Wildfire run-off impacts Lake Tahoe clarity
October 31, 2007
Wildfires may have a direct correlation with Lake Tahoe clarity levels ” the more the forest around the lake burns, the cloudier it becomes.
This and other fire-related issues were discussed during Fire Science, a lecture hosted by University of California, Davis at the Tahoe Center for Environmental Studies on the campus of Sierra Nevada College. The event was geared toward giving attendees a scientific understanding of fire and fuels management. Three lecturers were featured: University of Nevada, Reno professor Dr. Wally Miller; University of California, Berkeley Sagehen Creek field station supervisor Jeff Brown and North Lake Tahoe Fire Protection District Chief Mike Brown.
Miller unveiled the results of a UNR study showing that wildfires release nitrogen, phosphorous and sulfur into the soil.
“We don’t know for sure if these nutrients make their way into the lake, but we do know soil sediment only travels with water in the form of runoff, so rain could release these into the lake,” Miller said.
He said that both nitrogen and phosphorous negatively affect lake clarity levels by enhancing algae.
“The more biomass you have in the lake, the less visibility you get,” Miller said.
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Miller also stated that following wildfires, large amounts of sulfur were found in the soil under a charred area. He was unsure what impacts sulfur has on lake clarity levels.
“We need to take a look at the sulfur levels simply because of the magnitude of sulfur we found after fires took place. It could be something, it could be nothing,” Miller said.
He said the best way to reduce the amount of nutrients in soil runoff that could potentially reach the lake was to implement a series of mechanical thinning operations around the basin. He recommended the forests be treated for fuels reduction and then subjected to controlled burns. He said that while this combination doesn’t necessarily reduce the amount of nutrients in the soil, it reduces the likelihood the nutrients will runoff with rain water. Miller explained this is because the nutrients concentrate within the soil heavily after a wildfire, whereas with a small, controlled burn the nutrients are more evenly dispersed.
Jeff Brown presented information he has collected while working at the Sagehen Creek field station. There, scientists have explored SPLATs (strategically placed land area treatments). A SPLAT is fuels reduction treatment in strategic areas of a forest, meant to slow a wildfire’s advance. It involves thinning a forest’s fuels in staggered strips of the forest.
In Sagehen, Jeff Brown’s team of scientists created computerized SPLATs across the forest and saw two things. One is that the SPLAT-protected zones were very effective in slowing fires, and the other is that fuels reduction is most effective when 20 percent of the forest is thinned.
A complete thinning of fuels, Jeff Brown said, is not cost effective and doesn’t slow a fire’s advance by much.
“The first 20 percent of the thinning process produces the most bang for your buck. More than that doesn’t do too much to interrupt a fire,” Jeff Brown said.
Chief Mike Brown said that his hand crews have been busy thinning the forest around Incline Village to protect the community with a halo of fuels-reduced areas.
“Our halo creates a quarter-mile buffer zone between ourselves and other fire districts, so we can slow a fire coming from out of the area or one that originates in Incline from jumping to another district,” Mike Brown said.
The NLTFPD is working toward creating good defensible space around Incline by encouraging everyone to take responsibility for defensible space on private property, Mike Brown said.
“There are three conditions that affects fire behavior, fuel, weather and topography. Fuel is the only one you can control and our goal is to keep these fires on the ground at a low intensity,” Mike Brown said.
The next fire lecture, Fire Behavior, is scheduled for Nov. 13 at the Tahoe Center for Environmental Sciences. It will feature noted fire expert and UC Berkeley professor Scott Stephens. It begins at 5:30 p.m. with a no-host bar; the lecture begins at 6 p.m. A $5 donation is requested.