Which nutrient triggers aquatic plant growth in freshwater systems?

• A. Phosphorus (P)
• B. Nitrogen (N)
• C. Potassium (K)
• D. Carbon (C)

Answer: (A)

In freshwater systems, phosphorus is the nutrient that most often limits primary production. When phosphorus is available, aquatic plants and algae can grow rapidly, so adding or inputting phosphorus tends to trigger a noticeable growth response. This is why controlling phosphorus inputs from fertilizers, detergents, or runoff is a key strategy to prevent harmful blooms in lakes and streams.

Nitrogen is also needed for growth, but in many freshwater environments it is not the primary bottleneck, so it doesn’t trigger blooms as strongly as phosphorus. Potassium is essential for plant function but is not usually the limiting nutrient for aquatic plant growth in these waters. Carbon is generally available in sufficient amounts in freshwater, so it doesn’t typically limit growth either.