ALUM INJECTION INTO SEDIMENTS FOR PHOSPHORUS INACTIVATION AND MACROPHYTE CONTROL

ABSTRACT

Aluminum sulfate was injected directly into lake sediments in an attempt to create a phosphorus-limiting environment to control macrophyte growth. The experimental site was located in a shallow lagoon off Lake Wingra, Wisconsin, which historically supports a dense, monotypic stand of Myriophyllum spicatum. A pump and probe mechanism was developed for sediment injection and alum was injected into experimental plots in late May 1986 at a dosage of 200 mg Al³⁺/L. Following injection, total dissolved phosphorus was reduced to a mean of 70 μg/L in interstitial Water at 13 cm sediment depth, compared to a mean of 460 μg/L in control plots at the same sediment depth. Phosphorus remained significantly lower in treated plots for at least 2 months. Alkalinity and pH were not significantly reduced; dissolved aluminum levels increased immediately following injection, but only in sediment-surface samples in harvested plots. No reduction in biomass attributable to alum treatment was observed during the 1986 growing season. No differences were seen in the percent phosphorus by dry weight in plant vegetation but lower percent phosphorus in root tissue was attributable to the alum treatment. Phosphorus mobilization from sediments and incorporation in plant tissue appears to have been more rapid in alum treated plots compared to controls.