July 30 – Zoned Out

Today’s factismal: This year’s Gulf of Mexico Dead Zone is slightly larger than the state of Connecticut.

Every year, spring and summer floods wash tons of fertilizer and top soil off of farms in America’s breadbasket and into the mighty Mississippi. The nutrient-rich water flows downstream and out into the Gulf of Mexico where it spreads over the denser ocean water, creating an all-you-can-eat restaurant for algae and other phytoplankton (autotrophs that convert sunlight into energy). They respond by happily converting carbon dioxide into oxygen while going about the business of turning one alga into a thousand algae; in marine biology terms, they bloom.

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

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

And that bloom of phytoplankton attracts krill and copepods and other critters that like to feed on autotrophs. However, what these critters excrete isn’t oxygen; it is used autotroph in the form of copepod crap that sinks to the bottom of the ocean. The copepod droppings are then eaten by bacteria that live on the ocean floor. (Isn’t the circle of life beautiful?) 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”.

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 is a bit of a puzzle. Based on the expected rainfall, it was forecast to be fairly large (8,000 sq mi). Instead, it is just middlin’ (5,840 sq mi). The marine biologists think that what happened is that the strong winds during the spring spread the nutrient-rich water over a larger area and mixed it more thoroughly with the ocean water so that the area that was starved of oxygen was smaller. But they aren’t sure, because they need more data.

This year's dead zone is smaller than expected (but still plenty big) (Image courtesy NOAA)

This year’s dead zone is smaller than expected (but still plenty big)
(Image courtesy Louisiana Universities Marine Consortium)

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:
http://products.coastalscience.noaa.gov/pmn/default.aspx

2 thoughts on “July 30 – Zoned Out

  1. Pingback: July 30 – Zoning In | Little facts about science

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

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