Largest Gulf of Mexico Dead Zone in more than a decadeEvery year, farmers throughout the central Uni
Largest Gulf of Mexico Dead Zone in more than a decadeEvery year, farmers throughout the central United States deploy large amounts of nitrogen- and phosphorus-based fertilizers to help grow food. Every year, rains come. That water picks up a portion of those fertilizers and carries it downstream, where it eventually causes what is known as the Gulf of Mexico Dead Zone.Dead zones occur in the ocean in areas where there is too much biologic productivity. When ocean-living algae dies, it sinks and begins to decay, using up oxygen in the process. If there isn’t enough oxygen to use up all the algae, the ocean can run out of oxygen, creating areas that are “hypoxic” or “anoxic”, free of the oxygen that other animal species need to live. For example, if fish swim into these zones, they will literally die of suffocation.In June, areas in Mississippi and the Ohio River Valley received above-average rainfall (http://tmblr.co/Zyv2Js1r39Jl4). That rainfall washed the year’s fertilizers down the Mississippi River system and into the Gulf of Mexico, where it fed the growth of algae plumes that have since died, using up the oxygen. This cycle happens every year, but because of the timing and volume of the flow, this year’s dead zone is the second largest on record and the largest since 2002.These dead zones push fish and other economically important species out of their normal habitats and can also put populations under stress by reducing their numbers, so they’re not only an environmental issue, they’re an economic issue. The US Environmental Protection Agency and the Gulf of Mexico/Mississippi River Watershed Nutrient Task Force have set a goal of reducing the areal extent of the dead zones to below 5000 square kilometers, but the 16,700 square kilometer dead zone this year shows that goal is far from being met. The area defined as the dead zone is marked in black on this figure and the degree of oxygen depletion is colored in red – the darkest red areas are extremely low oxygen, far below where animal life can find enough oxygen to live.The Gulf of Mexico Dead Zone is likely the world’s best-monitored dead zone and it is the 2nd largest human-caused dead zone, next to the one that appears in the Baltic Sea.-JBBImage credit: NOAAhttp://1.usa.gov/1N8hgdnRead more:http://bit.ly/1K5FFNK -- source link
#science#environment#dead zone#anoxic#anoxia#hypoxic#hypoxia#fertilizer#pollution#nitrogen#phosphorus#mississippi river#louisiana#chemistry#oxygen