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Soil conservation still short of goal

Patrick McCartney

Editor’s Note: Today is the second installment in the Tahoe Daily Tribune’s examination of the Tahoe Regional Planning Agency’s five-year evaluation of Lake Tahoe’s environment. Today, a look at soil conservation.

When scientists study the cause of Lake Tahoe’s alarming loss of clarity, their attention quickly turns to the native soil that covers much of the Tahoe Basin’s 207,000 acres.

Formed by weathering and the decay of natural vegetation over the millennia, the highly granitic soils are vulnerable to erosion when they are disturbed. And as the soil washes into tributaries that feed Lake Tahoe, it carries minerals, such as phosphorus, that stimulate the growth of algae in the lake.

Along with atmospheric nitrogen, phosphorus from erosion is believed to be the largest culprit behind a 30-percent loss of Lake Tahoe’s clarity since 1968.

But while soil erosion has contributed to the decline in Lake Tahoe’s famed clarity, the rich soil deposited in the basin’s stream zones acts as a natural filter, removing nutrients and other minerals from the water before it enters the lake.

Since identifying in 1982 the nine principal goals in restoring Lake Tahoe’s environment, the Tahoe Regional Planning Agency has attempted to reduce the amount of new disturbance to the soil, reduce the amount of hard coverage and restore potentially valuable wetlands.

According to its 1996 evaluation of the basin’s environment, however, the TRPA has fallen short of its long-range and interim goals to prevent new erosion and restore damaged wetlands.

The bistate agency has estimated that about 4,400 acres of the estimated 21,944 acres of wetland in the Tahoe Basin has been disturbed or developed. In 1982, the TRPA set a goal of restoring a fourth of the disturbed stream-zone soil to a natural state.

Yet, just 321 acres have been restored so far at a cost of $17.6 million, a pace that the agency wants to increase over the next five years.

Studies have demonstrated the effectiveness of wetlands in preventing unwanted nutrients from entering Lake Tahoe. A 1977 TRPA study showed that nitrogen, phosphate and silt were reduced between 73 and 94 percent by a stream zone.

“From a water-quality standpoint, hard coverage on a stream-environment zone is the worst problem,” said Joe Pepi, a TRPA senior planner and soil scientist. “What we would like to do is get the stream zones and flood plains back to treating water.”

Similarly, the TRPA reported that it has not been able to meet its goals of reducing the amount of hard or impervious coverage of basin soils by development. According to the agency’s research, 43,112 acres of the basin’s 207,000 acres have been disturbed or covered.

Since 1987, the TRPA has approved enough development to cover another 238 acres, while a total of 135 acres of hard coverage has been removed.

“We’re trying to control the amount of new ground coverage, and trying to catch up to the impacts from earlier development,” Pepi said about the agency’s soil conservation goals.

But land-use regulators have a long way to go before they can catch up to the explosive growth in the Tahoe Basin that began when Squaw Valley hosted the Winter Olympics in 1960. Since then, the population has grown by five times, with the summer population hitting an estimated 102,000 in the basin in 1995.

In coping with the erosion problems from road cuts and other development, the basin’s four counties, the city of South Lake Tahoe, the U.S. Forest Service and California and Nevada departments of transportation have spent $80 million since 1979 on erosion-control projects. The agencies made as much progress in the last four years as they had in the previous eight years, the TRPA reported in its 1996 evaluation.


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