“…(Durka et al, 1994 (Kendall et al, 2007). In addition, the δ 18 O value of NO 3 − in a sample is known to increase during biological processes such as plant and microbial assimilation of NO 3 − and denitrification (Granger et al, 2008(Granger et al, , 2010 (Costa et al, 2011;Michalski et al, 2004;Nakagawa et al, 2013Nakagawa et al, , 2018Tsunogai et al, 2010Tsunogai et al, , 2016 (Michalski et al, 2003(Michalski et al, , 2004. Moreover, Δ 17 O is stable during mass-dependent isotope fractionation processes such as assimilation and denitrification (Michalski et al, 2004 (Rose et al, 2015;Sebestyen et al, 2019;Tsunogai et al, 2014).…”