# Investigating the Impact of Wildfires on Lake Water Quality Using Earth Observation Satellites
## 3 Results
### Time of Occurrence of Chl-a and Turbidity Peaks after a Fire
When the timing of the peaks in Chl-a and turbidity that developed after a fire was analyzed by grouping lakes according to ecological characteristics, such as lake trophic conditions, we observed that oligotrophic lakes were slightly faster (mean \(\pm\) sd = 94 \(\pm\) 63 days) than mesotrophic (mean \(\pm\) sd = 105 \(\pm\) 64 days), eutrophic (mean \(\pm\) sd = 120 \(\pm\) 81 days), and hyper-eutrophic (mean \(\pm\) sd = 99 \(\pm\) 81 days) lakes in developing maximum Chl-a peaks after a fire (Figure 8a). In this analysis, trophic classification was slightly adjusted to include a representative number of lake years for each trophic group (i.e., oligotrophic lakes with annual mean Chl-a < 5 mg m\({}^{-3}\)). However, both first and maximum Chl-a peak concentrations were smaller in oligotrophic than in higher trophic lakes, as presented in Figure 8b showing scatterplots of the relationships between lake trophic status, expressed as Chl-a mean concentrations (over  
Figure 6: Frequency distribution, as percentage of lakes (annual data per each lake from 2017 to 2020), of the time interval [days] between the occurrence of a fire and the detection of the first peak (**a**) and the maximum peak (**b**) of Chl-a (green bars) and turbidity (black bars). the period 2017-2020), and Chl-a concentration of first peaks (Figure 8b) and maximum peaks (Figure 8c) developed after a fire. Figure 8: Boxplots of lake trophic classes (O = oligotrophic, M = mesotrophic, E = eutrophic, H = hypereutrophic) and timing (days) of max Chl-a peak development (**a**). Scatterplots between lake chlorophyll-a (Chl-a) mean concentration (2017–2020; mg m\({}^{-3}\)) and Chl-a concentration of first peaks (R\({}^{2}\) = 0.732, \(p\) < 0.001) (**b**) and maximum peaks (R\({}^{2}\) = 0.826, \(p\) < 0.001) (**c**). Figure 7: Scatterplot of the ratio of the burned area/burnable area at level 0–4 (BA/area at level 0–4) (**a**) and the ratio of the burned area/total burnable area in the catchment (BA/area total) (**b**) versus development time of maximum peaks of Chl-a (days) since fire occurrence in the studied lakes (lake_year). The black lines identify a ratio of 0.25. We also investigated whether the type of land cover burned influenced the timing of Chl-a and turbidity peaks. Using the clustering results of the burned land cover types presented in Table 1, we found a significant difference in ANOVA for Chl-a (\(p\) = 0.002) but not for turbidity (\(p\) > 0.05). A Bonferroni post-hoc test indicated that the difference was between Cluster 4 (corresponding to evergreen boreal forests) and Cluster 6 (deciduous broad leaves) (\(p\) = 0.007), with a mean of 63 \(\pm\) 50 days for Cluster 4 and 120 \(\pm\) 68 days for Cluster 6 (Figure 9). A difference in total annual precipitation (m) among these clusters was also found, being highest in Cluster 6 (mean of 0.91 \(\pm\) 0.46 m), while in contrast, the annual maximum values of the SPI were found to be significantly higher in Cluster 4 (mean of 1.72 \(\pm\) 0.80) (ANOVA \(p\) = 0.002).