Monday, September 20, 2021

A Bad Month for the Bay

 Chesapeake Bay Foundation, August Dead Zone Is Bad News for the Bay

The Chesapeake Bay Foundation raised concerns about Bay restoration efforts following the August dead zone report. The report, from the Maryland Department of Natural Resources and Old Dominion University, found that dissolved oxygen conditions in Maryland and Virginia were worse than average this August following two better-than-average months. The report attributed the increased size of the dead zone to significantly warmer temperatures, lower wind speeds, and greater precipitation.

So, as always, it comes down to weather. The good news is that sometime in late September or October, the water will cool off enough, and the wind will blow hard enough to restore oxygen to the whole water column. Of course, anything on the bottom covered by hypoxia is likely to be dead.

The Bay’s living resources, including fish, crabs, and oysters, require healthy levels of oxygen to survive. For example, Atlantic sturgeon, a federally endangered species, require 5 mg/l of dissolved oxygen throughout their range. An expanding dead zone may curtail recovery efforts for this ancient fish.

The solubility of oxygen in water depends on the temperature and salinity. At normal summer Bay temperatures and salinity, the solubility of oxygen is not a whole lot more than 5 mg/l. Water can be supersaturated with oxygen if plants are actively growing and producing it, but at night they respire and use oxygen.

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