Wally Miller

A Tale of Two Fires

Wildfires can be destructive to the immediate environment while they
burn but they may also have lasting detrimental effects on the ecosystem sometimes long after they’ve been put out. Wally Miller and his colleagues Dale Johnson and Roger Walker have compared research findings from two large wildfires in the Lake Tahoe Basin to see how they affected runoff water quality from burned watersheds.

Miller and his colleagues studied the effects of the Gondola wildfire that burned in 2002 and compared their findings to those reported by other investigators from the Angora wildfire which
occurred in 2007. They found that water from the overland flow runoff degraded sharply immediately following the Gondola wildfire, but generally improved after about three years. But Miller said that effect could change depending on the subsequent wet or dry water years.

An intense hailstorm fell on the Gondola site about two weeks after the wildfire.

“The runoff from that particular storm contained very high concentrations of ash, sediment, nitrogen and phosphorus, which are of concern to the lake,” Miller said.

Nutrients and sediment entering the lake can stimulate algae growth and increase suspension of fine particles in Lake Tahoe, both of which diminish lake clarity.

Miller found that the Gondola wildfire adversely affected runoff water quality to a much greater extent than that reported following the Angora Wildfire, which burned a much larger area.

“The good news is that the effects of wildfire on runoff water quality and other soil-related characteristics appear to be relatively short lived,” Miller said. “The bad news is that the potential impact on stream and lake water quality depends on whether or not the wildfire is followed by a major precipitation event on bare soil or an overall wet or dry year; something which is largely unpredictable.”

Miller and his colleagues are currently writing a report summarizing their comparison of the two wildfires’ potential long-term effects on the runoff water quality. He said their study shows that fire suppression has decreased the number of wildfires that burn in the basin. Still, when they do burn, a higher burn intensity coupled with a larger accumulation of organic debris can increase the potential for washing large amounts of nutrients and
sediments into the lake.

Much of Miller’s work explores the links between the upper watershed and the lake. Miller and his colleagues are currently examining how nutrients are cycled in the forest watershed, particularly in areas of nutrient accumulation.

“We’re now looking at the presence and distribution of nutrient hotspots in forest soils and whether they contribute to increased nutrient transport,” Miller said.

He believes it’s important to address how nutrients are cycled in surrounding watershed forests before they enter the stream and lake
ecosystems.

“For years the change in lake clarity has been related to enhanced nutrient loading and fine sediment loading,” Miller said. “If what goes on in the upper watersheds tends to influence that, then
it’s important.”