3.2 Time-since-fire effects
We found significance for time-since-fire on the effect for nitrate,
with higher nitrate pseudo yield in burned watersheds (lmer:p-value: < 0.05; Fig. 2, Table S1). To get a rough
approximation of how nitrate dynamics changed on an annual basis, we
performed a Sen-Theil linear regression model on the percent difference
through time (Hurtado,
2020). Nitrate increased across all sites by an estimated 29% per year
(Fig. S7). Interestingly, the variability of the effect size of nitrate
was significantly different (Levene’s test: F-value: 2.65, df: 6,95,
p-value < 0.05) through time, with greater variability
immediately following a wildfire and then becoming constrained further
through time (Fig. S8). Similarly to nitrate, we found significant
effects of time for DOC; however, with opposite directionality as DOC
pseudo yield in burned watersheds was lower for at least five years
(lmer : p-value: < 0.05; Fig. 2, Table S2). On average,
DOC was lower by 25% in the burned compared to the unburned watersheds
through the first 5 years, with no significant difference with
>10 years. DOC decreased across all sites by an estimated
3.2% per year (Fig. S9). Additionally, the variance of the effect size
through time was not significantly different (Levene’s test: F-value:
0.65, Df: 6, 48, p-value > 0.05; Fig. S10).