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The effect of episodic drought on dissolved organic carbon (DOC) dynamics in peatlands has been the subject of considerable debate, as decomposition and DOC production is thought to increase under aerobic conditions, yet decreased DOC concentrations have been observed during drought periods. Decreased DOC solubility due to drought-induced acidification driven by sulphur (S) redox reactions has been proposed as a causal mechanism; however evidence is based on a limited number of studies carried out at a few sites. To test this hypothesis on a range of different peats, we carried out controlled drought simulation experiments on peat cores collected from six sites across Great Britain. Our data show a concurrent increase in sulphate (SO4) and a decrease in DOC across all sites during simulated water table draw-down, although the magnitude of the relationship between SO4 and DOC differed between sites. Instead, we found a consistent relationship across all sites between DOC decrease and acidification measured by the pore water acid neutralising capacity (ANC). ANC provided a more consistent measure of drought-induced acidification than SO4 alone because it accounts for differences in base cation and acid anions concentrations between sites. Rewetting resulted in rapid DOC increases without a concurrent increase in soil respiration, suggesting DOC changes were primarily controlled by soil acidity not soil biota. These results highlight the need for an integrated analysis of hydrologically driven chemical and biological processes in peatlands to improve our understanding and ability to predict the interaction between atmospheric pollution and changing climatic conditions from plot to regional and global scales.

Various studies report substantial increases in intrinsic water-use efficiency (Wi), estimated using carbon isotopes in tree rings, suggesting trees are gaining increasingly more carbon per unit water lost due to increases in atmospheric CO2. Usually, reconstructions do not, however, correct for the effect of intrinsic developmental changes in Wi as trees grow larger. Here we show, by comparingWi across varying tree sizes at one CO2 level, that ignoring such developmental effects can severely affect inferences of trees’ Wi. Wi doubled or even tripled over a trees’ lifespan in three broadleaf species due to changes in tree height and light availability alone, and there are also weak trends for Pine trees. Developmental trends in broadleaf species are as large as the trends previously assigned to CO2 and climate. Credible future tree ring isotope studies require explicit accounting for species-specific developmental effects before CO2 and climate effects are inferred.

Although near-infrared spectroscopy (NIRS) enables bedside assessment of cerebral oxygenation, it provides little information on the cause of deoxygenation. The authors aimed to investigate the changes in cerebral oxygenation and haemoglobin concentration and their associations during paediatric cardiac surgery in order to elucidate the physiology underlying cerebral deoxygenation. An observational retrospective study on 399 patients who underwent paediatric cardiac surgery was conducted. With use of NIRS, cerebral oxygen saturation as expressed by tissue oxygen index (TOI) before and after surgery, concentration changes in oxygenated haemoglobin (Delta[HbO2]) and deoxygenated haemoglobin (Delta[HHb]) after surgery were studied as were the associations between these values and clinical variables. TOI decreased after surgery (preoperative versus postoperative value, 66.0% [56.9, 71.3] versus 63.2% [54.3, 69.4], median [25th, 75th percentile], P <0.001) and the decrease was greater in higher category groups in the Risk Adjusted Classification for Congenital Heart Surgery (RACHS-1). [HHb] increased from its baseline (+1.74 mumol/l [-1.57, +5.84], P <0.001) and the increase was greater in higher risk category groups. On the contrary, there was no evidence for a change in [HbO2] (+0.45 mumol/l [-4.76, +5.30], P=0.42). Cerebral oxygen saturation decreased after paediatric cardiac surgery and the decrease was greater in patients of higher risk groups. The increase in [HHb] was considered to play a predominant role in the cerebral deoxygenation noted, in particular in higher RACHS-1 category groups.

One challenge in providing extracorporeal circulation is to supply optimal flow while minimising adverse effects, such as haemolysis. To determine if the recent generation constrained vortex pumps with their inherent design improvements would lead to reduced red cell trauma, we undertook a study comparing three devices. Utilizing a simulated short-term ventricular assist circuit primed with whole human blood, we examined changes in plasma free haemoglobin values over a six-day period. The three pumps investigated were the Maquet Rotaflow, the Levitronix PediVAS and the Medos Deltastream DP3.This study demonstrated that all three pumps produced low levels of haemolysis and are suitable for use in a clinical environment. The Levitronix PediVAS was significantly less haemolytic than either the Rotaflow (p<0.05) or the DP3 (p<0.05). There was no significant difference in plasma free haemoglobin between the Rotaflow and the DP3 (p=0.71).

A shallow unconfined glaciofluvial aquifer in North Dakota (USA) has largest groundwater sulfate concentrations near the bottom boundary. A deltaic silt layer underlying the aquifer, at >16 m, is the modern proximate sulfate source for the aquifer. The original sulfate source was pyrite in the organic-rich shale component of the aquifer and silt grain matrix. An oxidizing event occurred during which grain-matrix pyrite sulfur was oxidized to sulfate. Thereafter the silt served as a “conserving” layer, slowly feeding sulfate into the lower part of the aquifer and the underlying till. A method was developed for estimating the approximate initial sulfate concentration in the source layer and the redistribution time since the oxidizing event, using a semi-generic convection–dispersion model. The convection–dispersion model and a model for the evolution of modern sulfate δ 34 S in silt-layer pore water from the initial grain-matrix pyrite δ 34 S, both estimated that the oxidizing event occurred several thousand years ago, and was likely related to the dry conditions of the Hypsithermal Interval. The silt layer also serves as an arsenic source. Results indicate that deltaic silts derived from organic-rich shale parent materials in a glacial environment can provide long-term sources for sulfate and arsenic and possibly other related oxidative weathering products.

We analyze the interannual chemical and isotopic composition of runoff from a large, high Arctic valley glacier over a 5 year period, during which drainage evolved from a long‐residence‐time drainage system feeding an artesian subglacial upwelling (SGU) at the glacier terminus to a shorter‐residence‐time drainage system feeding an ice‐marginal channel (IMC). Increased icemelt inputs to the SGU are thought to have triggered this evolution. This sequence of events provides a unique opportunity to identify coupling between subglacial hydrology and biogeochemical processes within drainage systems of differing residence time. The biogeochemistry of the SGU is consistent with prolonged contact between meltwaters and subglacial sediments, in which silicate dissolution is enhanced, anoxic processes (e.g., sulphate reduction) prevail, and microbially generated CO2 and sulphide oxidation drive mineral dissolution. Solute in the IMC was mainly derived from moraine pore waters which are added to the channel via extraglacial streams. These pore waters acquire solute predominantly via sulphide oxidation coupled to carbonate/silicate dissolution. We present the first evidence that microbially mediated processes may contribute a substantial proportion (80% in this case) of the total glacial solute flux, which includes coupling between microbial CO2‐generation and silicate/carbonate dissolution. The latter suggests the presence of biofilms in subglacial/ice‐marginal sediments, where local perturbation of the geochemical environment by release of protons, organic acids, and ligands stimulates mineral dissolution. These data enable inferences to be made regarding biogeochemical processes in longer‐residence‐time glacial systems, with implications for the future exploration of Antarctic subglacial lakes and other wet‐based ice sheet environments.

Pore-water sulphate concentrations show marked increases at depths >50 m at ODP sites 888 and 890/889 from the Cascadia Margin accretionary wedge. In the uppermost 10 m sulphate concentrations decrease with depth and sulphate δ34S and δ18O increase as sulphate is removed by bacterial sulphate reduction. Isotopic data show that sulphate formed below 50 m results from oxidation of early diagenetic pyrite and that oxygen in the sulphate molecules is derived from pore water. Fe3+ in the sediment is the probable oxidizing agent. The increased sulphate concentrations stimulate bacterial sulphate reduction at depths of 70-250 m and are thus important in sustaining deep bacterial activity.

At five European sites, differing in atmospheric S inputs by a factor of 6, and differing in S isotope signatures of these inputs by up to 14‰ (CDT), we investigated the direction and magnitude of an assimilation-related δ 34S shift and the relationship between atmospheric deposition and S retention in selected ecosystem compartments. Bulk precipitation and spruce throughfall were collected between 1994 and 1996 in the Isle of Mull (Scotland), Connemara (Ireland), Thorne Moors (England), Rybárenská slat' and Oceán (both Czech Republic) and analyzed for sulfate concentrations and δ 34S ratios. Eighteen replicate samples per site of living Sphagnum collected in unforested peatlands and 18 samples of spruce forest floor collected near each of the peatlands were also analyzed for S concentrations and δ 34S ratios. Assimilation of S was associated with a negative δ 34S shift. Plant tissues systematically preferred the light isotope 32S, on average by 2‰. There was a strong positive correlation between the non-marine portion of the atmospheric S input and total S concentration in forest floor and Sphagnum, respectively (R = 0.97 and R = 0.85). Elevated S inputs lead to higher S retention in these two organic-rich compartments of the ecosystem. It follows that equal emphasis must be placed on organic S as on adsorption/desorption of inorganic sulfate when studying acidification reversal in ecosystems. The sea-shore sites had rainfall enriched in the heavy isotope 34S due to an admixture of sea-spray. The inland sites had low δ 34S reflecting δ 34S of sulfur emitted from local coal-burning power stations. Sphagnum had always lower S contents and higher δ 34S ratios compared to forest floor. The within-site range of δ 34S ratios of Sphagnum and forest floor was wide (up to 12‰) suggesting that at least six replicate samples should be taken when using δ 34S as a tracer.

Stable isotopes of carbon (12C and 13C) and sulphur (32S and 34S) are fractionated during some of the transformations between reservoirs in the global carbon and sulphur cycles. The main processes controlling the isotopic composition of Earth surface reservoirs are, for carbon, photosynthesis, respiration and equilibration between oceanic dissolved inorganic carbon and atmospheric CO2, and, for sulphur, bacterial sulphate reduction and sulphide reoxidation. Thus the different reservoirs of carbon and sulphur in the global cycles attain characteristic isotopic compositions that can be used as a \"fingerprint\" for different carbon and sulphur sources and to track changes in the balance of carbon and sulphur stored in different reservoirs. These isotopic signals can be used both to examine contemporary anthropogenic impacts on the cycling of carbon and sulphur and, where isotopic compositions are faithfully preserved in ancient sediments, to examine historical changes in global geochemical cycles through geological time. A number of case studies are discussed to illustrate how isotopic techniques represent one of the most powerful and important tools available in the study of both the causes and affects of ancient and modern global environmental change.

Stratabound sulphur deposits of northern Iraq occur in folded Middle Miocene evaporites overlying Lower Miocene hydrocarbon reservoirs. Rocks hosting sulphur mainly comprise gypsum, dolomitic marl, carbonate mudstones and bioclastic dolomitized limestones, whereas the mineralized rocks are mainly composed of calcite and sulphur. Sulphur was formed by the oxidation of H2S produced from gypsum dissolution followed by sulphate reduction in the presence of hydrocarbons. Sulphate reduction occurred in a partially closed to closed system as reflected by the sulphur δ34S values of +7 per mil to +20 per mil (original gypsum +21 per mil). Host rock carbonates were calcitized by the dissolved carbonate formed by oxidation of the hydrocarbons, which produced low δ13C values (-14 to -32 per mil). Periodic invasion by meteoric water and elevated temperatures produced 18O-depleted compositions for the newly-formed calcite (down to -9 per mil) and dolomite (down to -7 per mil), and oxidized the H2S produced during sulphate reduction. These sulphur deposits formed through the favourable stratigraphic juxtaposition of gypsum sulphate, brines and hydrocarbons. Tectonically produced fracture permeability in carbonates allowed rising brines from the underlying hydrocarbon reservoirs to mix with laterally migrating and descending, sulphate-bearing meteoric waters and produced the oscillating redox conditions needed for the bacterial reduction of sulphate and the oxidation of sulphide.