# Investigating the Impact of Wildfires on Lake Water Quality Using Earth Observation Satellites
## 4 Discussion
Our findings align with recent studies [28] in shallow oligo-mesotrophic lakes, suggesting that clear unproductive lakes could experience post-fire increases in primary productivity, but also that post-fire dynamics of nutrients and light limitation are important factors. Results from studies on ecological assessments of European lakes [56] suggested that light conditions and mineral availability are significant drivers of Chl-a concentrations in oligotrophic lakes. In our dataset, although the effects of wildfires on eutrophic lakes seemed to be translated into relatively higher Chl-a peaks, it is however difficult to partition the influence of fires from other sources, given their often very dynamic phytoplankton communities. Post-fire Chl-a increases associated with high rainfall may be derived as much or more from other catchment point and non-point sources as from wildfires. Regarding land cover vegetation, we found differences among clusters of burned vegetation types in relation to Chl-a development timing after a fire, suggesting that vegetation communities might be an important factor in mediating responses in water ecosystems. However, precipitation events have likely played a concurrent role, as the highest maximum SPI was found for the vegetation cluster (Cluster 4--everygreen boreal forests) which had the fastest responses of Chl-a in lakes. Moreover, lakes included in the different clusters were located in diverse geographic areas (see map in Figure 1), with coniferous forests in Canada and North America (Cluster 4) and mixed deciduous broadleaves in the southern hemisphere (Cluster 6), indicating that biomes and their climatic variables, including related precipitation patterns, would be key factors for the temporal response of Chl-a. Our last analysis aimed at comparing pre- and post-fire water quality conditions in our studied lakes. During a six-month period after a major fire, lake Chl-a either increased or decreased in a similar number of lakes, indicating that lake specific ecological context is important to explain and predict potential responses to fires. In other studies investigating the effects of wildfires on lakes, post-fire changes in lake concentrations (i.e., nutrients) were not regularly observed. De Palma-Dow et al. [27] did not find a substantial change in total phosphorous concentrations up to three years post-fire and found no changes in relation to smaller fires when analyzing Clear Lake (California), despite the very large burned area and its proximity to the lake (40% of the watershed burned at 1 km from the shoreline). A study of boreal Alaskan lakes [24] found that nutrient concentrations were not sensitive to wildfires up to two years after the event. As climate change is a major contributor to significant wildfire events, floods, and extreme droughs, the effect on lake water quality conditions is in many ways unpredictable [72]. We analyzed in detail responses to fire occurrence in two African lakes with the largest burned areas recorded in this study and having different lake morphologies, the deep Lake Volta and the shallow and very large Lake Chad. In the former, lake Chl-a and turbidity concentrations remained stable with modest peak development, while in the latter more pronounced fluctuations were observed. Although Lake Volta had a greater ratio BA/A than Lake Chad, the response to wildfires was not accordingly more pronounced, likely due to lake morphology. Wildfire effects on lakes can be indeed highly site-specific, regardless of similarities in the geographical, morphological, and fire characteristics of lakes. In our study, for instance, we compared two African lakes in Zambia (Lake Mweru) and in Congo (Lake Mukenge) sharing very similar morphological and ecological characteristics and also affected by comparable fires.