Teaming up for Tahoe
If you visit Lake Tahoe anytime soon,
you’re likely to see them. They might be driving along the road, boating
near the shore or hiking on a streamside trail. They’ll seem like ordinary
people enjoying one of the world’s most extraordinary outdoor recreation
areas. But they’re not vacationers, they’re researchers. And they’re
not just enjoying the beauty of the lake, they’re studying it.
Over the past several years, more
and more of DRI’s scientists have turned their attention to the imminent
environmental problems of Lake Tahoe. At stake, particularly, are Tahoe’s
famous blue waters, whose clarity has been declining at an alarming rate. Much
of that decline can be attributed to sediments entering the lake, literally
muddying the waters, and nutrients, like phosphorous and nitrogen, encouraging
the growth of water-clouding phytoplankton and algae. The complex ecology of
the Tahoe Basin makes it a perfect fit for DRI and its broad-based, multidisciplinary
approach to environmental research. Tahoe is lucky to be having regular visits
from these researchers, as they turn science to the task of preserving a legendary
lake. Here are summaries of a few of DRI’s Tahoe-based projects focusing
on the problem of sediment and nutrient loading—how it enters the lake,
and how we might be able to stop it.
–Jackie Allen
At the Surface
Dr. John Tracy, Dr. Jim Thomas and Todd Mihevc are currently involved in a long-term
collaboration with researchers from the University of California, Davis that focuses
on how surface water runoff contributes sediment and nutrients to the lake’s
waters. With more than 30 automated samplers located around the lake, they will
investigate how different land uses—commercial, residential, recreational—and
different land types—various vegetation covers, soil content—influence
the amount of water-clouding substances entering the lake via surface sources.
What Lies Beneath
In another joint project with UC Davis, Tracy, Thomas and Mihevc will be looking
at how those same substances may be entering Tahoe via groundwater. Although no
sediments enter the lake via this source, groundwater does bring in nutrients,
as water from settling ponds and other standing sources recharges the groundwater
and eventually reaches the lake.
On the Road Again
Thomas and Mihevc are addressing
yet another sediment and nutrient source through a project with the Nevada Department
of Transportation. In this study they are evaluating the effectiveness of various
methods of removing sediments and nutrients from highway runoff in the basin.
These methods include “sealing” roadcuts with netting, rock, vegetation
or other materials; treating or filtering runoff from paved surfaces; and using
traps and basins to remove sediment from runoff water. The researchers are particularly
interested in how well these methods remove smaller particle sizes that are
not only a greater cause of clarity problems, but also carry some of the nutrients
required for algal growth.
In the Shallows
Dr. Kendrick Taylor has focused his investigation of Tahoe on the causes of clarity
loss close to shore, reasoning that this near-shore zone is the first portion
of the lake impacted by most incoming pollutants and will be the first portion
to respond to restoration activities. His goals are to identify which sections
of the shore are contributing the most clarity-degrading particles and the composition
of those particles. Taylor works from a specially designed research boat instrumented
to collect and analyze data “on-the-float,” essentially mapping the
near-shore water quality. Preliminary results have identified several short sections
of the shore that are causing most of the sediment and nutrient-loading problems.
Out of Thin Air
In collaboration with the California Air Re-sources Board and UC Davis, Dr. Judith
Chow, Dr. Hampden Kuhns and Dr. Vicken Etyemezian of DRI and Dr. Chris Damm of
Sierra Nevada College are approaching the problem of Tahoe water quality from
above. That’s because atmospheric deposition—air pollutants that eventually
reach the water—also contributes to Tahoe’s clarity problems. Chow,
Kuhns and Etyemezian are applying a hybrid approach that includes direct measurement
of pollutants collected on filter media using samples located throughout the basin,
including buoy stations on the lake’s surface. The investigators and student
research assistants are looking at the levels of motor vehicle exhaust, road dust
and wood-burning emissions in the basin. Motor vehicle exhaust will be collected
using roadside sampling devices and the effects of wood burning will be determined
through the use of controlled burns as well as sampling directly from residential
wood-burning appliances. Road dust emission are being measured with the new DRI-designed
TRAKER system, a specially equipped vehicle that monitors, measures and analyzes
airborne particles on-the-fly as they are kicked up by the front tires.
Under Cover
Tim Minor and Dr. Mary Cablk are using high-resolution satellite images to map
the amount of surface area in the Tahoe Basin that doesn’t allow snowmelt
and rainfall to soak into the ground. This “impervious cover”—things
like paved roads and parking lots—goes hand-in-hand with development and
adds to the runoff of silt and nutrient-laden water into the lake.
Into the Woods
The adjacent watersheds of the Tahoe Basin are important factors in addressing
clarity problems—what flows through the creeks and streams of the surrounding
forests eventually reaches the lake. This summer, Dr. Gayle Dana, Dr. Rick Susfalk,
and Dr. Paul Verburg will investigate Incline Creek and Third Creek watersheds
in the northeastern part of the Tahoe Basin, looking at how different land uses
and types—golf courses, ski resorts, residential communities, undeveloped
forests—influence nutrient and sediment loading. Dana is also involved in
a project measuring and monitoring evaporation from Lake Tahoe.
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