Reactive barriers: hydraulic performance and design enhancements

The remediation of contaminated ground water is a multibillion-dollar global industry. Permeable reactive barriers (PRBs) are one of the leading technologies being developed in the search for alternatives to the pump-and-treat method. Improving the hydraulic performance of these PRBs is an important part of maximizing their potential to the industry. Optimization of the hydraulic performance of a PRB can be defined in terms of finding the balance between capture, residence time, and PRB longevity that produces a minimum-cost acceptable design. Three-dimensional particle tracking was used to estimate capture zone and residence time distributions. Volumetric flow analysis was used for estimation of flow distribution across a PRB and in the identification of flow regimes that may affect the permeability or reactivity of portions of the PRB over time. Capture zone measurements extended below the base of partially penetrating PRBs and were measured upgradient from the portion of aquifer influenced by PRB emplacement. Hydraulic performance analysis of standard PRB designs confirmed previously presented research that identified the potential for significant variation in residence time and capture zone. These variations can result in the need to oversize the PRB to ensure that downgradient contaminant concentrations do not exceed imposed standards. The most useful PRB design enhancements for controlling residence time and capture variation were found to be customized downgradient gate faces, velocity equalization walls, deeper emplacement of the funnel than the gate, and careful manipulation of the hydraulic conductivity ratio between the gate and the aquifer.     

Full-Bayesian inversion of the Edwards Aquifer

The Bayesian inverse approach proposed by Woodbury and Ulrych (2000) is extended to estimate the transmissivity fields of highly heterogeneous aquifers for steady state ground water flow. Boundary conditions are Dirichlet and Neumann type, and sink and source terms are included. A first-order approximation of Taylor's series for the exponential terms introduced by sinks and sources or the Neumann condition in the governing equation is adopted. Such a treatment leads to a linear finite element formulation between hydraulic head and the logarithm of the transmissivity-denoted as ln(T)-perturbations. An updating procedure similar to that of Woodbury and Ulrych (2000) can be performed. This new algorithm is examined against a generic example. It is found that the linearized solution approximates the true solution with an R2 coefficient = 0.96 for an ln(T) variance of 9 for the test case. The addition of hydraulic head data is shown to improve the ln(T) estimates, in comparison to simply interpolating the sparse ln(T) data alone. The new Bayesian code is also employed to calibrate a high-resolution finite difference MODFLOW model of the Edwards Aquifer in southwest Texas. The posterior ln(T) field from this application yields better head fit when compared to the prior ln(T) field determined from upscaling and cokriging. We believe that traditional MODFLOW grids could be imported into the new Bayes code fairly seamlessly and thereby enhance existing calibration of many aquifers.     

Acid mine drainage biogeochemistry at Iron Mountain,California

The Richmond Mine at Iron Mountain, Shasta County, California, USA provides an excellent opportunity to study the chemical and biological controls on acid mine drainage (AMD) generation in situ, and to identify key factors controlling solution chemistry. Here we integrate four years of field-based geochemical data with 16S rRNA gene clone libraries and rRNA probe-based studies of microbial population structure, cultivation-based metabolic experiments, arsenopyrite surface colonization experiments, and results of intermediate sulfur species kinetics experiments to describe the Richmond Mine AMD system. Extremely acidic effluent (pH between 0.5 and 0.9) resulting from oxidation of approximately 1 × 10⁵ to 2 × 10⁵ moles pyrite/day contains up to 24 g/1 Fe, several g/1 Zn and hundreds of mg/l Cu. Geochemical conditions change markedly over time, and are reflected in changes in microbial populations. Molecular analyses of 232 small subunit ribosomal RNA (16S rRNA) gene sequences from six sites during a sampling time when lower temperature (<32°C), higher pH (>0.8) conditions predominated show the dominance of Fe-oxidizing prokaryotes such as Ferroplasma and Leptospirillum in the primary drainage communities. Leptospirillum group III accounts for the majority of Leptospirillum sequences, which we attribute to anomalous physical and geochemical regimes at that time. A couple of sites peripheral to the main drainage, "Red Pool" and a pyrite "Slump," were even higher in pH (>1) and the community compositions reflected this change in geochemical conditions. Several novel lineages were identified within the archaeal Thermoplasmatales order associated with the pyrite slump, and the Red Pool (pH 1.4) contained the only population of Acidithiobacillus. Relatively small populations of Sulfobacillus spp. and Acidithiobacillus caldus may metabolize elemental sulfur as an intermediate species in the oxidation of pyritic sulfide to sulfate. Experiments show that elemental sulfur which forms on pyrite surfaces is resistant to most oxidants; its solublization by unattached cells may indicate involvement of a microbially derived electron shuttle. The detachment of thiosulfate (S₂O₃^2-) as a leaving group in pyrite oxidation should result in the formation and persistence of tetrathionate in low pH ferric iron-rich AMD solutions. However, tetrathionate is not observed. Although a S₂O₃^2--like species may form as a surface-bound intermediate, data suggest that Fe³⁺ oxidizes the majority of sulfur to sulfate on the surface of pyrite. This may explain why microorganisms that can utilize intermediate sulfur species are scarce compared to Fe-oxidizing taxa at the Richmond Mine site.

     

The viviparous blenny (Zoarces viviparus) as a bioindicator of contaminant exposure: application of biomarkers of apoptosis and DNA damage

The viviparous blenny (Zoarces viviparus), also known as eelpout, is considered a suitable biomonitor for use in European estuarine and coastal waters. We have previously shown that Z. viviparus from the industrialised Tyne estuary (UK) display certain histopathologies (e.g., ovotestis and hepatic nuclear and cellular pleomorphism), which are associated with contaminant exposure [Mar. Environ. Res. 55 (2003) 137]. Furthermore, the prevalence of these pathologies was higher than in fish collected from a less contaminated reference site (the Alde estuary, UK). Here, tissue samples were collected from Z. viviparus from the Tyne and Alde estuaries (in the spring and autumn) and analysed for DNA adducts using the (32)P-postlabelling assay and for histopathology. Z. viviparus caught from the Tyne during the spring (56.4+/-18.5 adducts per 10(8) nucleotides) and autumn (63.1+/-7.5 adducts per 10(8) nucleotides) exhibited patterns of DNA adducts which indicated exposure to a complex mixture of genotoxins. In contrast, levels of DNA adducts in Z. viviparus from Alde estuary were significantly lower during both sampling periods. Histopathological changes to the gonads included intersex (ovotestis) and germ cell apoptosis (detected via the TUNEL assay) in male fish captured from the Tyne estuary. Further studies on the use of germ cell apoptotic rate at different estuarine sites are required if it is to be used as a reproductive biomarker of contaminant exposure in male fish.     

The beach: for enthusiasts of sun,surf and unusual geology,this is the place

The Carpinteria State Beach is a little known public park in Carpinteria, near Ventura, California, USA. Miocene‐age conglomerates and sandstone bluffs along the Pacific Ocean beachfront have featured continual natural oil seeps since the Pleistocene epoch. While not as famous as the La Brea Tar Pits of downtown Los Angeles, the park is the only public beach in North America where such a geological phenomenon is readily seen. Long used by the Chumash Indians for the asphaltum used to waterproof their seagoing canoes, asphaltum came into general use in the late nineteenth century. The beach is the former site of an industrial plant, devoted to removing and processing the asphaltum to yield many commercial products. Before it became a state park it served as a travel camp and a camp for World War II GIs suffering from battle fatigue.     

Photometric correction of Mercury's global color mosaic

During the third flyby of Mercury by the MESSENGER spacecraft, a dedicated disk-integrated photometric sequence was acquired with the wide-angle multispectral camera to observe Mercury's global photometric behavior in 11 spectral filters over as broad a range of phase angle as possible within the geometric constraints of the flyby. Extraction of disk-integrated measurements from images acquired during this sequence required careful accounting for scattered light and residual background effects. The photometric model fit to these measurements is shown to fit observed radiances at phase angles below 110°, possibly except where both solar incidence and emission angles are high (>70°). The complexity of the scattered light at wavelengths greater than 828 nm contributes to a less accurate photometric correction at these wavelengths. The model is used to correct the global imaging data set acquired at a variety of geometries to a common geometry of incidence angle=30°, emission angle=0°, and phase angle=30°, yielding a relatively seamless mosaic. The results here will be used to correct image mosaics of Mercury acquired in orbit.     

The global distribution of pyroclastic deposits on Mercury: The view from MESSENGER flybys 1–3

We present a global survey of candidate pyroclastic deposits on Mercury, derived from images obtained during MESSENGER flybys 1–3 that provided near-global coverage at resolutions between 5 and 0.5 km/pixel. Thirty-five deposits were identified and characterized and are located principally on the floors of craters, along rims of craters, and along the edge of the Caloris basin. Deposits are commonly centered on rimless, often irregularly shaped pits, mostly between 5 and 45 km in diameter. The deposits identified are generally similar in morphology and absolute reflectance to lunar pyroclastic deposits. Spectrally the deposits appear brighter and redder than background Mercury terrain. On the basis of the available coverage, the candidate pyroclastic deposits appear to be essentially globally distributed. The diameters of the deposits, when mapped to lunar gravity conditions, are larger than their lunar counterparts, implying that more abundant volatiles were present during the typical eruptive process than on the Moon. These observations indicate that if these deposits resulted from hawaiian-style eruptions, the volatile contents required would be between ～1600 and 16,000 ppm CO or an equivalent value of H₂O, CO₂, SO₂, or H₂S (for a more oxidizing interior), or N₂, S₂, CS₂, S₂Cl, Cl, Cl₂, or COS (for a more reducing interior). These abundances are much greater than those predicted by existing models for Mercury's formation. An apparent lack of small deposits, compared with the Moon, may be due to resolution effects, a topic that can be further assessed during the orbital phase of the MESSENGER mission. These results provide a framework within which orbital observations by MESSENGER and the future BepiColombo mission can be analyzed.     

新疆东天山图拉尔根大型铜镍矿床硫化物珠滴构造的特征及其对通道式成矿的指示

东天山图拉尔根岩浆铜镍硫化物矿床中产出一种不常见的硫化物珠滴状构造。这些硫化物珠滴粒度在5~20mm左右,是由磁黄铁矿、镍黄铁矿、黄铜矿等硫化物矿物组成的斑杂状硫化物集合体。野外观察发现硫化物珠滴具有各种几何形态,产出在稀疏浸染状硫化物和无矿化的辉石岩之间的部位。对图拉尔根杂岩体中发育的24个硫化物珠滴的统计结果显示,平缓厚层状矿化部位的硫化物珠滴呈水平方向拉长,陡倾薄层状矿化部位的硫化物珠滴呈陡倾拉长,珠滴的拉长方向和矿体的延伸方向一致。这表明在含矿母岩浆上升就位到中上地壳的过程中,硫化物珠滴受到熔浆流动的控制,因而其形态可以很好地指示通道式成矿硫化物熔体运动的方向。 硫化物珠滴的矿相学和电子探针数据表明其具有向地性特征,即磁黄铁矿和镍黄铁矿先结晶,沉淀在下部; 珠滴上部为后结晶的黄铜矿和其它富铜硫化物。这种元素分布可能对贯入块状硫化物矿石同样适用。碲化物和铋化物在硫化物珠滴中的含量明显高于其在早结晶的浸染状硫化物中的含量,表明富Te和Bi等元素及挥发份的熔体是在岩浆演化后期开始富集结晶的。     

Lessons from co-impacts assessment under the Mitigation Action Plans and Scenarios (MAPS) Programme

The MAPS Programme has been active in Brazil, Chile, Colombia and Peru in supporting the development of an evidence base to inform the processes involved in climate mitigation policy-making. The programme combines detailed quantitative analysis with an extensive stakeholder engagement process to provide policy and decision makers with the information required for long-term climate mitigation planning.

In recognition of the critical need to consider the developmental context and agenda in climate policy-making, the projects undertaken in these countries have experimented with various types of assessments of developmental impacts at both the macro and micro levels. These impacts have been collectively termed co-impacts to reflect the fact that these may be either positive or negative. In this article the value and challenges associated with co-impacts work for climate mitigation policy are considered. The value of including co-impacts analysis in the MAPS processes included increased stakeholder buy-in, making the case for mitigation action, informing INDCs and the prioritization of particular mitigation actions. Challenges include those associated with obtaining locally relevant data, the selection and operation of appropriate macro-economic models and analytical approaches and working with multidisciplinary teams.

The article concludes by making some suggestions to optimize co-impacts work, through reference to other bodies of literature. The authors highlight that this article is situated within a dominant approach to climate mitigation policy work in developing countries, which implicitly places the non-climate benefits of any action as secondary to the primary benefit of climate change mitigation and constructs an artificial separation of policy formulation and implementation. Practitioners are encouraged to reflect on the implications of these considerations in future efforts.

Policy relevance

One of the primary challenges to advancing climate mitigation policy in developing countries is that of perceived relevance: near-term development priorities are overwhelming. Identifying, understanding and engaging with the co-impacts of mitigation actions has emerged as one way of addressing this challenge. Although still at an experimental phase, experience with co-impacts analysis in the MAPS countries provides some useful lessons in how to develop this area of work.