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  • 1
    Language: English
    In: Science of the Total Environment, 15 January 2017, Vol.577, pp.329-339
    Description: Pre-dams are small reservoirs constructed upstream of the main drinking water reservoirs and are used for nutrient removal and sediment trapping. Little is known about the role of pre-dams regarding the production and decomposition of dissolved organic carbon (DOC) in relation to discharge and how this affects the quality of DOC in the water. We combined quantitative and qualitative investigations under different hydrological conditions at three pre-dams exhibiting a gradient from oligotrophic/high-DOC to eutrophic/low-DOC. All pre-dams were mainly autotrophic in their upper water layers. The ratio of OC production to total gained OC (i.e. OC import + OC production) decreased with increasing discharge. On average, 0–30% of the total gained OC was produced within the pre-dams. The amount of microbially decomposed DOC increased with the average water residence time (WRT) and with the trophic status of the pre-dams. Radiocarbon analyses of respired CO revealed that heterotrophic bacteria preferentially utilized old DOC components (195–395 years before present) under base flow conditions, whereas younger components (modern, i.e. OC produced after 1950) were utilized at high discharge. DOC quality changed significantly over the year within the pre-dams: High proportions of algae-derived DOC were observed during base flow in summer, and the freshness index (β/α ratio) decreased significantly with higher discharges. DOC production and quality changes in response to hydrological conditions should be considered for future water quality management in reservoirs, as climate scenarios for temperate regions predict decreased runoffs leading to longer WRT and increased eutrophication and production of algae-derived OC.
    Keywords: Carbon Isotopes ; 14c ; Autotrophy ; Microbial Decomposition ; Fluorescence ; Net Production ; Environmental Sciences ; Biology ; Public Health
    ISSN: 0048-9697
    E-ISSN: 1879-1026
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  • 2
    Language: English
    In: Journal of Microbiological Methods, February 2016, Vol.121, pp.8-10
    Description: A method for recovering CO respired by bacterioplankton for analysis of carbon isotopes was adapted for use with standard laboratory equipment without a technically demanding harvest line. The recovered CO was more depleted in C than the dissolved organic carbon (DOC) source, which suggests a selective respiration of older carbon.
    Keywords: Dissolved Organic Carbon (Doc) ; Inorganic Carbon (Ic) ; Degradation ; Carbon Isotopes ; Reservoir ; Biology
    ISSN: 0167-7012
    E-ISSN: 1872-8359
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  • 3
    Language: English
    In: Microbial Ecology, 2017, Vol.74(3), pp.534-549
    Description: Microbial decomposition of terrestrial carbon may be enhanced by the addition of easily decomposable compounds, a phenomenon referred to as priming effect. We investigated the microbial decomposition of terrestrial dissolved organic carbon (DOC) in one-stage and two-stage flow-through cultures (chemostats) in the absence and presence of growing phytoplankton as phytoplankton-derived organic matter might facilitate the mineralization of more refractory terrestrial compounds. Peat water and soil leachate were used as terrestrial substrates, and only slight DOC decomposition was observed in the absence of phytoplankton for both substrates. A priming effect was revealed via 14 C data. Priming was more pronounced for the peat water substrate than for the soil leachate. The total DOC concentrations increased for both substrates in the presence of phytoplankton due to exudation and cell lysis. Samples from the soil leachate experiments were analyzed using ultra-high-resolution mass spectrometry (FT-ICR MS). Predominantly, the same saturated, aliphatic molecules with H/C ratios 〉1.5 were completely decomposed in the absence and in the presence of phytoplankton. The decomposition of more stable molecules differed in their intensity. Oxidized and unsaturated molecules with H/C ratios 〈1.0 and O/C ratios 〉0.4 were more strongly decomposed in phytoplankton presence (i.e., under priming). We conclude that an aquatic priming effect is not easily detectable via net concentration changes alone, and that qualitative investigations of the DOC processed by bacterial decomposition are necessary to detect aquatic priming.
    Keywords: Radiocarbon ; C ; Ultra-high-resolution mass spectrometry ; FT-ICR MS ; DOM quality
    ISSN: 0095-3628
    E-ISSN: 1432-184X
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