorous, and chemical oxygen demand, which corresponded to the calculated correlation index. 相似文献
14.
Christophe Lcuyer Franois Fourel Magali Seris Romain Amiot Jean Goedert Laurent Simon 《Geostandards and Geoanalytical Research》2019,43(4):681-688
The large range of stable oxygen isotope values of phosphate‐bearing minerals and dissolved phosphate of inorganic or organic origin requires the availability of in‐house produced calibrated silver phosphate of which isotopic ratios must closely bracket those of studied samples. We propose a simple protocol to synthesise Ag3PO4 in a wide range of oxygen isotope compositions based on the equilibrium isotopic fractionation factor and the kinetics and temperature of isotopic exchange in the phosphate–water system. Ag3PO4 crystals were obtained from KH2PO4 that was dissolved in water of known oxygen isotope composition. Isotopic exchange between dissolved phosphate and water took place at a desired and constant temperature into PYREX? tubes that were placed in a high precision oven for defined run‐times. Samples were withdrawn at desired times, quenched in cold water and precipitated as Ag3PO4. We provide a calculation sheet that computes the δ18O of precipitated Ag3PO4 as a function of time, temperature and δ18O of both reactants KH2PO4 and H2O at t = 0. Predicted oxygen isotope compositions of synthesised silver phosphate range from ?7 to +31‰ VSMOW for a temperature range comprised between 110 and 130 °C and a range of water δ18O from ?20 to +15‰ VSMOW. 相似文献
15.
《Geochimica et cosmochimica acta》1987,51(1):29-43
Vertical and horizontal distributions of dissolved and suspended particulate Fe and Mn, and vertical fluxes of these metals (obtained with sediment traps) were determined throughout the Pacific Ocean. In general, dissolved Fe is low in surface and deep waters (0.1 to 0.7 nmol/kg), with maxima associated with the intermediate depth oxygen minimum zone (2.0 to 6.6 nmol/kg). Vertical distributions of dissolved Mn are similar to previous reports, exhibiting a surface maximum, a subsurface minimum, a Mn maximum layer coincident with the oxygen minimum zone, and lowest values in deep waters.Near-shore removal processes are more intense for dissolved Fe than for dissolved Mn. Dissolved Mn in the surface mixed layer remains elevated much farther offshore than dissolved Fe. Elevated near-surface dissolved Mn concentrations occur in the North Pacific Equatorial Current, suggesting transport from the eastern boundary. Near-surface mixed-layer dissolved Mn concentrations are higher in the North Pacific gyre reflecting enhanced northern hemisphere aeolian sources.Residence time estimates for the settling of refractory paniculate Fe and Mn from the upper water column are 62–220 days (Fe), and 105–235 days (Mn). In contrast, residence times for the scavenging of dissolved Fe and Mn are 2–13 years (Fe) and 3–74 years (Mn). Scavenging residence times for dissolved Mn based on horizontal mixing in the surface mixed layer of the northeast Pacific are 0.4 years (nearshore) to 19 years (1000 km offshore).There is no evidence for in situ Fe redox dissolution within sub-oxic waters in the eastern tropical North Pacific. Dissolved Fe appeared to be controlled by dissolution from sub-oxic sediments, with oxidative scavenging in the water column or upper sediment layers. However, in situ Mn dissolution within the oxygen minimum zone was evident. 相似文献
16.
气候变暖对湖泊物理、化学、生物和生态系统有着复杂而深刻的直接和间接影响,而具体影响随研究区域和水体表现不尽相同。气候变暖通过改变湖泊热力和溶解氧分层进而影响湖泊生物过程和生态系统结构与功能。从全球湖泊变暖趋势、长期缓慢气温上升、极端高温事件以及气候情景模拟等方面详细综述了气候变暖对湖泊热力及溶解氧分层影响的研究进展。研究表明,全球不同区域湖泊均存在不同程度的变暖趋势;长期缓慢气温上升和短期极端高温均会造成湖泊热力分层提前,分层结束推迟,分层时间延长,混合层和温跃层深度下降,以及热稳定性增加;相伴随的是溶解氧扩散深度和氧跃层深度明显下降,加剧了湖泊底部好氧和厌氧环境。除了这种直接影响外,气候变暖引起的流域降水、入湖物质的变化以及风速的变化也会对湖泊热力和溶解氧分层产生许多间接的影响,因此未来仍然需要更多的实验证据、经验和数值模型来验证和预测气候变暖对湖泊热力及溶解氧分层的影响。 相似文献
17.
石灰岩中游离二氧化硅化学物相分析方法的标准化研究 总被引：1，自引：1，他引：0
介绍了石灰岩中游离二氧化硅的化学物相分析方法,选择磷酸溶矿,再以氟硼酸解聚已溶出的硅酸,使游离二氧化硅与其他矿物分离,再用重量法进行测定,并按ＧＢ３７９－８６测试方法的精密度,通过实验室间试验确定标准测试方法的重复性和再现性,通过取样、制样、样品均匀性检查、精密度试验等步骤,对该方法进行了标准化研究。 相似文献
18.
《Chemical Geology》2002,182(2-4):179-194
A technique using isotope-ratio-monitoring gas chromatography-mass spectrometry (irmGCMS) and excimer laser fluorination for in situ oxygen isotope analysis of silicates is described. The irmGCMS and oxygen extraction line is connected by a newly developed interface, reducing the time for a single analysis to less than 10 min. The precision obtained for δ18O is similar to what has been reported for excimer laser fluorination using dual inlet systems. δ18O values of two olivine standards had 1σ precision of ±0.14‰ (n=19 and n=10) and that of Dörentrup quartz had ±0.17‰. Eleven analyses of a large zircon crystal had a precision of ±0.12‰. However, between 300 and 600 nmol oxygen was liberated for a single analysis, equivalent to cylindrical laser holes 250 to 350 μm in diameter and depth. In the future it will be feasible to measure the isotope ratio of cylindrical volumes 150 μm in diameter simply by reducing the volume of the extraction line. While this is still significantly larger than what is possible with ion probes, the ratios obtained by excimer laser-irmGCMS are highly accurate and precise without correction. The value of this technique for in situ oxygen isotope measurements is demonstrated with two rock slabs from metamorphic rocks of the Dabie–Sulu ultra-high-pressure belt, China. 相似文献
19.
泥灰岩中自生方解石的稀土元素酸溶方法研究 总被引：1，自引：0，他引：1
碳酸盐岩稀土元素是沉积环境示踪的理想参数,但由于自生沉积碳酸盐矿物的稀土元素含量远低于陆源黏土等其他矿物,在样品处理过程中少量陆源黏土矿物的溶解,将影响沉积环境的示踪。因此,如何在样品处理过程中避免陆源黏土矿物中稀土元素的释放,从而获得海洋环境自生沉淀形成的碳酸盐矿物中的元素方法非常重要。本文应用地层中常见的同一泥灰岩样品,分别用5%醋酸、5%盐酸、2%和5%硝酸浸取,采用0.5 h、1 h、2 h、3 h、6 h和24 h的反应时间,用X射线衍射法（XRD）分析酸不溶残渣矿物组成、电感耦合等离子体原子发射光谱法（ICP-AES）测定酸可溶相溶液的主元素和微量元素含量、电感耦合等离子体质谱法（ICP-MS）测定酸可溶相溶液的稀土元素含量,结果表明所有酸溶均可完全溶解泥灰岩中的方解石矿物,并有少量黏土发生溶解,导致稀土总量和Ce/Ce＊增高,但对Eu/Eu＊、LaN/YbN和Gd/Gd＊等参数没有影响。泥灰岩中自生方解石的稀土元素理想溶样条件是5%醋酸反应1 h以内,溶液的ICP-MS分析结果适用于示踪沉积环境的氧化还原条件。 相似文献
20.
磷酸盐氧同位素组成的测定方法及分馏机理研究进展 总被引：4，自引：0，他引：4
磷酸盐氧同位素组成在古气候和磷的生物地球化学循环研究中都具有十分重要的意义.测定方法和同位素的分馏机理是该类研究的基础.国际上已开展了一系列磷酸盐氧同位素的测定方法和分馏机理研究.在测定方法上,由初期的间接法,经高温还原/裂解法到氟化法,再演化到改进后的高温还原法(包括TC/EA-IRMS法),甚至激光原位技术,样品由实验室纯化学试剂扩展到各种复杂地质样品,在测量精确度、测量速度、样品用量、安全性和技术要求方面都有巨大改进.在分馏机理上,①尽管Longinelli等建立的关系式已获得了天然样品的验证,并认为是平衡分馏,但实验室模拟结果与其还存在较大差异(即没有达到平衡分馏).②在地表温度和pH条件下,无机过程均不会造成水体中溶解态磷酸盐和水之间的氧同位素交换.在高温(>70℃)及不同pH条件下,即使没有生物作用也会造成溶解磷酸盐和水分子之间进行氧的同位素交换,但不同实验室之间结果不一致.③在生物作用存在下,溶解无机磷酸盐和水之间在地表环境会发生强烈氧同位素交换,但除了PPase外,其余均没有达到平衡值.④磷灰石的氧同位素组成要比形成它的溶解态磷酸盐的值高1‰～1.4‰,因此在把Longinelli等关系式用于溶解态磷酸盐和水体系时,需要考虑该因素.同位素平衡分馏和条件有关,认为无机条件下的高温(>70℃)实验结果不一致,以及有生物参与的培养实验结果偏离平衡值,都是实验条件不同所致,包括pH、磷酸盐浓度、生物种类、生物量等. 相似文献