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  • 1
    In: Nature Geoscience, 2015
    Description: Oxygen accumulated in the surface waters of the Earth’s oceans1 and atmosphere2 several hundred million years before the Great Oxidation Event between 2.4 and 2.3 billion years ago3. Before the Great Oxidation Event, periods of enhanced submarine volcanism associated with mantle plume events4 supplied Fe(II) to sea water. These periods generally coincide with the disappearance of indicators of the presence of molecular oxygen in Archaean sedimentary records5. The presence of Fe(II) in the water column can lead to oxidative stress in some organisms as a result of reactions between Fe(II) and oxygen that produce reactive oxygen species6. Here we test the hypothesis that the upwelling of Fe(II)-rich, anoxic water into the photic zone during the late Archaean subjected oxygenic phototrophic bacteria to Fe(II) toxicity. In laboratory experiments, we found that supplying Fe(II) to the anoxic growth medium housing a common species of planktonic cyanobacteria decreased both the efficiency of oxygenic photosynthesis and their growth rates. We suggest that this occurs because of increasing intracellular concentrations of reactive oxygen species. We use geochemical modelling to show that Fe(II) toxicity in conditions found in the late Archaean photic zone could have substantially inhibited water column oxygen production, thus decreasing fluxes of oxygen to the atmosphere. We therefore propose that the timing of atmospheric oxygenation was controlled by the timing of submarine, plume-type volcanism, with Fe(II) toxicity as the modulating factor.
    Keywords: Geology;
    ISSN: 1752-0894
    E-ISSN: 17520908
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  • 2
    Language: English
    In: Nature Geoscience, 1/2010, Vol.3(1), pp.53-59
    Description: Bangladesh relies heavily on groundwater for the irrigation of dry-season rice. However, the groundwater used for irrigation often contains high concentrations of arsenic, potentially jeopardizing the future of rice production in the country. In seasonally flooded fields, topsoil arsenic concentrations decrease during the monsoon season, suggesting that flooding attenuates arsenic accumulation in the soils. Here we examine the chemistry of soil porewater and floodwater during the monsoon season in rice paddies in Munshiganj, Bangladesh, to assess whether flooding releases significant quantities of arsenic from the soils. We estimate that between 51 and 250 mg m -2 of soil arsenic is released into floodwater during the monsoon season. This corresponds to a loss of 13-62% of the arsenic added to soils through irrigation each year. The arsenic was distributed throughout the entire floodwater column by vertical mixing and was laterally removed when the floodwater receded. We conclude that monsoon floodwater removes a large amount of the arsenic added to paddy soils through irrigation, and suggest that non-flooded soils are particularly at risk of arsenic accumulation.
    Keywords: Environmental Geology ; Hydrochemistry ; Arsenic ; Asia ; Bangladesh ; Dynamics ; Floods ; Ganges River Basin ; Geochemistry ; Ground Water ; Hydrochemistry ; Indian Peninsula ; Metals ; Monsoons ; Munshiganj Bangladesh ; Numerical Models ; Paddy Soils ; Pollution ; Pore Water ; Soil Pollution ; Soils ; Transport;
    ISSN: 1752-0894
    E-ISSN: 1752-0908
    Source: Nature Publishing Group (via CrossRef)
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  • 3
    In: Nature Geoscience, 2009, Vol.3(1), p.53
    ISSN: 1752-0894
    E-ISSN: 1752-0908
    Source: Nature Publishing Group
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