Size of the Dead Zone

The "Dead Zone" in the Gulf of Mexico, the area of low-oxygen waters fuelled by nitrogen from the Mississippi River, is expected to be 17,353 km2 this summer according to scientists at NOAA and a consortium of Louisiana Universities.

The Mississippi dumps a massive amount of nitrogen, largely in the form of the soluble ion nitrate, into the Gulf each spring. It promotes the growth of a lot of algae, which eventually sinks to the bottom and decomposes. This consumes much of the oxygen in the bottom waters, making life tough for bottom-dwelling fish and creatures like shrimp.

The nitrogen mostly comes from farms in the Midwest and central US, particularly from practices like applying lots of fertilizer to corn (you can read a bit about this on my site). But the amount that ends up at the mouth of the Mississippi in a given year also a lot to do with the weather. To put it simply, if it rains very hard in the Corn Belt, more nitrogen leaches out of the soil and runs into the rivers and streams.

The group of scientists is able to roughly forecasts of the extent of hypoxia each year based on the amount of nitrate measured in the Mississippi River during the spring [together with data from the previous year, since nitrogen also gets recycled in the coastal sediments]. My own work is examining whether you can take these forecasts back a step further, by looking at the rainfall in certain places.

The way to combat the Dead Zone is to reduce the input of nitrogen in the Mississippi. It won't be easy. Nitrogen levels probably need to be reduced by 50-60%. That means changing the way crops are grown - something I talked about in the "Surf or Turf" study - and/or embark on an extensive wetland restoration program.

Otherwise, in a given year, there's always a chance that a hurricane will strike the area, and the strong wind and wave action will mix up the waters and replenish the bottom with oxygen (as Ivan did). But let's not hope for that.