Hierarchy of Point Source Management Approaches to Mitigate Cyanobacteria Blooms

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

Lewis Molot, York University, Faculty of Environmental Studies, [email protected]
Sherry Schiff, University of Waterloo, [email protected]
Jason Venkiteswaran, University of Waterloo, [email protected]
Mark Verschoor, York University, [email protected]
Helen Baulch, University of Saskatchewan, [email protected]
Scott Higgins, Freshwater Institute, Fisheries and Oceans Canada, [email protected]

Abstract

Watershed-scale approaches to cyanobacteria bloom management have empirically relied on total P removal to lower productivity. Recent work suggests this is most effective when TP load is low enough to maintain high redox at the sediment surface, thus preventing internal Fe²⁺ loading, a trigger for cyanobacteria dominance in warm waters (Verschoor et al. 2017). This suggests a hierarchy of approaches to point source nutrient management based on maintaining high sediment redox: 1) TP removal; 2) nitrification, then 3) denitrification. If TP loads can be lowered enough to protect sediment redox, supplemental N management is not necessary. If low TP loads can’t be reached, then nitrification may offer some additional redox protection in waters with high inputs of reduced forms of N by lowering in situ oxygen demand and discharging nitrate, whose consumption increases redox. N removal lowers in situ oxygen consumption but will not starve N₂-fixing blooms of N unless Mo, essential to N₂ fixation, is depleted very early in the bloom (Molot 2017). Establishing a case for N management depends on whether a TP target to maintain high redox can be practically achieved, the extent and type of N loading, and the availability of Mo which varies across Canada.

1. Keyword
cyanophyta

2. Keyword
anaerobic conditions

3. Keyword
nutrients

4. Additional Keyword
nutrient management