Lake Erie algal blooms have been linked to phosphorus runoff from which sources, leading to management actions like load reductions and monitoring?

• A. Phosphorus runoff from agriculture and urban sources; HABs toxins; degrade water quality; management includes load reductions, agricultural BMPs, wastewater treatment improvements, and monitoring.
• B. Nitrogen deposition from the atmosphere is the sole cause.
• C. Phosphorus from geological sources is the primary driver.
• D. No human activity contributes to these blooms.

Answer: (D)

The main idea is that phosphorus is the nutrient that most commonly triggers algal blooms in Lake Erie, especially the harmful ones. When phosphorus enters the lake from human activities, it fuels rapid algae growth, leading to blooms that can produce toxins and degrade water quality.

Phosphorus comes into the lake from both agricultural and urban sources. In agriculture, fertilizer and manure can run off fields into streams and rivers, especially after rain. In urban areas, stormwater carries phosphorus from lawn fertilizers, car washes, and other sources, and some wastewater discharges add phosphorus to the system. Because these nonpoint and some point sources elevate phosphorus levels, management focuses on reducing those loads. That’s why actions include improving agricultural practices (like careful fertilizer timing and placement, buffer strips, cover crops, and conservation tillage), upgrading wastewater treatment to remove more phosphorus, and implementing monitoring to track loads and the effectiveness of controls.

Why not the other ideas: atmospheric nitrogen deposition and geological sources can contribute to nutrient levels, but they are not the primary drivers of the Lake Erie HABs compared with phosphorus inputs from human activities. And there is clear evidence that human actions contribute to the phosphorus loads leading to blooms, so saying no human activity is involved isn’t accurate.

In short, phosphorus runoff from agriculture and urban sources is the key link to Lake Erie HABs, which is why load reductions and monitoring are the core management responses.