Fertilizer runoff and algal blooms are a significant environmental challenge, linked by excess nutrients entering aquatic ecosystems. Runoff occurs when excess nutrients from agricultural or urban areas are carried by water into lakes, rivers, and coastal waters. This influx fuels rapid algal growth, leading to algal blooms, which impact water quality and aquatic life.
Essential Elements in Fertilizer
Fertilizers supply essential nutrients, primarily nitrogen (N) and phosphorus (P), for plant growth. Nitrogen is vital for leafy development; phosphorus aids energy transfer and root development. While crucial for land plants, excess N and P in aquatic environments become problematic. Too much acts as a potent aquatic fertilizer, disrupting the ecosystem’s natural balance.
Movement of Nutrients to Waterways
Nutrients from fertilizers move into waterways through various pathways, influenced by rainfall, irrigation, and landscape. Surface runoff carries dissolved nutrients and nutrient-laden soil particles directly into streams, rivers, and lakes. Leaching involves nutrients percolating through soil into groundwater, eventually discharging into surface water bodies. Erosion also transports soil particles, to which phosphorus often binds, into water systems. Heavy rainfall or excessive irrigation accelerates this transport from agricultural and urban landscapes into aquatic environments.
How Excess Nutrients Drive Algal Growth
Excess nitrogen and phosphorus in aquatic systems initiate eutrophication, accelerating algal growth. These nutrients act as a fertilizer for algae and cyanobacteria (blue-green algae). Abundant nutrients lead to rapid proliferation, forming dense algal mats or blooms that discolor the water. This excessive growth appears as thick green, blue-green, red, or brown layers on the water surface. Warm temperatures and calm water further enhance this expansion, allowing algae to dominate.
Ecological Shifts from Algal Proliferation
Algal blooms trigger ecological shifts in aquatic ecosystems. Dense algal mats block sunlight from deeper water, inhibiting photosynthesis in submerged plants and causing their decline. As algae and other aquatic vegetation die, bacteria decompose this organic matter, consuming dissolved oxygen and leading to hypoxia (low oxygen) or anoxia (no oxygen). These low-oxygen environments, often called “dead zones,” become inhospitable for most aquatic organisms, causing significant mortality and food web disruption. Some algal blooms also produce toxins that can harm aquatic life and pose risks to human health.
Strategies for Nutrient Management
Addressing nutrient runoff requires a multifaceted approach. In agriculture, precision fertilization applies nutrients more efficiently to reduce excess runoff. Practices like planting cover crops (absorbing leftover nutrients) and establishing riparian buffers (vegetated strips along waterways) filter runoff. Urban stormwater management minimizes nutrient transport from developed areas, using green infrastructure like rain gardens, permeable pavements, and constructed wetlands to capture and filter stormwater. Improvements in wastewater treatment facilities also remove nitrogen and phosphorus from sewage before discharge, preventing their contribution to blooms and protecting water quality and healthy aquatic ecosystems.