加速溶剂萃取技术提取海洋沉积物中游离态脂肪酸的方法研究

脂肪酸是沉积物中含量最丰富的脂类标记物之一,其存在形式主要有游离态脂肪酸和结合态脂肪酸。游离态脂肪酸可由溶剂直接提取,结合态脂肪酸是在已提取出游离态脂肪酸的沉积物残渣中加入酸碱加热后再用溶剂提取。加速溶剂萃取技术(ASE)因成本低和操作毒性小,在脂肪酸研究中得到了广泛的应用。本文采集东海近海海域沉积物作为研究样本,由于其中游离态脂肪酸含量丰富,而结合态脂肪酸含量过低,测定结果精密度差,难以作为方法研究对象,因此主要针对游离态脂肪酸应用加速溶剂萃取法进行提取,研究了各种实验条件,包括萃取剂、萃取温度、静态萃取时间和循环次数的选择与优化。分析结果表明,甲醇-二氯甲烷(V:V,1:3)更适合作为萃取剂;随着萃取温度、静态萃取时间、循环次数的增加,不同类型脂肪酸的提取效率各不相同,以涵盖碳原子数最多为先决条件,以脂肪酸的萃取效率最大化为依据,确定了加速溶剂萃取的实验条件是:萃取温度110℃,静态提取时间10 min,循环3次。用这种处理方法5次测定沉积物样品中游离态脂肪酸的精密度为3.3%~19.0%,其替代物回收率为72.2%~104.6%。该方法应用于分析实际海洋沉积物样品,相比于传统的索氏提取法,流程简单,极大地提高了工作效率。     

Hydrological processes of a rainforest headwater swamp from natural chemical tracing in Nsimi watershed,Cameroon

The hydrological role of a headwater swamp in a tropical rainforest is studied using chloride mass balance (CMB) and end‐member mixing analysis. There are three main contributions to streamflow: (1) the hillside bedrock aquifer, (2) overland flow from the swamp during storm events and (3) groundwater flow from the swamp aquifer. Before rainfall events of the wet season, the pre‐event water comprises a mix of 80% of bedrock aquifer and 20% of swamp aquifer. During storms, the relative contribution of overland flow increases according to the rainfall intensity and the initial saturation rate of the pre‐event water reservoirs. The yearly contribution of overland flow from the swamp to the stream is about 31%. The relationship between the swamp and the stream fluctuates with space and time. Generally, the swamp is drained by the stream; however, at the end of long dry seasons, after the first rains, indirect recharge occurs from the stream to the swamp with a hydraulic gradient inversion in the swamp aquifer. The net contribution of the swamp aquifer to the stream is only 4%, which is much lower than the hillside aquifer contribution of about 65%. Recharge on the swamp being very low, these results suggest that, except for a few storms at the end of the dry season, the Nsimi swamp does not contribute to flood attenuation. Evapotranspiration is higher on the hillside than in the swamp. Nevertheless, depletion of water stored within the swamp is dominated by evaporation rather than by its contribution to streamflow. The export of solutes through swamp groundwater flow below the weir is low (<7%). Nevertheless, the swamp is the most active area of weathering in the watershed. Copyright © 2011 John Wiley & Sons, Ltd.     

Transit time evaluation using a chloride concentration input step shift after forest cutting in a Japanese headwater catchment

Mean transit times were estimated for a small headwater catchment in Japan (the Fukuroyamasawa Experimental Watershed) using the step shift in input chloride (Cl^?) concentrations that occurred immediately after an episode of forest clear‐cutting. Measured Cl^? concentrations in stream water began to decrease immediately after clear‐cutting, and this trend continued for 6 years. Before clear‐cutting, the input Cl^? concentrations were controlled by wet and dry deposition processes, and most of the dry Cl^? deposition was collected by the forest canopy and reached the ground as throughfall and stemflow. After clear‐cutting, dry deposition was no longer collected by the canopy in this way, thus causing a sharp decrease in input Cl^? concentrations. By comparing measured Cl^? concentrations in stream water with estimates based on the input and evaporative Cl^? concentrations, it was shown that the decrease in stream water Cl^? concentrations was caused mainly by this step shift in the Cl^? input. It was proposed that the change in Cl^? concentrations after forest cutting could be used to represent the replacement of ‘old’ water that existed before cutting by ‘new’ water that was supplied after cutting. The breakthrough curve for the new water fraction gave an approximately exponential distribution of transit times in flow‐corrected time. The mean flow‐corrected transit time was estimated as 1068 days (runoff: 3497 mm). It was therefore concluded that the step change in input Cl^? concentrations immediately following forest clear‐cutting could be successfully used to estimate transit times for the entire catchment. Copyright © 2009 John Wiley & Sons, Ltd.     

Seasonal and interannual variations of nitrate and chloride in stream waters related to spatial and temporal patterns of groundwater concentrations in agricultural catchments

Nitrate concentrations in streamwater of agricultural catchments often exhibit interannual variations, which are supposed to result from land‐use changes, as well as seasonal variations mainly explained by the effect of hydrological and biogeochemical cycles. In catchments on impervious bedrock, seasonal variations of nitrate concentrations in streamwater are usually characterized by higher nitrate concentrations in winter than in summer. However, intermediate or inverse cycles with higher concentrations in summer are sometimes observed. An experimental study was carried out to assess the mechanisms that determine the seasonal cycles of streamwater nitrate concentrations in intensive agricultural catchments. Temporal and spatial patterns of groundwater concentrations were investigated in two adjacent catchments located in south‐western Brittany (France), characterized by different seasonal variations of streamwater nitrate concentrations. Wells were drilled across the hillslope at depths ranging from 1·5 to 20 m. Dynamics of the water table were monitored and the groundwater nitrate and chloride concentrations were measured weekly over 2 years. Results highlighted that groundwater was partitioned into downslope domains, where denitrification induced lower nitrate concentrations than into mid‐slope and upslope domains. For one catchment, high subsurface flow with high nitrate concentrations during high water periods and active denitrification during low water periods explained the higher streamwater nitrate concentrations in winter than in summer. For the other catchment, the high contribution of groundwater with high nitrate concentrations smoothed or inverted this trend. Increasing bromide/chloride ratio and nitrate concentrations with depth argued for an effect of past agricultural pressure on this catchment. The relative contribution of flows in time and correlatively the spatial origin of waters, function of the depth and the location on the hillslope, and their chemical characteristics control seasonal cycles of streamwater nitrate concentrations and can influence their interannual trends. Copyright © 2004 John Wiley & Sons, Ltd.     

盐渍土冻结温度的试验研究

冻结温度是判别土体是否处于冻结状态的指标,在人工冻结和数值模拟计算中影响冻结壁的厚度和计算精度.通过采用不同土体添加不同的盐分,对不同含水量和含盐量土体进行盐渍土的冻结温度试验,考虑了不同因素对土体冻结温度的影响.实验表明：不论何种土含有何种离子,土体的冻结温度随含盐量的增加而降低,随含水量的增加而增大;土中易溶盐的含...     

Sources of dissolved organic carbon during stormflow in a headwater agricultural catchment

Increasing dissolved organic carbon (DOC) concentrations have been reported during the last 15 years in streams from the United Kingdom, Northern Europe and North America. Identifying the sources of DOC and the controls of the delivery to the stream is important to understand the significance of these trends. This relies on the availability of observations of DOC dynamics during storm events, since much of the DOC export from soils to streams occurs during high flows. This study analyses DOC data for eight storm events during winter 2005–2006 in a small agricultural experimental catchment—the Kervidy‐Naizin experimental catchment—located in Western France. A four end‐member mixing approach was applied to the eight monitored storm events to identify DOC sources and quantify their respective contribution to DOC stream fluxes, using DOC, nitrate, sulphate and chloride as tracers. The results show that DOC concentrations in the stream at the outlet of this catchment increase markedly during storm events. The slope of the linear regression between DOC concentration and discharge was not constant for the eight events and depended on pre‐event hydrological conditions. Between 64 and 86% of the DOC that enter the stream during storms originated from the upper layers of the riparian wetland soils. The variation of the delivery of DOC seems to be controlled by hydrological processes only, the wetland soils acting as a non‐limiting store. Copyright © 2009 John Wiley & Sons, Ltd.     

Chloride as a signature indicator of soil textural and hydrologic stratigraphies in variable charge deep profiles

Soil properties that influence water movement through profiles are important for determining flow paths, reactions between soil and solute, and the ultimate destination of solutes. This is particularly important in high rainfall environments. For highly weathered deep profiles, we hypothesize that abrupt changes in the distribution of the quotient [QT = (silt + sand)/clay] reflect the boundaries between textural units or textural (TS) and hydrologic (HS) stratigraphies. As a result, QT can be used as a parameter to characterize TS and as a surrogate for HS. Secondly, we propose that if chloride distributions were correlated with QT, under non‐limiting anion exchange, then chloride distributions can be used as a signature indicator of TS and HS. Soil cores to a depth of 12·5 m were taken from 16 locations in the wet tropical Johnstone River catchment of northeast Queensland, Australia. The cores belong to nine variable charge soil types and were under sugarcane (Saccharum officinarum‐S) production, which included the use of potassium chloride, for several decades. The cores were segmented at 1 m depth increments and subsamples were analysed for chloride, pH, soil water content (θ), clay, silt and sand contents. Selected bores were capped to serve as piezometers to monitor groundwater dynamics. Depth incremented QT, θ and chloride correlated, each individually, significantly with the corresponding profile depth increments, indicating the presence of textural, hydrologic and chloride gradients in profiles. However, rapid increases in QT down the profile indicated abrupt changes in TS, suggesting that QT can be used as a parameter to characterize TS and as a surrogate for HS. Abrupt changes in chloride distributions were similar to QT, suggesting that chloride distributions can be used as a signature indicator of QT (TS) and HS. Groundwater data indicated that chloride distributions depended, at least partially, on groundwater dynamics, providing further support to our hypothesis that chloride distribution can be used as a signature indicator of HS. Copyright © 2005 John Wiley & Sons, Ltd.     

DABS—C1柱前衍生高效液相色谱法测定对虾肌肉中18种游离氨基酸

建立一种以DABS-Cl为柱前衍生剂，利用反相高效液相色谱测定对虾肌肉中18种游离氨基酸的方法。结果表明，在50min内18种氨基酸得到完全分离，各氨基酸相关系数均大于0．997，氨基酸的回收率在86．60%-107．27％之间（胱氨酸除外），方法的检出限为0．18~o．66mg／L，相对标准偏差为3．53％-8．51％（天冬氨酸除外）。     

Using a fluctuating tracer to estimate hyporheic exchange in restored and unrestored reaches of the Truckee River,Nevada, USA

The goal of this research was to compare hyporheic activity in recently restored and adjacent un‐restored reaches of the Truckee River downstream from the Reno/Sparks metropolitan area. The installation of rocky riffles and raised channel bed elevations in the restored reaches may have increased the degree of surface–subsurface interaction. A fluctuating chloride concentration signal served as the tracer, induced by the variable influx of higher salinity water several miles upstream from the study reach. The solute transport model, OTIS, was used in conjunction with the hydrodynamic model, DYNHYD5, to estimate transient storage parameters under unsteady flow conditions. The model was calibrated to chloride concentrations measured over a period of three days at six in‐stream locations representing restored and un‐restored reaches. An automated parameter estimation algorithm (SCE‐UA) was used to optimize parameters for multiple reaches simultaneously and generate a distribution of parameter estimates. Results suggest that the transient storage zone cross‐sectional area (A_s) is larger in the restored reaches than in the unrestored reaches, but the exchange coefficient (α) is smaller, leading to increased hyporheic residence time and hydrologic retention in the vicinity of channel reconstructions. Scenarios were used to simulate the potential effects of increased subsurface residence time on denitrification and in‐stream NO₃‐N concentrations. Monte Carlo analysis was performed to assess uncertainty in the simulation results and show the potential for greater nutrient retention in the lower Truckee River as a result of channel restoration. Copyright © 2009 John Wiley & Sons, Ltd.     

Retention of chloride in soil and cycling of organic matter‐bound chlorine

Chloride (Cl_inorg) is generally considered to be a hydrologically and chemically inert substance. Past research suggests that Cl_inorg participates in a complex biogeochemical cycle involving the formation of organically bound chlorine (Cl_org). The present study examines whether Cl_org cycling is sufficiently extensive as to influence the geochemical cycling of Cl_inorg. Undisturbed soil cores were collected in a coniferous forest soil in SE Sweden. The cores were stored in climate chambers for three months, irrigated with artificial rain, and the leachate was collected and analysed. The water balance of the lysimeters could be well described, and we found that 20–50% of the chlorine leached from the lysimeters was organically bound and that the amounts lost did not decrease with time. This strongly suggests that a substantial amount of Cl_org forms in topsoil, and that subsequent leaching to deeper layers causes a considerable withdrawal of Cl_inorg. The concentration of both organic carbon and Cl_org in the leachate was considerably higher than concentrations observed in the runoff in the actual catchment, suggesting that organic matter precipitates or is mineralized on its way through the soil. Copyright © 2005 John Wiley & Sons, Ltd.