Final answer:
Algal blooms are a type of water pollution caused by the overuse of fertilizers containing nitrogen and phosphorus and the improper treatment of sewage and farm animal waste. These nutrients lead to the excessive growth of algae, which upon dying, results in oxygen depletion and the formation of dead zones where aquatic life cannot survive. Human activities, such as the application of fertilizers and use of phosphorus-based detergents, significantly contribute to this problem.
Step-by-step explanation:
Algal blooms act as a form of water pollution by contributing to the process known as eutrophication. This occurs when the runoff containing nitrogen and phosphorus, typically from fertilizers used in agricultural and residential areas, enters water bodies leading to the excessive growth of algae. The growth is so prolific that when these algae die, the bacteria decompose the organic matter, consuming oxygen and creating dead zones, where the oxygen level is so low that aquatic organisms cannot survive. Humans contribute to this problem through the overuse of fertilizers and the improper treatment of sewage and farm animal waste.
An example of a human-contributed problem is the use of phosphorus-containing detergents, which were popular in the 1950s and significantly increased the amount of phosphorus available to algae in the water, leading to algal overgrowth and subsequent eutrophication. Cultural eutrophication due to human activities has been challenging to combat because it is primarily caused by nonpoint source pollution, which is difficult to regulate, and because nitrogen and phosphorus are difficult to remove from wastewater.