Base neutralizing capacity of sediments from an acidic lake

The base neutralizing capacity (BNC), or alkalinity consumption, of acidic lake sediments may influence the amount of neutralizing agent required to neutralize a lake if the sediment BNC is large relative to the BNC of overlying waters. The extent ofin situ sediment BNC in acidic Bowland Lake (pH 5.0) was inferred by (1) measuring the loss of Ca-45 to acidic sediments from labeled lake water neutralized with CaCO₃, and (2) measuring exchangeable Ca in sediments collected prior to and following neutralization of Bowland Lake with calcite (CaCO₃). The sediment BNC derived from the Ca-45 radiolabeling experiment was 0.01 mg CaCO₃ g^?1 w wt. The mean losses of Ca-45 from the aqueous phase of neutralized and untreated sediment/water mixtures were not significantly different. The mean pH of both neutralized and untreated mixtures decreased to 4.0 during the incubation, possibly because of oxidation of reduced sediments. Sediment BNC estimates derived from literature data for several lakes may be overestimated because of the inclusion of anoxic sediments containing significant amounts of reduced Fe. There was no significant difference in exchangeable Ca between sediments from untreated Bowland Lake and sediments collected 10 m after whole-lake neutralization indicating that little of the supplied alkalinity had been lost to the sediments. Hence,in situ sediment BNC was probably small in Bowland Lake.