Using microcosms to assess aeration, cement, and clay mitigation of iron contaminated lake sediments

Abstract

A sediment‐water phase laboratory microcosm experiment was designed to assess iron dynamics for Fall Creek Lake located in the Cumberland Plateau Region of Tennessee, the United States. Aeration, clay, and cement treatments were compared with control. Representing the lake hypolimnion, microcosms were maintained under dark conditions at 9 ± 1 °C for six months. For the initial six weeks, the dissolved oxygen (DO) concentration in clay, cement and control microcosms was 5–6 mg/L The DO in the aerated microcosms was 10–11 mg/L. After six weeks, the DO concentration was reduced by nitrogen purging to 0–2 mg/L in all microcosms except the aerated one. All treatment microcosms demonstrated significantly lower water column iron concentrations. The rate and extent of iron release from lake sediments to water was influenced by mechanisms involving oxidation and sorption processes. Of the treatments, aeration and clay appeared to be effective in capturing iron released from sediments. Cement treatment caused high pH (10–11), high ammonia concentration (2.5 mg‐N/L), and depressed bacterial density. Although efficient at capturing iron, cement treatment would not constitute a realistic environmental application because of unacceptable pH shifts in the water column.