Smoke from regional wildfires alters lake ecology

Abstract

Wildfire smoke often covers areas larger than the burned area, yet the impacts of smoke on nearby aquatic ecosystems are understudied. In the summer of 2018, wildfire smoke covered Castle Lake (California, USA) for 55 days. We quantified the influence of smoke on the lake by comparing the physics, chemistry, productivity, and animal ecology in the prior four years (2014–2017) to the smoke year (2018). Smoke reduced incident ultraviolet-B (UV-B) radiation by 31% and photosynthetically active radiation (PAR) by 11%. Similarly, underwater UV-B and PAR decreased by 65 and 44%, respectively, and lake heat content decreased by 7%. While the nutrient limitation of primary production did not change, shallow production in the offshore habitat increased by 109%, likely due to a release from photoinhibition. In contrast, deep-water, primary production decreased and the deep-water peak in chlorophyll a did not develop, likely due to reduced PAR. Despite the structural changes in primary production, light, and temperature, we observed little significant change in zooplankton biomass, community composition, or migration pattern. Trout were absent from the littoral-benthic habitat during the smoke period. The duration and intensity of smoke influences light regimes, heat content, and productivity, with differing responses to consumers.

Environmental effects of stratospheric ozone depletion, UV radiation, and interactions with climate change: UNEP Environmental Effects Assessment Panel, Update 2021

“…Increased abundance of aerosols resulting from wildfire smoke and the dust and plant volatile compounds released during droughts can decrease the amount of UV radiation and change the spectral composition of sunlight received by organisms at ground level [ 109 ]. Notably, changes in air quality resulting from fires and droughts can occur well beyond the location of these events [ 32 , 110 , 111 ].…”

“…For example, the plants that colonise open habitats and tolerate high UV radiation may include more introduced and fewer specialised or endemic species [107,108] which may, in turn, have negative consequences for biodiversity. Increased abundance of aerosols resulting from wildfire smoke and the dust and plant volatile compounds released during droughts can decrease the amount of UV radiation and change the spectral composition of sunlight received by organisms at ground level [109]. Notably, changes in air quality resulting from fires and droughts can occur well beyond the location of these events [32,110,111].…”

Wildfire Smoke Effects on Lake‐Habitat Specific Metabolism: Toward a Conceptual Understanding

“…However, we recognize that our study only covered the epilimnetic zone of the lake, and that PAR reduction could have lessened productivity at greater depths or caused a shift in the depth of the euphotic zone. Scordo et al (2021) found that after smoke reduced PAR at depth (12.5 m and lower) in Castle Lake, the deep chlorophyll-a and productivity maximum (15-20 m) did not develop. Giling et al (2017) showed that metalimnetic contribution to whole-lake metabolism can be highly variable.…”

“…Also, the year 2018 had the highest mean (51 ± 5 μg m −3 ) and maximum (143 μg m −3 ) value of PM 2.5 when smoke was present (Figure 3a). During 2018, our study period began on August 1st, 13 days after the smoke conditions started (Scordo et al., 2021). Within our study period, smoke cover occurred between August 1–19, August 21–25, August 29–30, and September 5–10.…”

“…solar radiation can decrease water temperatures and affect physical mixing dynamics (David et al, 2018;Scordo et al, 2021;Figure 1a). Smoke particles deposited directly on lakes or transported into lakes through runoff from the watershed affect aquatic ecosystems by suppressing light and altering nutrient supply to algae (Goldman et al, 1990;Scordo et al, 2021; Figure 1a). The deposition of particles may contribute nutrients (Earl & Blinn, 2003) and stimulate pelagic primary productivity (Tang et al, 2021).…”