Reducing the phosphorus surplus in the Lake Winnipeg watershed though biomass harvest

Session: Soil Health: Role on Nutrient Losses from Agricultural Soils (2)

Matthew McCandless, IISD Experimental Lakes Area Inc., [email protected]

Abstract

Like many of the world’s lakes, Lake Winnipeg is eutrophying. Efforts to reduce the prevalence of algal blooms on the lake requires detailed understanding of nutrient loading dynamics in the watershed. Previous studies indicate the primary source of nutrient loads to Lake Winnipeg is non-point sources associated with the Red River watershed, spanning U.S. states (North Dakota, Minnesota, South Dakota) and 2 Canadian province (Manitoba, Saskatchewan). This presentation summarizes analysis and modelling to (1) determine the surplus of phosphorus fertilizer accumulating on farmland in the Manitoba portion of the Lake Winnipeg watershed, and (2) model how management and use of excess agricultural biomass and wetland vegetation can eliminate this surplus.

The analysis found an average P surplus over the past 25 years of 9,200 tonnes per year, or 3.6 kg/ha/yr of farmland; though the surplus is on a decreasing trend. This P surplus is around ten times higher than P loading estimates based on water quality measurements. This suggests growing accumulation of P may not yet be finding its way to the tributaries. Further analysis reveals that use of agricultural biomass and harvest of wetland vegetation can eliminate the surplus, effectively mining down accumulations of P in the watershed.

Twitter handle of presenter
@mattmccandless