“…Denitrification and anammox remove fixed N by reducing NO 3 − or nitrite (NO 2 − ) and producing nitrogen gas (N 2 ), while DNRA alters the mobility of the fixed N, without removing it, by reducing NO 3 − to NH 4 + . Nitrification and denitrification have been widely studied in rivers and streams as important mediators of N transport (Böhlke et al, 2009;Duff et al, 2008;Groffman et al, 2005;Hinkle et al, 2001;Mulholland et al, 2009;Peterson et al, 2001), and all of these processes have been found in groundwater and lake sediments (Hampel et al, 2018;Li et al, 2017;Miller & Smith, 2009;Rissanen et al, 2013;Rysgaard et al, 1993;Salk et al, 2018;Smith et al, 2015;Smith & Duff, 1988;Smith et al, 1991b;Stoliker et al, 2016;Washbourne et al, 2011). Abiotic reactions, such as the oxidation of iron (Fe +2 ) by NO 2 − producing nitrous oxide (N 2 O), can also contribute to N-species cycling (Klueglein et al, 2014;Klueglein & Kappler, 2013).…”