Recent media coverage has drawn attention to the fact that bacteria are capable of consuming crude oil – so, you might ask, why don’t we release massive quantities of it into the Gulf for a feast of monumental proportions?
It is indeed true that bacteria will consume the massive amount of oil that is pouring into the Gulf of Mexico. Because the waters of the Gulf of Mexico are very warm, they will do so very efficiently. The rate of bacterial degradation is much more rapid in warm water than in colder, more northern waters. One Step Forward – but it’s not that simple.
After a closer look at bacterial degradation and its ramifications, we end up taking two steps back.
When large amounts of organic matter are present in the ocean, bacterial populations that consume that organic matter grow rapidly and reach very high population densities.
Like fish, mollusks, copepods, and crustaceans, these marine bacteria breathe dissolved oxygen from water, which is a healthy part of ocean chemistry at normal levels. The problem occurs when bacteria reach such high population densities that they extract all (or at least most) of the dissolved oxygen in the water they occupy. Such areas of oxygen-depleted water are known as hypoxic zones. Hypoxic zones kill other creatures that need oxygen to survive: the fish, copepods, crustaceans and mollusks that now unsuccessfully compete with the bacterial populations for oxygen. Hypoxic zones are known as dead zones, which are areas with no living organisms. The bacterial breakdown of the massive amounts of oil will create huge dead zones in the waters of the Gulf of Mexico. Take one step back.
Nitrogen, a crucial marine nutrient, makes up between 0.1 – 2.0% of many Gulf crude oils by weight. When bacteria break down and consume crude oil, they release nitrogen from the oil into the surrounding water, where microscopic plant cells called phytoplankton rapidly take it up. Phytoplankton densities are normally limited by a scarcity of nitrogen in the ocean, but when large amounts of nitrogen are available to phytoplankton, their populations increase very rapidly. These rapid population explosions are known as phytoplankton blooms. Some phytoplankton blooms produce toxins that kill marine animals and cause significant human health impacts. These are especially common in the Gulf of Mexico during the summer and fall months. Take a second step back.
To make matters worse, when a phytoplankton bloom eventually dies, the individual cells sink and are consumed by bacterial populations. This bacterial decomposition consumes oxygen and causes more dead zones, which brings us back to step one. The dead zones kill marine life and the bacteria release – you guessed it – nitrogen; which of course, will be taken up by phytoplankton. Do you see the pattern emerging here?
So, if you hear the good news that bacteria will take care of cleaning up the oil spill, don’t be lulled into complacency by believing that all is fine and dandy. Realize that the impacts of this event can cascade through our oceans long after the last beaches and birds are cleaned and the cameras have moved on to another story.