Combined biogeochemical cycling of iron, sulphur, carbon and metal(oid)s (As, Pb, Cu, Zn, Cd, Ni, U, Th) in the water column of acidic pit lakes
| Autor: | Sánchez España, Francisco Javier |
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| Rok vydání: | 2017 |
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| Zdroj: | Digital.CSIC. Repositorio Institucional del CSIC instname |
| Popis: | American-Chemical-Society. National Meeting on Advanced Materials, Technologies, Systems, and Processes. (23º. 2017. San Francisco, California) Acidic pit lakes are outstanding natural laboratories to study biogeochemical cycling at redox boundaries under extreme (low pH, high-metal, nutrient-deficient) conditions. These redox boundaries are located a few meters below the lake surface (pelagic redoxclines) and at the sediment/water interface (benthic redoxclines). The results obtained during years of field, experimental and modelling studies in pit lakes of the Iberian Pyrite Belt (SW Spain) show that the nature and intensity of this redox cycling chiefly depends on the microbial ecology (biomass, diversity) which in turn varies with the availability of energy (e.g., light) and organic carbon. The most intense cycling occurs in pelagic redoxclines, where the primary production of phytoplanktonic microalgae provides organic compounds for a number of bacterial consortia, including iron-oxidizers, iron-reducers, sulphur-oxidizers and sulphate-reducers. Pelagic redoxclines may show different sub-layers or micro-niches which are vertically arranged, and which include an upper horizon of heterotrophic bacteria able to degrade algal exudates, a transitional layer of Fe(III)-reducers which use both dissolved and particulate Fe(III) as their terminal electron acceptor, and a bottom sub-layer of sulphate reducers that produce H2S as a metabolic by-product. The reductive dissolution of schwertmannite leads to the release of previously adsorbed toxic elements like As, Cu, Cr or Pb, but also nutrients such as phosphate. A few centimetres below the Fe(III)-reducing zone, the released metals react with the dissolved H2S and form insoluble metal sulphides (e.g., As2S3, CuS, PbS) which settle further down in the water column. At some meters below these redoxclines, however, some of these metal sulphides (e.g., CuS) may redissolve again via chemical or biological S oxidation leading to a new metal release back into the deep waters of the lake. Biogeochemical cycling at the sediment/water interface is less intense as a result of limited carbon input and absence of light to sustain primary production. The microbial reduction of schwertmannite leads to the release of Fe(II), As and PO43- back into the water column. These solutes move upwards by ionic diffusion and eventually reach the pelagic redoxcline, where Fe(II) re-oxidation fuels a new stage of precipitation and sorption. Instituto Geológico y Minero de España, España |
| Databáze: | OpenAIRE |
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