Road sanding and salting is receiving more and more scientific attention at Tahoe, according to several abstracts presented at the 5th Biennial Lake Tahoe Basin Science Conference this spring.
Scientists suspect that dust from paved roads is a major source of the fine sediment that’s causing the decline in lake clarity. Fine sediment is smaller than a human hair, and is a concern because it can remain suspended in the lake for decades, rather than settling to the bottom as do larger particles.
Scientists at the Desert Research Institute in Reno studied sources of fine sediment in “atmospheric deposition,” or pollution that falls into the lake from the air. Atmospheric deposition is responsible for 15 percent of overall pollution clouding lake clarity. Scientists looked at several sources, including vehicle emissions, wood burning, wildfires and road dust. They found that road dust is the major source of the larger fine particles that enter the lake via the air, particularly in South Lake Tahoe, where traffic is the greatest. The major source of the smallest fine particles was wood burning during fall and winter months, followed by vehicle emissions. Scientists found little evidence that wildfires in or out of the basin were a major contributor. Researchers are continuing to study stormwater runoff to see how much road sand flows into the lake when picked up by rain and snowmelt.
Fine particles from road dust contain a high amount of phosphorous, one of the nutrients that causes algae growth. Research showed that the low-phosphorous sand, combined with a de-icing solution, can reduce phosphorus input by a factor of four, but the materials should be swiftly removed and prevented from entering the Lake. Researchers have also identified the most effective street sweepers for picking up fine sediment.