The effects of wildfire on water quality: summary and implications for water quality management

Abstract:

Wildfires are growing in frequency and extent, and although the air quality and health effects of wildfire smoke are well recognized, impacts on water quality and aquatic ecosystems also occur. As a result, wildfire can affect the US Environmental Protection Agency’s mission area to protect clean water. For instance, as much as two-thirds of US freshwater supply comes from forested watersheds, raising the possibility of disruption or contamination by fire-generated stressors. Further, fires can impact developed landscape water resources directly by burning in the wildland-urban interface (WUI), home to over 30% of the US population. To better understand potential impacts, we developed a conceptual model linking EPA water program endpoints to wildfire. We then reviewed available literature on model endpoints and pathways. We recorded the directionality, magnitude, and duration of effects. Across studies, fire generally increased streamflow, sediments, water temperature, and a suite of chemicals, including nitrogen, metals, and polycyclic aromatic hydrocarbons. Effect magnitudes varied depending predominantly on fire severity. Notably, many metal concentrations recorded post-fire exceeded regulatory or guidance levels. Most effects lasted less than 10 years, with some longer exceptions. Our review also identified gaps in knowledge. A few endpoints (e.g., sediment, nitrogen, metals) have received the most research attention, whereas others (e.g., dissolved oxygen, disinfection byproducts) have received much less. With a few notable exceptions, we also found that little is known about the water quality effects if built structures, such as houses or pipes, are burned in the WUI. This lack of knowledge is evident even though fires are becoming more frequent and the WUI continues to expand. We anticipate this review will help local, state, tribal, and federal water managers better understand and prepare for the full suite of water quality impacts from fire. We also hope knowledge gaps identified in this review will inform future research. Disclaimer: The views expressed are those of the authors and do not necessarily reflect the views or policies of the EPA.