What Are Cyanobacterial Blooms?
- Algae blooms usually occur in nutrient-rich environmental conditions. Often, blooms arise in water exposed to significant agricultural runoff. High concentrations of phosphates in fertilizers provide abundant food for cyanobacteria, which tend to populate rapidly. Blooms can occur in rivers, lakes and oceans, often disrupting ecosystems and making large areas less suitable for other living creatures. Algae blooms can result in hypoxia, which is a state of depleted oxygen in the water. Some forms of cyanobacteria also produce toxins that can be detrimental to aquatic life and humans.
- Cyanobacteria have a short life cycle. Algae grow quickly during a bloom, but then the individual bacteria quickly die, resulting in a large amount of dead organic matter in the water. The decomposition of the dead matter requires oxygen, which becomes depleted in the surrounding water. The lack of dissolved oxygen in the water can kill plants and fish, resulting in a dead zone. Large seasonal dead zones exist at the mouth of the Mississippi River in the Gulf of Mexico, and at the mouth of the Columbia River in the Pacific Ocean.
- In addition to hypoxia, Harmful Algae Blooms can produce toxins detrimental to marine life, and can even be harmful to humans. While most forms of cyanobacteria are not toxic, some produce forms of neurotoxins that can kill marine life, and bioaccumulate in the food chain. The most likely threat to humans comes from ingesting water containing toxic bacteria, possibly while swimming, or from eating contaminated shellfish.
- Not all algae blooms arise due to agricultural pollution or other human causes. At times algae populations can be transported by ocean currents from offshore to coastal locations. Situations of ocean upwelling can increase algae populations, which may continue to grow in the naturally nutrient-rich coastal waters. Naturally occurring algae blooms can at times be enhanced when they meet polluted waters, resulting in an acceleration of the bloom process.