Controlling Wolffia using alum in a pond

Abstract

An alum injection system delivered an alum “micro-floc” to an urban pond from 1997 through 2010 to reduce phosphorus from the water and thereby control Wolffia. Phosphorus concentrations in the pond were reduced from 170 μg/L (pretreatment average) to generally <50 μg/L with few exceptions (posttreatment). Wolffia coverage in the pond was reduced from 70–100% (pretreatment) to <10–20% coverage (posttreatment) after initial fine tuning of the system and 2 bulk alum additions to inactivate sediment phosphorus. Alum additions to urban ponds and stormwater detention basins can control Wolffia as well as enhance phosphorus retention efficiency for the protection of downstream resources.