Estimation of tributary total phosphorus loads to Hamilton Harbour, Ontario, Canada, using a series of regression equations

Event-based sampling was conducted from July 2010 to May 2012 at four stations in the watersheds of Hamilton Harbour, Ontario, Canada, with the primary objective of estimating total phosphorus (TP) loads. Eighty-seven 24-hour, level-weighted composite samples were collected during a variety of catchment states (rain, snowmelt, baseflow), and TP concentrations were regressed against flow or precipitation in an attempt to mitigate the considerable loading estimation bias arising from event-scale hysteresis. Annual average TP loads were estimated for 2008 to 2012 and were the highest from the Desjardins Canal (17.4 kg/d to 65.6 kg/d), followed by Red Hill Creek (6.4 kg/d to 25.8 kg/d), Grindstone Creek (3.4 kg/d to 33.4 kg/d), and Indian Creek (3.0 kg/d to 7.9 kg/d). Daily TP loads varied by three orders of magnitude between wet and dry conditions, with storm events driving peak daily loads in the urban watersheds, and spring freshet in the agricultural and wetland influenced watersheds. Areal TP loads were higher from the urban relative to the agricultural watersheds. This study demonstrated that the tributaries did not meet the Hamilton Harbour Remedial Action Plan (HH RAP) initial target of 65 kg/d in 2008 to 2011 but did in 2012. Comparison of three loading methods emphasized the vital role of characterizing TP concentrations during high flow events. The higher resolution TP loads generated in this study will assist the HH RAP in forming additional remedial actions in the watersheds for delisting the Hamilton Harbour Area of Concern.