Phosphorus and Water Quality: Causes, Impacts, and Sustainable Management

Phosphorus is essential for plant and algae growth in freshwater ecosystems. However, when phosphorus levels exceed natural background concentrations, they can trigger a cascade of water quality issues—most notably, harmful algal blooms and oxygen depletion. Understanding how phosphorus affects lakes and ponds is the first step in developing effective management practices.

How Phosphorus Enters Aquatic Systems: Phosphorus typically reaches waterbodies from both point and non-point sources. Point sources include wastewater treatment facilities and septic systems, while non-point sources encompass stormwater runoff, lawn and agricultural fertilizers, and eroded soil. These inputs lead to elevated nutrient levels and support the rapid proliferation of algae.

Algae blooms not only reduce water clarity, but also consume oxygen during decomposition, leading to hypoxic (low oxygen) conditions. This can negatively impact fish and other aquatic organisms. Blue-green algae, or cyanobacteria, are particularly concerning because they can produce toxins harmful to pets, wildlife, and people.

In-Lake Phosphorus Management Techniques: One of the most effective ways to control phosphorus levels already present in a lake or pond is through in-lake phosphorus binding. This method targets the phosphorus in the water column and sediment to limit its biological availability.

1. Alum Treatment (Aluminum Sulfate): When alum is added to water, it reacts with free phosphorus to form a stable compound that settles at the lake bottom. This reduces the nutrient availability that algae depend on.
2. Lanthanum-Modified Clays: These products offer an alternative binding method, forming long-lasting complexes with phosphate. They are especially effective in lakes where sediment continues to release phosphorus—a process known as internal loading.
3. Shoreline Buffers and Wetland Restoration: Vegetative buffers help capture phosphorus-laden runoff before it reaches the water. Similarly, constructed or restored wetlands serve as nutrient sinks, promoting natural filtration processes.

Watershed Approaches for Long-Term Management: Reducing phosphorus inputs at the watershed level is crucial for sustainable water quality improvements. Strategies include:

• Nutrient Management Plans: Farmers and landowners can use soil tests and crop nutrient needs to guide fertilizer application.
• Stormwater Infrastructure: Retention ponds, bioswales, and permeable surfaces help slow and filter stormwater runoff.
• Erosion Prevention: Keeping topsoil in place through vegetation and stabilizing banks prevents sediment-bound phosphorus from washing into lakes and ponds.
• Community Engagement and Education: Public awareness and participation in reducing nutrient inputs—from household fertilizers to septic system maintenance—can significantly support phosphorus control efforts.
  

Considering Sediment Removal: When internal phosphorus loading is severe, sediment removal through hydraulic dredging may be considered. This method can effectively remove accumulated nutrients, but it requires careful planning and environmental oversight. Often, dredging is followed by phosphorus binding treatments to help maintain water quality.

Phosphorus management is a complex but essential part of lake and pond stewardship. By understanding how phosphorus behaves and applying both in-lake treatments and watershed-based strategies, communities can support healthier, more resilient aquatic ecosystems for the future.

Contact Wisconsin Lake and Pond Resource today to schedule a water quality assessment and take the first step toward cleaner, healthier water.

About Wisconsin Lake & Pond Resource, A Jones Lake Management Partner

Wisconsin Lake & Pond Resource specializes in comprehensive lake and pond management solutions, including algae and aquatic weed control, aeration, hydraulic dredging, erosion control, and fisheries management. As a Jones Lake Management Partner, we serve a diverse range of clients, including HOAs, golf courses, municipalities, and private lake owners. With a commitment to science-driven strategies and environmental sustainability, Wisconsin Lake & Pond Resource helps maintain and restore aquatic ecosystems for long-term health and enjoyment.