Short-term effects of a buffered alum treatment on Green Lake sediment phosphorus speciation

Abstract

Green Lake, Washington, was treated with a dose of 24 mg Al/L aluminum sulfate (alum) and sodium aluminate during March–April 2004 to reduce dissolved phosphorus concentrations to ameliorate a variety of eutrophication-related problems. Four sediment cores collected six months after the alum treatment in Green Lake were used to examine the short-term effects of alum on sediment phosphorus speciation. Peaks in aluminum bound phosphorus (Al-P) and total aluminum (Tot-Al) were observed in three of the four cores analyzed, resulting in an average ratio of added Al to Al-P formed (Al:Al-P) of 112:1. By comparing this ratio to the average ratio of ~11:1 found in other alum-treated Washington lakes, it can be inferred that approximately 10% of the binding capacity of the added Al had been utilized. Assuming a final ratio of Al:Al-P of 11:1, the added Al has the potential capacity to bind a total of 21.6 g/m2 of P. The amount of sediment inorganic P that supports internal loading (Fe-P and labile-P) in the fall of 2004 was determined to be 2.8 g/m2. Thus the quantity of alum added to Green Lake should be sufficient to inactivate the remaining inorganic mobile-P and to control future P mobilization from the pool of organic sediment P.