Predicting the response of Gulf of Mexico hypoxia to variations in Mississippi River nitrogen load
Limnol. Oceanogr., 48(3), 2003, 951-956 | DOI: 10.4319/lo.2003.48.3.0951
ABSTRACT: The effects of nutrient loading from the Mississippi River basin on the areal extent of hypoxia in the northern Gulf of Mexico were examined using a novel application of a dissolved oxygen model for a river. The model,driven by river nitrogen load and a simple parameterization of ocean dynamics, reproduced 17 yr of observed hypoxia location and extent, subpycnocline oxygen consumption, and cross-pycnocline oxygen flux. With Monte Carlo analysis, we illustrate through hindcasts back to 1968 that extensive regions of low oxygen were not common before the mid-1970s. The Mississippi River Watershed/Gulf of Mexico Hypoxia Task Force set a goal to reduce the 5-yr running average size of the Gulfs hypoxic zone to less than 5,000 km2 by 2015 and suggested that a 30% reduction from the 1980-1996 average nitrogen load is needed to reach that goal. Here we show that 30% might not be sufficient to reach that goal when year-to-year variability in ocean dynamics is considered.