Sediment and nutrient loadings to Lake Ontario: methodological arguments

Abstract

Environmental issues frequently require values for sediment and nutrient loads in river systems. Except in rare instances, such values must be drawn from existing surveillance data which may not reflect sampling strategies pertinent to the issue at hand. In particular, the time variant and nonlinear relationships between discharge and both suspended sediment and sediment-related parameters such as phosphorus cannot be captured in detail by surveillance data, Nevertheless, such data collected routinely by the Ontario Ministry of the Environment accurately reflect the relative loadings both in terms of unit and total yields in five basins where detailed suspended sediment data are available. Although surveillance data underestimate the absolute values of suspended sediment loads calculated from detailed sediment information, these data do capture the relative monthly and seasonal contributions to annual suspended sediment load. A comparison of three methods for calculating annual unit and total loadings of suspended and solute components from surveillance information indicates that annual mean data convey information which is not significantly less adequate than monthly aggregations of data.