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A plume-scale mass balance is developed to assess the natural attenuation (NA) of dissolved organic contaminants in fractured, dual-porosity aquifers. This methodology can be used to evaluate contaminant distribution within the aquifer, plume source term, contaminant biodegradation and plume status. The approach is illustrated for a site on the UK Upper Chalk aquifer impacted by petroleum fuel containing methyl tert-butyl ether (MTBE) and tert-amyl methyl ether (TAME). Variability in site investigation data and uncertainty in the mass balance were assessed using probabilistic analysis. The analysis shows that benzene, toluene, m/p-xylene and o-xylene (BTEX) compounds are biodegraded primarily by denitrification and sulfate reduction in the aquifer, with an equivalent plume-scale first-order biodegradation rate of 0.49 a−1. Other biodegradation processes are less important. Sorption contributes to hydrocarbon attenuation in the aquifer but is less important for MTBE and TAME. Uncertainty in the plume source term and site hydrogeological parameters had the greatest effect on the mass balance. The probabilistic analysis enabled the most likely long-term composition of the plume source term to be deduced and provided a site-specific estimate of contaminant mass flux for the prediction of plume development. The mass balance methodology provides a novel approach to improve NA assessments for petroleum hydrocarbons and other organic contaminants in these aquifer settings. Supplementary material: Plume organic chemistry, aquifer hydraulic conductivity and probability distribution functions used for mass balance inputs are available at https://doi.org/10.6084/m9.figshare.c.7016429 Thematic collection: This article is part of the Monitoring the aquifers collection available at: https://www.lyellcollection.org/topic/collections/monitoring-the-aquifers [ABSTRACT FROM AUTHOR]

Stable isotope ratios of sulfur ([[delta].sup.34]5) and oxygen ([[delta].sup.18]O) in marine sulfate respond to changes in fluxes and processes in the global sulfur cycle. The two isotope systems respond on different time scales to different factors affecting the global sulfur cycle. Sulfur isotopes respond primarily to the relative fluxes of weathering-derived sulfate to the oceans versus the net flux of sulfur exported from the oceans as pyrite in marine sediments. At the present day, this response is relatively slow (~20 Ma) because of the large size of the marine sulfate reservoir; ancient oceans had lower sulfate concentrations and thus sulfate residence times may have been shorter. The [[delta].sup.34]S of marine sulfate is also sensitive to the development of a significant reservoir of [H.sub.2]S in ancient stratified oceans. Sulfate--oxygen isotopes respond primarily to changes in the cycling of sulfur in the oceans and marine sediments. Sulfur isproportionation, oxic and anaerobic sulfide oxidation all impart different [[delta].sup.18]O signatures to marine sulfate; the relative importance of these different processes is in turn controlled by the distribution of redox conditions and microbial ecology of sea-floor sediments. The mutual interpretation of changes in marine sulfate [[delta].sup.34]S and [[delta].sup.18]O can thus give rather precise information on the nature of changes in global sulfur cycling. Recently, records of isotope compositions of ancient marine sulfate have become available through the analysis of carbonate-associated sulfate (CAS) in limestones and marine biogenic barite, both of which provide far more continuous records than previous data based primarily on marine evaporite sulfate minerals. We review a number of case studies which use sulfur or combined sulfur and oxygen isotopic records derived from CAS and biogenic barite. Proterozoic CAS-sulfur isotope datasets often show marked variations over very small stratigraphic intervals (e.g. 20%[omicron] over 300 m). When examined in conjunction with estimates of deposition rates, they are used to infer a new evolutionary curve of marine sulfate concentrations and therefore a protracted oxidation of the Earth's biosphere. Through the retaceous-Tertiary interval, the marine sulfate-sulfur record is characterised by significant periods of relative stability punctuated by phases of more rapid change (limited to 7%[omicron] variation over the last 130 Ma). The Carboniferous was characterized essentially by a gradual change of 9%[omicron] over 60 Ma. By contrast, at the Permian-Triassic boundary, extreme changes occur over very short geological time scales (14%[omicron] over Keywords: marine sulfate; global geochemical cycles; sulfur isotopes; oxygen isotopes

The dynamics of sulfur adsorption in forest soils and the topsoil sulfur concentrations were analyzed from selected sites in Czech Republic by utilizing stable isotopes of delta34S. High concentrations of delta34S were detected from forest topsoil and mineral soils indicating conditions that are suitable for bacterial sulfate reduction. Furthermore, the concentration of sulfur isotopes in forests moss varied significantly with the delta34S concentrations of forest topsoils.

The Harrogate mineral waters exhibit a wide range of mineralization, with the most concentrated reaching half-seawater salinity and containing abundant sulphide. Comparison of new and historical chemical data shows that the major element composition of the main wells has remained essentially constant for over 200 years. The most saline wells have similar chemistry and a number of species ([Na.sup.+], [K.sup.+], [Li.sup.+], [Ca.sup.2+],[Mg.sup.2+], [Sr.sup.2+]) behave conservatively with [Cl.sup.-]. The more dilute wells have the same characteristic ratios of these species to [Cl.sup.-] and thus originate by simple dilution of the brine component. The non-conservative species (mainly [Mathematical Expression Omitted] and [Mathematical Expression Omitted]) are those which are affected by sulphur redox reactions. Stable isotopes show the waters to be meteoric in origin; this and the chemical characteristics of the brines (87Sr/86Sr, [Sr.sup.2+]/[Cl.sup.-], [Li.sup.+]/[Cl.sup.-]) point to a meteoric-derived formational brine as the source of the salinity with dilution by local shallow groundwater. Sulphur isotope data show the sulphate in the dilute waters could be derived by oxidation of pyrite in Carboniferous mudstones by shallow groundwaters. Total sulphur concentrations in the saline waters are similar to the dilute waters and hence bacterial reduction of sulphate in the local shallow groundwater can account for the sulphide in the wells. Keywords: groundwater, sulphur, mixing, salinity.

Various types of pyrite morphotypes formed within fossil steinkerns can be found in pyritized graptolites. The light sulfur isotopic compositions of diagenetic pyrites proved the occurrence of early diagenesis and depositional setting. A variation in diagenetic circumstances can make the later formed pyrite isotopically light and possess some early diagenetic characteristics.

Although pyrite is ubiquitous in fine-grained, organic, carbon-bearing marine sediments, it is only rarely involved in the preservation of soft-bodied organisms. Beecher's Trilobite Bed in Upper Ordovician strata of New York State is an exception--it is classic locality for trilobites having appendages and other soft tissues preserved in pyrite. The relative timing and duration of the formation of pyrite associated with the fossils and their host sediments were determined by use of sulfur isotope ratios. The exoskeleton and appendages of the trilobites show relatively light sulfur isotope values in contrast to the enclosing sediment, which is characterized by a substantial excursion to heavy isotope values. Preservation of soft parts requires rapid burial of carcasses in sediments otherwise low in metabolizable organic matter. In these circumstances, pyrite formation within the sediments is suppressed; thus, concentrations of sulfate and reactive iron are initially high enough to promote early, rapid, and extensive pyritization of nonmineralized tissue.