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TECHNICAL REPORTS

Surface Water Quality

Controlling Tailwater Sediment and Phosphorus Concentrations with Polyacrylamide in the Imperial Valley, California

^a Department of Environmental Sciences, University of California, Riverside, CA 92521
^b Kent SeaTech, P.O. Box 757, Mecca, CA

^* Corresponding author (chrisa{at}mail.ucr.edu)

Received for publication June 15, 2005. External loading of phosphorus (P) from agricultural surface discharge (tailwater) is the main cause of excessive algae growth and the eutrophication of the Salton Sea, California. Continuous polyacrylamide (PAM) applications to agricultural irrigation water inflows were evaluated as a means of reducing sediment and P in tailwater. Zero (control) and 1 mg L^–1 PAM (PAM₁) treatments were compared at 17 Imperial Valley field sites. Five and 10 mg L^–1 PAM treatments (PAM₅, PAM₁₀) were conducted at one site. The particulate phosphorus (P_p) fraction was determined as the difference between total phosphorus (P_t) and the soluble phosphorus (P_s) fraction. We observed 73, 82, and 98% turbidity reduction with PAM₁, PAM₅, and PAM₁₀ treatments. Although eight field sites had control tailwater sediment concentrations above the New River total maximum daily loads (TMDL), all but one were made compliant during their paired PAM₁ treatments. While PAM₁ and PAM₁₀ reduced tail water P_p by 31 and 78%, none of the treatments tested reduced P_s. This may have been caused by high irrigation water Na concentrations which would reduce Ca adsorption and Ca–phosphate bridging on the PAM. The PAM₁ treatments resulted in <0.5 mg L^–1 drain water polyacrylamide concentrations 1.6 km downstream of PAM addition, while PAM₅ and PAM₁₀ treatments produced >2 mg L^–1 drain water polyacrylamide concentrations. We concluded that, although PAM practically eliminates Imperial Valley tailwater sediment loads, it does not effectively reduce tailwater P_s, the P fraction most responsible for the eutrophication of the Salton Sea.

Abbreviations: DOM, dissolved organic matter • OPP, liquid orthophosphate phosphorus fertilizer • PAM, water-soluble anionic polyacrylamide powder • P_p, particulate phosphorus • P_s, soluble phosphorus • P_t, total phosphorus • TMDL, total maximum daily load • TSS, total suspended solids