Effects of Air Pollutants from Wildfires on Downwind Ecosystems: Observations, Knowledge Gaps, and Questions for Assessing Risk

Abstract

Wildfires have increased in frequency and area burned, trends expected to continue with climate change. Among other effects, fires release pollutants into the atmosphere, representing a risk to human health and downwind terrestrial and aquatic ecosystems. While human health risks are well studied, the ecological impacts to downwind ecosystems are not, and this gap may present a constraint on developing an adequate assessment of the ecological risks associated with downwind wildfire exposure. Here, we first screened the scientific literature to assess general knowledge about pathways and end points of a conceptual model linking wildfire generated pollutants and other materials to downwind ecosystems. We found a substantial body of literature on the composition of wildfire derived pollution and materials in the atmosphere and subsequent transport, yet little observational or experimental work on their effects on downwind ecological end points. This dearth of information raises many questions related to adequately assessing the ecological risk of downwind exposure, especially given increasing wildfire trends. To guide future research, we pose eight questions within the wellestablished US EPA ecological risk assessment paradigm that if answered would greatly improve ecological risk assessment and, ultimately, management strategies needed to reduce potential wildfire impacts.

Wildfire-Derived Pyrogenic Organic Matter Posing Overlooked Emerging Risks to Aquatic Ecosystems

“…Postfire watershed erosion and runoff increase the fraction of PyOM in organic carbon, acting as nutrients and contaminants (e.g., polycyclic aromatic hydrocarbons) for several years or more. , This can lead to exceedances of drinking water standards and aquatic life tolerances (Figure b). The substantial amount of PyOM from erosion affects various water quality evaluation indicators, including dissolved oxygen, transparency, turbidity (i.e., suspended solids), temperature, salinity, pH, conductivity, etc.…”

“…Wildfires, increasing in frequency and extent burned, are a trend expected to continue as climate change prevails, affecting the air, soil, and water quality as well as posing human and environmental health risks. , Wildfires produce substantial amounts of pyrogenic organic matter (PyOM), estimated at ∼128 ± 84 Tg per year globally . The PyOM could be subsequently introduced into different water bodies via atmospheric deposition or overland flow into aquatic environments.…”

Wildfire smoke impacts lake ecosystems

“…For any given lake, a lake smoke‐day was defined as a day on which any portion of the lake boundary intersected with an area characterized as smoke by NOAA HMS, which categorizes daily smoke density as light (low), medium, or heavy (high) based on the aerosol optical depth (AOD) from visible satellite imagery (see Supporting Information for details). This smoke‐day concept, here for the first time applied in the context of lakes, has previously been used to demonstrate smoke exposure by ecoregion, and provides a basis for this lake‐specific metric (Paul et al., 2023). Smoke‐days for each lake were subsequently summed on an annual basis.…”

“…We currently lack a sense of scope, synthetic understanding of, or conceptual framework for identifying and understanding the effects of smoke across a broad range of lentic ecosystems. Aside from one example of a conceptual model of wildfire‐generated pollutants that includes effects on aquatic ecosystems broadly (Paul et al., 2023), conceptual models to date have drawn primarily from case studies of single systems, or have focused on the effects of wildfires burning within watersheds rather than the effects of smoke and ash at broader spatial scales (McCullough et al., 2019; Paul et al., 2022; Scordo et al., 2022). Our analysis addresses these critical knowledge gaps directly by: (1) quantifying lake exposure to smoke through space and time across the North American continent during 3 years of wildfire activity (2019–2021); (2) reviewing the current understanding of the mechanisms by which smoke affects physical, chemical, and biological aspects of lakes; (3) developing a conceptual framework that synthesizes known and theoretical impacts of smoke on lakes; and (4) identifying research priorities for future studies.…”

The hydrocarbon pollution crisis: Harnessing the earth hydrocarbon‐degrading microbiome

“…The decarbonization is also expected to have a beneficial impact on decreasing the industrial release of hydrocarbons into the environment by reducing oil spill frequency and consequences (Little et al., 2021 ). In addition to the direct contribution of hydrocarbons resulting from the continued use of fossil fuels, the human activities also generate indirect inputs such as wildfires introducing polycyclic aromatic hydrocarbon (PAH) into the environment (Campos et al., 2019 ; Paul et al., 2023 ). Particularly “mega fires,” which burn large forest areas, are becoming more frequent as a consequence of climate change (Bracewell et al., 2023 ; van Oldenborgh et al., 2021 ).…”