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

Abstract

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 (PAM 1 ) treatments were compared at 17 Imperial Valley field sites. Five and 10 mg L −1 PAM treatments (PAM 5 , PAM 10 ) 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 PAM 1 , PAM 5 , and PAM 10 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 PAM 1 treatments. While PAM 1 and PAM 10 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 PAM 1 treatments resulted in <0.5 mg L −1 drain water polyacrylamide concentrations 1.6 km downstream of PAM addition, while PAM 5 and PAM 10 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.