If you work or live near the Mississippi River watershed you may be inadvertently contributing to the Gulf of Mexico’s dead zone, an area where fish and other marine life cannot survive. This section of the Gulf, which was measured in 2019 to be about 6,952 square miles, has such a low dissolved oxygen concentration that it cannot sustain marine life. The fish cannot breathe in it! The severe depletion of oxygen in this area is caused by oxygen consuming bacteria. These bacteria decay dead algae which are plentiful due to the large number of algae blooms exacerbated by nutrient rich water entering the Gulf from the Mississippi River from urban and agricultural water sheds. For the last 33 years, scientists have been measuring the size of this dead zone and the 2019 size was the 8th largest in that time. The current goal is to reduce nutrient inputs in the Mississippi River watershed and achieve a five-year average dead zone size of 1,900 square miles by 2035.
I found this extremely interesting because I had no idea there was such a large dead zone in the Gulf. The figure above shows the sizes over the recorded history. To put the area size in prospective it is the equivalent to about the size of New Jersey for the top 5 recorded years. A dead zone of this magnitude can have many deleterious effects on the ecosystem and the local economy as it can “reduce the reproductive capabilities of some fish species and slow shrimp growth, leading to reductions in the average size of shrimp.”
Another thing I found interesting was the effects that storms can have on the dead zone size. It makes sense that when a large storm comes in it will mix the water, but I had never thought about the effects this could have on dissolved oxygen concentrations. It temporarily increases the dissolved oxygen concentration, but this effect is only temporary with past research showing it will reform in about a week.