Irrigation Effects on Algae Bloom

Algae

• Planktonic, blue-green algae, the type of algae associated with blooms, are simple plants that function much like other plants. They occur naturally, floating freely, in all types of water --- fresh, salt or brackish. Algae produce their own food like other plants through photosynthesis. Although this group of algae is called blue-green algae, it also can be yellow, red, orange or brown, depending on the species.

Blooms

• Algae occur naturally in waterways, and so do algal blooms. In a marine ecosystem, cold water upwellings bring nutrients to the surface that stimulate rapid algae growth. Larger organisms then feed on the abundant algae. In a freshwater environment, slow-moving water that sees little sunlight is also prone to algae blooms. The local aquatic wildlife keeps the algae bloom under control. However, algal blooms created by unnatural means create toxic environments.

Irrigation

• The water's nutrient content, especially the amount of phosphorus, plays an important role in causing algal blooms. Phosphorus is one of the most important nutrients plants need to grow. In agriculture, when crops strip the soil of its nutrients, growers apply fertilizers to replace the missing nutrients. If too much fertilizer is applied or if the fertilizer is not worked into the soil, irrigation and precipitation wash the fertilizer away and carry it to lakes and ponds where it stimulates an algal bloom.

Toxic Results

• Although the local ecosystem adjusts to handle a naturally occurring algal bloom, one stimulated by the influx of nutrients from agricultural irrigation becomes toxic. The algae deplete the water of oxygen, killing aquatic vegetation and fish. The bloom also blocks sunlight from reaching other aquatic vegetation. Lastly, some species produce toxins that are lethal to the aquatic wildlife.