low-pH Zone Research Articles

Two-dimensional modeling of CO2 mineral trapping through the oxalate‑carbonate pathway: Influence of the root system model

Two-dimensional reactive transport models, one with a simplified root system and the other accounting for dynamically evolving root architecture, were constructed to examine the influence of model complexity on capturing the effect of soil-root dynamics relating to the Oxalate Carbonate Pathway (OCP) of the Iroko tree over 170 years. Oxidation of oxalate from fallen tree tissue by soil bacteria enables local soil pH increase, leading to the sequestration of atmospheric carbon in carbonate minerals (calcite) in the shallow soil surrounding the tree. Simulations of both root models corroborate previous one-dimensional models of the OCP focused on Ca and C mass balance, where high weathering rates of Ca-containing silicate minerals in bedrock, along with contributions from groundwater, provided sufficient Ca for precipitation of observed quantities of calcite. Both simulations demonstrate the development of a distinct high pH zone where oxalate is oxidized, Ca accumulates, and calcite precipitates (OCP zone); and a low pH zone where roots collect Ca, later returned to the top soil as calcium oxalate (Total Root Extent/TRE zone) via litterfall. While the extent of OCP zone development near the ground surface was very similar between simulations, differences in localized root water uptake between the two approaches resulted in variation in water and solute transport and influenced the geometry of the OCP zone at depth, with implications for calcite precipitation in the soil. Trends in CO2 and O2 partial pressures in the OCP zone were mirrored in the TRE zone, suggesting linkage between the two zones with regard to gas transport. Near the end of the tree's lifespan, results indicate that soil permeability decreases due to calcite precipitation may limit O2 ingress and availability in the shallow soil, while trapping CO2 released from the oxidation of organics in the shallow soil, with implications for the long-term sustainability of the OCP itself.

Structural and Functional Analyses of Motile Fauna Associated with Cystoseira brachycarpa along a Gradient of Ocean Acidification in a CO2-Vent System off Panarea (Aeolian Islands, Italy)

Ocean acidification (OA), one of the main climate-change-related stressors linked to increasing CO2 concentration in the atmosphere, is considered an important threat to marine biodiversity and habitats. Studies on CO2-vents systems, naturally acidified environments that mimic future ocean scenarios, help to explore the sensitivity of species and to understand how benthic communities rearrange their structure and functioning under the pressure of OA. We addressed this problem by studying the benthic invertebrates associated with a habitat-forming brown alga (Cystoseira brachycarpa) in the Bottaro crater vents system off Panarea island (Tyrrhenian Sea, Italy), by sampling along an OA gradient from the proximity of the main venting area (station B3, pH 7.9) to a control zone (B1 station, pH 8.1). Samples were collected in September 2016 and 2018. A total of 184 taxa and 23 different functional traits have been identified, considering feeding habit, motility, size, reproductive and developmental biology, and occurrence of calcareous structures. Invertebrates are distributed according to the distance from the high venting zone and low pH levels and results very consistent between the two investigated years. In the low-pH area (B3), 43% of the species are selected. The functional traits of the fauna mirror this zonation pattern, mainly changing the relative proportion of the number of individuals of the various functional guilds along the OA gradient. Invertebrates inhabiting the low-pH zone are mainly composed of weakly or non-calcified species, with small size, burrower/tubicolous habit, omnivorous or suspension feeders, and with direct development and brooding habit. In the other stations, heavily calcified forms, herbivore and herbivore/detritivore, and with medium (1–5 cm) and large (>5 cm) sizes prevail, showing indirect benthic and planktic development. The taxonomic analysis, coupled with functional aspects, increases our prediction of which traits could be potentially more advantageous for species to adapt to the hypothesized scenarios of OA, and identify present and future winner and/or loser organisms in the future ocean of the Anthropocene.

Ocean Acidification and Mollusc Settlement in Posidonia oceanica Meadows: Does the Seagrass Buffer Lower pH Effects at CO2 Vents?

Ocean acidification has been broadly recognised to have effects on the structure and functioning of marine benthic communities. The selection of tolerant or vulnerable species can also occur during settlement phases, especially for calcifying organisms which are more vulnerable to low pH–high pCO2 conditions. Here, we use three natural CO2 vents (Castello Aragonese north and south sides, and Vullatura, Ischia, Italy) to assess the effect of a decrease of seawater pH on the settlement of Mollusca in Posidonia oceanica meadows, and to test the possible buffering effect provided by the seagrass. Artificial collectors were installed and collected after 33 days, during April–May 2019, in three different microhabitats within the meadow (canopy, bottom/rhizome level, and dead matte without plant cover), following a pH decreasing gradient from an extremely low pH zone (pH < 7.4), to ambient pH conditions (pH = 8.10). A total of 4659 specimens of Mollusca, belonging to 57 different taxa, were collected. The number of taxa was lower in low and extremely low pH conditions. Reduced mollusc assemblages were reported at the acidified stations, where few taxa accounted for a high number of individuals. Multivariate analyses revealed significant differences in mollusc assemblages among pH conditions, microhabitat, and the interaction of these two factors. Acanthocardia echinata, Alvania lineata, Alvania sp. juv, Eatonina fulgida, Hiatella arctica, Mytilys galloprovincialis, Musculus subpictus, Phorcus sp. juv, and Rissoa variabilis were the species mostly found in low and extremely low pH stations, and were all relatively robust to acidified conditions. Samples placed on the dead matte under acidified conditions at the Vullatura vent showed lower diversity and abundances if compared to canopy and bottom/rhizome samples, suggesting a possible buffering role of the Posidonia on mollusc settlement. Our study provides new evidence of shifts in marine benthic communities due to ocean acidification and evidence of how P. oceanica meadows could mitigate its effects on associated biota in light of future climate change.

A CFD model for predicting protein aggregation in low-pH virial inactivation for mAb production.

Significant amounts of soluble product aggregates were observed in the low-pH viral inactivation (VI) operation during an initial scale-up run for an immunoglobulin-G 4 (IgG4) monoclonal antibody (mAb IgG4-N1). Being earlier in development, a scale-down model did not exist, nor was it practical to use costly Protein A eluate (PAE) for testing the VI process at scale, thus, a computational fluid dynamics (CFD)-based high-molecular weight (HMW) prediction model was developed for troubleshooting and risk mitigation. It was previously reported that the IgG4-N1 molecules upon exposure to low pH tend to change into transient and partially unfolded monomers during VI acidification (i.e., VIA) and form aggregates after neutralization (i.e., VIN). Therefore, the CFD model reported here focuses on the VIA step. The model mimics the continuous addition of acid to PAE and tracks acid distribution during VIA. Based on the simulated low-pH zone (≤pH 3.3) profiles and PAE properties, the integrated low-pH zone (ILPZ) value was obtained to predict HMW level at the VI step. The simulations were performed to examine the operating parameters, such as agitation speed, acid addition rate, and protein concentration of PAE, of the pilot scale (50-200 L) runs. The conditions with predictions of no product aggregation risk were recommended to the real scale-up runs, resulted in 100% success rate of the consecutive 12 pilot-scale runs. This study demonstrated that the CFD-based HMW prediction model could be used as a tool to facilitate the scale up of the low-pH VI process directly from bench to pilot/production scale.

Simultaneous removal of bioaerosols, odors and volatile organic compounds from a wastewater treatment plant by a full-scale integrated reactor

Biological control of odors and bioaerosols in wastewater treatment plants (WWTPs) have gained more attention in recent years. The simultaneous removal of odors, volatile organic compounds (VOCs) and bioaerosols in each unit of a full-scale integrated-reactor (FIR) in a sludge dewatering room was investigated. The average removal efficiencies (REs) of odors, VOCs and bioaerosols were recorded as 98.5 %, 94.7 % and 86.4 %, respectively, at an inlet flow rate of 5760 m3/h. The RE of each unit decreased, and the activated carbon adsorption zone (AZ) played a more important role as the inlet flow rate increased. The REs of hydrophilic compounds were higher than those of hydrophobic compounds. For bioaerosols, roughly 35 % of airborne heterotrophic bacteria (HB) was removed in the low-pH zone (LPZ) while over 30 % of total fungi (TF) was removed in the neutral-pH zone (NPZ). Most bioaerosols removed by the biofilter (BF) had a particle size larger than 4.7 μm while bioaerosols with small particle size were apt to be adsorbed by AZ. The microbial community in the BF changed significantly at different units. Health risks were found to be associated with H2S rather than with bioaerosols at the FIR outlet.

Cubic plasma membrane domains stabilize and restrict zones for pH band formation in Chara internodal cells

ABSTRACTCharacean internodal cells display acid and alkaline regions along their surface when exposed to light. The acidification facilitates uptake of carbon required for photosynthesis. In the genus Chara, cubic plasma membrane domains, known as charasomes, were first described five decades ago. Their size and abundance varies along the cell surface and it has been conjectured that the charasome coverage correlates with the pH banding pattern. In this study, we used fluorescein isothiocyanate-dextran (FITC-dextran) and confocal laser scanning microscopy to map the pH profile at high spatial and temporal resolution. In parallel, we stained the charasomes with styryl dyes and investigated their distribution in relation to the fluorescence pattern of FITC-dextran. In both internodal cells of the branchlets and of the main axis, we found that charasomes were small and sparse at the alkaline bands but large and abundant at the acidic regions. Our findings confirm the existence of cell surface regions predisposed to generate either high or low pH zones. We provide evidence that areas with high charasome abundance stabilize and restrict the position of the acidic bands whereas regions with low charasome abundance allow the formation of either stable or unstable alkaline bands.

Pathways for external alkalinization in intact and in microwounded Chara cells are differentially sensitive to wortmannin

ABSTRACTProton flows across the plant cell membranes play a major role in electrogenesis and regulation of photosynthesis and ion balance. The profiles of external pH along the illuminated internodal cells of characean algae consist of alternating high- and low-pH zones that are spatially coordinated with the distribution of photosynthetic activity of chloroplasts underlying these zones. The results based on confocal laser scanning fluorescence microscopy, pH microsensors, and pulse-amplitude-modulated chlorophyll microfluorometry revealed that the coordination of H+ transport and photosynthesis is disrupted by the 2 different environmental cues (low light and wounding) and by a chemical, wortmannin interfering with the inositol phospholipid metabolism. On the one hand, the transition from moderate to low irradiance diminished the peaks in the profiles of photosystem II (PSII) quantum efficiency but did not remove the pH bands. On the other hand, the microwounding of the internode with a glass micropipette, impacting primarily the cell wall, resulted in a rapid local alkalinization of the external medium (by 2–2.5 pH units) near the cell surface, thus mimicking the appearance of natural pH bands. Despite their seeming similarity, the alkaline bands of intact cells were eliminated by wortmannin, whereas the wound-induced alkalinization was insensitive to this drug. Furthermore, the attenuation of natural pH bands in wortmannin-treated cells was accompanied by the enhancement in spatial heterogeneity of PSII efficiency and electron transport rates, which indicates the complexity of chloroplast–plasma membrane interactions. The results suggest that the light- and wound-induced alkaline areas on the cell surface are associated with different ion-transport systems.

Photoregulation of photosystem II activity mediated by cytoplasmic streaming in Chara and its relation to pH bands

Chloroplasts in vivo exposed to strong light export assimilates and excess reducing power to the cytoplasm for metabolic conversions and allocation to neighboring and distant organelles. The cytoplasmic streaming, being particularly fast in characean internodes, distributes the exported metabolites from brightly illuminated cell spots to light-limited regions, which is evident from the transient increase in chlorophyll fluorescence of shaded areas in response to illumination of distant cell regions situated upstream the liquid flow. It is not yet known whether long-distance communications between anchored chloroplasts are interfered by pH banding that commonly arises in characean internodes under the action of continuous or fluctuating light. In this study, microfluorometry, pH-microsensors, and local illumination were combined to examine long-distance transport and subsequent reentry of photosynthetic metabolites, including triose phosphates, into chloroplasts of cell regions producing external alkaline and acid bands. The lateral transmission of metabolic signals between distant chloroplasts was found to operate effectively in cell areas underlying acid zones but was almost fully blocked under alkaline zones. The rates of linear electron flow in chloroplasts of these regions were nearly equal under dim background light, but differed substantially at high light when availability of CO2, rather than irradiance, was the rate-limiting factor. Different productions of assimilates by chloroplasts underlying CO2-sufficient acid and CO2-deficient alkaline zones were a cause for contrasting manifestations of long-distance transport of photosynthetic metabolites. Nonuniform cytoplasmic pH in cells exhibiting pH bands might contribute to different activities of metabolic translocators under high and low pH zones.

Coralline algae in a naturally acidified ecosystem persist by maintaining control of skeletal mineralogy and size.

To understand the effects of ocean acidification (OA) on marine calcifiers, the trade-offs among different sublethal responses within individual species and the emergent effects of these trade-offs must be determined in an ecosystem setting. Crustose coralline algae (CCA) provide a model to test the ecological consequences of such sublethal effects as they are important in ecosystem functioning, service provision, carbon cycling and use dissolved inorganic carbon to calcify and photosynthesize. Settlement tiles were placed in ambient pH, low pH and extremely low pH conditions for 14 months at a natural CO2 vent. The size, magnesium (Mg) content and molecular-scale skeletal disorder of CCA patches were assessed at 3.5, 6.5 and 14 months from tile deployment. Despite reductions in their abundance in low pH, the largest CCA from ambient and low pH zones were of similar sizes and had similar Mg content and skeletal disorder. This suggests that the most resilient CCA in low pH did not trade-off skeletal structure to maintain growth. CCA that settled in the extremely low pH, however, were significantly smaller and exhibited altered skeletal mineralogy (high Mg calcite to gypsum (hydrated calcium sulfate)), although at present it is unclear if these mineralogical changes offered any fitness benefits in extreme low pH. This field assessment of biological effects of OA provides endpoint information needed to generate an ecosystem relevant understanding of calcifying system persistence.

Distribution and functional traits of polychaetes in a CO2 vent system: winners and losers among closely related species

This authors' personal copy may not be publicly or systematically copied or distributed, or posted on the Open Web, except with written permission of the copyright holder(s). It may be distributed to interested individuals on request. MARINE ECOLOGY PROGRESS SERIES Mar Ecol Prog Ser Vol. 550: 121–134, 2016 doi: 10.3354/meps11727 Published May 25 Distribution and functional traits of polychaetes in a CO 2 vent system: winners and losers among closely related species M. C. Gambi 1 , L. Musco 2, 6, *, A. Giangrande 3 , F. Badalamenti 2 , F. Micheli 4 , K. J. Kroeker 5 Stazione Zoologica Anton Dohrn - Integrative Marine Ecology, Villa Dohrn-Benthic Ecology Center, 80077 Ischia, Napoli, Italy Laboratory of Marine Ecology - IAMC - CNR, 91014 Castellammare del Golfo, Italy University of Salento, DiSTeBA, 73100 Lecce, Italy Hopkins Marine Station, Stanford University, Pacific Grove, CA 93950, USA University of California at Santa Cruz, Santa Cruz, CA 95064, USA Present address: Stazione Zoologica Anton Dohrn, 80121 Napoli, Italy ABSTRACT: We report on fine taxonomic and functional analyses of polychaetes associated with rocky reefs along a gradient of ocean acidification (OA) at the volcanic CO 2 vent system off the Castello Aragonese (Ischia Island, Italy). Percent cover of algae and sessile invertebrates (a deter- minant of polychaete distribution) was classified into functional groups to disentangle the direct effects of low pH on polychaete abundance from the indirect effects of pH on habitat and other species associations. A total of 6459 polychaete specimens belonging to 83 taxa were collected. Polychaete species richness and abundance dramatically dropped under the extreme low pH con- ditions due to the disappearance of both calcifying and non-calcifying species. Differences in dis- tribution patterns indicate that the decreasing pH modified the structure and biological traits of polychaete assemblages independent of changes in habitat. A detailed taxonomic analysis high- lighted species-specific responses to OA, with closely related species having opposing responses to decreasing pH. This resulted in an increase in the abundance of filter feeders and herbivores with decreasing pH, while sessile polychaetes disappeared in the extreme low pH zones, and were replaced by discretely motile forms. Reproductive traits of the polychaete assemblages changed as well, with brooding species dominating the most acidified zones. The few taxa that were abundant in extreme low pH conditions showed high tolerance to OA (e.g. Amphiglena mediterranea, Syllis prolifera, Platynereis cf. dumerilii, Parafabricia mazzellae, Brifacia aragonen- sis), and are promising models for further studies on the responses of benthic organisms to the effects of reduced pH. KEY WORDS: Annelida · Algal cover · Ocean acidification · Hard bottoms · pH gradient · Covariation · Mediterranean Sea · Functional trait analysis Resale or republication not permitted without written consent of the publisher Increased anthropogenic CO 2 emissions are pre- dicted to be among the major drivers of global change in the coming century in both terrestrial and marine ecosystems (Gattuso & Buddemeier 2000, IPCC 2014). Large among-species variation in bio- logical responses to CO 2 -induced ocean acidification (OA) is evident in the literature, but it is biased towards calcifying organisms (Ries et al. 2009, Kroeker et al. 2010, 2013a), with most available data derived from laboratory or mesocosm studies (Fabry et al. 2008, Feely et al. 2009, Kroeker et al. 2010, 2013a). However, recent studies performed in natu- *Corresponding author: luigi.musco@szn.it © Inter-Research 2016 · www.int-res.com INTRODUCTION

Geochemistry of two shallow CO2 seeps in Shikine Island (Japan) and their potential for ocean acidification research

Shallow CO2 seeps, where CO2 gas is venting underwater, offer great potential for studies into the effects of ocean acidification at the ecosystem level. To our knowledge, only two tropical system and two temperate systems of such seeps have been described worldwide. Here we describe two new temperate systems: the Mikama Bay and Ashitsuke sites, located on Shikine Island, Japan. The Mikama Bay site is located in a shallow bay. Investigation of the gas and water chemistry showed that the gas contained 98% CO2 and up to 90 ppm H2S. Total alkalinity was constant in time and space with an average of 2265±10 μ mol kg−1. Mapping of Eh and pH showed that the low pH zones were the largest when currents were moderate. Under moderate currents, Eh values were globally higher and total sulfides concentration lower, supporting that a longer residence time of the bay water allow the oxidation of the sulfides to sulfates. Zones suitable for acidification studies: with a pH lower than 8.0, low saturation state of calcite and aragonite, and non-detectable sulfide concentration, can be defined a few meters from the main venting zone. The second site, Ashitsuke, is located in the inter-tidal zone on a shore composed of boulders. Several areas showed reduced pH sometimes restricted to a few meters and up to 20 m long along the shoreline. Temperature was higher in some of the reduced pH zones suggesting the presence of hot springs in addition to vents. This paper also highlights the need for discovering additional CO2 seeps, which by their nature often lack comparable replicates and can be confounded by factors other than CO2. In this regard, Japan offers great potential as it is home to numerous active volcanoes, representing potential venting sites in climates ranging from tropical to sub-polar.

Community dynamics and ecosystem simplification in a high-CO 2 ocean

Disturbances are natural features of ecosystems that promote variability in the community and ultimately maintain diversity. Although it is recognized that global change will affect environmental disturbance regimes, our understanding of the community dynamics governing ecosystem recovery and the maintenance of functional diversity in future scenarios is very limited. Here, we use one of the few ecosystems naturally exposed to future scenarios of environmental change to examine disturbance and recovery dynamics. We examine the recovery patterns of marine species from a physical disturbance across different acidification regimes caused by volcanic CO2 vents. Plots of shallow rocky reef were cleared of all species in areas of ambient, low, and extreme low pH that correspond to near-future and extreme scenarios for ocean acidification. Our results illustrate how acidification decreases the variability of communities, resulting in homogenization and reduced functional diversity at a landscape scale. Whereas the recovery trajectories in ambient pH were highly variable and resulted in a diverse range of assemblages, recovery was more predictable with acidification and consistently resulted in very similar algal-dominated assemblages. Furthermore, low pH zones had fewer signs of biological disturbance (primarily sea urchin grazing) and increased recovery rates of the dominant taxa (primarily fleshy algae). Together, our results highlight how environmental change can cause ecosystem simplification via environmentally mediated changes in community dynamics in the near future, with cascading impacts on functional diversity and ecosystem function.

The effect of ocean acidification on early algal colonization stages at natural CO2 vents

Marine algae exhibit different responses to ocean acidification, suggesting that a decrease in pH does not always favour marine photosynthetic organisms. In order to understand the effect of acidification on algal community development, early colonization stages were investigated using carbon dioxide vents around the Castello Aragonese (Ischia, Italy) as a natural laboratory. Settlement tiles were placed in zones with different pH (normal, medium and low), and species composition and coverage measured after 2, 3 and 4 months of deployment. The number of species decreased by 4 and 18 % at medium and low pH zones, respectively (P < 0.05). The structure of the algal assemblage differed between pH zones during the 4 months of the experiment, due to the addition and/or replacement of new species. This leads to a change in the succession of morphological forms as soft crustose algae replaced calcareous species, and turf species were dominant in cover; more complex thalli started to occur only at medium pH. These results support previous findings that ocean acidification will induce changes in benthic algal communities.

Shallow sand-filled niches beneath drip emitters made reclamation of an impermeable saline-sodic soil possible while cropping with Lycium barbarum L.

The native soils of large areas of the Ningxia Plain in northwest China are saline-sodic, known as takyric solonetz, with very low saturated hydraulic conductivities (ks<0.1mm/d). A 3-year field experiment was conducted to determine if reclamation could be achieved while growing Lycium barbarum L. using drip irrigation where soil beneath the drip emitters, near the plants, was replaced with sand in niches that were 0.2m ground diameter and 0.2m deep. The purpose of sand-filled niche was to increase the area over which infiltration of water occurs thereby reducing the application rates to values that more closely matched the saturated hydraulic conductivity of the native soil. The initial values for ECe, pHs, and SAR of the surface soil was 12dS/m, 9.4 and 44.1(mmol/L)0.5, respectively. After deep tillage, beds (1m wide, 0.5m high) were formed. The drip lines were placed on beds covered with plastic. L. barbarum L. seedlings were then planted. Five water treatments were based on the soil matric potential (SMP), measured with tensiometers installed 0.2m beneath the emitter, used to trigger an irrigation of 5mm: the SMP levels were −5kPa (S1), −10kPa (S2), −15kPa (S3), −20kPa (S4), and −25kPa (S5). The salinity and SAR of the applied water were 2.14dS/m and 6.02(mmol/L)0.5. Considerable reclamation was achieved in three years. The low-salinity and the low-pH zone, which formed under the drip line during the first year, enlarged year by year. The average ECe and pHs in root zone increased with decreasing (more negative) SMP. The average SAR in root zone decreased sharply in the first year, then leveled off in the next two years. After 3 years, S3 and S4 had the better survival (∼80%) and higher fruit yields, around 900kg/ha, which were close to the level in local farmland. Our findings indicated that a sand-filled niche beneath the drip emitter could be adopted for the reclamation of saline-sodic wasteland in Ningxia Plain, northwest China, and an SMP of −10kPa in the first two years and −20kPa from the third year could be used to trigger drip irrigation while cropping L. barbarum L.

Application of high altitude and ground-based spectroradiometry to mapping hazardous low-pH material derived from the Sokolov open-pit mine

Mineral spectroradiometry, both from airborne/spaceborne sensors and ground measurements, represents an alternative to conventional methods and an efficient way to characterize mines and assess the potential for acid mine drainage (AMD) discharge. High-altitude spectroradiometry (advanced spaceborne thermal emission and reflection radiometer [ASTER] satellite data) together with ground- and laboratory-based spectroradiometry (ASD Filedspec spectroradiometer) were employed in order to identify the locations of the most significant sources of AMD discharge at the Sokolov lignite open-pit mines, Czech Republic. As a result, a map with delineated low-pH zones was created and validated using the ground truth data.

Real‐Time Spatial Gene Expression Analysis within Current‐Producing Biofilms

The expression of genes involved in central metabolism and extracellular electron transfer was examined in real-time in current-producing anode biofilms of Geobacter sulfurreducens. Strains of G. sulfurreducens were generated, in which the expression of the gene for a short half-life fluorescent protein was placed under control of the promoter of the genes of interest. Anode biofilms were grown in a chamber that permitted direct examination of the cell fluorescence with confocal scanning laser microscopy. Studies on nifD and citrate synthase expression in response to environmental changes demonstrated that the reporter system revealed initiation and termination of gene transcription. Uniform expression throughout the biofilms was noted for the genes for citrate synthase; PilA, the structural protein of the conductive pili; and OmcZ, a c-type cytochrome essential for optimal current production, which was localized at the anode-biofilm interface. These results demonstrate that even cells at great distance from the anode, or within expected low-pH zones, are metabolically active and likely to contribute to current production and that there are factors other than gene expression differences influencing the distribution of OmcZ. This real-time reporter approach is likely to be a useful tool in optimizing the design of technologies relying on microbe-electrode interactions.

Divergent ecosystem responses within a benthic marine community to ocean acidification

Ocean acidification is predicted to impact all areas of the oceans and affect a diversity of marine organisms. However, the diversity of responses among species prevents clear predictions about the impact of acidification at the ecosystem level. Here, we used shallow water CO(2) vents in the Mediterranean Sea as a model system to examine emergent ecosystem responses to ocean acidification in rocky reef communities. We assessed in situ benthic invertebrate communities in three distinct pH zones (ambient, low, and extreme low), which differed in both the mean and variability of seawater pH along a continuous gradient. We found fewer taxa, reduced taxonomic evenness, and lower biomass in the extreme low pH zones. However, the number of individuals did not differ among pH zones, suggesting that there is density compensation through population blooms of small acidification-tolerant taxa. Furthermore, the trophic structure of the invertebrate community shifted to fewer trophic groups and dominance by generalists in extreme low pH, suggesting that there may be a simplification of food webs with ocean acidification. Despite high variation in individual species' responses, our findings indicate that ocean acidification decreases the diversity, biomass, and trophic complexity of benthic marine communities. These results suggest that a loss of biodiversity and ecosystem function is expected under extreme acidification scenarios.

Geochemical effects of deeply buried Cu–Au mineralization on transported regolith in an arid terrain

ABSTRACT The presence of transported regolith commonly restricts the dispersion of trace elements from mineralized bedrock or in situ regolith to surface, especially in arid terrains. Where dispersion through transported regolith does occur, low-concentration haloes derived from mineralization may be masked by other surficial geochemical processes. Substantial changes to the mineralogy and mineral distribution within transported regolith, as a result of H + released from oxidizing sulphide mineralization and other reactions, has been recognized in a number of regolith settings. Various approaches to detection of such features have been developed, but their application has met with limited success in arid environments typical of Australia. The Mandamah Cu–Au deposit, in central–western New South Wales, is covered by c . 50 m of transported regolith and c . 30 m of saprolite. The top 2 m of regolith in the region is characterized by an organic-rich surface layer with neutral pH, followed by a high-pH zone with pedogenic carbonate development and a lower selvage of gypsum, and an underlying low-pH zone displaying Fe mottling. The principal effects of mineralization in the upper transported regolith are depletion of ammonium acetate-extractable Ca, S and Na, a reduction in the cation exchange capacity, the presence of non-carbonate alkalinity and a low soil electrical conductivity. There is no indication of transport to surface and accumulation of elements related to the mineralization, such as Cu, Mo, Au or S. A model to account for these patterns, based partly on existing dispersion models, involves a prograde stage of alteration of clay mineralogy with redistribution of carbonates and some elements as a result of the development of an acid chimney above the oxidizing mineralization during periods of elevated water tables and a subsequent retrograde stage involving a redistribution of mobile elements into the area of the former acid chimney following the onset of more arid conditions.

Mathematical modeling of the dissolving and deposition processes during solution seepage in a porous medium

A mathematical model that describes solution seepage in a porous medium and the processes of mineral dissolving and secondary deposition is proposed. Self-similar solutions describing the motion of the leading and trailing fronts, that is, the boundaries of the complete-dissolving zone, are determined. The main features of the processes under consideration are studied and numerical calculations are performed. It is shown that the model describes well the experimental data on mineral leaching by sulfate solutions. The dynamics of mineral extraction from productive solutions in a medium with a nonuniformacidity distribution are investigated. It is shown that, in the elevated-PH zones, the mineral is dissolved; whereas, in the low-acidity zones, secondary deposition of the mineral occurs. In the latter case, after the work has been completed, the bed may contain more or less considerable mineral resources, depending on the extent of the low-PH zone and its proximity to an extraction well.

Distribution and mobility of arsenic in the Río Dulce alluvial aquifers in Santiago del Estero Province, Argentina

Factors controlling arsenic (As) mobilization in the aquifers of the Río Dulce alluvial cone were investigated. Groundwater analyses show severe As contamination (average concentration of 743 μg/L) from geogenic sources, but spatial variability of As concentration is considerable. Sequential leaching of sediment samples from unsaturated zone using de-ionised water, bicarbonate, acetate, and oxalate extracted As to different extents. Sediment oxalate extraction showed that Al and Mn oxide and hydroxides are more abundant than Fe oxides and hydroxides, in spite of similar total Fe, Mn, and Al concentrations in the sediment. Speciation calculations performed for saturated zone samples indicated that Fe and Al oxides and hydroxides are stable in groundwater, suggesting that As adsorption processes may be to some extent controlled by the presence of Fe and Al mineral phases. Principal Component Analysis (PCA) showed that As is related to F, V, Mo, B, Si, most likely due to their common origin in volcanic ash. This suggests the volcanic ash as the probable source of groundwater As. Locally, elevated pH values linked to carbonate dissolution, cation exchange, and dissolution of silicates promote release of adsorbed As. Another factor contributing to the release of As locally may be the input of organic matter from excessive irrigation. The conceptual model of As release includes: i) As influx from dissolution of volcanic glass in volcanic ash, ii) adsorption of As on the surface of Fe and Al mineral phases in relatively low pH zones, and iii) high mobility of As in high pH zones. Future work should be focused on the determination of mineralogical forms of As in volcanic ash and on detailed investigation on factors controlling As mobility.