Friday, July 12, 2019

Wind Saves the Bay from a Bad Report Card

When average is good, from MDDNR: Late June 2019 Hypoxia Report
Maryland Department of Natural Resourcesmonitoring shows that dissolved oxygen conditions in the state’s portion of the Chesapeake Bay mainstem were better than expected in late June. The hypoxic water volume — areas with less than 2 mg/l oxygen — was 0.69 cubic miles, which is well below the late June 1985-2018 average of 1.15 cubic miles, and an improvement from the 1.13 cubic miles of hypoxia observed in early June. No anoxic zones — areas with less than 0.2 mg/l oxygen — were observed.

An important caveat to these improved results is the effect of wind. On June 21, three days prior to the June 24-26 main bay sampling, the average daily wind speed was 15 knots with periods over 25 knots. These winds helped to mix oxygen from the surface into deeper waters. The lower Maryland bay was sampled on June 24 and it is evident on the inset map that waters were still somewhat mixed, with hypoxic conditions constricted across the bay, and starting lower in the water column at about 20 meters deep.

When sampling resumed in the mid-Maryland portion of the bay on June 25, hypoxic conditions were resuming, and appearing at 10 meters and below. If sampling had occurred several days later, average hypoxic results for the period might have been observed. These results provide scientists and managers with additional insight on the expected duration of improved conditions after a sustained wind event.

In the beginning of June, the National Oceanic and Atmospheric Administration, U.S. Geological Survey, University of Maryland Center for Environmental Science and University of Michigan scientists predicted a large hypoxic volume for the bay in 2019 due to higher flows last fall and this spring, and higher nitrogen loading from the Susquehanna and Potomac Rivers.
I haven't said anything before because I wasn't sure, but I think we did have a slight "crab jubilee" here a few days ago, when I saw crabs and a few fish, including Hog Chokers, in shallow water. This is caused when SW winds drag deep, low oxygen water up into the shallow waters. Serious events can cause fish and crab kills

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