Updating St. Lawrence River watershed phosphorus budgets

Overview

Previous St. Lawrence watershed phosphorus budgets showed an increasing P surplus through the majority of agricultural sub-watersheds, largely due to increased fertilizer use (MacDonald and Bennett 2009) . Policies enacted in the 1980s appear to have slowed the rate of increase in surplus accumulation, but the last calculations were completed for the year 2001. In this project, we extend the budgets to include 2011 and 2021 to investigate the impact of changes in agricultural management over the past 20 years.

Project Lead: Anna Pieper

Collaborators: E Bennett, Graham MacDonald

Approach

We calculated surface budgets for agricultural P in the Saint Lawrence River sub-basin, which is mainly found in the province of Quebec and stretches to eastern Ontario and the northern parts of the United States of New York and Vermont. We closely followed the methods laid out by MacDonald and Bennett to allow the results of 2011 and 2021 to be comparable to earlier calculations of P surpluses in the Saint Lawrence watershed.