Snowmelt and growing season phosphorus flux in an agricultural watershed in south-central Alberta, Canada

Abstract

A three-year study was conducted to examine the spatial and temporal variability of phosphorus concentrations and mass loads within four sub-basins in the Crowfoot Creek watershed in southern Alberta, Canada. Monitoring was carried out at the inflows and outflows of the four sub-basins from mid-March until the end of October in 1997 to 1999. Data were collected on flow, total phosphorus (TP) and total dissolved phosphorus (TDP). The TP and TDP concentrations increased and were greatest during spring snowmelt and rainfall runoff events. Median TP concentrations varied from 0.022 to 1.141 mg L-1 and median TDP concentrations varied from 0.005 to 1.031 mg L-1. Within the sub-basins, phosphorus concentrations generally increased between inflow and outflows. The presence of grassland and well-developed crop cover adjacent to the watercourses generally resulted in a greater proportion of TDP in runoff. The proportion of TP as TDP varied from 31 to 97% and appeared to be affected by the timing of the storm and antecedent moisture conditions of the soil. The proportion of phosphorus exported during events made up from 1 to 83% of the total phosphorus load during the post-spring runoff period. Phosphorus concentrations exceeded Alberta surface water quality guidelines most of the time; however, the addition of irrigation return flow water generally improved water quality in Crowfoot Creek. Copyright © 2005, CAWQ.