July 30 – Zoning In

Today’s factismal: This year’s Gulf of Mexico Dead Zone is half as big as last year’s!

Just when you thought that there was no good news on the environmental front, we get this: the 2014 “dead zone” in the Gulf of Mexico is just half as big as last year’s! Of course, that means that it still covers an area the size of Delaware (roughly 5,000 square miles) and still wreaks massive havoc on fish stocks, crawfish, and shrimp, but at least it is headed in the right direction. This isn’t the first time that we’ve had a small dead zone (it was just 2,800 square miles in 2011) but it does indicate that remedial measures along the Mississippi are having an effect.

But why should what happens in Ohio, Illinois, Arkansas, and 28 other states have an effect on the Gulf of Mexico? It all happens because of the fertilizer. The Mississippi and its tributaries gathers run off from farms in 31 states; quite often, that run off includes fertilizer and top soil. Those two nutrients wash all the way down into the Gulf of Mexico where it forms a thin lens over the denser, saltier ocean water. This had the effect of ringing the dinner bell for algae and phytoplankton (those autotrophs we were just discussing) and they respond by gorging themselves on the nutrients and running off to make little baby algae and phytoplankton; it becomes what a biologist calls a “bloom” and swimmers call “yucky”.

Water from the Mississippi and other rivers carries nutrients into the Gulf, creating dead zones (red) (Image courtesy MMM)

Water from the Mississippi and other rivers carries nutrients into the Gulf, creating dead zones (red)
(Image courtesy LUMC)

The process doesn’t stop there. All that blooming phytoplankton brings in hungry little critters like krill and copepods. These critters feast on the phytoplankton and algae and excrete used autotroph that drops to the ocean flooor where it feeds colonies of bacteria (sorry, Sponge Bob!).  And that’s where the trouble starts, because the bacteria use up so much oxygen when they eat the slimy scat that nothing else can live in the ocean column above them; they create a “dead zone” devoid of oxygen.

How to create a dead zone (Image courtesy Louisiana Universities Marine Consortium)

How to create a dead zone
(Image courtesy Louisiana Universities Marine Consortium)

This isn’t a new problem; according to sediment cores, there’s been a summertime dead zone in the Gulf of Mexico for more than a century. But the size of the dead zone has changed over the years. During drought years, the dead zone shrinks because less fertilizer is washed to the ocean. And during wet years, the dead zone gets bigger. But this year’s dead zone, like last year’s, is making the researchers go “hmm…” That’s because both years the dead zone was much smaller than predicted. And that’s what makes this exciting science!

In English class, getting the wrong answer two times in a row means that you’ll have to repeat the semester. But in science, when something stops working (such as a prediction methods that gave good results before) what it means is that you’re on the brink of discovering something new.  But big discoveries need big data – and that’s where you come in! The marine biologists at the National Centers for Coastal Ocean Science would love to have you help them monitor the number and types of phytoplankton in the water near where you live. They’ve set up the Phytoplankton Monitoring Project, where you can volunteer to do a plankton tow (more fun than it sounds) and enter your results. They are particularly interested in getting groups of Girl Scouts or Boy Scouts to adopt an area and take samples twice a month. To learn more, float on over to:

One thought on “July 30 – Zoning In

  1. Pingback: August 6 – In The Zone | Little facts about science

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