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Phosphate control may be the key to reduction

July 24, 2001

SALTON CITY — Control of phosphates may be the key to eventually reducing the Salton Sea's eutrophic conditions, according to a recently published scientific paper.

According to a Salton Sea Authority press release, the paper suggests testing a chemical used for the past 50 years to control algal blooms in other lakes and reservoirs to neutralize the phosphates that flow into the sea from municipal and agricultural runoff.

Eutrophication is a natural process in which a body of water becomes rich in dissolved nutrients. For the Salton Sea, it means high fish populations, massive fish die-offs as well as the noxious odors that at times permeate the lake.

While nitrogen and phosphorous are nearly always the chemical elements that act as primary nutrients to create eutrophic conditions in lakes, the scientists found phosphorus is the main controlling factor in producing those conditions in the Salton Sea, the release states.

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"Think of it as building houses," said the paper's editor, Jim Setmire, a U.S. Geological Survey hydrologist working with the U.S. Bureau of Reclamation.

"Even if you have an infinite amount of wood, but only enough nails for two houses, how many homes can you build? In this case, nitrates are the ‘wood' and phosphates the ‘nails.' We are attempting to limit the number of eutrophic ‘houses' by taking away the ‘nails,' " he said.

According to the paper, the addition of aluminum sulfate, also known as alum, to the New and Alamo rivers may help to deal with the phosphates.

While the sheer size of the Salton Sea prohibits direct treatment in the lake, the scientists state the alum treatment "may be able to be added to the tributaries to tie up the phosphorus before the water enters the Salton Sea."

The paper is titled "Eutrophic Conditions at the Salton Sea." It stems from a workshop last September at the University of California, Riverside.

In addition to Setmire, eight other scientists from California universities and government agencies contributed to the work.

"These highly qualified scientists have given us important insights into the eutrophication of the Salton Sea," said Tom Kirk, executive director of the Salton Sea Authority.

"The question of eutrophication at the sea is a complex one, but as we have tried to do throughout the restoration effort we have responded to concerns raised and taken a science-based approach to addressing these issues," Kirk said.

The SSA recently received a $570,000 grant from the state Water Resources Control Board to determine the most efficient and cost-effective means to reduce phosphorus loading from external sources. This project will investigate the alum treatment as well as control of phosphorus-containing sediments.

The scientists state that introduction of the alum to the rivers "at or near their outlets to the Salton Sea could remove significant loads of phosphorus and decrease the eutrophication of the sea."

They caution, however, it will take up to five years for an effect on eutrophication to be seen.

The paper recommends experiments be initiated to investigate the ratio of alum to phosphorus and the possible addition of polymers that would be needed to remove at least 80 percent of incoming phosphorus.

The paper points out that alum "has been added to lakes and reservoirs since the 1950s to control algal blooms by reducing internal phosphorus loading." It states that when added to water, it forms aluminum hydroxide that works to absorb the phosphorus, thereby forming a chemical barrier to the sediments.

The scientists also determined that while nutrients have flowed into the sea at increased rates over the last 30 years, because of some unknown process in the water the eutrophic state of the sea is virtually unchanged since the 1960s.

Phosphorus comes mostly from external sources such as agricultural and municipal runoff that flows into the Salton Sea via the New and Alamo rivers.

Scientists estimate a reduction of 50 to 80 percent from external sources will be needed to reduce eutrophication in the sea.

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