Spatiotemporal Controls on the Delivery of Dissolved Organic Matter to Streams Following a Wildfire

Abstract

Fire regimes in the western US are changing, with patterns in burn area and burn severity becoming disconnected from historical fire regimes (Haugo et al., 2019). These shifting fire patterns are of increasing concern for watershed biogeochemical processes when considering the known impacts of wildfire on water quality and aquatic ecosystem health, which can persist for years post-fire (Bladon et al., 2014;Emelko et al., 2016;Niemeyer et al., 2020). The intermediate-and long-term influences of wildfires on water quality are diverse across affected watersheds Santos et al., 2019;Sherson et al., 2015). Post-fire stream water chemistry, for example, is thought to result from an interplay between biogeochemical and hydrologic processes impacted by fire, such as water availability and soil water repellency (Niemeyer et al., 2020). In fact, the environmental fate of fire-impacted materials-also termed pyrogenic organic matter (PyOM)-is thought to be determined by its first interactions in water post-fire (Masiello & Berhe, 2020). The short-term hydrological response to fires is also regionally dependent. For example, high hydrological connectivity between hillslopes and streams in highland regions of the western US accelerates the delivery of water to streams post-fire (Hallema et al., 2017). This immediate hydrologic response is dependent on a complexity of factors that alter the chemical and physical properties of the watershed soils, including burn severity (Moody et al., 2016).

Appearance of Recalcitrant Dissolved Black Carbon and Dissolved Organic Sulfur in River Waters Following Wildfire Events

“…The globally increasing extreme high temperatures in recent decades have led to a rise in wildfires, posing a significant threat to global ecosystems and impacting ecological security. Wildfires typically transport pyrogenic organic matter and nutrients to rivers through interactions with the hydrological cycle . Our study highlighted that atmosphere ash deposition was likely responsible for the high levels of DOC and DBC in locations close to the wildfire areas, but wind direction on the sampling day also played a role.…”

“…Meanwhile, the strong coupling between atmospheric OC and BC during wildfires in this area ( Figure S4 ) also indicated that riverine DOC and DBC were likely sourced from ash deposition. Studies have also found a coupling of DOC and certain water quality parameters, such as turbidity, 13 , 14 suggesting that DOM likely originated from mobilized surface materials due to postfire runoff and erosion. 13 Salinity has been widely documented to negatively correlate with aquatic DBC via affecting the physical and photochemical processes of DBC.…”

“…Ding et al reported that there was no correlation between recent fire activities and in-stream dissolved organic carbon (DOC) and DBC concentrations. , However, Dittmar et al observed continued export of riverine DBC and DOC each year in the rainy season after major fire activity . The concentrations of DOC in streamwater were also identified to be primarily driven by local hydrology during the first storm event occurring 1 month after the fire . Generally, most studies have investigated the correlation between wildfires and riverine DOM/DBC over an extended period, occurring several months or years after the wildfires took place. , Environmental drivers, especially hydrology during rain and storm events are recognized as significant factors determining the postfire export of DOC and DBC. ,,, However, in scenarios where there is no rainfall, the immediate impacts of wildfires on aquatic DOM and DBC within a few days postfire remain poorly understood.…”

“… 7 The concentrations of DOC in streamwater were also identified to be primarily driven by local hydrology during the first storm event occurring 1 month after the fire. 13 Generally, most studies have investigated the correlation between wildfires and riverine DOM/DBC over an extended period, occurring several months or years after the wildfires took place. 7 , 14 Environmental drivers, especially hydrology during rain and storm events are recognized as significant factors determining the postfire export of DOC and DBC.…”

Hydrology, rather than wildfire burn extent, determines post‐fire organic and black carbon export from mountain rivers in central coastal California

“…2). However, increases in water discharge have been related to increases in DOC and DBC export (Raymond and Saiers 2010;Dhillon and Inamdar 2014;Wagner et al 2015;Roebuck et al 2018Roebuck et al , 2022. There is also evidence that storm events can enhance the amounts of wildfire-generated chromophoric DOM exported during storm events (Roebuck et al 2022).…”