Impact of Sea-Level Rise on Sea Water Intrusion in Coastal Aquifers

Despite its purported importance, previous studies of the influence of sea-level rise on coastal aquifers have focused on specific sites, and a generalized systematic analysis of the general case of the sea water intrusion response to sea-level rise has not been reported. In this study, a simple conceptual framework is used to provide a first-order assessment of sea water intrusion changes in coastal unconfined aquifers in response to sea-level rise. Two conceptual models are tested: (1) flux-controlled systems, in which ground water discharge to the sea is persistent despite changes in sea level, and (2) head-controlled systems, whereby ground water abstractions or surface features maintain the head condition in the aquifer despite sea-level changes. The conceptualization assumes steady-state conditions, a sharp interface sea water-fresh water transition zone, homogeneous and isotropic aquifer properties, and constant recharge. In the case of constant flux conditions, the upper limit for sea water intrusion due to sea-level rise (up to 1.5 m is tested) is no greater than 50 m for typical values of recharge, hydraulic conductivity, and aquifer depth. This is in striking contrast to the constant head cases, in which the magnitude of salt water toe migration is on the order of hundreds of meters to several kilometers for the same sea-level rise. This study has highlighted the importance of inland boundary conditions on the sea-level rise impact. It identifies combinations of hydrogeologic parameters that control whether large or small salt water toe migration will occur for any given change in a hydrogeologic variable.     

Effect of a Freshwater Layer Overlying Salt Water on the Regime of Replacement in Confined Coastal Aquifers

A mathematical model of fresh groundwater flow from a semi-infinite confined aquifer into a sea (pool, trench, and the like) filled with salt water and having a freshwater layer above its horizon. To study this problem a mixed boundary-value problem of the theory of analytical functions is formulated and solved with the use of the Polubarinova-Kochina method. The obtained exact analytical relationships and numerical calculations are used to perform a detailed hydrodynamic analysis of the effect of the freshwater layer and other physical parameters of the model on the character and the extent of displacement.     

Effect of Sea‐Level Rise on Salt Water Intrusion near a Coastal Well Field in Southeastern Florida

A variable‐density groundwater flow and dispersive solute transport model was developed for the shallow coastal aquifer system near a municipal supply well field in southeastern Florida. The model was calibrated for a 105‐year period (1900 to 2005). An analysis with the model suggests that well‐field withdrawals were the dominant cause of salt water intrusion near the well field, and that historical sea‐level rise, which is similar to lower‐bound projections of future sea‐level rise, exacerbated the extent of salt water intrusion. Average 2005 hydrologic conditions were used for 100‐year sensitivity simulations aimed at quantifying the effect of projected rises in sea level on fresh coastal groundwater resources near the well field. Use of average 2005 hydrologic conditions and a constant sea level result in total dissolved solids (TDS) concentration of the well field exceeding drinking water standards after 70 years. When sea‐level rise is included in the simulations, drinking water standards are exceeded 10 to 21 years earlier, depending on the specified rate of sea‐level rise.     

Non-equilibrium compaction and abnormal pore-fluid pressures: effects on rock properties1

Knowledge of pore pressure using seismic data will help in planning the drilling process to control potentially dangerous abnormal pressures. Various physical processes cause anomalous pressures on an underground fluid. Non-equilibrium compaction is a significant process of overpressure generation. This occurs when the sedimentation rate is so rapid that the pore fluids do not have a chance to 'escape' from the pore space.
The model assumes a closed system and that the pore space is filled with water and hydrocarbon in a liquid state. Balancing mass and volume fractions yields the fluid pressure versus time of deposition and depth of burial. Thermal effects are taken into account. The pore pressure, together with the confining pressure, determines the effective pressure which, in turn, determines the bulk moduli of the rock matrix.
We assume a sandstone saturated with hydrocarbons and water, for which calibration of the model with experimental data is possible. The seismic velocities and attenuation factors are computed by using Biot's theory of dynamic poroelasticity and the generalized linear solid. The example shows that the formation can be overpressured or underpressured depending on the properties of the saturating fluid. Wave velocities and quality factors decrease with decreasing differential pressure. The effect is important below approximately 20 MPa. The model is in good agreement with experimental data for Berea sandstone and provides a tool for predicting pore pressure from seismic attributes.     

微囊藻水华的资源化利用:吸附重金属离子Cu2+、Cd2+和Ni2+的实验研究

为将捞取的微囊藻水华资源化,用作重金属生物吸附剂,本文研究了在不同金属离子浓度和不同pH条件下微囊藻水华对重金属Cu²⁺、Cd²⁺和Ni²⁺的吸附效果.研究结果显示,重金属离子浓度分别为20.00、60.00、100.00和140.00μg/ml时,150 mg干重微囊藻水华对Cu²⁺的去除率分别为67.79%、37.47%、35.93%和34.70%,对Cd²⁺的去除率分别为73.31%、65.87%、60.09%和42.37%,对Ni²⁺的去除率分别为47.89%、31.87%、28.46%和21.61%.在较低的重金属浓度(20.00μg/ml)下,微囊藻对3种重金属的去除率最高.但从单位微囊藻生物量吸附重金属量来看,金属离子初始浓度越高,吸附重金属的总量越高;在相同金属浓度下,微囊藻水华对3种金属的吸附效率:Cd²⁺ > Cu²⁺ > Ni²⁺.微囊藻吸附Cu²⁺的最适pH为5.0,Cd²⁺和Ni²⁺均为6.0,20.00μg/ml浓度时去除率分别达到了71.90%、85.67%和55.43%.微囊藻裂解释放的可溶性物质对重金属吸附影响不大.研究结果显示微囊藻水华可作为重金属吸附剂有效地运用于重金属污水处理.     

青藏高原湖泊Mg~(2+)、Ca~(2+)和Mg/Ca盐度指示意义的初步分析

总结了青藏高原地区400多个湖泊湖水的Mg2+、Ca2+和Mg/Ca等水化指标与湖水盐度的相关关系,以及这种关系随着湖水变化(不同采样时间和采样点以及自然蒸发)而产生的变化规律.结果表明:青藏高原湖泊湖水的Mg2+浓度与盐度具有较为稳定的正相关关系,而Ca2+和Mg/Ca与盐度的相关性较弱.在对于某一特定水化学类型的湖泊,一般碳酸盐型湖泊的Mg2+、Ca2+以及Mg/Ca等指标与盐度均没有明显的相关性;硫酸盐型湖泊中Mg2+浓度和盐度呈现较高的正相关关系,而Ca2+以及Mg/Ca与盐度的相关性仍很弱;而在氯化物型湖泊中,Mg2+浓度与盐度呈更高的正相关性,Ca2+浓度也与盐度呈一定的正相关性,Mg/Ca这一指标与盐度的相关性依然很弱.而对某一特定湖泊,在不同演化阶段或不同的采样地点,Mg2+浓度与盐度仍然保持明显的正相关关系,而Ca2+以及Mg/Ca与盐度的相关性仍然不稳定或很弱.在青藏高原作古环境重建应用的时候,湖水Mg2+浓度是古盐度一个较好的转换指标,而Ca2+以及Mg/Ca的古盐度指示意义相对较弱.     

Stable Isotopes (δ18O, δ2H) of Pore Waters in Clay-Rich Aquitards: A Comparison and Evaluation of Measurement Techniques

Pore water collected from piezometers installed in a thick clay-rich till were used to compare and evaluate four techniques for obtaining δD and δ¹⁸O values in these media. The techniques included mechanical squeezing, centrifugation, azeotropic distillation, and a direct soil-water equilibration technique. Direct CO₂-core equilibration yielded sufficiently accurate and reproducible δ¹⁸O results of pore water in clay-rich tills. In addition, this method eliminated the need for labor-intensive complete extraction of water from the geologic media. Mechanical squeezing and centrifugation produced results similar to direct equilibration. However, both of these methods exhibited a greater degree of variability and were laborious and more time consuming. Small differences in δ¹⁸O values between piezometer water and equilibrated, squeezed, and centhfuged samples suggested that each method collected different fractions of the clay-water reservoir. Although these subtle differences were not conclusive, they did suggest the presence of weakly bound water and highlighted the difference between these three techniques for determining the stable isotopic composition of pore water in clay-rich aquitards. Azeotropic distillation produced a high level of discrepancy in δD andδ¹⁸O results compared to the other methods. Incomplete extraction was considered the most probable cause of this error. The results of this study suggested that direct equilibration is the best method for determining detailed δD and δ¹⁸O values of pore water in clay-rich aquitards.     

The location of Fe3+ ions in forsterite (Mg2SiO4)

The electron spin resonance spectrum of Fe³⁺ in a single crystal of forsterite was studied. Two distinct patterns of about equal intensities were observed which are due to Fe³⁺ at two distinct positions with 4a (M1)and4c (M2or Si) symmetry of Pbnm. The assignment of the 4c pattern to Fe³⁺ ions at the Si position cannot be excluded by symmetry but it is unlikely. The Hamiltonian parameters A and E/D are consistent with the conclusion that Fe³⁺ in this crystal is disordered over two distinct octahedral positions.