Topic: Effects of Southern California Wildfires on Storm Water Metals and PAHS
Speaker: Eric Stein, PhD, Southern California Coastal Water Research Project
Dr. Eric Stein is a principal scientist at the Southern California Coastal Water Research Project (SCCWRP), where he is head of the Biology Department. Dr. Stein oversees a variety of projects related to in-stream and coastal water quality, bioassessment, hydromodification, watershed modeling, and assessment of wetlands and other aquatic resources. His research focuses on effects of human activities on the condition of aquatic ecosystems, and on developing tools to better assess and manage those effects. Prior to joining SCCWRP in 2002, Dr. Stein spent six years as a Senior Project Manager with the Regulatory Branch of the Los Angeles District Corps of Engineers, and four years with a private consulting firm.
Synopsis:Periodic wildfires are a natural component of southern California's forest and scrubland and are essential to maintaining overall ecological health of these systems. However, relatively little attention has been paid to the effects of post-fire runoff on downstream loading of pollutants, such as metals and organic compounds. These compounds may be of particular interest if burned areas drain to impaired waterbodies. In addition to the direct effects of runoff from burned landscapes, the materials left behind in ash at the burn location can be carried away from the fire in smoke and ash. Subsequent atmospheric deposition can markedly increase the quantity of various constituents available to storm flows downwind of fires. The goal of this study is to assess regional patterns of runoff and contaminant loading from wildfires in urban fringe areas of southern California. Post-fire stormwater runoff was sampled from five wildfires that each burned between 115 and 658 km2 of natural open space between 2003 and 2009. Between two and five storm events were sampled per site over the first one to two years following the fires for basic constituents, metals, nutrients, Total Suspended Solids, Polycyclic Aromatic Hydrocarbons (PAHs - atmospheric pollutants caused by fires) and various halogens. Results were compared to data from 16 unburned natural areas and 6 developed sites. Mean copper, lead and zinc flux (kg/km2) were between 112 and 736 fold higher from burned catchments and total phosphorous was up to 921 fold higher compared to unburned natural areas. PAH flux was four times greater from burned areas than from adjacent urban areas. Ash fallout on nearby unburned watersheds also resulted in a three-fold increase in metals and PAHs. Attenuation appears to be driven mainly by rainfall magnitude.
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