Distribution and Magnitude of Legacy Agricultural Phosphorus in the Canadian Lake Erie Watershed

Session: 41a. - Great Lakes Harmful Algal Blooms Research from Watershed Influence to Ecosystem Effects

Pamela Joosse, Agriculture and Agri-Food Canada, [email protected]
Keith Reid, AAFC, [email protected]
K. Bruce MacDonald, Independent Consultant, [email protected]

Abstract

Phosphorus is stored in and released from organic and mineral materials in soils and sediments on lake and stream bottoms, flood plains, stormwater ponds and agricultural fields. These “legacy” sources of phosphorus can be re-mobilized and thus add to loadings — even when current practices are geared to phosphorus reduction.  Therefore, it is important to understand the distribution and magnitude of legacy P sources. Agricultural legacy P is considered the P that resides in cropland soil, accumulated from historic applications of manure and fertilizers in excess of that removed in harvested crops.  The best current estimate for legacy soil P values in Ontario, that is geographically explicit, is from the model for the Indicator of Risk of Water Contamination by Phosphorus (IROWC-P). The IROWC-P generates a “cumulative phosphorus (P)” value in kg P/ha for each Soil Landscape of Canada (SLC).  The cumulative P represents the sum of the annual P balances (inputs of manure and fertilizer minus the crop P removals) on cropland and improved pasture in an SLC during the period from 1961-2011. Recent updates to the IROWC-P estimation of soil P and results for the Lake Erie basin as to patterns and trends will be presented.

1. Keyword
phosphorus

2. Keyword
Lake Erie

3. Keyword
indicators

4. Additional Keyword
soil

5. Additional Keyword
legacy