Hypoxia Survey

Hypoxia 06 Hypoxia 07 Hypoxia 03 Hypoxia 01 Hypoxia 05 Hypoxia 04 Hypoxia 02

The Mississippi-Atchafalaya River Basin drains approximately 40 percent of the United States’ land area, delivering freshwater, sediments, and large quantities of nutrients to the Gulf of Mexico. In summer, dissolved oxygen levels decline below 2 mg/liter in Gulf bottom waters, resulting in hypoxic (low dissolved oxygen concentrations) over a large area on the Louisiana Coastal Shelf 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 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.

Task Summary

  • Identified and enumerated algal taxa present in each sample.
  • Determined algal biovolumes and percentage of each taxon in the samples.
  • Calculated diversity indices and summary statistics.
  • Reported the presence of potentially toxic algal species.


The algal data was used to better define the extent of hypoxic waters in the Gulf and to determine the effect of discharge variations from the Mississippi-Atchafalaya River Basin on water column biota. Ultimately the results will improve water quality models of the Gulf of Mexico and the Mississippi-Atchafalaya River Basin. Use of these models 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 data set (with multiple years and locations sampled) can be used as background data to compare with environmental conditions following the 2010 Deepwater Horizon oil spill.

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