Rising concentrations of atmospheric carbon dioxide are causing acidification of the oceans. This results in changes to the concentrations of key chemical species such as hydroxide, carbonate and ...bicarbonate ions. These changes will affect the distribution of different forms of trace metals. Using IPCC data for pCO2 and pH under four future emissions scenarios (to the year 2100) we use a chemical speciation model to predict changes in the distribution of organic and inorganic forms of trace metals. Under a scenario where emissions peak after the year 2100, predicted free ion Al, Fe, Cu, and Pb concentrations increase by factors of up to approximately 21, 2.4, 1.5, and 2.0 respectively. Concentrations of organically complexed metal typically have a lower sensitivity to ocean acidification induced changes. Concentrations of organically complexed Mn, Cu, Zn, and Cd fall by up to 10%, while those of organically complexed Fe, Co, and Ni rise by up to 14%. Although modest, these changes may have significance for the biological availability of metals given the close adaptation of marine microorganisms to their environment.
Melting of the Greenland Ice Sheet is a leading cause of land-ice mass loss and cryosphere-attributed sea level rise. Blooms of pigmented glacier ice algae lower ice albedo and accelerate surface ...melting in the ice sheet's southwest sector. Although glacier ice algae cause up to 13% of the surface melting in this region, the controls on bloom development remain poorly understood. Here we show a direct link between mineral phosphorus in surface ice and glacier ice algae biomass through the quantification of solid and fluid phase phosphorus reservoirs in surface habitats across the southwest ablation zone of the ice sheet. We demonstrate that nutrients from mineral dust likely drive glacier ice algal growth, and thereby identify mineral dust as a secondary control on ice sheet melting.
A concept for the disposal of intermediate level radioactive wastes involves emplacement within a geological disposal facility, followed by backfilling of the facility with cement. When the closed ...facility is re-saturated with groundwater, this will create a high pH environment due to dissolution of the cement minerals. Dissolved organic matter (DOM; defined here as naturally occurring organic acids and humin) will be present in the groundwater at a concentration that reflects the host rock environment and the recharge source and pathway. Interactions between DOM and radionuclides may enhance transport away from the facility and are an important consideration in safety performance assessments. This review specifically focuses on studies of DOM–radionuclide interactions at the high pH range that is expected during a repository lifetime. Whilst the vast majority of available data cover binary (DOM–radionuclide) and batch ternary systems (mineral–radionuclide–DOM), this review also covers other potentially important areas, such as reversibility kinetics and redox processes that can be mediated by DOM.
Acidification of airborne dust particles can dramatically increase the amount of bioavailable phosphorus (P) deposited on the surface ocean. Experiments were conducted to simulate atmospheric ...processes and determine the dissolution behavior of P compounds in dust and dust precursor soils. Acid dissolution occurs rapidly (seconds to minutes) and is controlled by the amount of H⁺ ions present. For H⁺ < 10−4 mol/g of dust, 1–10% of the total P is dissolved, largely as a result of dissolution of surface-bound forms. At H⁺ > 10−4 mol/g of dust, the amount of P (and calcium) released has a direct proportionality to the amount of H⁺ consumed until all inorganic P minerals are exhausted and the final pH remains acidic. Once dissolved, P will stay in solution due to slow precipitation kinetics. Dissolution of apatite-P (Ap-P), the major mineral phase in dust (79–96%), occurs whether calcium carbonate (calcite) is present or not, although the increase in dissolved P is greater if calcite is absent or if the particles are externally mixed. The system was modeled adequately as a simple mixture of Ap-P and calcite. P dissolves readily by acid processes in the atmosphere in contrast to iron, which dissolves more slowly and is subject to reprecipitation at cloud water pH. We show that acidification can increase bioavailable P deposition over large areas of the globe, and may explain much of the previously observed patterns of variability in leachable P in oceanic areas where primary productivity is limited by this nutrient (e.g., Mediterranean).
Understanding metal and proton toxicity under field conditions requires consideration of the complex nature of chemicals in mixtures. Here, we demonstrate a novel method that relates streamwater ...concentrations of cationic metallic species and protons to a field ecological index of biodiversity. The model WHAM-
F
TOX postulates that cation binding sites of aquatic macroinvertebrates can be represented by the functional groups of natural organic matter (humic acid), as described by the Windermere Humic Aqueous Model (WHAM6), and supporting field evidence is presented. We define a toxicity function (
F
TOX) by summing the products: (amount of invertebrate-bound cation)
×
(cation-specific toxicity coefficient,
α
i
). Species richness data for Ephemeroptera, Plecoptera and Trichoptera (EPT), are then described with a lower threshold of
F
TOX, below which all organisms are present and toxic effects are absent, and an upper threshold above which organisms are absent. Between the thresholds the number of species declines linearly with
F
TOX. We parameterised the model with chemistry and EPT data for low-order streamwaters affected by acid deposition and/or abandoned mines, representing a total of 412 sites across three continents. The fitting made use of quantile regression, to take into account reduced species richness caused by (unknown) factors other than cation toxicity. Parameters were derived for the four most common or abundant cations, with values of
α
i
following the sequence (increasing toxicity) H
+
<
Al
<
Zn
<
Cu. For waters affected mainly by H
+ and Al,
F
TOX shows a steady decline with increasing pH, crossing the lower threshold near to pH 7. Competition effects among cations mean that toxicity due to Cu and Zn is rare at lower pH values, and occurs mostly between pH 6 and 8.
•Leaching efficiencies of lixiviants with various cation/anion formulas were studied.•Ammonium chloride is an optimum lixivient over other salt solutions.•Al mobilisation is minimised, improving ...downstream processing efficiency.•Low lixivient volumes (compared to pore volumes) can achieve high recovery.
Rare earth elements (REEs) are in increasing demand due to rapidly rising use in consumer technology, the automotive industry and in renewable energy generation systems, amongst other technology sectors. Ion-adsorption type REE ore deposits are currently being exploited in China’s southern provinces and there is increasing interest in identifying potential reserves globally. Here we investigated the extraction of REEs from an ion-adsorption clay sampled at a surficial deposit in Madagascar. Using a 1 M NH4Cl lixiviant salt solution, chosen based on experimental evidence to maximise REE extraction, minimises undesirable dissolved Al in eluate. Lower Al concentration in solution reduces its interference with NH4+ in oxalate precipitation of REEs in the extraction process. We show that NH4Cl solutions can be used to efficiently extract REE with relatively low lixivient volumes in a through-flow column system. We show that when extraction with a pulse of lixiviant is followed by a rinsing step, there are several identifiable stages during the extraction process, including a marked increase in total lanthanides extracted, which is correlated with the breakthrough of ammonium ions, and where the eluted dissolved Al concentration decreases from its peak concentration.
Recent estimates of nutrient budgets for the Eastern Mediterranean Sea (EMS) indicate that atmospheric aerosols play a significant role as suppliers of macro- and micro- nutrients to its Low Nutrient ...Low Chlorophyll water. Here we present the first mesocosm experimental study that examines the overall response of the oligotrophic EMS surface mixed layer (Cretan Sea, May 2012) to two different types of natural aerosol additions, “pure” Saharan dust (SD, 1.6 mg l-1) and mixed aerosols (A - polluted and desert origin, 1 mg l-1). We describe the rationale, the experimental set-up, the chemical characteristics of the ambient water and aerosols and the relative maximal biological impacts that resulted from the added aerosols. The two treatments, run in triplicates (3 m3 each), were compared to control-unamended runs. Leaching of approximately 2.1-2.8 and 2.2-3.7 nmol PO4 and 20-26 and 53-55 nmol NOx was measured per each milligram of SD and A, respectively, representing an addition of approximately 30% of the ambient phosphate concentrations. The nitrate/phosphate ratios added in the A treatment were twice than those added in the SD treatment. Both types of dry aerosols triggered a positive change (25-600% normalized per 1 mg l-1 addition) in most of the rate and state variables that were measured: bacterial abundance (BA), bacterial production (BP), Synechococcus (Syn) abundance, chlorophyll-a (chl-a), primary production (PP) and dinitrogen fixation (N2-fix), with relative changes among them following the sequence BP>PP≈N2-fix>chl-a≈BA≈Syn. Our results show that the ‘polluted’ aerosols triggered a relatively larger biological change compared to the SD amendments (per a similar amount of mass addition), especially regarding BP and PP. We speculate that despite the co-limitation of P and N in the EMS, the additional N released by the A treatment may have triggered the relatively larger response in most of the rate and state variables as compared to SD. An implication of our study is that a warmer atmosphere in the future may increase dust emissions and influence the intensity and length of the already well stratified water column in the EMS and hence the impact of the aerosols as a significant external source of new nutrients.
The hypothesis that reducing conditions exist in localized zones of high organic matter, termed microniches, was first suggested over a century ago, but only relatively recently have high-resolution ...techniques been available to investigate them. In any sediment containing benthic fauna, bioturbation affects the distribution of a number of redox-sensitive components. Direct faecal deposition and the death of fauna may be expected to cause particles of labile organic matter (microniches) to be distributed heterogeneously within the sediment. This review discusses the significance and future direction of microniche studies by considering, exclusively, data obtained on a sub-mm scale that provide significant evidence for the existence and properties of microniches. Microelectrodes and planar optodes have shown the significant effect of burrowing organisms on localized O
2 distributions and revealed distinct depletions in O
2 due to microniches. Localized increases in pCO
2 and decreases in pH measured by optodes were attributed to elevated activity at microniches. Diffusive gradients in thin-films have shown isolated supersaturation of metals and sulphide, providing evidence for possible simultaneous oxidation of organic matter by sulphate and iron oxides. The stochastic nature of these data and the lack of information for the same precise location hinders interpretation in terms of sediment diagenesis. If microniches are known to account for a significant proportion of organic matter degradation, re-examination of the current understanding of sedimentary diagenesis may be needed. Further investigation on the distribution and frequency of microniches is required, including a wider range of analytes, in order to estimate their cumulative effect on element diagenesis, immobilisation/remobilisation processes and ultimately pollutant fate.
Acid processes in the atmosphere, particularly those caused by anthropogenic acid gases, increase the amount of bioavailable P in dust and hence are predicted to increase microbial biomass and ...primary productivity when supplied to oceanic surface waters. This is likely to be particularly important in the Eastern Mediterranean Sea (EMS), which is P limited during the winter bloom and N&P co-limited for phytoplankton in summer. However, it is not clear how the acid processes acting on Saharan dust will affect the microbial biomass and primary productivity in the EMS. Here, we carried out bioassay manipulations on EMS surface water on which Saharan dust was added as dust (Z), acid treated dust (ZA), dust plus excess N (ZN), and acid treated dust with excess N (ZNA) during springtime (May 2012) and measured bacterioplankton biomass, metabolic, and other relevant chemical and biological parameters. We show that acid treatment of Saharan dust increased the amount of bioavailable P supplied by a factor of ~40 compared to non-acidified dust (18.4 vs. 0.45 nmoles P mg super(-1) dust, respectively). The increase in chlorophyll, primary, and bacterial productivity for treatments Z and ZA were controlled by the amount of N added with the dust while those for treatments ZN and ZNA (in which excessive N was added) were controlled by the amount of P added. These results confirm that the surface waters were N&P co-limited for phytoplankton during springtime. However, total chlorophyll and primary productivity in the acid treated dust additions (ZA and ZNA) were less than predicted from that calculated from the amount of the potentially limiting nutrient added. This biological inhibition was interpreted as being due to labile trace metals being added with the acidified dust. A probable cause for this biological inhibition was the addition of dissolved Al, which forms potentially toxic Al nanoparticles when added to seawater. Thus, the effect of anthropogenic acid processes in the atmosphere, while increasing the flux of bioavailable P from dust to the surface ocean, may also add toxic trace metals such as Al, which moderate the fertilizing effect of the added nutrients.
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