Investigating the Impact of Wildfire Disturbance and Microclimate on Carbon and Water Fluxes in a Coastal Fog-Influenced Grassland Ecosystem
Author: Jessica Solis
Faculty Supervisor: Sara Baguskas
Department: School of the Environment
Coastal grassland ecosystems are vulnerable to increased wildfire risk driven by anthropogenic warming. Coastal advection fog is a meteorological phenomenon that dominates in the summertime in California and mitigates heat and water stress. Our research aims to understand how coastal fog and wildfire disturbance impact carbon and water fluxes from these ecosystems. We conducted our study in a coastal grassland in Santa Cruz County, California. We compared two sites, one with high burn severity and ‘high fog’ frequency and one with low burn severity and ‘low fog’ frequency. Burn severity was determined using the Normalized Burn Ratio index applied to Sentinel-2A imagery. We used a closed chamber approach to measure carbon dioxide and water vapor fluxes from similar plant communities (grasses and herbs) within 0.75 m2 plots (n=6 plots) at each site. We installed a passive fog collector, meteorological station, and pyrgeometer at each site to characterize fog events and local climate conditions. We measured soil moisture (0-10 cm) in each plot during chamber sampling. On average, net ecosystem exchange (NEE) values indicate that our sites were a CO2 sink in June (NEE = -0.24 ± 0.14 mgCO2 m-2 s-1). At the site with high burn severity and ‘high fog’ frequency, NEE, gross primary productivity (GPP), and evapotranspiration rates were 115%, 88%, and 101% greater, respectively, compared to the low burn and ‘low fog’ site. Between foggy and non-foggy periods, we found that, on average, the site with low burn severity was a stronger sink during fog events (NEEFog= -0.33 mgCO2 m-2 s-1, NEENoFog= -0.07 mgCO2 m-2 s-1) and the high burn severity site was a stronger sink during non-foggy periods (NEEFog= -0.16 mg CO2 m-2 s-1, NEENoFog= -0.25 mgCO2 m-2 s-1). Average GPP was greater at the low burn severity site when fog was present (GPPFog= -0.39 mgCO2 m-2 s-1, GPPNoFog= -0.08 mgCO2 m-2 s-1) while GPP was greater at the high burn severity site during non-foggy periods (GPPFog= -0.19 mgCO2 m-2 s-1, GPPNoFog= -0.34 mgCO2 m-2 s-1). In July, our sites were a CO2 sink (NEE= -0.12 ± 0.07 mgCO2 m-2 s-1), but not as strong as in June. Our findings support the idea that coastal microclimate, particularly fog events, directly affect carbon and water dynamics in a coastal grassland recovering from wildfire disturbance.