Less oxygen dissolved in the water is often referred to as a dead zone (in red above). (Photo: NOAA)
Dead zone forecasts vary widely
Friday, June 22, 2012, 22:20 (GMT + 9)
A team of National Oceanic and Atmospheric Administration- (NOAA) supported scientists is predicting that this year’s Gulf of Mexico hypoxic zone could range from a low of approximately 1,197 sqmi to as much as 6,213 sqmi. The wide range is the result of using two different forecast models.
The forecast is based on Mississippi River nutrient inputs compiled annually by the US Geological Survey (USGS).
The smaller dead zone forecast, covering an area slightly larger than the state of Rhode Island, comes from researchers from the University of Michigan. Their predicted size is based solely on the current year’s spring nutrient inputs from the Mississippi River which are significantly lower than average due to drought conditions throughout much of the watershed.
The larger dead zone forecast, the equivalent of an area the size of the state of Connecticut, is from Louisiana Universities Marine Consortium and Louisiana State University scientists. The Louisiana forecast model includes prior year’s nutrient inputs which can remain in bottom sediments and be recycled the following year. Last year’s flood, followed by this year’s low flows, increased the influence of this “carryover effect” on the second model’s prediction.
During May 2012, streamflow in the Mississippi and Atchafalaya rivers were nearly half that of normal conditions. This resulted in a decrease in the amount of nitrogen transported by the rivers into the Gulf.
Photo Courtesy of FIS Member National Oceanic and Atmospheric Administration NOAA/NMFS
According to USGS estimates, 58,100 tonnes of nitrogen (in the form of nitrite plus nitrate) were transported in May 2012 by the Mississippi and Atchafalaya Rivers to the northern Gulf. The amount of nitrogen transported to the Gulf in May 2012 was 56 per cent lower than average May nitrogen loads estimated in the last 33 years.
The two smallest recorded dead zones to date are in 2000 when it measured 1,696 sqmi and a 15 sqmi dead zone in 1988. Last year’s dead zone measured 6,765 sqmi. The largest hypoxic zone measured to date occurred in 2002 encompassing more than 8,400 sqmi.
“This forecast is a good example of NOAA, USGS and university partnerships delivering ecological forecasts that quantify the linkages between the watershed and the coast,” said Jane Lubchenco, PhD, undersecretary of commerce for oceans and atmosphere and NOAA administrator. “Regardless of the size of the dead zone, we should not lose sight of the ongoing need to reduce the flow of nutrients to the Mississippi River and thus the Gulf.”
The actual size of the 2012 hypoxic zone will be released following a NOAA-supported monitoring survey led by the Louisiana Universities Marine Consortium between 27 July and 3 August. Collecting these data is an annual requirement of the Mississippi River/Gulf of Mexico Watershed Nutrient Task Force Action Plan.
Additional NOAA-supported surveys led by the National Marine Fisheries Service (NMFS) and Texas A&M University will also provide an indication of the progression of the dead zone during the year.