Biogeochemical and biophysical responses to episodes of wildfire smoke from natural ecosystems in southwestern British Columbia, Canada.

Area burned, number of fires, seasonal fire severity, and fire season length are all expected to increase in Canada, with largely unquantified ecosystem feedbacks. However, there are few observational studies measuring the ecosystem-scale biogeochemical and biophysical properties during smoke episodes, and hence accessing productivity effects of changes in incident diffuse photosynthetically active radiation (PAR). In this study, we leverage two long-term eddy covariance measurement sites in forest and wetland to study four smoke episodes, which happened at different times and differed in length, over four different years. We found that the highest decrease of shortwave irradiance due to smoke was about 50% in July and August but increased to about 90% when the smoke arrived in September. When the smoke arrived in the later stage of summer, impacts on H and LE were also greatest. Smoke generally increased the diffuse fraction from ~0.30 to ~0.50 and turned both sites into stronger carbon-dioxide (CO2) sinks with increased productivity of ~18% and ~7% at the forest and wetland sites, respectively. However, when the diffuse fraction exceeded 0.80 as a result of dense smoke, both ecosystems became CO2 sources as total PAR dropped to low values. The results suggest that this kind of natural experiment is important for validating future predictions of smoke-productivity feedbacks. [ABSTRACT FROM AUTHOR]