Examining total phosphorus concentrations in the Whitson River watershed, Sudbury, Ontario, Canada

Abstract

Spatial analysis of water quality in a watershed is often difficult to accomplish due to the lack of extensive data available. Water quality data available at the provincial level is usually limited to a few sampling locations and typically disregards sampling from headwaters catchments. Not having sampling from headwater catchments ignores key factors in understanding how headwater catchments impact downstream water quality and flow. Headwater catchments can have more variability in water quality and are more sensitive to climate or land use changes. This study examines Total Phosphorus (TP) concentrations in the Whitson River, a mixed land-use Precambrian Shield watershed, located in Northeastern Ontario, Canada. TP samples were collected biweekly at numerous sites over two years from nested catchments spanning headwaters to downstream along the main channel, with individual catchments ranging in size across the watershed. Here, spatial and seasonal variability of TP in the watershed was investigated using nutrient-based water quality observations across an extensive range of flow conditions, an approach that potentially demonstrates point source inputs that are constant over time. Spatial trends in the Whitson River watershed showed distinctly higher and more variable TP observed across headwater sites, compared to main channel and lake sites that were lower and more consistent in TP. Catchments in the headwaters range in percent impacted area and percent wetlands, with no simple relationship with the percent impacted area and TP values or percent wetlands and TP. Percent groundwater and TP vary between seasons, with spring of 2022 having both TP and the percent groundwater increased moving downstream, with the most downstream location having elevated amounts of TP and percent groundwater out of all main channel locations. The assessment of TP within the Whitson River watershed shows areas of concern and provides information that will be valuable in future management.