Seasonal and spatial distribution patterns of atmospheric phosphorus deposition to Lake Simcoe, ON

Abstract

A decline in the water quality of Lake Simcoe, Ontario has been observed over the past few decades. This decline has been attributed to excessive loading of the limiting nutrient phosphorus. Atmospheric deposition of phosphorus is a major non-point source contributing 25–50% of the total phosphorus (TP) load entering Lake Simcoe. The objectives of this study were to quantify seasonal variability of atmospheric TP deposition on Lake Simcoe and to estimate spatial distribution patterns of atmospheric TP deposition on Lake Simcoe. Based on the 1995–2007 period of records, on average 35% of the annual bulk atmospheric TP load occurs in the spring, while the summer, autumn and winter account for 45%, 13% and 7%, respectively. The autumn and winter loads are more or less consistent and exhibit little change much from year to year; however, the summer load can vary greatly. Spatially, the Northwest and Southeast quadrants of the lake show the highest atmospheric TP deposition during the spring and summer months. Most of the soils with the highest vulnerability for wind erosion are located in these quadrants and the dominant winds blow in the NW–SE direction.