Phosphorus losses in surface runoff and subsurface drainage waters on two agricultural fbelds in quebec

摘要

Concentrations of phosphorus (P) above the water quality guideline of 0.03 mg L~(-1) are commonly found in rivers draining agricultural lands in Quebec. This gives rise to eutrophication, which has become quite problematic in some parts of Quebec. Agricultural nonpoint source pollution is the dominant source of this P. While the links between P losses, surface runoff, erosion and manure management are reasonably well understood, there is far less information available on the movement of P via subsurface tile drainage systems. Since the majority of intensively managed agricultural lands in Quebec are subsurface drained, this represents a major knowledge gap. Two field sites, located in the Pike River Watershed of Southwestern Quebec, which drains into Lake Champlain, have been instrumented to measure and sample surface runoff and tile drainage waters. Monitoring has been ongoing since October 2000. Results are reported here for the six site-years of data.Subsurface drainage was the dominant pathway by which water left the fields. On average, tile drainage accounted for 81% of the total annual drainage. Surface runoff was responsible for majority of the annual P losses. It accounted for 60% of the annualtotal, which was on average 1.09 kg/ha. The flow weighted average annual P concentration in subsurface drainage waters ranged between 0.06 mg L"1 and 0.37 mg L"1. The flow weighted average annual P concentration in surface runoff waters ranged between 0.20 mg L"1 and 2.15 mg IS1. On average, P concentrations in surface runoff were 10.9 times higher than those found in subsurface drainage waters, indicating that subsurface drainage may reduce annual P losses. These results also reveal that soil test P and percent P saturation are, on their own, inadequate indicators of potential for P pollution.