annual dead zones

See the following -

Why This Year's Gulf Dead Zone Is Twice As Big As Last Year's

Tom Philpott | Mother Jones | August 14, 2013

[...] This year's "biological desert" (NOAA's phrase) is much bigger than last year's, below, which was relatively tiny because Midwestern droughts limited the amount of runoff that made it into the Gulf. At about 2,900 square miles, the 2012 edition measured up to be about a third as large as Delaware. Read More »