Hypoxification

Eventually, all the nitrogen, phosphorous, and potassium from fertilizers and other human sources travel down the Mississippi River Drainage Basin and ultimately end up in the Gulf of Mexico. These chemicals, all specifically manufactured to stimulate the growth of crops, have a similar, but disastrous effect in the gulf.


Normally, different species of cyanobacteria and algae that live in the ocean are limited in growth because the nutrients they require for growth (nitrogen, phosphorous, etc.) aren’t readily available to them. This is due to most of the nutrients being depleted in the soil by land plants before it gets to them.

However, with the anthropogenically increased nutrient input from the Mississippi River Basin, the algae and cyanobacteria growth is no longer limited and the cells of these organisms explode in numbers in response (known as algal blooms). This in itself wouldn’t seem like that big of a problem. Why wouldn’t we want more photosynthetic algae to convert the ever-increasing CO2 in the atmosphere to oxygen and possible decrease the effects of global warming? Sadly, this is not the case. When the massive amounts of these organisms die and sink to the bottom of the gulf, different species of bacteria, archaea, and other decomposers use them as food. The decomposers use so much oxygen in cellular respiration that oxygen levels in the gulf waters decline to less than 2 ppm dissolved O2. This lack of oxygen makes the affected waters of the gulf “hypoxic” and nearly impossible to support fish, shrimp, and other organisms that require oxygen. This process is known as eutrophication. Because it cannot support these organisms, the area affected is deemed the “dead zone” of the Gulf of Mexico. 

Although the dead zone’s area fluctuates with the amount of nutrients present in the water and from year to year, its estimated area is around 6,500-7,800 square miles (close to the size of New Jersey). Even though the dead zone itself has a “set” boundary (the area that is hypoxic), its extended implications are profound. Marine life that goes anywhere near the hypoxic waters is able to feel that the low oxygen (similar to how we would feel if we in a closed space for too long) and will instinctively avoid an area even farther outside the dead zone.

The evolutionary balance between land plants and sea plants that has been keeping the Earth “working” for the past millions of years is slowly being broken and its harmful effects can clearly be seen through the Gulf of Mexico Dead Zone. The next question to ask now is what do we do about it?