Geologic factors controlling groundwater chemistry in the coastal aquifer system of Douala/Cameroon: implication for groundwater system functioning

Douala city, located in the littoral province of Cameroon, receives abundant rainfall quantities due to its geographical position in the Gulf of Guinea and bears considerable surface water and groundwater resources. Due to socioeconomic development and rapid demographic growth in the city and its consequences of unplanned urbanization and improper sanitation system, these water resources are poorly protected and managed. Streams in the Wouri watershed receive large amounts of wastewater discharge, and hundreds of boreholes have been drilled into the aquifer system without any management plan. A detailed hydrodynamic and hydrogeochemistry study in Douala town and its environs was conducted to get a better insight into the groundwater system functioning in order to provide information for the sustainable management and protection of the groundwater resource. Two field campaigns were carried out with 187 samples collected and analyzed for major ions, stable isotopes (¹⁸O, ²H), and tritium ³H. The results of the sampling have shown that the weathering of silicate minerals is the dominant geochemical process affecting groundwater chemistry in this system. However, acid rainfall in the humid climate has also caused carbonate mineral dissolution, amorphous silica deposition, and ion exchange reactions to occur in aquifers in the region. The various water types identified were categorized into four major clusters C1 to C4, based on the major ion composition and the local hydrogeological conditions. Environmental isotope data reveal that modern-to-submodern waters occur in the phreatic Quaternary/Mio-Pliocene and Oligocene/Upper Eocene aquifers, respectively. These results corroborate with the conceptual model built where modern groundwater types indicated silicate mineral weathering and calcite dissolution (C1 and C2), whereas submodern groundwater mostly showed silica deposition, ion exchange, and, to a lesser extent, carbonate mineral dissolution (C3 and C4). This improved understanding of the aquifer system functioning is essential to provide a reasonable basis for effective control measures and sustainable water management.     

Microbial community composition and environmental response characteristics of typical brackish groundwater in the North China Plain

To reveal the microbial community composition of regional shallow porous brackish groundwater and its response characteristics to groundwater environment, the first and second aquifers in Taocheng District,Hengshui City were selected, and 10 groundwater source samples were collected for hydrochemical analysis and microbial 16S RNA gene V4–V5 regional sequencing. The results showed that the shallow brackish groundwater in the study area is weakly alkaline and has high ion content. The hydrochemic...     

Laboratory study of the clogging process and factors affecting clogging in a tailings dam

Laboratory simulation of clogging in the Lixi tailings dam (Shaanxi Province, China) is urgently required because clogging is an important factor affecting the dam stability. This work firstly presents the results of ferrous iron oxidation experiments using buffer solution. The results indicate that the ferrous iron oxidation follows first order kinetics, and the oxidation process is strongly dependent on pH, a higher pH resulting in a higher oxidation rate. Furthermore, when the pH exceeds 7.0, the oxidation rate constant increases significantly. Secondly, a column experiment was carried out under the conditions of the pH ranging from 6.8 to 7.5 and the natural oxygen supply. Ferrous iron oxidation and precipitation were found to reach equilibrium under these conditions. After 23 days, the column experiment was stopped when the clogging materials blocked the column outlet. The clogging materials were found to be a mixture of ferric hydroxide and its converted products, and these existed in amorphous form with a loose cluster microstructure according to the results of XRD and SEM.     

1929—1930年中国极端冷冬事件的重建*

气候变暖背景下,极端寒冷事件仍有发生且常伴随严重的经济、社会影响,需要更为深入的研究。1929—1930年极端冷冬事件作为增暖背景下的极端冷事件,对其研究相对缺乏。通过收集并分析民国时期的气象器测资料和报刊资料,对1929—1930年中国极端冷冬事件进行探讨。结果表明: (1)本次冷冬的空间范围包括华北地区、长江流域(重庆至入海口段)和北疆地区,西北地区可能存在冷冬;寒冷的核心时段为1929年12月到次年1月。(2)本次冷冬时空范围内的地区月平均气温极端性强,华北、长江流域的12月份均温都超过十年一遇的冷事件水平,长江流域、北疆地区的1月份均温均超过五十年一遇水平;但月最低气温的极端性较弱,大部分站点月的最低温达到五年一遇水平,部分站点月超过十年一遇水平。(3)本次冷冬至少经历了7次区域性或全国性的降温事件,其中有3次降温事件达到全国性寒潮事件标准,时段分别为12月1—5日、12月16—20日和1月1—5日;其中第1次和第3次是影响中国的典型中路寒潮路径,第2次降温过程的时空特征不显著。(4)综合本次冷冬前旱后涝气候特点、该时段内ENSO(厄尔尼诺-南方涛动)指数的变化以及前人对ENSO和中国气候变异的关系研究,推测1920s末到1930s初期的气象灾害很大程度受影响于ENSO事件。     

Quantification of groundwater recharge and river bed clogging by daily water level measurements in a check dam

Check dams are one of the methods of managed aquifer recharge to augment groundwater storage in regions with non-perennial rivers. The objectives of this study were to quantify the groundwater recharge from a check dam in the Arani River, north of Chennai, India, and to assess the clogging of the riverbed. The water level in the check dam was measured daily for 3 years from 2010 to 2013. Other field investigations carried out include measurement of the topographic elevation of the riverbed using the differential global positioning system. Based on the water balance method, the quantity of water evaporated and recharged was estimated. A comparison of 3-year daily water level measurements indicated that there is no clogging in the riverbed during the study period, as this check dam is fitted with a sluice gate which is operated at appropriate times to flush out the sediments.     

Prevention of well clogging during aquifer storage of turbid tile drainage water rich in dissolved organic carbon and nutrients

Well clogging was studied at an aquifer storage transfer and recovery (ASTR) site used to secure freshwater supply for a flower bulb farm. Tile drainage water (TDW) was collected from a 10-ha parcel, stored in a sandy brackish coastal aquifer via well injection in wet periods, and reused during dry periods. This ASTR application has been susceptible to clogging, as the TDW composition largely exceeded most clogging mitigation guidelines. TDW pretreatment by sand filtration did not cause substantial clogging at a smaller ASR site (2 ha) at the same farm. In the current (10 ha) system, sand filtration was substituted by 40-μm disc filters to lower costs (by 10,000–30,000 Euro) and reduce space (by 50–100 m²). This measure treated TDW insufficiently and injection wells rapidly clogged. Chemical, biological, and physical clogging occurred, as observed from elemental, organic carbon, 16S rRNA, and grain-size distribution analyses of the clogging material. Physical clogging by particles was the main cause, based on the strong relation between injected turbidity load and normalized well injectivity. Periodical backflushing of injection wells improved operation, although the disc filters clogged when the turbidity increased (up to 165 NTU) during a severe rainfall event (44 mm in 3 days). Automated periodical backflushing, together with regulating the maximum turbidity (<20 NTU) of the TDW, protected ASTR operation, but reduced the injected TDW volume by ~20–25%. The studied clogging-prevention measures collectively are only viable as an alternative for sand filtration when the injected volume remains sufficient to secure the farmer’s needs for irrigation.

     

Understanding of the biochemical events in a chemo-bioreactor during continuous acid mine drainage treatment

Spent mushroom compost (SMC) is widely used as reactor matrix in passive bioreactor involving sulfate reducing bacteria (SRB) for acid mine drainage (AMD) treatment. Follow-up our previous report, recent work has been established the extent of activity, sustained organic carbon availability, and the biochemical events of successive alkalinity producing system-based chemo-bioreactor for continuous performance using SMC. Removal of iron and sulfate from influent was over 77 and 90%, respectively, for first 13 weeks, while sulfate removal efficiency suddenly dropped down to 31% thereafter. Ahead of 13th week, process failure was beginning to be noticed when available dissolved organic carbon (DOC) value dropped down to 50 mg/L. SRB population was mostly affected with DOC drought at this stage. Sulfur was one of the major elements found with other tested metals in blackish green effluent precipitate. Sulfide compounds of the tested metals were formed on both exhausted chemo-bioreactor bed and precipitate. FTIR analysis indicated that SMC was responsible for metal binding and available nutrients supply. The present study revealed the feasibility of SMC as a host for treating AMD by this chemo-bioreactor that will assist in designing the continuous treatment practice.     

Monitoring groundwater flow and chemical and isotopic composition at a demonstration site for carbon dioxide storage in a depleted natural gas reservoir

Between March 2008 and August 2009, 65,445 tonnes of ∼75 mol% CO₂ gas were injected in a depleted natural gas reservoir approximately 2000 m below surface at the Otway project site in Victoria, Australia. Groundwater flow and composition were monitored biannually in two overlying aquifers between June 2006 and March 2011, spanning the pre-, syn- and post-injection periods. The shallower (∼0–100 m), unconfined, porous and karstic aquifer of the Port Campbell Limestone and the deeper (∼600–900 m), confined and porous aquifer of the Dilwyn Formation contain valuable fresh to brackish water resources. Groundwater levels in either aquifer have not been affected by the drilling, pumping and injection activities that were taking place, or by the rainfall increase during the project. In terms of groundwater composition, the Port Campbell Limestone groundwater is brackish (electrical conductivity = 801–3900 μS cm⁻¹), cool (temperature = 12.9–22.5 °C), and near-neutral (pH = 6.62–7.45), whilst the Dilwyn Aquifer groundwater is fresher (electrical conductivity = 505–1473 μS cm⁻¹), warmer (temperature = 42.5–48.5 °C), and more alkaline (pH = 7.43–9.35). Carbonate dissolution, evapotranspiration and cation exchange control the composition of the groundwaters. Comparing the chemical and isotopic composition of the groundwaters collected before, during and after injection shows no statistically significant changes; even if they were statistically significant, they are mostly not consistent with those expected if CO₂ addition had taken place. The monitoring program reveals no impact on the groundwater resources attributable to the C storage demonstration project.     

地热对井运行系统中回灌井堵塞原因浅析及预防措施

人工回灌做为提高地热资源利用率、防止地面沉降、减少尾水排放、实现地热资源的可持续利用的最有效手段,已在地学界达成共识。基岩岩溶裂隙型热储对井回灌取得的良好效果使人们看到了回灌技术的广阔应用前景,但有些热储尤其是孔隙型热储回灌量的衰减问题一直未能得到彻底解决,各种因素引起的堵塞是主要原因。本文根据天津市历年的回灌试验,就造成地热回灌堵塞的多种原因进行了分析,并提出了可能的解决办法。     

Carbon isotope fractionation in phospholipid fatty acid biomarkers of bacteria and fungi native to an acid mine drainage lake

This study identifies isotope signatures associated with autotrophic and heterotrophic microbial communities that may provide a means to determine carbon cycling relationships in situ for acid mine drainage (AMD) sites. Stable carbon isotope ratios (δ¹³C) of carbon sources, bulk cells, and membrane phospholipids (PLFA) were measured for autotrophic and heterotrophic microbial enrichment cultures from a mine tailings impoundment in northern Ontario, Canada, and for pure strains of the sulfur oxidizing bacteria Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans. The autotrophic enrichments had indistinguishable PLFA distributions from the pure cultures, and the PLFA cyc-C_19:0 was determined to be a unique biomarker in this system for these sulfur oxidizing bacteria. The PLFA distributions produced by the heterotrophic enrichments were distinct from the autotrophic distributions and the C_18:2 PLFA was identified as a biomarker for these heterotrophic enrichments. Genetic analysis (16S, 18S rRNA) of the heterotrophic cultures indicated that these communities were primarily composed of Acremonium fungi.Stable carbon isotope analysis revealed that bulk cellular material in all autotrophic cultures was depleted in δ¹³C by 5.6–10.9‰ relative to their atmospheric CO₂ derived carbon source, suggesting that inorganic carbon fixation in these cultures is carbon limited. Individual PLFA from these autotrophs were further depleted by 8.2–14.6‰ compared to the bulk cell δ¹³C, which are among the largest biosynthetic isotope fractionation factors between bulk cell and PLFA reported in the literature. In contrast, the heterotrophic bulk cells were not significantly fractionated in δ¹³C relative to their carbon source and heterotrophic PLFA ranged from 3‰ enriched to 4‰ depleted relative to the isotopic composition of their total biomass. These distinct PLFA biomarkers and isotopic fractionations associated with autotrophic and heterotrophic activity in this laboratory study provide potential biomarkers for delineating autotrophic and heterotrophic carbon cycling in AMD environments.     

Early diagenesis of fatty acids in lacustrine sediments—III. Changes in fatty acid composition in the sediments from a brackish water lake

A 3-m sediment core taken from Lake Suigetsu, in which a shift from fresh to brackish water occurred about three hundred years ago, has been examined for variation with depth of organic carbon and fatty acids. From the difference in total amounts of sulphur between sediments under fresh and brackish water environments, the surface sediments above approximately 35 cm depth were deduced to be accumulated under a brackish water environment. The total contents of organic carbon and fatty acids, and percentage composition of fatty acids gave discontinuous profiles above and below the 35–40 cm sediment layer. At a depth of 12.5 cm, the distribution in chain length of the fatty acids changed from a unimodal (the predominance of C₁₂-C₁₈ over C₂₀-C₃₄) to a bimodal pattern, which was mirrored by the composition diversity index (CDI).Although the fatty acids in the surface sediments (0–40 cm) from Lake Suigetsu seemed to suffer milder degradation through microbial activity than those in a core (0–150 cm) from Lake Suwa, a freshwater eutrophic lake, both lacustrine sediments showed similar trends in the alteration of fatty acid composition with depth.     

Vertical distribution, stability and evolution of groundwater composition in granite suitable for storage of spent nuclear fuel

Granite with extremely low permeability has been selected to host a repository of spent nuclear fuel in the Czech Republic. Three boreholes were drilled in a test site of the Podlesi granite stock in the Krusne hory Mts. The holes were located 10 m apart. After hydraulic tests, four sections in one of the boreholes were separated by packers at depth of 69-111, 111-161, 161-220 and 220-300 m. Samples of groundwater from each section were periodically collected for chemical and isotopic analysis. Groundwater from fractures in the granite stock does not belong to a single and uniform groundwater body in spite of that the granite is chemically and mineralogically homogeneous. There are three water bodies, which are only partly hydraulically connected. They are： （1） The groundwater in the oxidation zone to a depth of about 111 m. （2） The groundwater of the zone of hydrolysis of alumosilicates from 111 to 220 m. （3） The groundwater of the zone of hydrolysis of alumosilicates below the depth of 220 m from a different fracture system than the water from the above sections. The total dissolved solids of water increase with depth. The Ca-SO4 component predominates in the near surface water body while Na-HCO3 component predominates in the two deeper water bodies. Water from the oxidation zone contains higher concentrations of iron and other trace metals. The chemical composition of water in the three water bodies changed during the 14 months of sampling. No steady state was reached during this time. The changes displayed systematic trends. The ratio Ca/Na increased and the ratio HCO3/SO4 decreased with time in the shallow water body. In contrast, the ratio CafNa decreased and HCO3/SO4 fluctuated without an obvious trend in the deeper water bodies. An unusually high concentration of dissolved organic carbon （DOC） was found in the lowest section of the test borehole. The concentration of DOC was 150 mg/L at the beginning of sampling. The isotopic composition was δ^13C=-27.6 ‰. The concentration of DOC dropped both towards the surface and with time.     

全氟羧酸化合物在氟化工园区土壤-植物中的分布及组成特征

本次研究分析了典型氟化学工业园区周边不同植物及其根际和非根际土壤中全氟羧酸(perfluorinated carboxylic acid, PFCA)的含量、组成及分布特征。结果显示, PFCA在根际土壤和非根际土壤的浓度范围分别为9.6～160 ng/g和7.2～300 ng/g。根际土壤(rhizospheric soil, RS)和非根际土壤(non-rhizopsheric soil, NRS)中PFCA的浓度比值(c_ratio=c_RS/c_NRS)显示, PFCA并未呈现出根际富集效应。PFCA在植物地上部和根部的浓度范围分别为6.0～630 ng/g和6.1～570 ng/g。全氟辛酸(perfluorooctanoic acid, PFOA)是土壤和植物组织中最主要的全氟羧酸化合物,其浓度在根际土、非根际土、植物根部和地上部分别占总PFCA的(53±18)%、(51±22)%、(80±6.7)%和(34±18)%。短链(C₄～C₈)的PFCA,包括全氟丁酸(perf...     

Evolving fluid composition during prograde metamorphism in subduction zones: A new approach using carbonate-bearing assemblages in the pelitic system

The changing XCO₂ in fluids during the progressive metamorphism in Sanbagawa belt of the Cretaceous subduction zone, Japan, was estimated by a newly proposed method. The subduction zone meta-sediments are characterized commonly by four-phase assemblages in the CaO–NaAlO₂–KAlO₂–Al₂O₃ system with excess quartz and a CO₂–H₂O binary fluid phase. Using the common assemblage of calcite–albite–muscovite–clinozoisite, XCO₂ of the fluid was estimated to be from about 0.0001–0.0005 (the lowest grade chlorite zone), through 0.004–0.01 (garnet zone), 0.01–0.05 (albite–biotite zone) to 0.06–0.2 (oligoclase–biotite zone).The paragenetic relationship of meta-sediments from the subduction zones was compared in a wide P–T range to cover the stability fields of aragonite and jadeite. As a result, an excellent P–T–XCO₂ relationship was delineated to serve as a quantitative monitor for the evolving fluid composition during the progressive metamorphism in subduction zones.     

人工回灌过程中富里酸和Cu(Ⅱ)对多孔介质悬浮物堵塞的影响

地下水人工回灌是解决地下水超采问题的有效措施,悬浮颗粒物堵塞是影响回灌进行的技术瓶颈。目前多数研究聚焦在悬浮物堵塞方面,然而地表回灌水中重金属离子以及腐殖质对多孔介质物理堵塞的影响缺乏研究。本研究采用室内渗流砂柱试验研究富里酸、Cu(Ⅱ)以及两者共存对多孔介质悬浮物堵塞的影响,分别采用高岭土（SS组）、富里酸+高岭土（SS+FA组）、富里酸+Cu(Ⅱ)+高岭土（SS+FA+Cu组）配置模拟回灌用水。研究结果表明：（1）回灌结束时,SS组、SS+FA组、SS+FA+Cu组多孔介质整体相对渗透系数K’分别降至0.233,0.095,0.182。SS组和SS+FA+Cu组在中上层（0~7.50 cm）相对渗透系数K’均降至0.28以下,而在底层（7.50~10.50 cm）相对渗透系数K’仅降至0.45左右,说明2组多孔介质中上层重度堵塞（0相似文献   

A study on the impact of weathering in groundwater chemistry of a hard rock aquifer

Hydrogeochemistry of groundwater in hard rock terrain are mainly governed by lithology and land use practices. A study area near Madurai region of central Tamil Nadu was selected with various litho-units and a hard rock sedimentary contact with an unconformity. Land use practices in these regions are also varied with lithology. The study was conducted by collecting 54 groundwater samples spatially covering the major litho-units. Collected samples were analyzed for electrical conductivity, pH, total dissolved solids (TDS), temperature, Ca, Mg, Na, K, Cl, HCO₃, NO₃, H₄SiO₄, PO₄, and SO₄. The results of the samples analyzed found to vary spatially. Dominance of ion shows that the alkalies are predominant and HCO₃ is the dominant anion. Piper facies show that the samples are alkali-carbonate type indicating the predominance of weathering. Most of the parameters exceed the drinking water permissible limit. Standard plots and statistical analysis also indicate weathering as the major process governing the hydrogeochemistry of the groundwater in the region. Relative mobility of cations indicates that the rate of liberation of alkalies from the lithology is more prominent.     

山西柳林泉域地下水化学信息的因子—克立格分析

本文尝试将因子分析与克立格法相结合,用以分析柳林泉域地下水化学资料,获取到地下水成因,循环深度等方面的信息。研究表明,因子－克立格法是一种有效,实用的研究区域水文地质问题的分析方法。     

台兰河山前地下储水构造及地下水库可行性研究

根据台兰河流域冲洪积扇地形地貌特征、储水构造以及水资源特点,讨论了建设地下水库的可行性,并以正在试验的台兰河地下水库示范工程为例,分析了"横坎尔井"式地下水库的特点是库容大、自压滴灌、节约能源、"引渗回补"具有强大调蓄功能进行可行性研究,为干旱区水资源的合理开发利用提供新的思路。     

Variations in the carbon isotope composition and production yield of various pyrolysis products under open and closed system conditions

Production rates and carbon isotopic compositions of various pyrolysis products were investigated for three sediments from the Williston Basin under open and closed pyrolysis conditions in the temperature range of 300–600°C.Both parameters do not show any significant differences for kerogens and carbon dioxides with the analytical procedure. Contrary to open system pyrolysis, however, decreasing yields of pyrolysates and higher amounts of gaseous hydrocarbons (C_2–4 compounds) at temperatures of 500 and 600°C, point to their decomposition to give ultimately methane.Moreover, these pyrolysis products display distinct carbon isotopic variations under open and closed pyrolysis conditions. They are due to a kinetic isotope effect, i.e. the preferential cleavage of ¹²C-¹²C over ¹³C-¹²C bonds, but the extent of the shift in isotopic composition seems to depend primarily on the reservoir size and the type of source material.     

The composition and role of the fluid in migmatites: a fluid inclusion study of the Front Range rocks

Monophase negative-crystal shaped CO₂ inclusions occurring isolated, in small clusters, or in well-healed intragranular fractures are common in the leucosome quartz of the 1700m.y.-old migmatites from the east-central Colorado Front Range. They are, however, quite rare in the mafic selvage and paleosome (host rock) quartz. The mode of occurrence suggests that these are the earliest inclusions to form. In addition to the difference in abundance of the inclusions, there is a difference in CO₂-density distribution between migmatitic zones. The temperatures of homogenization for the leucosome inclusions range and +l°C from –67° C to +20° C with two maxima (at –21° C) while those for the paleosome and selvage inclusions are –37° C to +20° C with a single maximum at + 5° C. These differences between the migmatitic zones which occur on the scale of a few centimeters suggest that the formation of these inclusions was related to the migmatization process. The densities corresponding to the Th maxima are appropriate for the P-T conditions for migmatization estimated from the mineral geobarometer/geothermometer. These inclusions must contain nearly pure CO₂, as their final melting temperatures (–56.5° to –57.2° C) are very close to that of the triple point of CO₂. Their composition also was confirmed by Raman spectroscopic analyses.It has been proposed by other workers that CO₂ fluid in the inclusions could form from an H₂O-CO₂ fluid when H₂O is partitioned into the silicate melt. Such partitioning should result in some early H₂O-rich inclusions: H₂O must be released as the melt crystallizes. As found in migmatites from other areas, most aqueous inclusions in the Front Range rocks are obviously much younger than the early CO₂ ones. However, early H₂O-rich fluid may still be preserved, at least in three ways: (A) in rare, isolated or clustered inclusions within quartz inclusions in feldspar; (B) as inclusions in microcline porphyroblasts; (C) in hydrous alteration products of feldspar. (A) contain dilute fluids, 1 to 6 wt% NaCl equivalent. The densities of (A) as well as those of the early CO₂ inclusions found in the quartz inclusions in feldspar are appropriate for the range of P — T conditions estimated for migmatization. These early inclusions must have been preserved because of protected environment. Inclusions (B), found to contain H₂O (and possibly CO₂) by infrared analyses, must be early because they are absent from recrystallized grains. (B) and (C) are much more common in the leucosome than in the other zones suggesting that they are related to migmatization process. The concentration of early CO₂ inclusions in the leucosome is consistent with the model of migmatization in which fluid concentration in the leucosome was a cause of melting.