氯离子质量平衡法应用问题刍议

氯离子质量平衡法(CMB)利用惰性示踪剂Cl-可以揭示区域地下水平均补给速率,补给事件和环境、气候变化事件等信息,可为相关研究提供可靠的信息。虽然该方法简单、有效,已经得到大量应用,但是也具有明显的局限性。综述了基于CMB法的相关研究,回溯了该方法的提出和演化,讨论了其主要假设条件和应用的局限性,阐明为了准确地应用该方法需要加强的方面。首先要重视氯离子干沉降的观测和研究。其次要加强氯离子沉降空间变化的观测和研究。在方法上要注意综合采用多种示踪剂、土壤理化性质和平行钻孔等手段来研究。最后要加强对氯离子平衡过程,及其相关的自然过程和人类活动的研究。对促进氯离子质量平衡法在地下水研究方面的应用和发展,具有一定的参考价值。     

Clogging mechanisms and preventive measures in artificial recharge systems

Groundwater which occurs in fractured rock or porous aquifers or other geological weak zones such as faults and fractures is usually extracted via boreholes, hand wells or other sources such as springs.Water scarcity has become a severe problem due to many factors, such as an alarming increase in population and per capita water consumption, over exploitation of groundwater resources and abrupt global climatic change along with its related eco-environmental geological problems. In such situation, application of artificial recharge systems(e.g. surface recharge basin and deep injection well systems) can help to effectively manage and augment the unitization of groundwater resources. However, the clogging problem,which may be caused by a complex interdependent mechanisms of physical, chemical and biological has been a challenge for the efficacy and the implementation of recharge facilities. Clogging can reduce the permeability, recharge rate and longevity of recharge facilities and increase the operational and maintenance costs. Major influencing factors associated with the occurrence of clogging include the chemical composition of groundwater(both the recharge water and native groundwater), aquifer medium and microbial diversity, together with other environmental factors such as temperature, pressure, total dissolved solids, total soluble salts, pH, Eh, nutrients, gases, carbonates and others; these factors ultimately increase the piezometric head but reduce the permeability and infiltration rates of porous/seepage media.Pretreatment of recharge water can minimize the potential clogging. In the case of clogged wells,rehabilitation methods need to be deployed. In the meantime, there is an urgent needs to understand the basic causes and developmental processes/mechanisms of clogging in order to mitigate this problem. This paper reviews the major clogging mechanisms and their possible preventive measures and redevelopments in artificial recharge systems.     

半干旱地区沙地麻黄人工栽培技术研究

在深入研究麻黄野生生长特性的基础上,对在半干旱沙地开展麻黄人工栽培过程中的苗木繁育、栽培管理等相关的技术问题进行了较深入的研究。结果表明:①1%浓度的尿素溶液和糖液分别可使麻黄种子发芽率提高10%和26.3%,浓度≥3%时对种子发芽不利;②苗木栽植前应用水或50mg·kg^-1生根粉液浸根,浸根后可提高苗木成活率8%~10%;③栽植麻黄最好选择平坦沙壤地,以利麻黄的高产稳产,流动半流动沙地也可种植,但种植前应进行地面防沙处理;④栽植后应加强水肥管理,特别是要适量追施化肥,用量为尿素11.25g·m^-2加二铵11.25g·m^-2;⑤麻黄人工栽植可提高其有效成份麻黄碱含量,改善其品质。     

Simulations of measures to control lava flows

We evaluated the quantitative effects of artificial barriers, water-cooling and guiding channels on lava flow using the lava simulation program LavaSIM. Lava flow is basically subject to the topography around the path, effusive rate and viscosity. To prevent damage due to lava flow, we conducted experiments in controlling the flow direction, velocity and temperature. The simulation demonstrated that artificial barriers can successfully change the direction of a lava flow and is more effective when placed nearly parallel to the flow direction at a point where the topography is not very steep, while a barrier placed perpendicular to the flow direction can only stop the flux temporarily, ultimately allowing the solidified crust to accumulate and causing the following mass to go over the barrier. The water-cooling trial was also effective in controlling the direction and temperature, although the amount of water was as much order as 10⁵ m³. The guiding channels successfully control the direction and inundated area but only in local areas.     

基于二维相干性自锚式悬索桥的地震响应研究

一般在非一致地震激励的模拟中采用一维相干模型,即模型中只含有沿地震波传播方向的变量,但垂直于地震波传播方向两点距离较远(如横桥向)时,会存在相干性.本文基于二维相干模型,应用三角级数法,考虑频率对视波速的影响、地震波传播滞后对非平稳调制函数的影响,生成某自锚式悬索桥桥址处各支点的人工地震波.利用该地震波研究不同激励方式对自锚式悬索桥结构的地震响应,并与基于一维相干的地震响应结果进行了对比,从中得到一些有意义的结论.     

Impact of geometrical properties on permeability and fluid phase distribution in porous media

To predict fluid phase distribution in porous media, the effect of geometric properties on flow processes must be understood. In this study, we analyze the effect of volume, surface, curvature and connectivity (the four Minkowski functionals) on the hydraulic conductivity and the water retention curve. For that purpose, we generated 12 artificial structures with 800³ voxels (the units of a 3D image) and compared them with a scanned sand sample of the same size. The structures were generated with a Boolean model based on a random distribution of overlapping ellipsoids whose size and shape were chosen to fulfill the criteria of the measured functionals. The pore structure of sand material was mapped with X-rays from synchrotrons.     

Amelioration of marine farming impact on the benthic environment using artificial reefs as biofilters

An in situ monitoring of the sediment characteristics and macrobenthic communities was undertaken at a marine fish culture site in subtropical waters of Hong Kong before and after the deployment of biofilters which were made of cement concrete artificial reef (AR) structures. According to the distance to the boundary of the fish cages, 6 points were selected as sampling stations: 2 at the fish cages, 2 near the boundary of the fish culture area, and 2 reference sites further away from the culture area. Bimonthly sediment samples were collected for analysis of silt-clay fraction (SCF), moisture content (MC), total organic carbon (TOC), total Kjeldahl nitrogen (TKN) and total phosphorus (TP). The macrobenthos (>0.5mm) present in the sediment were sorted, identified and enumerated. TOC, TKN and TP levels at the fish cage stations were consistently higher than those at the reference stations over the 1-year pre-AR and 2-year post-AR deployment monitoring period. The diversity of macrofauna was significantly reduced at the fish cage stations relative to the reference sites. The intermediary stations near the fish culture area showed a transitional state of disturbance. Over the 2-year post-AR deployment period, TOC, TKN and TP showed a decreasing trend at the fish cage and intermediary stations. More diverse macrofaunal communities were recorded at the fish cage stations, with species diversity H'increasing from 0-1 at the beginning of the AR deployment to H'>2 at the end of the study. The present results demonstrated that artificial reefs can improve the benthic abiotic environment and biotic conditions beneath fish rafts which are deteriorated due to farming activities.     

Approximating groundwater age distributions using simple streamtube models and multiple tracers

We use a streamtube based decomposition and a recently developed, simple relationship between tracer concentrations and ages to estimate groundwater age distributions. The decomposition assumes that an age distribution can be approximated using a superposition of linearly independent streamtubes. Transport in each streamtube is modeled with inverse Gaussian functions, the parameters of which are inferred from radiometric tracer concentrations. Three simple sampling methods are considered for weakly and moderately heterogeneous aquifers and the method gives reasonable approximations in both systems. The method is sensitive to errors in the measured concentrations but some of these errors are easily identifiable and a range of plausible age distributions can still be found. The method was then tested in a highly heterogeneous system and reasonable estimates of the age distribution were also obtained. The simplicity of this method and its insensitivity to the heterogeneity structure suggest that this approach may be an effective tool for obtaining estimates of age distributions in natural systems.     

ROAD SALT ACCUMULATION IN HIGHWAY SNOW BANKS AND TRANSPORT THROUGH THE UNSATURATED ZONE OF THE OAK RIDGES MORAINE,SOUTHERN ONTARIO

Pathways and fate of road deicing salt (NaCl) applied during the 1994–1995 winter were studied for a 14-km section of a major highway that crosses the Oak Ridges Moraine in southern Ontario. Total salt applications over the winter ranged from 29 to 74 kg m⁻¹ of highway, and NaCl concentrations in snow banks adjacent to the roadway reached 9400 mg l⁻¹ during the later stages of snow cover development. This salt was released to the ground surface during snowmelt. Sodium chloride (NaCl) loadings to soil from snow cover during the final melt phase were relatively uniform along the study section (3–5 kg NaCl m⁻¹ of highway). However, the snowpack at all transects retained <50% of applied NaCl, and this shortfall probably reflected direct runoff and infiltration of saline meltwater from the road surface into the adjacent shoulder and right-of-way. Cation exchange with Ca²⁺ in near-surface soils most likely resulted in preferential retention of Na⁺ relative to Cl⁻, although total storage of NaCl in upper soil horizons by winter's end was <15% of deicing salt applications. An environmental tracer (¹⁸O) was used to trace movement of saline meltwater through the unsaturated zone underlying the highway. Average meltwater particle velocities at a site underlain by loam soils were 0.02 m d⁻¹, and ca. 280 mm of water was displaced below a depth of 1.86 m over a 78-day period in the spring and summer of 1995. Sodium ion and chloride ion concentrations in water sampled in late summer 1995 at depths >2 m exceeded 500 mg l⁻¹ and 1000 mg l⁻¹, respectively. Approximately 75% of the net flux of NaCl below the upper soil was retained in the 0–2.8 m depth interval at this site, and results from more permeable soils traversed by the highway indicate an even greater penetration of the annual NaCl application into the unsaturated zone along the moraine. This saline water likely recharges groundwater in this portion of the Oak Ridges Moraine.     

昆仑山断层围陷波的分析和研究

对2001年昆仑山口西Ms81级地震产生的断层带,布设了沿断层和横跨断层的两条人工地震测线.通过对观测资料的定量分析和处理,求得了昆仑山断层带内部的细结构.分析工作包括从S波震相开始的振幅谱计算、速度频散计算、群速度测量,并用面波频散方法反演S波速度结构,用振幅谱比的方法估计断层带的Q值.野外试验结果表明,S波震相与围陷波组的时间差随炮点与台站之间距离增大而增加,在断层带外的测点上观测到与断层带相关的场地效应.最后得出昆仑山断层带宽度为250m、速度结构为断层内低速的分层结构和Q值为15（断层内）和30（围岩）.虽然昆仑山口西地震的震级比美国加州Landers地震的震级（Ms76）大,且地震产生的破裂带长度长得多,但是这两个地震断层带的宽度却相差不大.