The researchers investigated the use of alum, a type of salt that has been used to treat phosphorus-rich lakes for decades. They also cleaned water from the rivers flowing into the Salton Sea with polyacrylamide, a new type of polymer used increasingly for reducing sediment loss from agricultural fields.
Results from the study appear in the November/December issue of the Journal of Environmental Quality.
"Removing phosphorus from the inflow reduces algae growth, improves water clarity and decreases the odors common at the lake," said Christopher Amrhein, professor of soil and environmental sciences and the lead author of the paper. "We found that alum and polyacrylamide were highly effective in removing both dissolved phosphorus and suspended sediment in the river waters entering the lake."
Both phosphorus - a fertilizer nutrient that occurs both dissolved in the river water and attached to the sediments suspended in the rivers - and silt contribute to algae growth, odors, low dissolved oxygen and fish-kills in the Salton Sea.
A clean-up of the Salton Sea and consequent development of the surrounding region could help meet the needs of California's growing population, support commercial growth in the neighboring Imperial and Coachella Valleys and achieve high property values in an area that is easily accessible from cities such as Los Angeles, San Diego and Riverside. An improvement of the environmental conditions in the Salton Sea region also could facilitate the region's development as a water-sports recreational area.
Currently, state and federal agencies are working to develop a comprehens ive restoration plan to return the Salton Sea to its former condition as a high-quality aquatic ecosystem and recreation area. One aspect of this restoration plan will be the management and control of nutrient inputs to the lake.
Inflow water into the Salton Sea by way of the Whitewater River, the New River and the Alamo River contains fertilizer nutrients from agricultural runoff and municipal effluent. These nutrients, particularly phosphorus, deteriorate the quality of the lake's water by encouraging algae growth.
"Water treatment technology and on-farm management of fertilizers appear to be the best approaches for reducing algae blooms in the Salton Sea," Amrhein said.
Unless measures are taken to clean the Salton Sea, evaporation will result in the sea being too salty for fish, resulting also in the loss of fish-eating birds frequenting an area that is home also to several endangered bird species and visited by millions of waterfowl every year.
Massive fish kills are a common occurrence at the Salton Sea, however, because of low dissolved oxygen, high hydrogen sulfide and ammonia concentrations, high temperatures and an increasing level of salinity.
Due to noxious odors emanating from the Salton Sea, a 32 kilometer-long State Recreation Area on the northeast shore remains under-used.
"The Salton Sea at one time attracted more visitors than Yellowstone National Park," Amrhein said. "If nothing is done, this sea will shrink, exposing lake sediments that could generate dust and worsen air quality. Fish and fish-eating birds would disappear in 10-30 years, and be replaced perhaps by birds that eat brine shrimp. And the sea would continue to smell, which might even get worse. Doing something to address the Salton Sea's problems on the other hand could greatly stimulate eco-tourism here and boost the economy of this region."
L. B. Mason, C. C. Goodson, M. R. Matsumoto and M. A. Anderson of UCR assisted with th e study, which was conducted in 2003-2005. The California State Water Resources Control Board and the Salton Sea Authority provided financial support.
Details of the study:
Phosphorus is contributed to the Salton Sea in both colloidal and dissolved forms. Alum and polyacrylamide are commonly used in municipal wastewater treatment to remove phosphorus and solids, and then the sludge is collected and disposed.
Alum, or aluminum sulfate, is the most widely used coagulant in water treatment. It forms solid amorphous aluminum hydroxide in water, which incorporates soluble phosphorus into its structure. The amorphous aluminum hydroxide, or "floc," combines with the other coagulated suspended solids and settles out.
Polyacrylamide is a synthetic polymer used in soil applications to reduce erosion, promote flocculation (the process by which clays, polymers, or other small charged particles become attached and form a fragile structure, called a floc) and enhance salt removal. Used in wastewater treatment, it enhances coagulation and settling. The polymer acts as a coagulant aid by chemically bridging reactive groups and increasing floc size.