Nutrient Ratios and Algal Blooms

a limiting nutrient

the nutrient in shortest supply relative to biological demand which controls primary production

• phosphorus is most often the limiting nutrient

• when limiting nutrient increases, algal biomass increases

redfield ratio

N:P = 16:1 (tells us if phosphorus or nitrogen is limiting nutrient)

nitrogen limited

N:P < 16

cyanobacteria thrive because they can fix their own nitrogen

phosphorus limited

N:P > 16

few cyanobacteria and limits algal growth

impacts of changes in nutrient ratios

• reduced water clarity

• toxin production

• food web disruption

• hypoxia following bloom decay

phosphorus reduction

*preferred strategy for managing nutrient controls

controls total productivity and prevents cyanobacterial dominance