Applied Geochemistry (v.20, #10)

Groundwater fluxes into a submerged sinkhole area, Central Italy, using radon and water chemistry by P. Tuccimei; R. Salvati; G. Capelli; M.C. Delitala; P. Primavera (1831-1847).
The groundwater contribution into Green Lake and Black Lake (Vescovo Lakes Group), two cover collapse sinkholes in Pontina Plain (Central Italy), was estimated using water chemistry and a 222Rn budget. These data can constrain the interactions between sinkholes and deep seated fluid circulation, with a special focus on the possibility of the bedrock karst aquifer feeding the lake. The Rn budget accounted for all quantifiable surface and subsurface input and output fluxes including the flux across the sediment–water interface. The total value of groundwater discharge into Green Lake and Black Lake (∼540 ± 160 L s−1) obtained from the Rn budget is lower than, but comparable with historical data on the springs group discharge estimated in the same period of the year (800 ± 90 L s−1). Besides being an indirect test for the reliability of the Rn-budget “tool”, it confirms that both Green and Black Lake are effectively springs and not simply “water filled” sinkholes. New data on the water chemistry and the groundwater fluxes into the sinkhole area of Vescovo Lakes allows the assessment of the mechanism responsible for sinkhole formation in Pontina Plain and suggests the necessity of monitoring the changes of physical and chemical parameters of groundwater below the plain in order to mitigate the associated risk.

Preliminary geochemical evidence of groundwater contamination in coral islands of Xi-Sha, South China Sea by Zhouqing Xie; Liguang Sun; Pengfei Zhang; Sanping Zhao; Xuebin Yin; Xiaodong Liu; Bangbo Cheng (1848-1856).
Geochemical data on dissolved major, minor and trace constituents in groundwater samples from Xi-Sha coral islands (Paratas Islands) reveal the main processes responsible for their geochemical evolution. Multivariate statistical analysis indicates four sources of solutes: (1) seawater intrusion due to limited groundwater recharge; (2) leaching of heavy metals from imported granite soil; (3) leaching of toxic elements such as As due to guano-soil erosion and historical phosphatic guano mining; and (4) local and regional contamination characterized by high loadings of Cu, Ag and Hg. Although process 1 dominates the geochemical characteristics of the groundwater, process 4 indicates the significant role of anthropogenic impact by local (e.g., Cu) and regional (e.g., Hg) sources. Such contamination in groundwater will potentially impose adverse effects on the fragile ecosystem of the coral islands. It is necessary to monitor microorganisms associated with human feces in the nearshore water column as well as nutrient levels in coastal waters in order to further assess the impact of human activities on the ecosystem of these islands.

Statistical characterization of a large geochemical database and effect of sample size by Chaosheng Zhang; Frank T. Manheim; John Hinde; Jeffrey N. Grossman (1857-1874).
The authors investigated statistical distributions for concentrations of chemical elements from the National Geochemical Survey (NGS) database of the U.S. Geological Survey. At the time of this study, the NGS data set encompasses 48,544 stream sediment and soil samples from the conterminous United States analyzed by ICP-AES following a 4-acid near-total digestion. This report includes 27 elements: Al, Ca, Fe, K, Mg, Na, P, Ti, Ba, Ce, Co, Cr, Cu, Ga, La, Li, Mn, Nb, Nd, Ni, Pb, Sc, Sr, Th, V, Y and Zn. The goal and challenge for the statistical overview was to delineate chemical distributions in a complex, heterogeneous data set spanning a large geographic range (the conterminous United States), and many different geological provinces and rock types. After declustering to create a uniform spatial sample distribution with 16,511 samples, histograms and quantile–quantile (Q–Q) plots were employed to delineate subpopulations that have coherent chemical and mineral affinities.Probability groupings are discerned by changes in slope (kinks) on the plots. Major rock-forming elements, e.g., Al, Ca, K and Na, tend to display linear segments on normal Q–Q plots. These segments can commonly be linked to petrologic or mineralogical associations. For example, linear segments on K and Na plots reflect dilution of clay minerals by quartz sand (low in K and Na). Minor and trace element relationships are best displayed on lognormal Q–Q plots. These sensitively reflect discrete relationships in subpopulations within the wide range of the data. For example, small but distinctly log-linear subpopulations for Pb, Cu, Zn and Ag are interpreted to represent ore-grade enrichment of naturally occurring minerals such as sulfides.None of the 27 chemical elements could pass the test for either normal or lognormal distribution on the declustered data set. Part of the reasons relate to the presence of mixtures of subpopulations and outliers. Random samples of the data set with successively smaller numbers of data points showed that few elements passed standard statistical tests for normality or log-normality until sample size decreased to a few hundred data points. Large sample size enhances the power of statistical tests, and leads to rejection of most statistical hypotheses for real data sets. For large sample sizes (e.g., n  > 1000), graphical methods such as histogram, stem-and-leaf, and probability plots are recommended for rough judgement of probability distribution if needed.

Geochemical characteristics of Tertiary saline lacustrine oils in the Western Qaidam Basin, northwest China by Zhu Yangming; Weng Huanxin; Su Aiguo; Liang Digang; Peng Dehua (1875-1889).
Based on the systematic analyses of light hydrocarbon, saturate, aromatic fractions and C isotopes of over 40 oil samples along with related Tertiary source rocks collected from the western Qaidam basin, the geochemical characteristics of the Tertiary saline lacustrine oils in this region was investigated. The oils are characterized by bimodal n-alkane distributions with odd-to-even (C11–C17) and even-to-odd (C18–C28) predominance, low Pr/Ph (mostly lower than 0.6), high concentration of gammacerane, C35 hopane and methylated MTTCs, reflecting the high salinity and anoxic setting typical of a saline lacustrine depositional environment. Mango’s K 1 values in the saline oils are highly variable (0.99–1.63), and could be associated with the facies-dependent parameters such as Pr/Ph and gammacerane indexes. Compared with other Tertiary oils, the studied Tertiary saline oils are marked by enhanced C28 sterane abundance (30% or more of C27–C29 homologues), possibly derived from halophilic algae. It is noted that the geochemical parameters of the oils in various oilfields exhibit regular spatial changes, which are consistent with the depositional phase variations of the source rocks. The oils have uncommon heavy C isotopic ratios (−24‰ to −26‰) and a flat shape of the individual n-alkane isotope profile, and show isotopic characteristics similar to marine organic matter. The appearance of oleanane and high 24/(24 + 27)-norcholestane ratios (0.57–0.87) in the saline oils and source rocks confirm a Tertiary organic source.

Impact of irrigation with As rich groundwater on soil and crops: A geochemical case study in West Bengal Delta Plain, India by S. Norra; Z.A. Berner; P. Agarwala; F. Wagner; D. Chandrasekharam; D. Stüben (1890-1906).
The distribution of As was explored in soils and crops in order to investigate the influence of irrigation with As rich groundwater on the soil–plant system, and to determine its impact on the environment and human health. The study was carried out in an intensively cultivated agricultural area of the Bengal Delta Plain, West Bengal, India. Soils, plants, and irrigation water from adjacent rice and wheat fields were analysed for As and other elements. Irrigation water has concentrations of up to 780 μg L−1 As in the study area. Rice and wheat grains are not contaminated by As (about 0.3 and 0.7 mg kg−1, respectively), but concentrations in rice roots were found to be 169–178 mg kg−1 As, which is more than 20 times higher than value of 7.7 mg kg−1 measured at the uncontaminated reference site. This high content is due to an Fe-rich plaque which coats the rice roots. A significant increase of As concentration was registered also in the stems of the rice plants irrigated with As rich groundwater (6.55–7.06, relative to 0.36 mg kg−1 As in the reference plant). Arsenic concentration in the uppermost soil layers of the rice paddy field (38 mg kg−1) was found to be roughly twice as high as in the soil of the less intensively watered wheat field (18 mg kg−1) and more than 5 times higher than in the soil of a rice paddy irrigated with uncontaminated water (7 mg kg−1). In both soil sections As contents decreased downwards to 11 mg kg−1 at 100–110 cm depth, approaching the background value of 5–10 mg kg−1 measured in an unaffected reference area. Sequential extraction experiments show that most of the mobile As in soils is bound to Fe-oxides. Though no tight correlation was found between Fe and As in the bulk soil samples, these experiments coupled with μ-synchrotron radiation XRF analysis of single soil particles from the rice paddy also indicates that additional to the mobile fraction a substantial part of As is immobilized in (chiefly Fe bearing) silicates. In rice soil some As was also found in the sulphide-bearing phase of the extraction.

Soil from an infiltration trench for highway runoff was leached in columns alternately with NaCl and de-ionised water to simulate the runoff of de-icing salt into the trench followed by snowmelt or rainwater. Simultaneously, two columns with the same soil were leached with de-ionised water throughout the experiment. In addition, the groundwater below the infiltration trench was sampled on some occasions. The column leachate and groundwater were split into two sub samples, one was filtered though a 0.45 μm filter; both were analysed for Pb, Cd, Zn, Fe and total organic carbon (TOC). The column experiment showed clearly that an extensive mobilisation of Pb occurred in low electrolyte water leaching following NaCl leaching. The high Pb concentration coincided with peaks in Fe and TOC concentrations and implied colloid-assisted transport. Conversely, Cd and Zn concentrations were raised in the NaCl leachate and a high correlation with Cl showed that Cl complexes are important for the mobilisation, although a pH effect and ionic exchange cannot be excluded. Only 0.15% and 0.06% of the total amount of Pb was leached from the columns leached with alternating NaCl and deionised water confirming the usual hypotheses about the high immobility of Pb in soils. However, on one occasion when the ionic strength and pH was the lowest measured the concentration of Pb in groundwater sampled from 2.5 m depth was 27 μg L−1 in the dissolved phase (<0.45 μm) and 77 μg L−1 in the particle phase (>0.45 μm). These Pb concentrations are almost 3 and 8 times above the Swedish limit for drinking water quality. Accordingly, in spite of the immobility of Pb the accumulation in roadside soils is so large that groundwater quality is threatened. In conclusion, the study suggests that roadside soils impacted by NaCl from de-icing operations contribute Pb to groundwater by colloid-assisted transport.

Net alkalinity and net acidity 1: Theoretical considerations by Carl S. Kirby; Charles A. Cravotta (1920-1940).
Net acidity and net alkalinity are widely used, poorly defined, and commonly misunderstood parameters for the characterization of mine drainage. The authors explain theoretical expressions of 3 types of alkalinity (caustic, phenolphthalein, and total) and acidity (mineral, CO2, and total). Except for rarely-invoked negative alkalinity, theoretically defined total alkalinity is closely analogous to measured alkalinity and presents few practical interpretation problems. Theoretically defined “CO2-acidity” is closely related to most standard titration methods with an endpoint pH of 8.3 used for determining acidity in mine drainage, but it is unfortunately named because CO2 is intentionally driven off during titration of mine-drainage samples. Using the proton condition/mass-action approach and employing graphs to illustrate speciation with changes in pH, the authors explore the concept of principal components and how to assign acidity contributions to aqueous species commonly present in mine drainage. Acidity is defined in mine drainage based on aqueous speciation at the sample pH and on the capacity of these species to undergo hydrolysis to pH 8.3. Application of this definition shows that the computed acidity in mg L−1 as CaCO3 (based on pH and analytical concentrations of dissolved FeII, FeIII, Mn, and Al in mg L−1): acidity calculated = 50 { 1000 ( 10 - pH ) + [ 2 ( Fe II ) + 3 ( Fe III ) ] / 56 + 2 ( Mn ) / 55 + 3 ( Al ) / 27 } underestimates contributions from HSO 4 - and H+, but overestimates the acidity due to Fe3+ and Al3+. However, these errors tend to approximately cancel each other.It is demonstrated that “net alkalinity” is a valid mathematical construction based on theoretical definitions of alkalinity and acidity. Further, it is shown that, for most mine-drainage solutions, a useful net alkalinity value can be derived from: (1) alkalinity and acidity values based on aqueous speciation, (2) measured alkalinity minus calculated acidity, or (3) taking the negative of the value obtained in a standard method “hot peroxide” acidity titration, provided that labs report negative values. The authors recommend the third approach; i.e., net alkalinity = −Hot Acidity.

Net alkalinity and net acidity 2: Practical considerations by Carl S. Kirby; Charles A. Cravotta (1941-1964).
The pH, alkalinity, and acidity of mine drainage and associated waters can be misinterpreted because of the chemical instability of samples and possible misunderstandings of standard analytical method results. Synthetic and field samples of mine drainage having various initial pH values and concentrations of dissolved metals and alkalinity were titrated by several methods, and the results were compared to alkalinity and acidity calculated based on dissolved solutes. The pH, alkalinity, and acidity were compared between fresh, unoxidized and aged, oxidized samples.Data for Pennsylvania coal mine drainage indicates that the pH of fresh samples was predominantly acidic (pH 2.5–4) or near neutral (pH 6–7); ≈ 25% of the samples had pH values between 5 and 6. Following oxidation, no samples had pH values between 5 and 6.The Standard Method Alkalinity titration is constrained to yield values >0. Most calculated and measured alkalinities for samples with positive alkalinities were in close agreement. However, for low-pH samples, the calculated alkalinity can be negative due to negative contributions by dissolved metals that may oxidize and hydrolyze.The Standard Method hot peroxide treatment titration for acidity determination (Hot Acidity) accurately indicates the potential for pH to decrease to acidic values after complete degassing of CO2 and oxidation of Fe and Mn, and it indicates either the excess alkalinity or that required for neutralization of the sample. The Hot Acidity directly measures net acidity (= −net alkalinity). Samples that had near-neutral pH after oxidation had negative Hot Acidity; samples that had pH < 6.3 after oxidation had positive Hot Acidity. Samples with similar pH values before oxidation had dissimilar Hot Acidities due to variations in their alkalinities and dissolved Fe, Mn, and Al concentrations. Hot Acidity was approximately equal to net acidity calculated based on initial pH and dissolved concentrations of Fe, Mn, and Al minus the initial alkalinity. Acidity calculated from the pH and dissolved metals concentrations, assuming equivalents of 2 per mole of Fe and Mn and 3 per mole of Al, was equivalent to that calculated based on complete aqueous speciation of FeII/FeIII. Despite changes in the pH, alkalinity, and metals concentrations, the Hot Acidities were comparable for fresh and most aged samples.A meaningful “net” acidity can be determined from a measured Hot Acidity or by calculation from the pH, alkalinity, and dissolved metals concentrations. The use of net alkalinity = (Alkalinitymeasured  − Hot Aciditymeasured) to design mine drainage treatment can lead to systems with insufficient Alkalinity to neutralize metal and H+ acidity and is not recommended. The use of net alkalinity = −Hot Acidity titration is recommended for the planning of mine drainage treatment. The use of net alkalinity = (Alkalinitymeasured  − Aciditycalculated) is recommended with some cautions.

Reconstructing seawater column 90Sr based upon 210Pb/226Ra disequilibrium dating of mollusk shells by M. Baskaran; Gi-Hoon Hong; Suk-Hyun Kim; William J. Wardle (1965-1973).
The shells of marine and fresh water mollusks can serve as effective archives in retrieving information on natural and anthropogenic environmental changes. The advantage of using bivalves is that they integrate water chemistry changes into their shells during their life span. Retrospective study of environmental changes and pollutants using bivalve shells requires precise determination of the time of incorporation into the abiotic environmental matrix (here after age) of the specimen. For the first time, a set of archived bivalve samples (for which date of the death/collection is known) has been analyzed to establish the ages of mollusk shells using the 210Pb–226Ra disequilibrium method. In addition, Sr and 90Sr were analysed. The ages obtained using the 210Pb/226Ra disequilibrium dating method agrees well with the calendar years calculated from the date of death/collection. The ages obtained can be utilized to reconstruct the 90Sr levels in the water column at sites where the mollusk shells were collected.
Keywords: Bivalves; 210Pb-dating; 210Pb/226Ra disequilibrium; 90Sr in seawater;

Problems related to the crystallization and deposition of heavy organic fractions during production, transportation and storage of crude oils can lead to considerable financial losses for the petroleum industry. The heavy organic fractions may include paraffins or waxes, resins, asphaltenes, and organometallic compounds that exist in crude oils in various quantities, states, and forms. The severity of the deposition problems varies widely and depends on factors such as the crude oil composition, operating conditions in the reservoir and production procedures. Problems associated with the solid deposits may be encountered anywhere in the production process from the reservoir to the refinery. In this paper, it is proposed to focus on production problems associated with certain fields in Tunisia. The problems manifested themselves through the accumulation of solid deposits in the storage tanks at a Tunisian terminal and originated from the mixtures of various crude oils transported to the terminal by pipeline. The principal analytical method for the characterization of the solids was high temperature gas chromatography following concentration of the wax fraction through a modification of the conventional acetone precipitation technique.
Keywords: Crude oils; Paraffins; Waxes; Tunisia; HTGC; Asphaltenes; Storage tanks; Solid deposits;