Reducing sediment phosphorus release rates in long lake through the use of calcium nitrate

Abstract

The effect of injecting different dosage rates of calcium nitrate into the bottom sediments of Long Lake in New Brighton, Minn., was observed in a laboratory study. The purpose of the study was to determine the minimum dosage necessary to reduce phosphorus release rates from the sediments to satisfactory levels. The study included measurement of sediment phosphorus release rates under both aerobic and anaerobic conditions, and evaluated the effect of adding ferric chloride to the sediments along with the calcium nitrate. The addition of ferric chloride was included in the study to determine if the iron available in the sediment was adequate to sorb the PO4−3when oxidized conditions were provided. The study concluded that at least for the short term (90 days), injection of calcium nitrate could eliminate virtually all phosphorus release from the sediments previously releasing phosphorus at a rate of 7 mg P/m2/day, and actually result in the sediments becoming a sink for phosphorus in the water column. The study also concluded that although the addition of iron enhanced the calcium nitrate treatment’s effectiveness, similar results could be achieved by increasing the calcium nitrate dose slightly and not adding the iron, which was a more cost-effective alternative. © 1984 Taylor & Francis Group, LLC.