4.1 Across studies, comparisons of concentrations showed clear trends in nitrate, but not for DOC
Studies in this meta-analysis reported relatively consistent trends for nitrate concentration differences between reference and burned watershed, whereas studies reported that DOC concentrations were more variable due to wildfire. The majority of studies (80%) reported elevated concentrations of nitrate following a wildfire (e.g. Coombs & Melack, 2013; Mast & Clow, 2008; Rhea et al., 2021), while 20% of the studies saw a decline in concentrations of nitrate (e.g. Abbott et al., 2021; Oliver et al., 2012). Interestingly, 20% of the studies observed the highest concentrations of nitrate up to three years following a wildfire, suggesting a delayed response (e.g. Gerla & Galloway, 1998; Murphy et al., 2015; Tiedemann, 1973). For DOC, 55% of the studies found that DOC concentrations were higher in burned watersheds and remained elevated throughout their study period (e.g. Crandall et al., 2021; Hickenbottom et al., 2023; Murphy et al., 2018; Oliver et al., 2012). Meanwhile, 27% of studies observed an immediate effect of elevated DOC concentrations, especially during flushing events, and then found DOC levels declined to background conditions (e.g. Murphy et al., 2015; Uzun et al., 2020; Writer et al., 2014). Lastly, 36% of studies reported either a marginal effect of wildfire on DOC or decreases in DOC concentrations following the studied wildfire (e.g. Abbott et al., 2021; Mast & Clow, 2008; Rhea et al., 2021; Wagner et al., 2015).