A limiting nutrient is a missing nutrient among three nutrients needed. For seawater it is nitrogen, and for freshwater it is phosphorus.
A limiting nutrient is a chemical necessary
for plant growth — but is available in
smaller quantities than needed for algae to
increase their abundance. Once the limiting
nutrient in a waterbody is exhausted, the population
of algae stops expanding. If more of the limiting
nutrient is added, larger algal populations will
result until their growth is again limited by nutrients
or by other limiting environmental factors.