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MDFRC item.March 2011. DOI: 10.1021/es103535k.The acid generation mechanisms and neutralizing capacities of sulfidic sediments from two inland wetlands have been studied in order to understand the response of these types of systems to drying events. The two systems show vastly different responses to oxidation, with one (Bottle Bend (BB) lagoon) having virtually no acid neutralizing capacity (ANC) and the other (Psyche Bend (PB) lagoon) an ANC that is an order of magnitude greater than the acid generation potential. While BB strongly acidifies during oxidation the free acid generation is less than that expected from the measured proton production and consumption processes, with additional proton consumption attributed to the formation of an acid-anion (chloride) FeIII (oxyhydr)oxide product, similar to akaganite (Fe(OH)2.7Cl0.3). While such products can partially attenuate the acidification of these systems, resilience to acidification is primarily imparted by sediment ANC.

People and water intersect in the movement of sediment downstream in rivers. Social processes and geomorphological processes become entangled as each system moves in ways that trigger corresponding responses from the other. Long-term dialectical relationships emerge that span multiple human generations. The power of sediment and water to change physical environments is in constant tension with the power of human actions informed by social, cultural, legal, economic and engineering imperatives. The Pacific Rim gold rushes that began in the mid-nineteenth century provide an opportunity to examine how the interplay of people, water and sediment unfolds over historic time. The mass discharge of mining sediment in California and Victoria that began over 150 years ago was a catastrophic human alteration of river systems. Subsequently, mining sediment has had a long and complex entanglement with society and rivers in both regions and continues to be an active agent in reshaping riparian environments. Mining sediments also have a toxic legacy as associated contaminants, including mercury and arsenic, that are discharged into waterways and dispersed in windblown dust. The changes to river systems caused by gold mining committed societies and rivers to new trajectories of mutual engagement. Anthropogenically induced sedimentation that resulted from mining is an issue that will continue to impact watersheds for generations to come.

Mobilisation of large volumes of bedrock, regolith and soil has long been a characteristic feature of metal mining. Prior to the 20th century this was most efficiently achieved through harnessing the motive power of water. Large-scale water use in mining produced waste sands, gravels and silts that were flushed downstream, triggering changes in stream and floodplain morphology and function. During the 19th century the shift from artisanal to industrialised mining resulted in a rapid increase in the scale and extent of environmental change. This paper presents results from a multi-disciplinary research program investigating the environmental effects of 19th-century gold mining on waterways in south-eastern Australia. Archaeological and geospatial landscape survey are combined with historical data modelling and geomorphological analysis to examine the extractive processes that produced sediment in headwater regions and how this influenced fluvial processes operating on downstream waterways and floodplains. Our case study of the Three Mile-Hodgson Creek system on the Ovens (Beechworth) goldfield in north-east Victoria indicates that miners mobilised up to 7.3 million m3 of sediment in this small catchment alone. Results of the research suggest that tailings dams and sludge channels in this catchment are important archaeological evidence for early attempts to manage industrial waste.

Contamination of freshwaters is increasing globally, with microalgae considered one of the most sensitive taxa to metal pollution. Here, we used 72 h bioassays to explore the biochemical effects of copper (Cu) on the amino acid (AA) profile and proteome of Chlorella sp. and advance our understanding of the molecular changes that occur in algal cells during exposure to environmentally realistic Cu concentrations. The Cu concentrations required to inhibit algal growth rate by 10% (EC10) and 50% (EC50) were 1.0 (0.7–1.2) µg L−1 and 2.0 (1.9–2.4) µg L−1, respectively. The AA profile of Chlorella sp. showed increases in glycine and decreases in isoleucine, leucine, valine, and arginine, with increasing Cu. Proteomic analysis revealed the modulation of several proteins involved in energy production pathways, including: photosynthesis, carbon fixation, glycolysis, and oxidative phosphorylation, which likely assists in meeting increased energy demands under Cu-stressed conditions. Copper exposure also caused up-regulation of cellular processes and signalling proteins, and the down-regulation of proteins related to ribosomal structure and protein translation. These changes in biomolecular pathways have direct effects on the AA profile and total protein content and provide an explanation for the observed changes in amino acid profile, cell growth and morphology. This study shows the complex mode of action of Cu on Chlorella under environmentally realistic Cu concentrations and highlights several potential biomarkers for future investigations.

The Victorian gold rush began in 1851, resulting in massive demographic, land use, and social changes (Serle 1968). Rivers, during much of the gold mining history of Victoria, were used as a “free” resource, both to extract and process sediment. The effect on river systems around the state was catastrophic. A quarter of the length of the main streams was damaged. Even though the devastating environmental impact of Victorian gold mining was recognised at the time, it appears to have been forgotten today (Figure 1). This is despite extensive documentation of the number of mining operations, methods used, resultant environmental impacts and consequent legislation. The ARC discovery project “Rivers of gold” set up a multi-disciplinary team to try and reconstruct the historical development of mining across the state of Victoria, and to determine the legacy of this mining.

Macroinvertebrates play a key role in aquatic food webs, with amino acids (AA) playing an important role in determining their nutritional value to higher consumers. This study aimed to determine whether AA profile varies among four macroinvertebrate taxa, spatially and seasonally (summer/winter). The freshwater prawn, Macrobrachium australiense; freshwater shrimp, Paratya australiensis; freshwater snail, Physa sp. and caddisfly, Triplectides sp. were collected from seven sites along the Murray–Darling Basin, Australia. Sampling was conducted during summer 2015 (October–December), winter 2016 (May–June) and summer 2016 (October–December). AA profiles were found to be significantly different among the four taxa, with the highest total amino acid content found in decapods (M. australiense and P. australiensis). Based on the total essential AA content from our study, decapods had higher nutritional value compared to Physa. Seasonal variations in AA profiles of decapods were observed, with an increased proportion of the non-essential amino acid glycine and decreased proportion of different essential AAs found in individuals collected during winter compared to summer. No seasonal variation in the AA profiles of Physa sp. or Triplectides sp. was shown. Spatial variation in the AA profile of macroinvertebrates was only recorded in P. australiense during winter 2016. These findings expand the current understanding of the AA profile of freshwater macroinvertebrates showing that AA profiles are taxa specific and vary seasonally and spatially depending on taxa.

Anthropogenic effects lead to nonrandom alterations to macroinvertebrate communities, which may lead to alteration of the ‘micronutrient landscapes’ experienced by higher consumers. Underst...

A significant but previously unquantified factor in anthropogenic change in Australian rivers was the release of large volumes of sediment produced by gold mining in the 19th century. This material, known historically as ‘sludge’, rapidly entered waterways adjacent to mining areas and caused major environmental damage. We interrogate detailed historical records from the colony of Victoria spanning the period 1859 to 1891 to reconstruct the temporal and spatial distribution of sediment volumes released by mining activity. Based on these records, we estimate that at least 650 million m3 of material was released into rivers in the 19th century, exceeding natural sediment yield to rivers by an average 140 times. Although the sediment yield per river is not high when compared with examples around the world, the widespread impacts of sludge distinguishes the case of Victoria. The sludge affected three-quarters of catchments in the state due to the large number of small mining operations spread over hundreds of creeks and gullies across the colony. The impacts of sludge to rivers and farmland filled newspapers for more than 50 years and generated numerous parliamentary inquiries. Today, the impacts are largely forgotten and unrecognised, as are the continuing impacts on aquatic systems. The estimates generated in this study provide a basis for understanding the continuing impact of historical mining on Victorian rivers.

Acid mine drainage (AMD) is one of the major environmental problems impacting aquatic ecosystems globally. We studied changes in the community composition of macroinvertebrates and amino acid (AA) profiles of dominant taxa along an AMD contamination gradient within the Dee River, Queensland, Australia to understand how AMD can affect the biomolecular composition of macroinvertebrates. Taxa richness and community composition of macroinvertebrates changed widely along the AMD gradient with significantly lower taxa richness recorded at the polluted sites compared to upstream and downstream sites. The Dipteran families: Chironomidae and Ceratopogonidae, the Odonata family Gomphidae, and the Coleoptera family Dytiscidae were the only families found at all sampling sites and were used here for AA analysis. There were significant variations in the AA profiles among the studied taxa. The AA profile of each taxon also varied among upstream, polluted and downstream sites suggesting that contamination of a river system with acid mine drainage not only alters the overall macroinvertebrate community composition but also significantly influences the AA profile of organisms that are tolerant to AMD. This study highlights the potential of using AA profiling to study the response of aquatic organisms to contamination gradients such as those associated with AMD.

The export of fixed carbon from peatlands is likely important in driving freshwater ecosystem productivity in head water streams. Here we studied the stream composition from three peatlands, and the sub-catchment containing these peatlands, in response to a natural storm event. We investigated the dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) mobilised by this event as well as the dissolved combined amino acids (DCAAs; proteins, peptides and free AAs) component of the DOC/DON. The storm pulse was characterised by a strong DOC/DON/DCAA pulse reflecting the mobilisation of materials from the peat profile. Through the storm cycle a transient increase in the C:N ratio of the DOC was observed (ranging over 20 – 50 across the four sites), likely reflecting the mobilisation of less decomposed material from higher in the peat soil profile. By comparing the DCAA and DON dynamics we show that a DCAA-rich component (fast-DCAA) is mobilised earlier in the storm cycle, likely reflecting a higher mobility in the peat soil. Similarly, comparison of the DCAA and DOC dynamics suggests that at least part of the DOC is mobilised more rapidly than fast-DCAA (fast-DOC). While we may not expect the composition of a storm pulse to be uniform through the cycle, this study shows that within the DOC and DON pools there is spatial and temporal separation of molecular groups. Proteins (in principal) represent both highly bioavailable N-sources as well as potential biological trigger molecules, so our work shows that these compounds are more dominant in the early part (rising limb) of the storm pulse. This understanding of the changing composition of DOC through a storm peak also provides greater insight into the concentration-discharge (C-Q) response of peatlands; our work shows that the activation of water paths higher in the peat profile at high flows leads to the mobilisation of different pools of DOC such that the molecular characteristics of DOC change through the storm cycle.

The headwater streams originating in the Australian Alps are the highest water yielding landscape in South-Eastern Australia and are projected to be impacted by climate change through longer dry periods and more episodic rainfall. In this work we studied the major ion and DOC responses of three alpine peatlands (and the broader catchment containing these systems) to a high intensity (summer) storm event. Despite the high volume of rainfall, major ions in stream waters remained strongly chemostatic throughout the event. This was particularly the case for Ca2+ and Mg2+, as well as the alkalinity by association, and suggests that chemical regulation of these particular cations occurs through rapid equilibration processes. DOC concentrations increased during the storm pulse, leading to a shift in alkalinity partitioning from bicarbonate to organic anions and a decrease in pH, mediated by the CO2 saturation levels in the stream water. Our results suggest that alkalinity generation (Ca2+ and Mg2+ acquisition) and partitioning (DOC export) are decoupled processes that may respond differently to repeat storm events depending on the capacity of these systems to provide these constituents. Under extreme case scenarios depletion of DOC (at constant alkalinity) would lead to a smaller pH dip during a storm pulse, while depletion of alkalinity would lead to a larger pH dip, with buffering controlled by free acid. We have not identified the mechanism for the chemostasis of Ca2+ and Mg2+ (and therefore alkalinity) in this work, but this will be critical to understanding the capacity of these peatlands to respond to repeat and more intense storm events.

Three permanent alpine springs and their associated pools in the Australian Alps were studied over a summer season to understand their hydrochemical function and characterise the (previously unreported) aquatic macroinvertebrate communities. These “source” pools represent an extremely limited habitat within Australian alpine peatlands and are likely vulnerable to groundwater flow changes associated with climate change. The pools provide an extremely stable habitat for 30 macroinvertebrate taxa in the harsh alpine environment with near chemostatic conditions and pool temperatures constrained to 5.6–6.3°C despite air temperatures varying between −4.5°C and 30.6°C. Although small in area source pools have a significant effect on nitrate concentrations (decreases) and pH (increases) of waters flowing to downstream Sphagnum-dominated peatlands. The macroinvertebrate communities were distinctly different to that found in peatlands and headwater streams and were dominated by the amphipod Austrocrangonyx sp. (76.6% of total abundance), despite the low pH conditions (pH 5.27–5.56). Some of the macroinvertebrate taxa (Nannochorista, Anzacladius, and Parochlus) have a Gondwanan and circum-Antarctic distribution, similar to the bryophytes that also occur in these pools (Bartramia and Blindia). These source pools contribute to the diversity of alpine fauna and should be separately recognised and protected.

Dissolved organic matter (DOM) within freshwaters is essential for broad ecosystem function. The concentration and type of DOM within rivers depends on the relative contributions of allochthonous sources and the production and consumption of DOM by microbes. In this work we have examined the temporal patterns in DOM quality and productivity in three lowland rivers in dryland Australia using fluorescence excitation emission scans. We assessed the production and consumption of DOM within light and dark bottle assays to quantify the relative contribution of bacteria and algae to the DOM pool and simultaneously assessed whether the systems were autotrophic or heterotrophic. DOM varied temporally within the three river systems over the course of the study period. Characterisation of DOM within light and dark bottles following a 6-hour incubation revealed microbial consumption of a humic-like component and production of protein-like components similar in nature to the amino acids tryptophan and tyrosine. The lack of a significant difference in DOM quality between the light and dark bottles indicated that the protein-like DOM is likely derived from bacterial activity. Respiration was shown to be higher than gross primary production in both whole river and bottle assays, yielding negative net production values and demonstrating that these rivers were predominately heterotrophic. Our work suggests that bacterial metabolism of DOM may be a significant contributor to the production of protein-like components within heterotrophic freshwater systems.

Humans modify prey communities and hence alter the availability of nutrients to wild carnivores. Such changes in amino acid ‘landscapes’ are likely to affect the growth of individuals, and potentially the success of populations. This study aimed to determine whether amino acid composition of animal prey alone affects protein synthesis efficiency and N wastage of a freshwater carnivore. River blackfish (Gadopsis marmoratus) were fed two diets differing only in amino acid composition: the first diet was formulated to match the composition of the fish themselves, representing a balanced ‘ideal protein’, whereas the second diet was produced to match the composition of a prey item, namely the shrimp Macrobrachium australiense. By measuring the postprandial increase in metabolic rate (specific dynamic action) and ammonia excretion, it was found that the amino acid composition of the fish diet was associated with an increase in protein synthesis, whereas the shrimp diet doubled the amount of dietary amino acids directed to pathways of catabolic energy production and N wastage. This study adds to the stoichiometric ecology literature by showing that changes in the amino acid composition of food webs could affect carnivore growth and nutrient cycling.

Significant amounts of sulfuric acid (H2SO4) rich saline water can be produced by the oxidation of sulfide minerals contained in inland acid sulfate soils (IASS). In the absence of carbonate minerals, the dissolution of phyllosilicate minerals is one of very few processes that can provide long-term acid neutralisation. It is therefore important to understand the acid dissolution behavior of naturally occurring clay minerals from IASS under saline–acidic solutions. The objective of this study was to investigate the dissolution of a natural clay-rich sample under saline–acidic conditions (pH 1–4; ionic strengths = 0.01 and 0.25 M; 25 °C) and over a range of temperatures (25–45 °C; pH 1 and pH 4). The clay-rich sample referred to as Bottle Bend clay (BB clay) used was from an IASS (Bottle Bend lagoon) in south-western New South Wales (Australia) and contained smectite (40%), illite (27%), kaolinite (26%) and quartz (6%). Acid dissolution of the BB clay was initially rapid, as indicated by the fast release of cations (Si, Al, K, Fe, Mg). Relatively higher Al (pH 4) and K (pH 2–4) release was obtained from BB clay dissolution in higher ionic strength solutions compared to the lower ionic strength solutions. The steady state dissolution rate (as determined from Si, Al and Fe release rates; RSi, RAl, RFe) increased with decreasing solution pH and increasing temperature. For example, the highest log RSi value was obtained at pH 1 and 45 °C (−9.07 mol g−1 s−1), while the lowest log RSi value was obtained at pH 4 and 25 °C (−11.20 mol g−1 s−1). A comparison of these results with pure mineral dissolution rates from the literature suggests that the BB clay dissolved at a much faster rate compared to the pure mineral samples. Apparent activation energies calculated for the clay sample varied over the range 76.6 kJ mol−1 (pH 1) to 37.7 kJ mol−1 (pH 4) which compare very well with the activation energy values for acidic dissolution of monomineralic samples e.g. montmorillonite from previous studies. The acid neutralisation capacity (ANC) of the clay sample was calculated from the release of all structural cations except Si (i.e. Al, Fe, K, Mg). According to these calculations an ANC of 1.11 kg H2SO4/tonne clay/day was provided by clay dissolution at pH 1 (I = 0.25 M, 25 °C) compared to an ANC of 0.21 kg H2SO4/tonne clay/day at pH 4 (I = 0.25 M, 25 °C). The highest ANC of 6.91 kg H2SO4/tonne clay/day was provided by clay dissolution at pH 1 and at 45 °C (I = 0.25 M), which is more than three times higher than the ANC provided under the similar solution conditions at 25 °C. In wetlands with little solid phase buffering available apart from clay minerals, it is imperative to consider the potential ANC provided by the dissolution of abundantly occurring phyllosilicate minerals in devising rehabilitation schemes.

Increased sulfate levels caused by salinisation associated with water table elevation has led to reduced sulfur accumulation in many inland (historically fresh) water bodies. Subsequent oxidation of the accumulated reduced sulfur is acid generating and, in the absence of sufficient acid-neutralising capacity, results in wetland acidification and associated toxic effects. Although alkalinity is generated during sulfate reduction, if this is not captured in a solid phase it may be removed from the reduction site via surface or groundwater exchange. This study examines the processes controlling the generation and retention of acid-neutralising capacity during the reduction phase. We use thermodynamic modelling to demonstrate that the ionic composition of a wetland’s source water, particularly the calcium to sulfate ratio, is an important factor in determining whether sufficient alkalinity can be stored (as calcium carbonate) during sulfate reduction to avoid acidification upon re-oxidation. Through controlled reactor experiments, where microbial sulfate reduction was induced in a wetland sediment suspension in the presence of a range of calcium (and magnesium) concentrations, we confirm the importance of carbonate precipitation for alkalinity storage. The reactor experiments also highlight the role of the sediment for solid-phase alkalinity storage and subsequent acid buffering and show that the extreme pH values predicted by modelling based on ionic composition alone are attenuated in the presence of natural sediment. We outline an approach in which wetland source water composition and sediment buffering properties could be coupled to a hydrologic model to allow determination of the risk of wetland acidification during a sulfate reduction–oxidation cycle.

We report on the synthesis and As adsorption properties of a novel chitosan – iron (oxyhydr)oxide composite material for the remediation of arsenic-contaminated water supplies. FE-SEM, Mossbauer spectroscopy, ICP-OES and synchrotron (Bulk XAS, μXRF) techniques were applied to determine the composition of the new material and investigate the As uptake efficiency and mechanism. The iron (oxyhydr)oxide phase has been identified as a nano-sized goethite, well dispersed in the chitosan matrix, leading to the name ‘chitosan goethite bionanocomposite’ (CGB). The CGB material is prepared in the form of beads of high density and excellent compression strength; the embedding of the goethite nanoparticles in the chitosan matrix allows for the high adsorption capacity of nanoparticles to be realized. CGB beads remove both As(III) and As(V) efficiently from water, over the pH range 5–9, negating the need for pre-oxidation of As(III). Kinetic studies and μXRF analysis of CGB bead sections show that diffusion-adsorption of As(V) into CGB beads is faster than for As(III). Using CGB beads, synthetic high-arsenic water (0.5 mg-As/L) could be purified to world drinking standard level (

Phosphorus is an important nutrient for plants and algae, and can be the limiting nutrient in aquatic ecosystems. However, oversupply can lead to significant water quality issues. The largest source and sink of P in most aquatic systems is the sediment. As a consequence of drought, in many places sediments that normally would have remained inundated are now being desiccated. Based on previous studies, it is often difficult to predict what impact drying will have on the cycling of P. This is because most of these studies have looked at drying across a chronosequence in the field, where there may be differences in sediment composition or microbial community structure. In this paper we present the results of a study where sediment was exposed to progressively more severe drying in the laboratory - starting with wet sediment, followed by air drying and then sequential oven drying at 30, 50 and 85 °C. Drying resulted in a shift in P speciation, notably with an increase in NaHCO3-extractable reactive P and a decline in NaHCO3-extractable unreactive P, likely indicating an increase in bioavailable, easily exchangeable P. Drying also resulted in a decline in the microbial-P fraction. Drying significantly affected the P adsorption characteristics of the sediment. The total amount of P adsorbed by the sediment and the linear adsorption co-efficient both declined, while the amount of native P adsorbed to the sediment and the equilibrium P concentration both increased. Drying also affected iron speciation with a shift from more reactive oxalate-extractable Fe to more recalcitrant citrate-dithionate-bicarbonate-extractable Fe, suggesting an increase in iron crystallinity and hence decrease in P adsorption capacity. The increase in crystallinity is consistent with Fe EXAFS results, which showed that drying resulted in an increase in edge-sharing neighbours. We hypothesise that the shifts in P speciation, the decline in P adsorption capacity, the increase in the equilibrium P concentration, as well as the death of micro-organisms (as evidenced by a decline in microbial P) on drying all contribute to the Birch effect - the initial pulse of P and/or N upon inundation of dried soils or sediments.

The prevalence of sulphidic sediments in inland wetlands has been only recently recognized in many parts of the world, including Australia. The exposure of sulphidic sediments in these wetlands due to natural and human induced drying events has resulted in the oxidation of iron sulfide minerals, the formation of secondary iron minerals characteristic of acid sulfate soils and the release of highly acidic solutions. The objective of this study was to determine the mineralogy and morphology of sediments collected from the oxidized surface horizon (0–5 cm) of an inland acid sulfate soil located in south-western New South Wales (NSW), Australia. Random powder X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning transmission electron microscopy combined with energy dispersive X-ray spectroscopy (STEM–EDS) techniques were used to characterize the minerals present in these sediments. Akaganeite was identified as the major mineral phase in the sediments; K-jarosite was also determined in small amounts in some sediments. The XRD patterns of sequentially washed (E-pure® water–0.01 M HCl–0.01 M EDTA) sediment samples showed all akaganeite peaks; the Rietveld refinement of these patterns also revealed a predominance of akaganeite. The chemical analyses of the original and washed sediments using STEM–EDS clearly showed the presence of akaganeite as a pure mineral phase with an average Fe/Cl mole ratio of 6.7 and a structural formula of Fe 8 O 8 (OH) 6.8 (Cl) 1.2 . These findings show that the extreme saline–acidic solutions (pH ∼ 2, EC = 216 dS/m) at the Bottle Bend lagoon provide ideal conditions for the crystallization of this rarely forming mineral.

The dissolution rate of illite, a common clay mineral in Australian soils, was studied in saline–acidic solutions under far from equilibrium conditions. The clay fraction of Na-saturated Silver Hill illite (K1.38Na0.05)(Al2.87Mg0.46Fe3+0.39Fe2+0.28Ti0.07)[Si7.02Al0.98]O20(OH)4 was used for this study. The dissolution rates were measured using flow-through reactors at 25 ± 1 °C, solution pH range of 1.0–4.25 (H2SO4) and at two ionic strengths (0.01 and 0.25 M) maintained using NaCl solution. Illite dissolution rates were calculated from the steady state release rates of Al and Si. The dissolution stoichiometry was determined from Al/Si, K/Si, Mg/Si and Fe/Si ratios. The release rates of cations were highly incongruent during the initial stage of experiments, with a preferential release of Al and K over Si in majority of the experiments. An Al/Si ratio >1 was observed at pH 2 and 3 while a ratio close to the stoichiometric composition was observed at pH 1 and 4 at the higher ionic strength. A relatively higher K+ release rate was observed at I = 0.25 in 2–4 pH range than at I = 0.01, possibly due to ion exchange reaction between Na+ from the solution and K+ from interlayer sites of illite. The steady state release rates of K, Fe and Mg were higher than Si over the entire pH range investigated in the study. From the point of view of the dominant structural cations (Si and Al), stoichiometric dissolution of illite occurred at pH 1–4 in the higher ionic strength experiments and at pH ⩽3 for the lower ionic strength experiments. The experiment at pH 4.25 and at the lower ionic strength exhibited lower RAl (dissolution rate calculated from steady state Al release) than RSi (dissolution rate calculated from steady state Si release), possibly due to the adsorption of dissolved Al as the output solutions were undersaturated with respect to gibbsite. The dissolution of illite appears to proceed with the removal of interlayer K followed by the dissolution of octahedral cations (Fe, Mg and Al), the dissolution of Si is the limiting step in the illite dissolution process. A dissolution rate law showing the dependence of illite dissolution rate on proton concentration in the acid-sulfate solutions was derived from the steady state dissolution rates and can be used in predicting the impact of illite dissolution in saline acid-sulfate environments. The fractional reaction orders of 0.32 (I = 0.25) and 0.36 (I = 0.01) obtained in the study for illite dissolution are similar to the values reported for smectite. The dissolution rate of illite is mainly controlled by solution pH and no effect of ionic strength was observed on the dissolution rates.

We identify the 10 major terrestrial and marine ecosystems in Australia most vulnerable to tipping points, in which modest environmental changes can cause disproportionately large changes in ecosystem properties. To accomplish this we independently surveyed the coauthors of this paper to produce a list of candidate ecosystems, and then refined this list during a 2-day workshop. The list includes (1) elevationally restricted mountain ecosystems, (2) tropical savannas, (3) coastal floodplains and wetlands, (4) coral reefs, (5) drier rainforests, (6) wetlands and floodplains in the Murray-Darling Basin, (7) the Mediterranean ecosystems of southwestern Australia, (8) offshore islands, (9) temperate eucalypt forests, and (10) salt marshes and mangroves. Some of these ecosystems are vulnerable to widespread phase-changes that could fundamentally alter ecosystem properties such as habitat structure, species composition, fire regimes, or carbon storage. Others appear susceptible to major changes across only part of their geographic range, whereas yet others are susceptible to a large-scale decline of key biotic components, such as small mammals or stream-dwelling amphibians. For each ecosystem we consider the intrinsic features and external drivers that render it susceptible to tipping points, and identify subtypes of the ecosystem that we deem to be especially vulnerable.

The chlorite group of minerals exhibit a wide range of surface charging properties in aqueous suspensions. A systematic review of the literature as it relates to the flotation, depression and surface properties of chlorite and related minerals was undertaken, with a view to using this information to help develop suitable reagent schemes which might allow the selective removal of chlorite from sulphide and oxide flotation systems. The surface charge on chlorite mineral particles originates from permanent charges on basal planes of the crystallites and pH dependent (amphoteric) charge on crystallite edges, typical of clay minerals. The net charge on chlorite particles depends upon the edge/face plane ratio (crystallite size), the solution pH and the presence of specifically adsorbing ions (principally Ca2+). Both cationic and anionic surfactants (collectors) are observed to adsorb on chlorite particles, over a wide range of pH conditions. This apparently contradictory behaviour is most likely due to...

Sericite is a fine grained muscovite mica, which is widely distributed in nature. It commonly occurs in many base metal ores, where it can become a major diluent in the concentrates produced from these ores, as well as in igneous rocks. It can be strongly recovered in flotation froths under circumstances where it is both wanted and unwanted. Muscovite, which does not have any inherent natural flotability, responds readily to cationic flotation collectors to yield concentrates of high grade and recovery from granitic or pegmatite deposits, and the technology for this separation is well established. Sericite, on the other hand, often reports strongly to concentrates from base metal ores in which it occurs. Under these circumstances, the rejection of the sericite from the froth product is generally difficult, but nevertheless important, in order to minimise contamination of the base metal concentrate. This contamination can cause problems in subsequent smelting and/or leaching. Because in these flota...

Understanding longitudinal trends in the processing of carbon in rivers represents a much conceptualised, but infrequently tested, issue in aquatic ecology. In this study, we conducted concurrent longitudinal examinations of three very different rivers in eastern Australia to determine whether general principles in river functioning exist across broad geographic and hydrologic scales. Specifically, we examined trends in ambient basic water chemistry, nutrient concentrations, dissolved organic carbon (DOC), extracellular enzymes and food web structure and functioning and conducted bioassays to examine the degree to which DOC and nutrients limit heterotrophic bacterial respiration. These parameters revealed striking similarities across all sites. For metazoan communities, stable isotope analysis showed that algal carbon was the dominant basal resource utilised by consumers in all three rivers, suggesting that in-stream primary producers strongly underpin trophic pathways regardless of the position within a catchment or catchment condition. Analyses of extracellular enzymes revealed that microbial communities are actively utilising DOC at all sites. In fact, heterotrophic microbial respiration was strongly limited by DOC at all sites, with nutrient additions resulting in only relatively minor increases in respiration. Ultimately, this study demonstrates that DOC and algal carbon are critically important drivers of ecosystem processes in Australian riverine ecosystems. Furthermore, across all of our sites and rivers, ambient nutrient concentrations did not influence carbon processing. The consistent longitudinal trends in river function identified in this study provide useful insights for catchment managers and modellers with respect to identifiying key principles that underpin ecosystem functioning in Australian rivers. Copyright © 2009 John Wiley & Sons, Ltd.

Environmental contextSphagnum moss is a widespread species in peatlands globally and responsible for a large fraction of carbon storage in these systems. We used synchrotron infrared microspectroscopy to characterise the acid-base properties of Sphagnum moss and the conditions under which calcium uptake can occur (essential for plant tissue integrity). The work allows a chemical model for Sphagnum distribution in the landscape to be proposed. AbstractSphagnum is one the major moss types responsible for the deposition of organic soils in peatland systems. The cell walls of this moss have a high proportion of carboxylated polysaccharides (polygalacturonic acids), which act as ion exchangers and are likely to be important for the structural integrity of the cell walls. We used synchrotron light source infrared microspectroscopy to characterise the acid-base and calcium complexation properties of the cell walls of Sphagnum cristatum stems, using freshly sectioned tissue confined in a flowing liquid cell with both normal water and D2O media. The Fourier transform infrared spectra of acid and base forms are consistent with those expected for protonated and deprotonated aliphatic carboxylic acids (such as uronic acids). Spectral deconvolution shows that the dominant aliphatic carboxylic groups in this material behave as a monoprotic acid (pKa=4.97–6.04). The cell wall material shows a high affinity for calcium, with a binding constant (K) in the range 103.9–104.7 (1:1 complex). The chemical complexation model developed here allows for the prediction of the chemical environment (e.g. pH, ionic content) under which Ca2+ uptake can occur, and provides an improved understanding for the observed distribution of Sphagnum in the landscape.

The flotation response of gersdorffite has been determined in a series of batch flotation tests in which a sulphide sample containing about 76% gersdorffite was floated from mixtures with quartz. Using xanthate as collector, the arsenide floated strongly at pH 9, irrespective of whether lime, sodium hydroxide or sodium carbonate was used as pH modifier. When the pH was raised further to 10 or more using lime, the flotability decreased sharply. Changing the pulp potential at pH 9 also strongly affected the flotation response. Above about − 230 mV SHE, the mineral floated strongly, but below this potential it was essentially non-flotable. As far as it was tested (up to + 400 mV SHE), no upper limiting potential was found. Adding cyanide to the grinding mill brought about only a weak depressant effect on subsequent gersdorffite flotation at both pH 9 and 10. However, adding the same amount of cyanide to the flotation cell produced a strong depressant effect at the same pH values. At both pH 9 and pH 10, a threshold cyanide addition existed below which gersdorffite floated strongly, and above which it did not. For the conditions used in this study, this addition equates to about 100 g/t at pH 9 and about 80 g/t at pH 10. A hypothesis for the depression effect is presented which is consistent with both the available flotation data and a series of diagnostic analyses of grinding and flotation pulps completed during the test work.

Selected-area electron diffraction (SAED) and energy dispersive analysis were used to study the structure of synthetic heavy-metal sorbed birnessites (MeBi). Samples were prepared by equilibrating a suspension of Na-rich buserite (NaBu) at pH4 in the presence of various heavy metal cations (Me), including Pb, Cd, Zn, and Cu. Five main types of SAED patterns were observed. Types I and II were observed only for ZnBi micro-crystals, and they both consist of two super-cell reflection networks related by a mirror plane parallel to the a *c* plane. In direct space, these twinned networks correspond to the hexagonal supercells with AH = BH = 7b/ 3, and AH = BH = 7b, for ZnBi type I and II, respectively. In the two varieties, the supercells result from an ordered distribution of vacant layer octahedra capped by interlayer Zn in ZnBi layers. This distribution is described by a hexagonal cell with AH = 7b. In ZnBi micro-crystals of type I, interstratified twinned right- and left-handed fragments are similar to chalcophanite (ZnMn3O7-3H2O - Wadsley 1955; Post and Appleman 1988), and distributions of vacant layer octahedra from adjacent layers are regularly shifted with respect to each other by 1/3 of the long diagonal of the hexagonal layer unit cell. In ZnBi micro-crystals of type II, distributions of vacant layer octahedra are not regularly shifted from one layer to the adjacent one. SAED patterns of types III and IV occur for PbBi, ZnBi, and CdBi micro-crystals and contain super-cell reflections distributed parallel to [100] * with a periodicity which is not commensurate with that of the MeBi sub-structure (a */2.15 and a*/5.25, respectively). The super-cell reflections result from the ordered distribution within MeBi layers of vacant layer sites capped by Me as pairs along the a axis. Within each pair, vacant sites are separated by 2a for type III, and by 5a for type IV. In one-layer monoclinic structures, the apparent incommensurability arises from the +a/3 shift between adjacent layers having a similar one-dimensional periodic distribution of interlayer Me located above and below vacant octahedra sharing three corners with Mnlayer octahedra (TC sites). Tetrahedral coordination of these Me cations in TC sites, as in ZnBi, leads to the formation of strong H-bonds between adjacent layers. A similar incommensurate effect occurs in one layer hexagonal MeBi if octahedrally coordinated Me cations periodically distributed along the a axis are located above and/or below empty tridentate cavities sharing three edges with Mnlayer octahedra ( VITE sites, PbBi). SAED patterns of type V contain only sub-cell reflections and were observed mostly for PbBi and CuBi micro-crystals. Three different conditions can lead to the absence of supercell reflections: (1) a low amount of sorbed Me (PbBi); (2) the presence of Me having a similar scattering power as that of Mn on a single side of vacant layer sites (CuBi); or (3) a random distribution of interlayer species.

Kinetic studies on the oxidation of ethyl xanthate (O-ethyl dithiocarbonate) by hydrogen peroxide have been conducted for a range of ethyl xanthate and hydrogen peroxide concentrations over the pH range 8–12. The initial reaction product is a canonical form of O-ethyl S-oxodithiocarbonate. Further oxidation leads to a bifurcation in the reaction pathway, with the formation of either O-ethyl thiocarbonate or a canonical form of O-ethyl S-oxoperoxydithiocarbonate. The partitioning of the reaction between these alternative reaction paths is pH dependent, with the proportion directed towards the O-ethyl thiocarbonate branch increasing over the pH range 10 to12. Further oxidation of O-ethyl thiocarbonate leads to the formation of O-ethyl S-oxothiocarbonate (or a canonical form thereof), analogous to the initial oxygen addition to ethyl xanthate. For both reaction branches the ultimate sulfur-containing product is sulfate. Apart from the process controlling the bifurcation, the reaction kinetics can be modelled as a series of bimolecular oxygen addition steps. This kinetic model is supported by hydroxyl radical scavenging experiments (using tert-butyl alcohol) that suggest no involvement by OH˙. The pH dependence of the rate parameters indicates that reaction occurs exclusively with H2O2 rather than HO2−, consistent with the expected nucleophilic attack at the peroxide oxygen. The process controlling the partitioning between the two alternative pathways is proposed to originate from an oxygen addition adduct of O-ethyl S-oxodithiocarbonate. This work reveals that a range of potential metal ion complexants may be produced in the industrial application of xanthates (primarily sulfide mineral extraction, but also including viscose rayon production and pesticide manufacture), and that the environmental chemistry of these reagents is more complex than has been previously appreciated.

The redox properties of Fe(II) adsorbed onto mineral surfaces have been highly studied over recent years due to the wide range of environmental contaminants that react with this species via abiotic processes. In this work the reactivity of Fe(II) adsorbed onto hydrous ferric oxide (HFO) has been studied using ferrocene (bis-cyclopentadienyl iron(II); Fc) derivatives as electron shuttles in cyclic voltammetry (CV) experiments. The observed amplification of the ferrocene oxidation peak in CV is attributed to reaction between the electrochemically generated ferrocenium (Fc(+)) ion and adsorbed Fe(II) species in a catalytic process (EC' mechanism). pH dependence studies show that the reaction rate increases with Fe(II) adsorption and is maintained in the absence of aqueous Fe(2+), providing strong evidence that the electron transfer process involves the adsorbed species. The rate of reaction between Fc(+) and adsorbed Fe(II) increases with the redox potential of the ferrocene derivative, as expected, with bimolecular rate constants in the range 10(3)-10(5) M(-1) s(-1). The ferrocene-mediated electrochemical method described has considerable promise in the development of a technique for measuring electron-transfer rates in geochemical and environmental systems.

The structural transformation of high pH Na-rich buserite (NaBu) to H-exchanged hexagonal birnessite (HBi) at low pH was studied by simulation of experimental X-ray diffraction patterns. Four HBi samples were prepared by equilibration of NaBu at constant pH in the range pH 5-2. The samples differ from each other by the presence of one (at pH 2 and 3) or two (at pH 4 and 5) phases, and by the structural heterogeneity of these phases which decreases with decreasing pH. The sample obtained at pH 5 is a 4:1 physical mixture of a 1H phase ( a = 4.940 A, b = a /√3 = 2.852 A, c = 7.235 A, β = 90°, γ = 90°) and of a 1M phase ( a = 4.940 A, b = a /√3 = 2.852 A, c = 7.235 A, β = 119.2°, γ = 90°) in which successive layers are shifted with respect to each other by + a /3 along the a axis as in chalcophanite. Both the 1H and 1M phases contain very few well-defined stacking faults at pH 5. At pH 4, the sample is a 8:5 physical mixture of a 1H phase containing 15% of monoclinic layer pairs and of a 1M phase containing 40% of orthogonal layer pairs. Any further decrease of the pH leads to the formation of a single defective 1H phase. This 1H phase contains 20% and 5% of monoclinic layer pairs at pH 3 and 2, respectively. Independent of pH, all phases contain 0.833 Mnlayer cations, 0.167 vacant layer sites, and 0.167 interlayer Mn cations located either above or below layer vacancies per octahedron. A structural formula is established at each pH. The origin of the observed phase and structural heterogeneities has been analyzed. 1H and 1M phases are assumed to inherit their specific structural and crystal chemical features from the two distinct NaBu modifications. NaBu type I, with a high proportion of Mn4+layer cations, is thought to be responsible for the monoclinic layer stacking because this configuration allows Mn cations from adjacent layers to be as far as possible from each other, thus minimizing the electrostatic repulsion between these high charge cations. In contrast, NaBu type II has a high interlayer charge induced by Mn3+layer for Mn4+layer substitutions. Consequently, the 1H phase has a high amount of interlayer protons and achieves compensation of the unfavorable overlap of layer and interlayer Mn cations, in projection on the ab -plane, by the presence of strong hydrogen bondings between layers. The higher proportion of defined stacking faults in both 1H and 1M phases at pH 4 compared to pH 5 can be attributed to the increase in reaction rate with decreasing pH. At lower pH (3 and 2) the formation of strong hydrogen bonds between adjacent layers controls the layer stacking mode and leads to the formation of a unique 1H phase. The proportion of well-defined stacking faults in this phase decreases from pH 3 to 2.

The reduction of ultrasmall colloidal covellite (CuS) has been examined using 1,1‘-bis(sulfonatopropyl)-4,4‘-bipyridinium radicals (ZV-) over the pH range 2.5−10. The corrosion process using this reductant is a one-electron-transfer process, producing colloidal Cu2S and H2S. It was observed that this process is partially reversible upon exposure of the irradiated sample to either elevated temperatures or air. In addition, at pH 2.5, the reaction was further complicated by the formation of molecular H2. At pH 9 ± 1 the reaction between ZV- and CuS ceased to be favorable.

Soluble Fe(II) is an important reductant in anoxic surficial fluids, due to fast redox kinetics of the Fe(II)/Fe(III) couple. However, its availability is limited in neutral and alkaline pH range by the solubility of FeS(s), Fe3(PO4)2, FeCO3(s) and other Fe(II) rich minerals. The adsorption of Fe(II) on a variety of mineral phases has been studied. It is shown that, provided enough surface area is available, adsorption is completed before the onset of precipitation, leading to Fe(II) surface species which are able to reduce compounds present in solution in a very efficient way. The abiotic reduction of a variety of N rich compounds (nitrites and nitrobenzenes) by sorbed Fe(II) has been reported in the literature. The observed initial rate of such reduction reactions is shown to be proportional to the FeIIIOFeIIOH° species concentration, in the same manner that the homogeneous oxygenation rate of Fe(II) is proportional to Fe(OH)2°(aq) concentration. The electron transfer in these reactions, appears to occur dominantly via an outer sphere mechanism. In contrast, the abiotic reduction of inorganics, such as U(VI) and Tc(VII), by sorbed Fe(II) involves inner sphere electron transfer mechanism. In the case of uranium reduction, three kinetic steps can be distinguished: the adsorption of the uranyl ion (formation of an inner sphere surface complex), followed by two reductive steps which lead to the formation of a UO2/Fe(OH)3 mixed solid phase. These surface-catalysed reduction reactions may have led to the formation of uranium mineral ores and to the removal of uranium from reducing surface waters.

The geochemistry of Co at the Earth's surface is closely associated with that of manganese oxides. This geochemical association results from the oxidation of highly soluble Co (super 2+) to weakly soluble Co (super 3+) species, coupled with the reduction of Mn (super 4+) or Mn (super 3+) ions, initially present in the manganese oxide sorbent, to soluble Mn (super 2+) . The structural mechanism of this Co immobilization-manganese oxide dissolution reaction was investigated at the buserite surface. Co-sorbed samples were prepared at different surface coverages by equilibrating a Na-exchanged buserite suspension in the presence of aqueous Co (super 2+) at pH 4. The structure of Co-sorbed birnessite obtained by drying buserite samples was determined by X-ray diffraction (XRD) and powder and polarized EXAFS spectroscopy. For each sample we determined the proportion of interlayer cations and layer vacancy sites, the Co (super 2+) /(Co (super 2+) +Co (super 3+) ) ratio, the nature of Co sorption crystallographic sites, and the proportion of interlayer vs. layer Co. From this in-depth structural characterization two distinct oxidation mechanisms were identified that occur concurrently with the transformation of low pH monoclinic buserite to hexagonal H-rich birnessite (Drits et al. 1997; Silvester et al. 1997). The first mechanism is associated with the fast disproportionation of layer Mn (super 3+) according to 2Mn (super 3+) layer -->Mn (super 4 + ) layer +[] layer + Mn (super 2+) solution , where [] denotes a vacant site. Divalent Co sorbs above or below a vacant site ([] 1 ) and is then oxidized by the nearest Mn (super 3+) layer . The resulting Co (super 3+) species fills the [] 1 position while the reduced Mn migrates to the interlayer or into solution creating a new vacant site ([] 2 ). This reaction can be written: Co (super 2+) solution +[] 1 + Mn (super 3+) layer --> Co (super 2+) interlayer + [] 1 Mn (super 3+) layer --> Co (super 3+) interlayer + [] 1 + Mn (super 2+) layer --> Co (super 3+) layer + [] 2 + Mn (super 2+) (sub sol/inter) . This mechanism may replicate along a Mn (super 3+) -rich row, and, because the density of vacancies remains constant, it can result in relatively high Co concentrations, as well as domains rich in Co (super 3+) layer -Mn (super 4+) layer . During the low-pH buserite transformation, about one-half of the layer Mn (super 3+) that does not disproportionate migrates from the layer to the interlayer space creating new vacancies, with the displaced Mn (super 3+) residing above or below these vacancies. The second oxidation mechanism involves the replacement of Mn (super 3+) interlayer by Co (super 3+) interlayer ; the latter may eventually migrate into layer vacancies depending on the chemical composition of octahedra surrounding the vacancy. The criterion for the migration of Co (super 3+) into layer vacancies is the need to avoid Mn (super 3+) layer -Co (super 3+) layer -Mn (super 3+) layer sequences. The suite of chemical reactions for this second mechanism can be schematically written: Co (super 2+) solution + Mn (super 3+) interlayer + [] --> Mn (super 2+) solution + Co (super 3+) interlayer + [] --> Mn (super 2+) solution + Co (super 3+) layer , the last step being conditional. In contrast to the first mechanism, this second mechanism decreases the density of vacant sites. At high surface coverage, Co-sorbed birnessite contains a substantial amount of unoxidized Co (super 2+) interlayer species despite some non-reduced Mn (super 3+) in the sorbent. This result can be explained by the sorption of Co (super 2+) solution ? onto vacant sites located in Co (super 3+) layer - and Mn (super 4+) layer -rich domains devoid of Mn (super 3+) . The number and size of these domains increase with the extent of oxidation and the total Co concentration in the solution, and this accounts for the decreasing capacity of buserite to oxidize Co. The weight of structural evidence indicates that Co is oxidized by Mn (super 3+) rather than Mn (super 4+) . Thermodynamic considerations indicate that under the solution pH conditions employed in this study Mn (super 3+) is the more likely electron sink for the oxidation of Co (super 2+) . This study also shows that the high affinity of Co for manganese oxides is not only due to its oxidation to weakly soluble Co (super 3+) species, but also because of the reducted layer strains from the substitution of Co (super 3+) for Mn (super 3+) . Results obtained for these model compounds were compared with those for natural Co-containing asbolane and lithiophorite (Manceau et al. 1987). This comparison indicates that the different structural mechanisms explored in the laboratory can satisfactorily account for the observations made on natural samples. Specifically, the present study proves that Co substitutes for Mn in natural phyllomanganates and allows us to eliminate the possibility of precipitation of discrete CoOOH particles.

Synthetic Na-rich birnessite (NaBi) and its low pH form, hexagonal birnessite (HBi), were studied by X-ray and selected-area electron diffraction (XRD, SAED). SAED patterns were also obtained for synthetic Sr-exchanged birnessite (SrBi) microcrystals in which Sr was substituted for Na. XRD confirmed the one-layer monoclinic structure of NaBi and the one-layer hexagonal structure of HBi with subcell parameters a = 5.172 Aa, b = 2.849 Aa, c = 7.34 Aa, beta = 103.3 degrees and a = 2.848 Aa, c = 7.19 Aa, gamma = 120 degrees , respectively. In addition to super-reflection networks, SAED patterns for NaBi and SrBi contain satellite reflections. On the basis of these experimental observations, structural models for NaBi and HBi are proposed. NaBi consists of almost vacancy-free Mn octahedral layers. The departure from the hexagonal symmetry of layers is caused by the Jahn-Teller distortion associated with the substitution of Mn (super 3+) for Mn (super 4+) . The supercell A = 3a parameter arises from the ordered distribution of Mn (super 3+) -rich rows parallel to [010] and separated from each other along [100] by two Mn (super 4+) rows. The superstructure in the b direction of NaBi type II (B = 3b) comes from the ordered distribution of Na cations in the interlayer space. The maximum value of the layer negative charge is equal to 0.333 v.u. per Mn atom and is obtained when Mn (super 3+) -rich rows are free of Mn (super 4+) . The idealized structural formula proposed for NaBi type II is Na (sub 0.333) (Mn (super 4+) (sub 0.722) Mn (super 3+) (sub 0.222) Mn (super 2+) (sub 0.055) )O 2 . NaBi type I has a lower amount of Mn (super 3+) and its ideal composition would vary from Na (sub 0.167) (Mn (super 4+) (sub 0.833) Mn (super 3+) (sub 0.167) )O 2 to Na (sub 0.25) (Mn (super 4+) (sub 0.75) Mn (super 3+) (sub 0.25) )O 2 . Satellites in SAED patterns of NaBi crystals result from the ordered distribution of Mn (super 4+) and Mn (super 2+) pairs in Mn (super 3+) -rich rows with a periodicity of 6b. The structure of HBi consists of hexagonal octahedral layers containing predominantly Mn (super 4+) with variable amounts of Mn (super 3+) and layer vacancies. The distribution of layer vacancies is inherited from the former Mn (super 3+) distribution in NaB. Interlayer Mn cations are located above or below vacant layer sites. The driving force of the NaBi to HBi transformation is probably the destabilization of Mn (super 3+) -rich rows at low pH.

Solution chemical techniques were used to study the conversion of synthetic Na-rich buserite (NaBu) to hexagonal (H 1 -exchanged) birnessite (HBi) at low pH. The low-pH reaction is broadly characterized by the exchange of structural Na 1 with solution H 1 and the partial loss of Mn 21 to the aqueous phase. The desorption of Na 1 in two temporally distinct steps indicates the existence of two types of binding sites for this cation. Mn 21 EXAFS measurements on Na-rich birnessite (NaBi) show that this mineral is primarily a layered structure formed by edge-sharing MnO6 octahedra, with no evidence for triple- corner (TC) sharing Mn. HBi is significantly different with strong evidence for TC-sharing Mn and therefore layer vacancies. The relative numbers of edge (E)-sharing and TC-shar- ing neighbors determined from EXAFS measurements on HBi is consistent with SAED results (Drits et al. 1997), which suggest that the layer vacancies are restricted to every third row of Mn cations, with 50% of the Mn sites along these rows vacant. The density of vacancies in the entire layer is therefore one in six of layer Mn sites. Polarized EXAFS measurements on orientated films of NaBi and HBi confirm the absence of TC-sharing Mn in NaBi and indicate that Mn adsorbed at layer vacancy sites in HBi at pH 4 is dominantly Mn 31 . The intensity of the TC-sharing contribution to the Mn EXAFS spectra of HBi samples increases with increasing pH from pH 2 to 5, and supports a mechanism of formation involving both the direct migration of layer Mn 31 to interlayer TC-sharing positions and re-adsorption of Mn 21 from solution onto layer vacancy sites. The migration of Mn 31 cations into the interlayer releases the steric strain associated with the Jahn-Teller distortion of these octahedra. This model of the NaBu-to-HBi conversion explains the transformation from orthogonal to hexagonal layer symmetry, respectively, as reported by Drits et al. (1997). Analysis of the Zn EXAFS spectrum of Zn 21 -exchanged birnessite shows that Zn 21 also occupies TC-sharing positions at layer vacancy sites. The results of this study strongly suggest that lattice cation vacancies are of critical importance in adsorption and electron transfer processes occurring at the surface of this mineral.

MDFRC item.Microcystins (MCs) are a group of hepatotoxins produced by cyanobacteria that have not had their functional role or the environmental factors that trigger production clearly determined. One suggestion is that microcystins are siderophores (i.e., ligands with an extremely high affinity with iron, typically with stability constants substantially greater than 10²⁵). In this work, we explore proton and iron binding with microcystin-LR (MC-LR). Using UV−visible spectroscopy and a HPLC peak retention time-based method, the two acid dissociation constants associated with the carboxylic groups of MC-LR were determined to be: pKa1 = 2.17 and pKa2 = 3.96. Cyclic voltammetry provides evidence for the formation of at least two FeIII-MC-LR complexes, with the FeIII reduction peak significantly shifted to more reducing potentials in the presence of MC-LR. These complexes have been interpreted as a rapidly formed initial complex (Complex 1) and a more stable, and slower forming, Complex 2. The stability constant for FeIII-MC-LR (Complex 2) was estimated to be approximately 10¹³ in 60% v/v MeOH/water at 0.1 M ionic strength. The electrochemical experiments provide no evidence for the formation of a complex between Fe2+ and MC-LR. Given that most MC-LR is released only upon cell lysis, and coupled with the moderate strength of the stability constant with FeIII determined in this study, it appears unlikely that that MC-LR is an extracellular siderophore. If MC-LR is involved in iron regulation in cyanobacteria, it is more likely as a shuttle for iron across the cell membrane or in intracellular processes.

Organic carbon is a critical component of aquatic systems, providing energy storage and transfer between organisms. Fungi are a major decomposer group in the aquatic carbon cycle, and are one of few groups thought to be capable of breaking down woody (lignified) tissue. In this work we have used high spatial resolution (synchrotron light source) infrared micro-spectroscopy to study the interaction between aquatic fungi and lignified leaf vein material (xylem) from River Redgum trees (E. camaldulensis) endemic to the lowland rivers of South-Eastern Australia. The work provides spatially explicit evidence that fungal colonisation of leaf litter involves the oxidative breakdown of lignin immediately adjacent to the fungal tissue and depletion of the lignin-bound cellulose. Cellulose depletion occurs over relatively short length scales (5–15 µm) and highlights the likely importance of mechanical breakdown in accessing the carbohydrate content of this resource. Low bioavailability compounds (oxidized lignin and polyphenols of plant origin) remain in colonised leaves, even after fungal activity diminishes, and suggests a possible pathway for the sequestration of carbon in wetlands. The work shows that fungi likely have a critical role in the partitioning of lignified material into a biodegradable fraction that can re-enter the aquatic carbon cycle, and a recalcitrant fraction that enters long-term storage in sediments or contribute to the formation of dissolved organic carbon in the water column.

The oxidation of Cr"' to CrV1 in aqueous suspensions of Na-buserite (Na4MnI4027*9H20) has been investigated as a function of the solution pH and solids concentration. The rate of CrV' formation in solution exhibits two apparent domains of rate control. At low solids concentrations the rate of reaction appears to be controlled by the transfer of an electron from Cr"' to the solid. At high solids concentrations the rate of Crvl formation appears to be controlled by the octahedral to tetrahedral coordination change that must occur during the oxidation of Cr"' to CrV1. A weak dependence of the rate of oxidation on the solution pH is observed, which is interpreted as evidence for an outer-sphere electron transfer process between Cr"' and the solid. Nabuserite pre-equilibrated at low pH (H-buserite) reacts considerably more slowly with Cr"'. This observation is correlated with an apparent retardation of Mn" release from the H-buserite solid and suggests some equilibration of the aqueous chromium species with the solid phase. An energy level model of electron transfer is presented which allows some quantitative understanding of both the pH dependence of this reaction and the reasons for the reduced reactivity of the H-buserite phase.

Environmental contextDissolved organic nitrogen often constitutes the largest portion of the dissolved nitrogen pool yet is a commonly overlooked nutrient source in aquatic systems. Terrestrially aged Eucalyptus camaldulensis, a common lowland leaf litter species, rapidly released proteinaceous dissolved organic nitrogen during the first 24h of leaching. The results indicate that terrestrial leaf litter may play an important role in satisfying nutrient demand within aquatic systems through both direct deposition and floodplain interactions. AbstractUnderstanding sources and forms of dissolved nitrogen is of critical importance to the management of aquatic systems worldwide. Dissolved organic nitrogen (DON) often constitutes the largest portion of the dissolved nitrogen pool, yet is commonly overlooked as a nutrient source to aquatic food webs, likely owing to its bound nature within organic material and the non-specific methods by which it is measured. In this study, we determined the protein and peptide (dissolved combined amino acid (DCAA)) contribution to DON leached from Eucalyptus camaldulensis leaves over 24h. The distribution of proteinaceous material in unleached and leached leaves was characterised using Fourier-transform infrared (FTIR) microspectroscopy to determine the likely source of DCAA within the leaf tissue. DCAAs were found to be a significant component (38.5%) of the leached DON; however, >90% of the leaf protein remained in the leaves after 24h. FTIR microspectroscopy shows that proteinaceous material is strongly partitioned to fungal colonised palisade cells in the leaf mesophyll, with evidence for depletion of this material after leaching. Comparison of leaching kinetics in the presence and absence of a microbial inhibitor (sodium azide) suggests that microbial uptake or adsorption commences within the timescales of these leaching experiments. The work shows that DON in the form of peptides and proteins leached from leaf litter is a likely source of bioavailable nutrients to in-stream and floodplain systems.

The accumulation of significant pools of sulfidic sediments in inland wetlands and creeks is an emerging risk for the management of inland waterways. We used replicated plot trials to appraise the viability of various strategies for neutralizing oxidized, acidified sulfidic sediments in a highly degraded wetland. Of the twenty different treatments trialed only addition of calcium hydroxide or calcium carbonate, burning of wood, and planting of Phragmites australis , Typha domingensis and Atriplex nummularia into beds prepared with CaCO 3 or P. australis and T. domingensis into beds of sediment and mulch, decreased total actual acidity (TAA) in the top 5 cm of sediment in the first two weeks following treatment. Only the calcium hydroxide treatments and planting of P. australis , T. domingensis and A. nummularia into beds prepared with CaCO 3 decreased TAA for a longer period of time (6 months). None of the treatments, except the planting of P. australis into beds prepared with lime, decreased TAA in the 5–30 cm layer of sediments. Therefore, the only effective treatment appears to be the application of highly alkaline ameliorants which need to be transported to the site. A survey of the wetland was undertaken to estimate the total amount of actual and potential acidity stored in the wetland's sediment and overlying water and showed that up to 1200 tonnes of calcium carbonate would be required to neutralise all of the actual and potential acidity in the 10 ha wetland. However, neutralisation of the remaining water in the wetland (about 12.5 ML) would produce approximately 2750 m 3 of metal rich sludge (approximately 100 tonnes dry weight) that would require separate disposal.

The stopped flow technique has been used to study the oxidation of ultrasmall colloidal chalcopyrite (CuFeS{sub 2}) particles (diameter 50-90 {angstrom}) by the one-electron oxidants hexacyanoferrate(III) (Fe(CN){sub 6}{sup 3{minus}}) and hexachloroiridate(IV) (IrCl{sub 6}{sup 2{minus}}) in aqueous solution. The stoichiometry of the initial oxidation step corresponds to the reaction CuFeS{sub 2(s)} + 5H{sub 2}O {yields} Cu(OH){sub 2(s)} + Fe(OH){sub 3(s)} + 2S{sub (s)}{sup 0} + 5H{sup +} + 5e{sup {minus}}. Further oxidation of the elemental sulfur results in the formation of S{sub 2}O{sub 3}{sup 2{minus}} and SO{sub 4}{sup 2{minus}} in solution, as determined by ion chromatography. Time-resolved measurement of both the oxidant and chalcopyrite concentrations has provided a detailed understanding of the mechanism involved in the oxidation of colloidal chalcopyrite. 88 refs., 11 figs., 2 tabs.