Exploring the Trends in Sediment and Phosphorus Concentrations and Loads in Part of the Canadian Great Lakes Basin

Abstract The specific objective of this study is to explore the long-term trend of total phosphorus (TP) and total suspended sediment (TSS) concentrations and loads (C/L)s in various streams/rivers in the Great Lakes Basin. This includes related statistical analyses, such as confidence intervals, to assess variability and identify cases where measures should be taken to reduce TSS and TP. Trend analysis of TSS and TP (C/L)s are performed, combining bootstrapping with the Weighted Regressions on Time, Discharge, and Season i.e., WRTDS_BT technique. The technique is used at ten selected monitoring stations of Northern Lake Erie, Eastern Lake Huron, and Lake Ontario & Niagara Peninsula in Ontario, Canada. Trend analysis over selected tributaries using flow-normalized (FN) TSS and TP (C/L)s reveals that trends in [FN-TSS] and [FN-TP] (C/L)s were highly variable, with significant decrease in a few stations. However, in most tributaries, TSS concentration levels are significantly higher than Canadian Water Quality Guidelines (CWQG) limit of 30 mg/L (following Toronto Region Conservation Authority (TRCA), Ontario) and TP concentration levels are significantly higher than the Ontario’s provincial water quality objectives (PWQO) limit of 0.03 mg/L. Measures to reduce TSS and TP is effective at five tributaries (Humber River, Don River, Saugeen River, Big Creek, Nottawasaga River). Although the drivers are not explicitly identified, potential attributions are discussed for policymakers in the study area.