Nepheloid Layer in Lake Ontario

A study was designed to investigate the existence and extent of a nepheloid layer in Lake Ontario. A transmissometer profile of the entire water column was obtained monthly from 94 stations in Lake Ontario during the period of August to December, 1981. The profiles indicated that a turbid layer at the lake bottom existed over the entire lake at water depths greater than 60 meters. The thickness of the layer averaged 22 meters in August and September, but doubled to 45 meters in October. In addition, the average transmission was lowered from 60 percent in August and September to 45 percent in October. A significant increase in soluble reactive phosphorus (SRP) and reactive silica (RSiO₂) in the nepheloid layer was observed. Quartz and calcite were the major mineral constituents of the suspended matter present in the layer. The particles in the nepheloid layer in the western basin of Lake Ontario consisted of many diatoms and some calcite particles and clay minerals. In the central and eastern basins the number of calcite particles significantly increased. Concentrations of Pb and Zn in the suspended matter sampled from the nepheloid layer at the Niagara River mouth were similar to those found in the 1-cm surface sediment at the same station (124 μg g^?1 Pb, 318 μg g^?1 Zn,and139 μg g^?1 Pb and 356 μg g^?l Zn, respectively).