We all expected a large ‘dead zone’ this summer. The river has been above flood stage, and well above the 1935 - present maximum since mid-June. As a result, the Bonnet Carré Spillway north of New Orleans has been opened twice delivering Mississippi River fresh water and nutrients to Lake Pontchartrain, Lake Borgne, Mississippi Sound, and offshore waters between the Chandeleur Islands and Mississippi barrier islands. Dense and toxic cyanobacterial blooms were generated in the wake of these nutrient-enrichment events.
Prior to Tropical Storm Barry, the NMFS SEAMAP groundfish survey cruise documented extensive hypoxia in the western Louisiana coastal region and well into Texas. SEAMAP did not cover the area in coastal Louisiana where others found hypoxia via other sources of information. And, documented hypoxia east of the Mississippi River for the stations they occupied similar to hypoxia distributions in 2011 mapped by Rabalais et al.
Then came TS Barry, but then it didn’t. While it wasn’t coming ashore, it brought strong winds and high waves to the area where summer hypoxia normally develops. While it was projected to be high surge and waves, there was a 6-ft storm surge predicted for the Mississippi River. Water this high along with the swollen river would jeopardize levees throughout the lower Mississippi River and the city of New Orleans. While Barry was indecisive about coming ashore, the winds and waves picked up along the Louisiana coast, especially in the area of the Atchafalaya delta and to the west.
I normally get media calls at the time of the forecast (many this year) and after the mapping cruise (yet to be seen). A second set of calls came this year prior to TS Barry with questions as to what the storm would do to hypoxia and the toxic cyanobacterial bloom.
I checked my crystal ball and discovered little that would help me. However, I had opinions anyway. The winds and waves would disrupt hypoxia, but it may redevelop by the time we depart on the cruise midnight on the 22nd, Monday night. My prediction is that hypoxia would develop more quickly on the eastern side of the study area than on the west shelf. However, there remains flood level discharge from the Atchafalaya to the western coastal waters and to the eastern side from the Mississippi River.
As for the cyanobacterial blooms, I predicted that they would be dissipated. These types of blooms like hot and calm water, which was prevalent when they occurred, but would likely dissipate during the storm. There would remain cells to propagate should the waters calm down and the water was warm. Bonnet Carre will remain open until an unknown time. My crystal ball cannot give me the extent of cyanobacterial bloom at this time, but some satellite views indicate they are reforming.
With this, we will begin loading the ship, RV Pelican, and depart later tonight. Still do not know if I want to go east or head to the west. Hours left to ponder.