Browsing by Subject "hapetus-pelkistysreaktio"

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  • Kujala, Katharina; Laamanen, Tiina; Khan, Uzair Akbar; Besold, Johannes; Planer-Friedrich, Britta (Elsevier BV, 2022)
    Soil Biology and Biochemistry
    Arsenic (As) and antimony (Sb) from mining-affected waters are efficiently removed in two treatment peatlands (TPs) in Northern Finland. However, the exact mechanisms behind this removal are not well resolved. Thus, the present study combines results from microcosm experiments and pilot-scale TPs on the effects of microbes, temperature, and carbon substrate to elucidate the role of peat microorganisms in As and Sb removal. The main As and Sb species in TP inflow water are arsenate and antimonate. In peat microcosms, they were quantitatively reduced, however, at rates about 20–400 times lower than previously reported from pure cultures, likely due to excess of other terminal electron acceptors, such as nitrate and sulfate. Addition of the microbial inhibitor sodium azide inhibited reduction, indicating that it is indeed microbially mediated. Arsenite and antimonite (re)oxidation, which is in situ likely limited to upper, oxic peat layers, was likewise observed in peat microcosms. Only for antimonite, oxidation also occurred abiotically, likely catalyzed by humic acids or metals. Process rates increased with increasing temperature, but all processes occurred also at low temperatures. Monitoring of pilot-scale TPs revealed only minor effects of winter conditions (i.e., low temperature and freezing) on arsenic and antimony removal. Formation of methylated oxyarsenates was observed to increase As mobility at the onset of freezing. From different carbon substrates tested, lactate slightly enhanced arsenate reduction and antimonate reduction was stimulated by acetate, lactate, and formate. However, a maximum rate enhancement of only 1.8 times indicates that carbon substrate availability is not the rate-limiting factor in microbial arsenate or antimonate reduction. The collective data indicate that microorganisms catalyze reduction and (re)oxidation of As and Sb species in the TPs, and even though temperature is a major factor controlling microbial As and Sb reduction/(re)oxidation, low inflow concentrations, long water residence times, and the presence of unfrozen peat in lower layers allow for efficient removal also under winter conditions.
  • Manka, Veera (Helsingin yliopisto, 2022)
    Eight active farms participated in the OSMO-project between years 2015 and 2018. Each farm had unique soil health related challenges. The aim of this work was to identify factors related to soil manganese concentration and mobility and develop tools and materials to help farmers better to understand manganese related soil health issues. Manganese cycling and mobility in soils was analysed through soil structure, electric conductivity (EC), SOM, pH and soil iron concentration. Soil manganese concentration was evaluated with three indicators: pH-corrected acid ammonium acetate + EDTA extractable manganese, acid ammonium acetate + EDTA extractable manganese and the amount of manganese available to plants based on the volume of soil available for root growth. Foliar fluorescence measurement to evaluate manganese deficiency in plant tissues is shortly discussed. Soil manganese concentrations and mobility in soil profiles varied because of soil chemical and biological properties but also because of farming practices and changes in physical soil properties. To improve manganese availability in arable farming, soil health analysis through multiple indicators together with consistent soil health improvement and crop rotation is recommended for all active farms. When using fluorescence measurements to evaluate the need for foliar manganese fertilisation, the use of control solution is necessary for reliable results. More research is needed on manganese efficient crops and crop rotation and its effects on manganese cycle and availability in soils. To improve scientific understanding on soil processes, more research is needed about soil redox-reactions, electric conductivity, pH and how the dynamic change in soil Eh-pH environment relates to soil health.