How does wildfire smoke influence the structure and function of lake ecosystems?

FACUNDO SCORDO; SUDEEP CHANDRA; ERIN SUENAGA; SUZANNE J. KELSON; FLAVIA TROMBONI; TIMOTHY J. CALDWELL; CRAIG E. WILLIAMSON; STEVEN SADRO; KEVIN C. ROSE

Virtual

Congreso; ASLO-SFS 2020; 2020

The Association for the Sciences of Limnology and Oceanography.

Smoke from even distant wildfires has the potential to influence lake ecosystem structure and function. In the summer of 2018, the airshed of Castle Lake (a subalpine, mesotrophic, 32 m deep lake located in northern California) was covered by smoke for 37 consecutive days as a consequence of wildfires outside the watershed. We analyzed how smoke affected Castle Lake by comparing historical (1998-2017) summer monitoring data with data collected in 2018. We measured the depth reached by 1 % photosynthetically active (PAR) and ultraviolet B (UVB) radiation, lake primary productivity (PPR), the concentration of chlorophyll a (chl a), zooplankton abundance and community composition, and trout abundance. From July to August 2018, the depths to which 1 % PAR and UVB penetrates decreased by 23 % (4.5 m) and 19 % (0.5 m), respectively. For the same period, in the previous four years, 1 % PAR decreased by 2.9 m, and UV increased by 0.2 m. During the smoke period, chl a was significantly lower at the deep chl a maximum (DCM; e.g., 20m = 1.09 ± 0.09 µg L-1) compared to the previous 20 years (20m = 6.52 ± 3.86 µg L-1). From July to August, in the top 3 m of the lake, PPR increased 35 % more in 2018 compared to previous years. In contrast, at the DCM, PPR decreased by 27 % in 2018, while in previous years, it increased by 43 %. During the smoke period, zooplankton richness decreased, Daphnia concentration at the pool mixed layer was higher during the day than at night, and no trout were caught. These results highlight that wildfire smoke influence lake ecosystem structure and function