What is the main cause of excessive growth of aquatic plants and algal blooms in fresh water systems?

The main cause of excessive growth of aquatic plants and algal blooms in freshwater systems is phosphorus. This nutrient acts as a key factor in stimulating plant growth, particularly algae. When phosphorus is present in significant quantities, primarily due to runoff from agricultural areas, wastewater discharges, or other sources, it can lead to an overabundance of nutrients in the water. This condition promotes algal blooms, which can disrupt aquatic ecosystems by blocking sunlight and diminishing oxygen levels in the water as the algae die and decompose.

While nitrogen also plays a role in plant growth and can contribute to algal blooms, phosphorus is typically more limiting in freshwater systems, making its presence a critical factor in these phenomena. Sediment accumulation affects water quality and can contribute to issues within aquatic ecosystems, but it does not directly cause algal blooms. Oxygen depletion is often a consequence of algal blooms rather than a cause; as algae die and decay, they consume oxygen, leading to insufficient levels for other aquatic organisms. Thus, phosphorus is recognized as the primary driver behind excessive growth in these environments.