Number range CHAPTER© 2003 by Leo Poppoff

November 20, 2003

Basin Watch

by

Leo Poppoff

INCLINE CREEK WATERSHED IS A GOOD SPOT FOR RESEARCH

In many ways, the Incline Creek Watershed is an ideal place to study the
effects of urban development on a forested hillside. The upper slopes
are undeveloped and forested. The lower portions include about 30
percent of Incline Village, which is a mix of residential and commercial
development. It also includes two golf courses and a ski area.

There\'s also a history of research projects beginning with a pioneering
study by P. A. Glancy of the USGS in the early 1970s. Early development
activities in Incline Village altered streams, causing a great deal of
sedimentation in Incline Creek. Glancy\'s work documented the extent of
sediment discharge to Lake Tahoe caused by that disturbance. Since then,
a number of graduate students have done their thesis research in that
watershed. So, there\'s a body of historical data on sediment and
nutrient discharge from Incline Creek to the lake. However, not much has
been done to understand the linkages between watershed processes and
stream discharges.

With funding from the National Science Foundation, Desert Research
Institute (DRI) and University of Nevada-Reno (UNR) scientists have been
laying the groundwork for such studies in the Incline Creek Watershed.
The project, under the leadership of Dr. Richard Susfalk, has been
developing data about biological and chemical processes within the
watershed in order to provide basic information needed for linkage
studies.

For example, Susfalk from DRI and D. Johnson from UNR are studying the
role of upland forests in retaining, cycling and releasing nutrients as
well as the role of shrubs on shallow soil water chemistry. They're also
learning how stream water chemistry changes with time and location, and
the role of Incline Creek in transferring nutrients and sediments from
undeveloped upland areas through urbanized areas and into the lake.

The health of little critters inhabiting the bottom of the creek was
documented by DRI scientists, C. Fritsen, D. Davis, and A. Mosier. UNR
researchers, M. Gustin and T. Giglini checked on the prevalence of
mercury in water, plants and soil.

Nutrients are cycled through vegetation, Susfalk explained. They take up
nutrients from the soil and incorporate them in their stems and leaves.
Then, those nutrients fall to the ground with the forest litter, which
breaks down and releases the nutrients back to the soil. Some shrubs,
such as squaw carpet, bitter brush and mountain alder, fix nitrogen in
the soil. That is, they take nitrogen from the air and release some of
it around their roots. To do this, nitrogen fixers use a little more
phosphorus than other shrubs do.

According to Susfalk and his associates, the most important of these
processes for stream water quality is nitrogen-fixing by mountain
alders. Alders grow along streambanks, so the nitrogen it concentrates
in the soil can be carried away by water as it erodes stream banks.

Researchers found that nitrogen and phosphorus concentrations were
higher in litter from shrubs, and in soils under shrubs, than under pine
trees. Shrubs by their nature are richer in nitrogen and phosphorus than
are trees. Still, those higher nutrient concentrations did not affect
the quality of ground water because the shrubs can utilize the
nutrients. And soil is very capable of adsorbing nutrients, especially
phosphorus, from water percolating down from the surface.

They also noted that runoff through shrub litter could carry nitrogen
and phosphorus to nearby streams. Susfalk explains that runoff could be
more important in the Tahoe Basin than elsewhere because of the steep
slopes.

Benthic macroinvertebrates, the little critters that live on the bottom
of streams, are affected by environmental perturbations. So their health
is an indicator of stream and watershed well being. Fritsen, Davis, and
Mosier note that riffle length, canopy cover, stream width and substrate
composition affect the little critters\' habitat. The diversity of
families of macroinvertebrates present in a stretch of stream, and the
presence of sensitive species, are indicators of the health of that
stretch.

What researchers found was that the diversity of organisms and the
number of sensitive species dropped significantly at the transition
between forested and developed areas. At Diamond Peak ski area, the
index used to assess sensitive species dropped by more than 50 percent.
An unexplained surprise was that the lowest index of sensitive species
was found in the restored lower reach of Incline Creek. Third Creek,
only 100 feet away, had a greater percentage of intolerant species, and,
hence, a greater index.

Natural processes are complex and hard to unravel. Studying the working
of a watershed, as the DRI and UNR scientists have been doing, is very
important and ought to be continued. It takes more than a snapshot to
fully understand what Mother Nature is up to. But, this National Science
Foundation grant is at an end.

The next research project in the watershed will look at the impacts of
land use on water quality. It will build on the basic work done by
Susfalk and his colleagues. We\'ll learn more about this research,
funded by the Nevada Department of Environmental Protection, later.

Comments? Send them to basinwatch@sbcglobal.net