Can Algal Bloom Decrease Oxygen Levels in Water?

[fish]

photosynthetic algae - photosynthesis takes place during daylight, CO2 is used and O2 is released. At night, aerobic respiration occurs, O2 is used and CO2 is given off.

If these two processes are in balance with each other (or are they?), how would an algal bloom decrease the O2 level in water? There would be more algae using up oxygen at night but also more would be producing oxygen during daylight?

 

[iansmith]

In a nutshell, the process is not balance but in a lake or on the coast other micro-organism are present. Algae bloom is cause by an increase of nitrogen phosphate run-off in many cases. As the algae and cyanobacteria grow, more organic matter is produce and this results in an increase of biochemical oxygen demand (BOD). Bacteria digest the organic matter and decrease the oxygen level.

 

[ravenprp]

Yes, an algal bloom can decrease oxygen levels in water. While it is true that photosynthetic algae produce oxygen during daylight, the rate at which they consume oxygen during nighttime respiration can outweigh the amount of oxygen produced during the day. This is especially true during an algal bloom, where there is a large and dense population of algae present. The excessive amount of algae can deplete the oxygen in the water faster than it can be replenished, leading to low oxygen levels in the water.

Additionally, algal blooms can also create a layer of scum or mat on the surface of the water, preventing oxygen from diffusing into the water from the atmosphere. This further decreases the available oxygen for other aquatic organisms.

Furthermore, algal blooms can also lead to eutrophication, where the excess nutrients from the algae can lead to an increase in the growth of other microorganisms such as bacteria. These bacteria also consume oxygen, further contributing to the depletion of oxygen levels in the water.

In conclusion, while photosynthetic algae do produce oxygen during the day, the rapid consumption of oxygen during nighttime respiration and other factors such as eutrophication can lead to a decrease in oxygen levels in water during an algal bloom.