Dissolved Manganese Concentrations Research Articles

Winter entrainment drives the mixed layer supply of manganese in the Southern Ocean

AbstractDespite the subnanomolar dissolved manganese concentrations that can co‐limit Southern Ocean primary production, their physical supply mechanisms during winter, for biological consumption in spring and summer have not yet been explored. During austral winter and spring 2019, two cruises were conducted in the Atlantic sector of the Southern Ocean, to determine the distribution and surface water supply mechanisms of dissolved manganese in the upper water column. The supply mechanisms were used to calculate the total flux of dissolved manganese to productive surface waters and were compared to biological consumption estimates. Mean dissolved manganese concentrations in the upper water column (< 500 m) during winter and spring were comparably low (≤ 0.34 nmol kg−1; p > 0.05), with seasonal mixed layer reservoir sizes averaging 65.21 ± 12.93 and 21.64 ± 19.32 μmol m−2, respectively. Winter entrainment contributed 89.33–99.99% (average 97.26% ± 5.28%) of the total dissolved manganese flux, while diapycnal diffusion contributed 0.52–10.58% (average 4.92% ± 5.14%), was identified as the dominant mechanisms for transporting dissolved manganese into the mixed layer in the subantarctic zone, polar frontal zone, and antarctic zone. Here, the winter physical supply rates were higher than the estimated consumption rates during spring, meeting phytoplankton biological demands. Whereas in the subtropical zone, the supply rates were lower than the consumption rates, indicating the presence of additional supply mechanisms such as coastal upwelling, which may help to meet the biological demands in this region.

Influence of ocean alkalinity enhancement with olivine or steel slag on a coastal plankton community in Tasmania

Abstract. Ocean alkalinity enhancement (OAE) aims to increase atmospheric CO2 sequestration in the oceans through the acceleration of chemical rock weathering. This could be achieved by grinding rocks containing alkaline minerals and adding the rock powder to the surface ocean where it dissolves and chemically locks CO2 in seawater as bicarbonate. However, CO2 sequestration during dissolution coincides with the release of potentially bioactive chemicals and may induce side effects. Here, we used 53 L microcosms to test how coastal plankton communities from Tasmania respond to OAE with olivine (mainly Mg2SiO4) or steel slag (mainly CaO and Ca(OH)2) as alkalinity sources. Three microcosms were left unperturbed and served as a control, three were enriched with olivine powder (1.9 g L−1), and three were enriched with steel slag powder (0.038 g L−1). Olivine and steel slag powders were of similar grain size. Olivine was added in a higher amount than the steel slag with the aim of compensating for the lower efficiency of olivine to deliver alkalinity over the 3-week experiment. Phytoplankton and zooplankton community responses as well as some biogeochemical parameters were monitored. Olivine and steel slag additions increased total alkalinity by 29 and 361 µmol kg−1, respectively, corresponding to a respective theoretical increase of 0.9 % and 14.8 % of the seawater storage capacity for atmospheric CO2. Olivine and steel slag released silicate nutrients into the seawater, but steel slag released considerably more and also significant amounts of phosphate. After 21 d, no significant difference was found in dissolved iron concentrations (>100 nmol L−1) in the treatments and the control. The slag addition increased dissolved manganese concentrations (771 nmol L−1), while olivine increased dissolved nickel concentrations (37 nmol L−1). There was no significant difference in total chlorophyll-a concentrations between the treatments and the control, likely due to nitrogen limitation of the phytoplankton community. However, flow cytometry results indicated an increase in the cellular abundance of several smaller (∼<20 µm) phytoplankton groups in the olivine treatment. The abundance of larger phytoplankton (∼>20 µm) decreased much more in the control than in the treatments after day 10. Furthermore, the maximum quantum yields of photosystem II (Fv/Fm) were higher in slag and olivine treatments, suggesting that mineral additions increased photosynthetic performance. The zooplankton community composition was also affected, with the most notable changes being observed in the dinoflagellate Noctiluca scintillans and the appendicularian Oikopleura sp. in the olivine treatment. Overall, the steel slag used here was more efficient for CO2 removal with OAE than the olivine over the 3-week timescale of the experiment. Furthermore, the steel slag appeared to induce less change in the plankton community than the olivine when comparing the CO2 removal potential of both minerals with the level of environmental impact that they caused.

A Study on Evaluation of Manganese Removal Efficiency by Oxidant types Based on Experimental Data

Objectives : The purpose of this study was to investigate the treatment efficiency according to the oxidant types for dissolved manganese in the inflow of raw water into the water treatment plant in Korea.Methods : Three types of oxidant were selected: chlorine, ozone, and potassium permanganate. Experimental factors influencing manganese removal efficiency were determined as dissolved manganese concentration in raw water, dose, water temperature, pH, and contact time. In addition, total experimental schemes were designed according to the design of experiments method. According to the designed analysis method, the mentioned factors were used as multi variables on which evaluate the manganese removal efficiency.Results and Discussion : When using chlorine, the effect of pH was the greatest, followed by dose, water temperature, and contact time in order to have a significant effect on removal efficiency. In the case of using ozone, the pH effect was relatively large at low concentration of dissolved manganese, and the dose effect was found to be greater as the concentration was increased. Also, when potassium permanganate was used, the effect of pH, contact time and temperature was insignificant, while the effect of dose was the greatest for manganese removal.Conclusion : The optimum dose of chlorine is about three times to secure a removal rate of about 40 to 80%. The optimum dose of ozone was 1.0 to 1.6 mg/L, and it was found that a removal rate of at least 40% or more could be secured. Also, the optimum dose of potassium permanganate is 1.7 to 2.5 times of the dissolved manganese concentration, and it is possible to secure a removal rate of at least 60%.

Lab-on-chip analyser for the in situ determination of dissolved manganese in seawater

A spectrophotometric approach for quantification of dissolved manganese (DMn) with 1-(2-pyridylazo)-2-naphthol (PAN) has been adapted for in situ application in coastal and estuarine waters. The analyser uses a submersible microfluidic lab-on-chip device, with low power (~ 1.5 W) and reagent consumption (63 µL per sample). Laboratory characterization showed an absorption coefficient of 40,838 ± 1127 L⋅mol−1⋅cm−1 and a detection limit of 27 nM, determined for a 34.6 mm long optical detection cell. Laboratory tests showed that long-term stability of the PAN reagent was achieved by addition of 4% v/v of a non-ionic surfactant (Triton-X100). To suppress iron (Fe) interferences with the PAN reagent, the Fe(III) masking agents deferoxamine mesylate (DFO-B) or disodium 4,5-dihydroxy-1,3-benzenedisulfonate (Tiron) were added and their Fe masking efficiencies were investigated. The analyser was tested during a deployment over several weeks in Kiel Fjord (Germany), with successful acquisition of 215 in situ data points. The time series was in good agreement with DMn concentrations determined from discretely collected samples analysed via inductively coupled plasma mass spectrometry (ICP-MS), exhibiting a mean accuracy of 87% over the full deployment duration (with an accuracy of > 99% for certain periods) and clear correlations to key hydrographic parameters.

Distribution and concentration of soluble manganese(II), soluble reactive Mn(III)-L, and particulate MnO2 in the Northwest Atlantic Ocean

As manganese cycles between its three oxidation states, encompassing soluble and particulate phases, it influences the biogeochemistry of organic carbon, nutrients, and many trace elements. However, measurements of manganese distributions and speciation in the open ocean have typically been based only on differentiating soluble (assumed to be manganese(II)) and particulate (assumed to be manganese(III,IV) oxides) forms. We measured particulate oxidized manganese (MnOx, where x ≈ 1.8–2), reactive soluble manganese(III) (soluble manganese(III) that forms a complex with desferrioxamine-B (Mn(III)-LDFOB)), and total dissolved manganese (dMnT; manganese(II) + Mn(III)-LDFOB) in Northwest Atlantic offshore waters (10–2600 m). Mn(III)-LDFOB concentrations were from below the detection limit (0.008 nM) up to 0.76 nM and measured throughout the water column with higher concentrations near the base of the euphotic zone (~ 100 m), in the oxygen minimum zone (OMZ), and generally increasing from below the OMZ into the bottom waters. MnOx ranged from 0.19 nM to 3.52 nM in the water column. Concentrations were high near the base of the euphotic zone where reactions of MnOx with organic material are the likely source of the Mn(III)-LDFOB observed there. Elevated MnOx was also occasionally found in deep waters likely due to turbidity layers resulting from sediment resuspension. Mn(III)-LDFOB accounted for up to 45% of the dMnT and up to 74% of the total oxidized manganese (Mn(III)-LDFOB + MnOx) in different regions of the water column. Mn(III)-LDFOB contributed 10–20% of the generally uniform total dissolved manganese concentration in the deep ocean. Both soluble and particulate oxidized forms of manganese (Mn(III)-L and MnOx) are a significant component of the deep water manganese pool and likely play a prominent role in oceanic redox chemistry and organic carbon re-mineralization.

Interactions between Escherichia coli survival and manganese and iron oxides in water under freeze-thaw

Pathogenic survivals were dramatically affected by Fe3+ and Mn2+ under freeze-thaw (FT), and the dissolutions of manganese and iron oxides (MIOs) were also accelerated under FT. But the mutual influences of pathogenic bacterial survival and MIOs under FT have not been profoundly explored yet. In this work, aqueous systems containing Escherichia coli as well as synthetic ferrihydrite (Fh) and manganese dioxide (MnO2) were experimented under simulated FT cycles to study the mutual influences of metal oxides and bacteria survival while oxide dissolutions and appearances, bacterial morphology and activities (survival number, cell surface hydrophobicity (CSH) and superoxide dismutase (SOD)) were obtained. The results showed that broken E. coli cells by ice growth were observed, but both oxides promoted E. coli survival under FT stress and prolonged bacterial survival time by 1.2–2.9 times, which were mainly attributed to the release of Fe3+ and Mn2+ caused by FT. The dissolutions of Fh and MnO2 under FT, which took place at a low level in absence of E. coli cells, were markedly enhanced with bacterial interferences by 2–8 times and higher dissolved manganese concentrations were detected than iron. This was probably because that concentrated organic matters which were released from broken cells, rejected into unfrozen liquid layer and acted as electron donors and ligands to oxide dissolution. Compared with Fh system, more significant promotion of E. coli survival under FT in MnO2 systems were found because of more SOD generations associated with high dissolved manganese concentrations and the stronger cellular protection by MnO2 aggregations. The results suggested that FT significantly influenced the interactions between metal oxides and bacterial in water, resulting to changes in pathogen activity and metal element cycling.

Release Mechanisms of Iron and Manganese from Sediments in Jinpen Reservoir

In response to the annual hypolimnetic anoxia in stratified reservoirs, water-lifting aerators (WLAs) were used in Jinpen Reservoir to supplement the dissolved oxygen in the bottom water and suppress the release of reduced pollutants from sediment. However, due to the influence of geomorphic characteristics at the bottom of the reservoir, there were some differences in the efficiency of artificial mixing and aeration. After the deactivation of WLAs, the dissolved oxygen in the bottom water of some deeper areas was rapidly depleted, resulting in the re-release of pollutants. To explore the release mechanisms and diffusion intensity of iron and manganese during this period, the representative samples in the main reservoir area were collected to measure the distribution of dissolved iron and manganese in the pore water and overlying water and calculate the diffusive flux of dissolved iron and manganese across the sediment-water interface. The results showed that the bottom water of the lower terrain rapidly entered the anaerobic condition after the system was deactivated, resulting in the release of a large amount of dissolved manganese into the overlying water, the maximum concentration of which was 0.42 mg·L-1. However, the bottom water of the higher terrain briefly entered a state of hypoxia, after which the dissolved oxygen concentration increased rapidly, so the dissolved manganese concentration increased moderately to 0.17 mg·L-1. The distribution of iron and manganese in the pore-water-overlying water showed that the dissolved manganese was released more easily into the overlying water than the iron under anaerobic conditions and constant accumulation in the upper sediments and overlying water. However, the release of dissolved iron was not only suppressed by dissolved oxygen but also by other oxidants such as manganese oxide. The diffusion flux of dissolved manganese declined after the system was deactivated. A mass balance calculation demonstrated that the accumulation of dissolved manganese in the anaerobic layer was not only related to the diffusion flux but also to the sedimentation flux and the thickness of the anaerobic layer. Therefore, the biogeochemical cycle of iron and manganese in the anaerobic layer requires further study.

Geochemistry of Manganese in Neutral to Alkaline Soils of Punjab, Northwest India and Its Availability to Wheat and Rice Plants

ABSTRACTManganese (Mn) release in 18 soil–water suspensions after their equilibration for 24 and 240 h periods at 25°C was studied in a laboratory experiment. Total dissolved Mn released into the soil solution was observed to increase from a range of 0.03–0.41 mg L−1 (mean = 0.13 mg L−1) to a range of 0.45–44.44 mg L−1 (mean = 22.40 mg L−1) with the increase in incubation periods from 24 to 240 h, respectively. The increase in Mn released was observed to be related with the redox potential (pe) induced by incubation conditions. After 24 h of equilibration period, pe of soil–water suspension ranged from −1.75 to 0.77 (mean = −0.24). Increasing the incubation period to 240 h, pe of soil–water suspensions declined in the range of −4.49 to −2.74 (mean = −3.29). Laboratory results of redox pe and corresponding dissolved manganese concentrations of some soil–water equilibrated systems were compared with the leaf Mn content in wheat and rice plants grown in the fields, from where soil samples were collected for laboratory experiment. These results demonstrated that decline in pe due to longer equilibration period (240 h) of soil–water systems in the laboratory experiment or keeping standing water for a couple of weeks in the fields for cultivation of rice crop results in higher release of Mn and eventually its higher uptake in rice than in wheat plants. Leaf manganese content in rice ranged from 94 to 185 mg kg−1, which was markedly higher than its range from 25 to 62 mg kg−1 found in the wheat grown at 10 different sites. Pourbaix diagrams were drawn for different soil–water systems containing carbonate, phosphate, or sulfate along with manganese. The presence of carbonate and phosphate anions along with manganese oxides minerals in the soil–water systems of all soils results in its precipitation as MnCO3 and MnHPO4, respectively, in both oxidized and reduced soil field environment. In Punjab, wheat and rice crops are generally cultivated on soils heavily fertilized with P fertilizers. The presence of phosphate anion with manganese oxides minerals in the soil–water systems of all soils results in the precipitation MnHPO4 in both oxidized and reduced soil field environment. Thus, in P-fertilized soil, MnHPO4 compound is even more predominant than aqueous Mn2+ and its solubility actually controlled the availability of Mn2+ to plants.

Physical and biological controls of dissolved manganese on the northern slope of the South China Sea

The South China Sea (SCS) is classified as an oligotrophic ocean because it has low nutrient and chlorophyll concentrations. We examined the biogeochemical cycle of dissolved manganese (DMn) on the northern slope of the SCS during two cruises (October 2014 and June 2015), and the effect of DMn enrichment on the growth of phytoplankton in field incubation experiments. DMn was measured spectrophotometrically by an on-line pre-concentration and flow injection analysis method. The concentration of DMn varied from 0.6 to 32.4 nM in the Pearl River Estuary, and decreased with distance from the coast. Moreover, DMn concentrations declined significantly (50–90%) as salinity increased between the Pearl River and the SCS. Vertical profiles of DMn reflected a typical scavenge-type distribution, and decreased with depth. Mixing between the Shelf Water and the Western Philippine Sea led to a Mn-rich plume (> 4 nM), which extended from the northern shelf into the slope regions of the SCS. The export of Mn-rich shelf waters was an important source of DMn for SCS, and this lateral input from the continental shelf could exceed atmospheric input. The incubation experiments showed that the addition of Mn stimulated phytoplankton growth. These results suggest that Mn may play an important role in regulating phytoplankton growth in the SCS.

Treatment of highly-colored surface water by a hybrid microfiltration membrane system incorporating ion-exchange

Abstract This study investigated the performance of a hybrid membrane filtration system to produce industrial water from highly-colored surface water. The system consists of a membrane filtration process with appropriate pretreatments, including coagulation, pre-chlorination, and anion exchange (IE) process. The results of the pilot-scale experiments revealed that the hybrid system can produce treated water with color of around 5 Pt-Co, dissolved manganese concentration of no more than 0.05 mg/L, and a silt density index (SDI) of no more than 5 when sufficient coagulant and sodium hypochlorite were dosed. Although the IE process effectively reduced the color of the water, a moderate increase in the color of the IE effluent was observed when there was a significant increase in the color of the raw water. This resulted in a severe membrane fouling, which was likely to be attributed to the excess production of inorganic sludge associated with the increased coagulant dosage required to achieve sufficient reduction of color. Such severe membrane fouling can be controlled by optimising the backwashing and relaxation frequencies during the membrane filtration. These results indicate that the hybrid system proposed is a suitable technology for treating highly-colored surface water.

Experimental calibration of manganese incorporation in foraminiferal calcite

In the context of recent climate change and increased anthropogenic activities in coastal areas, which both may have a negative impact on dissolved oxygen concentration, there is an increased interest to better understand the mechanisms and evolution leading to hypoxia in marine environments. The development of well calibrated proxies is crucial to obtain reliable environmental reconstructions of past oxygen content and of historical development of hypoxia. Manganese is a redox element of interest for this purpose because manganese oxides are reduced to soluble Mn2+ in oxygen-depleted conditions, which can be incorporated in biogenic calcite. The Mn/Ca ratio in benthic foraminiferal calcite is therefore a promising proxy to reconstruct past oxygen variations. In this study, we calibrate this proxy by measuring (with Laser Ablation ICP-MS) the Mn/Ca ratio of benthic foraminifera calcified under controlled conditions in laboratory experiments. Two benthic foraminiferal species (Ammonia tepida and Bulimina marginata) calcified in 4 different dissolved manganese concentrations (from 2.4 to 595 µmol L−1) corresponding to in situ Mn concentrations encountered in bottom and/or pore waters in low oxygen marine environments. There is a statistically significant positive linear correlation (R2 > 0.9) between Mn/Cacalcite and Mn/Caseawater. However, the two species show different partitioning coefficients (DMn of 0.086 and 0.621, for A. tepida and B. marginata, respectively), although they calcified in exactly the same stable conditions. These results highlight a strong species specific effect on Mn incorporation, which is probably due to different biological controls during biomineralisation processes. There is also ontogenetic variability (determined through a comparison of successive chambers) that is different between the two species and also varies as a function of the dissolved Mn concentration. A conceptual model is proposed to explain these data.

Distributions of Dissolved Manganese in the Surface Waters of the Tropical North-Eastern Atlantic Ocean

The tropical North-Eastern Atlantic (TNEA) Ocean region receives high atmospheric input every year, mostly from the Saharan dust and soil. This atmospheric dust and its deposition in the surface ocean are considered to be an important supply of nutrients and trace metal (e.g. dissolved manganese (DMn)) to the euphotic zone of the open ocean regions. Therefore, the objective of this study was to investigate the input of DMn from atmospheric sources and from nearby islands into the TNEA Ocean. A set of surface samples were collected from the Tropical NE Atlantic Ocean, and were analysed for DMn by using the flow injection analyser with chemiluminescence (FIA-CL). Results suggest the land-sources of DMn near to the Canary Islands, the Cape Verde Islands and the African Continent contributed the major inputs of DMn, where high DMn concentrations were determined, with the highest is 3.87±0.05 nM. The lateral advective flux of DMn was higher (47 μmol/m2/d) than the atmospheric flux of DMn (0.17 μmol/m2/d), thus making the shelf and sediment as the most prominent sources of DMn in the seawater close to the islands. From this atmospheric flux of DMn, it was then possible to estimate the DMn enrichment at further offshore dust event regions of 0.73 nM/yr and consistent with the DMn background concentrations. This support the low residence time calculated in dust event regions of around 1 year. In conclusion, the shelf and sediment are the most prominent DMn sources in the seawater close to the islands and mainland, while in further offshore, the atmospheric inputs are dominant.

Supplementary Materials (Distributions of Dissolved Manganese in the Surface Waters of the Tropical North-Eastern Atlantic Ocean)

The tropical North-Eastern Atlantic (TNEA) Ocean region receives high atmospheric input every year, mostly from the Saharan dust and soil. This atmospheric dust and its deposition in the surface ocean are considered to be an important supply of nutrients and trace metal (e.g. dissolved manganese (DMn)) to the euphotic zone of the open ocean regions. Therefore, the objective of this study was to investigate the input of DMn from atmospheric sources and from nearby islands into the TNEA Ocean. A set of surface samples were collected from the Tropical NE Atlantic Ocean, and were analysed for DMn by using the flow injection analyser with chemiluminescence (FIA-CL). Results suggest the land-sources of DMn near to the Canary Islands, the Cape Verde Islands and the African Continent contributed the major inputs of DMn, where high DMn concentrations were determined, with the highest is 3.87±0.05 nM. The lateral advective flux of DMn was higher (47 μmol/m2/d) than the atmospheric flux of DMn (0.17 μmol/m2/d), thus making the shelf and sediment as the most prominent sources of DMn in the seawater close to the islands. From this atmospheric flux of DMn, it was then possible to estimate the DMn enrichment at further offshore dust event regions of 0.73 nM/yr and consistent with the DMn background concentrations. This support the low residence time calculated in dust event regions of around 1 year. In conclusion, the shelf and sediment are the most prominent DMn sources in the seawater close to the islands and mainland, while in further offshore, the atmospheric inputs are dominant.

Strong responses of Southern Ocean phytoplankton communities to volcanic ash

AbstractVolcanic eruptions have been hypothesized as an iron supply mechanism for phytoplankton blooms; however, little direct evidence of stimulatory responses has been obtained in the field. Here we present the results of twenty‐one 1–2 day bottle enrichment experiments from cruises in the South Atlantic and Southern Ocean which conclusively demonstrated a photophysiological and biomass stimulation of phytoplankton communities following supply of basaltic or rhyolitic volcanic ash. Furthermore, experiments in the Southern Ocean demonstrated significant phytoplankton community responses to volcanic ash supply in the absence of responses to addition of dissolved iron alone. At these sites, dissolved manganese concentrations were among the lowest ever measured in seawater, and we therefore suggest that the enhanced response to ash may have been a result of the relief of manganese (co)limitation. Our results imply that volcanic ash deposition events could trigger extensive phytoplankton blooms, potentially capable of significant impacts on regional carbon cycling.

Performance Evaluation of the Michigan Filter Mound for Treating Milking Center Wastewater from a Small Dairy

A filter mound was built to treat the milking center wastewater from a 200-cow dairy farm in central Michigan. Wastewater flowed through three filter-equipped settling tanks and was pumped into the filter mound, which was sized to accommodate two milkings per day. A dosing rate of approximately 13 L m-2 d-1 was used. The pollutant removal performance of four treatment media was evaluated: unaerated shredded hardwood tree bark, passively aerated tree bark, hardwood tree wood chips, and Styrofoam chips. Pollutant removal performance was assessed by collecting samples in lysimeters at three locations for each of the four media beds: within the filter mound 0.5 m below the distribution lines, at the bed:soil interface, and 0.6 m beneath the bed:soil interface. Over the first 50 weeks of the project, the shredded tree bark removed 90% or more of total phosphorus, ammonia, total suspended solids, and E. coli bacteria. Wood chips were less effective, and Styrofoam chips provided essentially no treatment. Passive aeration of the shredded bark did not significantly affect pollutant removal. After 50 weeks, the dairy farm unexpectedly switched to three milkings per day, which hydraulically overloaded the filter mound, causing failure of the system, as evidenced by excess standing water around the base of the mound and clogging of filters. Leaching of naturally occurring metals from the soil under the filter mound was significant; dissolved manganese concentrations usually exceeded the human health-based drinking water criterion at the subsurface lysimeters beneath the aerated bark, wood chips, and Styrofoam chips, and dissolved iron often exceeded the drinking water criterion beneath the aerated bark bed. This study also documented operation and maintenance issues and costs, and developed a maintenance schedule. Solids buildup in the settling tanks, filters, and distribution lines was a major issue but was easily addressed. The filter mound cost approximately $30,000 (2010 U.S. dollars) to construct and $2,240 per year to operate and maintain.

Performance of point-of-use devices to remove manganese from drinking water

A recent epidemiological study reported significant cognitive deficits among children in relation with consumption of water with manganese concentrations in the order of 50–100 ug/L. Concerns for neurotoxic effects of manganese raises the need for evaluating the efficiency of domestic water treatment systems for removal of this metal. The objective of the present study was to determine whether POU devices are efficient at reducing dissolved manganese concentration in drinking water. Various devices were tested according to the NSF 53 protocol for general metals for high pH test water. Based on these assays, the pour-through filters were identified as the most promising POU devices, with dissolved manganese removal greater than 60% at 100% rated capacity, and greater than 45% at 200% rated capacity (influent Mn ≈1,000 μg/L). Under-the-sink filters using cationic exchange resins (i.e., water softeners) were also efficient at removing dissolved manganese but over a shorter operating life. Manganese leaching was also observed beyond their rated capacity, making them less robust treatments. The activated carbon block filters and other proprietary technologies were found to be inappropriate for dissolved manganese removal. Further evaluation of POU devices performance should evaluate the impact of hardness on process performance. The impact of particulate Mn should also be evaluated.

Spatial variability of cadmium, copper, manganese, nickel and zinc in the Port Curtis Estuary, Queensland, Australia

Port Curtis is a rapidly growing industrialised and urbanised harbour in Central Queensland, Australia. The spatial variability of trace metals in waters and suspended particulates was determined along axial transects within the harbour and in oceanic waters adjacent to Port Curtis. Dissolved metal concentrations were significantly elevated in Port Curtis compared with the concentrations measured in the adjacent coastal waters. Dissolved copper and zinc concentrations ranged from <19 to 800 and <31 to 580 ng L–1, respectively, and maxima were observed in inner harbour waters adjacent to the southern entrance to the Narrows and in close proximity to anthropogenic sources. Dissolved nickel concentrations were measured in the range of 110 to 900 ng L–1, and exhibited a maximum concentration in the central to northern Narrows, in an area that was not adjacent to anthropogenic sources. Dissolved manganese concentration maxima were measured in close proximity to the dissolved nickel maxima. It appears likely that the elevated dissolved metal concentrations in Port Curtis and the Narrows were not caused by a single point source, and are the result of several factors, including industrial activity around the foreshore, fluxes from sediment-porewater, low flushing durations, lower water pH and possibly episodic inputs from adjacent rivers.

Origin of high manganese concentrations in coal mine drainage, eastern Tennessee

The origin of high dissolved manganese concentrations in slightly acidic mine runoff from a surface mine operated by the Cumberland Coal Company in eastern Tennessee was investigated. Mineralogical and chemical analyses were performed on 31 samples of sandstone, shale, coal, and mudstone from the mine to identify the sources and stratigraphic distribution of high extractable manganese contents in the spoil materials. The samples were analyzed for their bulk mineral content by X-ray diffraction, net acid-base potential, and reaction to 2 or 4 chemical extraction procedures. A limited number of samples were analyzed for petrographic characteristics, clay mineral composition by X-ray diffraction, and mineral compositions by electron microprobe. Analysis of the data and consideration of the geochemical conditions at the mine were used to identify probable sources for the high extractable manganese contents. The results indicate 2 prominent, independent sources of extractable manganese. The first source is exchangeable manganese on clay minerals (mainly illite + muscovite and chlorite) and is concentrated in shale and mudstone rock types. The second and more significant source is manganese in siderite concretions and cement, mainly in shale and mudstone. Comparison to other coal-bearing strata indicates that manganese-rich siderite is common in fresh- to brackish-water subaqueous sediments that overlie coal. This is especially the case for coals formed in wet, tropical environments. Ratios of manganese to calcium and magnesium in mine runoff suggest that manganese from siderite is the major cause of the high dissolved manganese contents. A conceptual model is developed to explain the high manganese contents of the mine runoff. Oxidation of pyrite creates mildly acidic waters that are subsequently partially neutralized by reaction with impure siderite. Solubilized manganese remains dissolved in the slightly acidic runoff water, whereas dissolved iron precipitates as ferric hydroxide or goethite. Consideration of data from other coal mining regions suggests that similar reactions involving impure siderite may be responsible for high manganese concentrations in acidic to slightly acidic mine runoff. Geochemical reaction path modeling of pyrite and impure siderite with rainwater illustrate how resulting water compositions may vary depending on pyrite to siderite ratios in spoil materials. Spoil water compositions from the Cumberland mine are largely consistent with reaction of pyrite and impure siderite in proportions observed in the sediments; however, deviations may be explained by minor mixing with waters that reacted only with impure siderite or clay mineral exchange reactions.

The turbidity maximum zone of the Yenisei River (Siberia) and its impact on organic and inorganic proxies

A general overview of the processes taking place in the summer mixing zone of the fresh Yenisei River water with the marine waters of the Kara Sea is given in this study, with special emphasis on the interaction between bulk (total suspended matter), inorganic (Fe, Mn) and organic (suspended organic carbon, suspended nitrogen) proxies. Within the mixing zone, a zone of enhanced turbidity (maximum turbidity zone) was observed comparable to studies in other rivers. Flocculation of particles due to changes in salinity and hydrography cause this maximum turbidity zone, and resuspension additionally enhances the turbidity in the near-bottom layers. Organic matter behaves conservatively in the mixing zone in terms of its percentage of suspended matter. It, however, undergoes degradation as revealed by amino acid data. Inorganic, redox- and salinity-sensitive, proxies (Mn, Fe) behave non-conservatively. Dissolved iron is removed at low salinities (<2) due to precipitation of iron oxyhydroxides and adsorption of manganese on suspended particles, enhancing the Mn/Al ratio of the suspended matter in the same zone. At higher salinities within the mixing zone, Fe/Al and Mn/Al ratios of the suspended particles are depleted due to resuspension of sediment with lower Fe/Al and Mn/Al ratios. Dissolved manganese concentrations are significantly higher in the near-bottom layers of the mixing zone due to release from the anoxic sediment. All things considered, the Yenisei River mixing zone shows patterns similar to other world's rivers.

Manganese and iron distributions off central California influenced by upwelling and shelf width

In July 2002, a combination of underway mapping and discrete profiles revealed significant along-shore variability in the concentrations of manganese and iron in the vicinity of Monterey Bay, California. Both metals had lower concentrations in surface waters south of Monterey Bay, where the shelf is about 2.5 km wide, than north of Monterey Bay, where the shelf is about 10 km wide. During non-upwelling conditions over the northern broad shelf, dissolvable iron concentrations measured underway in surface waters reached 3.5 nmol L −1 and dissolved manganese reached 25 nmol L −1. In contrast, during non-upwelling conditions over the southern narrow shelf, dissolvable iron concentrations in surface waters were less than 1 nmol L −1 and dissolved manganese concentrations were less than 5 nmol L −1. A pair of vertical profiles at 1000 m water depth collected during an upwelling event showed dissolved manganese concentrations of 10 decreasing to 2 nmol L −1, and dissolvable iron concentrations of 12–20 nmol L −1 in the upper 100 m in the north, compared to 3.5–2 nmol L −1 Mn and ∼0.6 nmol L −1 Fe in the upper 100 m in the south, suggesting the effect of shelf width influences the chemistry of waters beyond the shelf. These observations are consistent with current understanding of the mechanism of iron supply to coastal upwelling systems: Iron from shelf sediments, predominantly associated with particles greater than 20 μm, is brought to the surface during upwelling conditions. We hypothesize that manganese oxides are brought to the surface with upwelling and are then reduced to dissolved manganese, perhaps by photoreduction, following a lag after upwelling. Greater phytoplankton biomass, primary productivity, and nutrient drawdown were observed over the broad shelf, consistent with the greater supply of iron. Incubation experiments conducted 20 km offshore in both regions, during a period of wind relaxation, confirm the potential of these sites to become limited by iron. There was no additional growth response when copper, manganese or cobalt was added in addition to iron. The growth response of surface water incubated with bottom sediment (4 nmol L −1 dissolvable Fe) was slightly greater than in control incubations, but less than in the presence of 4 nmol L −1 dissolved iron. This may indicate that dissolvable iron is not as bioavailable as dissolved iron, although the influence of additional inhibitory elements in the sediment cannot be ruled out.