The role of siderite on abiotic nitrite reduction by dissolved Fe(II)

Abstract

Iron redox reactions affect the fate and transformation of groundwater NO3-. Fe(II) present in groundwater as dissolved Fe(II) or Fe(II) sorbed onto mineral surfaces is oxidised into Fe(III) (oxyhydr)oxides using NO3- as an electron acceptor in anoxic conditions by biotic or abiotic means (Bryce et al., 2018). N2O is produced as an end product during abiotic nitrate-reducing Fe(II) oxidation (NRFO) (Wang et al., 2019). NO2-, an intermediate product during NO3- reduction by biotic or abiotic means, is chemically very reactive and readily reduced to N2O by abiotic means (Wankel et al., 2017). Studies have shown that Fe(II) minerals such as iron-rich smectites, green rust and siderite are reactive and can enhance abiotic NO2- reduction (Grabb et al., 2017). The occurrence of abiotic NO2- reduction leads to the relative segregation of the lighter and heavy isotopes of N and O (kinetic isotope fractionation, ε) (Chen & MacQuarrie, 2005) providing an effective tool to quantify abiotic NO2- reduction processes. In the light of this, batch experiments were performed to assess the potential of micro-sized siderite to enhance abiotic NO2- reduction in laboratory batch experiments.