Hypoxia Survey
   Gulf of Mexico from Texas to Florida

Overview
The Mississippi-Atchafalaya River Basin drains approximately 40 percent of the United States' land area, delivering freshwater, sediments, and nutrients to the Gulf of Mexico, thereby providing large quantities of nutrients to the Gulf. In summer dissolved oxygen levels decline below 2 mg/liter in bottom waters, resulting in hypoxic (low dissolved oxygen concentrations) on the Louisiana Coastal Shelf of the Gulf, west of the Mississippi River delta. In many cases hypoxic waters do not have enough oxygen to support fish and other aquatic animals. The U.S. Environmental Protection Agency (USEPA) initiated an intensive study of the northern Gulf of Mexico in 2002 to better characterize the area of hypoxia. Water & Air has analyzed 300 phytoplankton samples collected by the USEPA from Texas to Florida as part of this study.

Details

• Identification and enumeration of algal taxa present in each sample.
• Determination of algal biovolumes and percentage of each taxon in the samples.
• Calculation of diversity indices and summary statistics.
• Determination of the presence of potentially toxic species.

Results
Results from this study are being used to better define the extent of hypoxic waters in the Gulf and determine the effect discharge variations from the Mississippi-Atchafalaya River Basin have on it. Ultimately the results will be used to improve water quality models of the Gulf of Mexico and the Mississippi-Atchafalaya River Basin. Use of these models will allow better forecasting of the effect of management actions designed to reduce the areal extent of hypoxic waters, improve water quality, and protect aquatic habitats and biota in the area. This large database (multiple years and locations sampled) can be used in comparisons with data collected after the 2010 Deepwater Horizon Gulf oil spill.