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Every June to September, both states measure the volume and duration of hypoxia (lack of oxygen in the water), a constant concern in Chesapeake Bay. Crabs, fish, oysters and other creatures need oxygen to survive. However, pollution by runoff causes the proliferation of algae, which traps oxygen and hurts life in the bay.
Weather conditions play a major role in the bay's hypoxia levels, and this summer's record precipitation has proved it. The Maryland Department of Natural Resources (DNR) has announced the best July ever for dissolved oxygen conditions. This is because the samples were taken just after the rain showers caused historic water flows and high winds. As the DNR explains, "this freshwater wall, accompanied by sustained winds of 20 knots before sampling, reduced the stratification of the water column and mixed with the water." In the system, the Virginia Institute of Marine Sciences has also measured a "near-zero" hypoxic zone. end of July.
But that's not the whole story. Less than two months after the July record, the DNR and VIMS discovered that hypoxia conditions had reached near record levels worst September. MNR attributes this change to the milder temperature that lasted until October, but also to the increase in nutrient runoff caused by July's historic water flows.
After the record conditions and almost the worst conditions, summer hypoxia was average.
"The hypoxic volume was so low in late July and so high in early September, but overall, the hypoxic volume was roughly the same as last year," says Dr. Marjy Friedrichs, VIMS scientist and idea original annual hypoxia of Chesapeake Bay School Bulletin.
"Overall," she says, "our model indicates that the total amount of hypoxia in 2018 was similar to that of 2017, but that the seasonal patterns of hypoxia were very different. In addition to the sharp hypoxic decline of late July, the conditions of lack of oxygen began earlier and lasted longer in 2018 than in recent years. "
According to VIMS researchers, this trend could be related to climate change. Related research conducted by the recent VIMS Ph.D. Ike Irby, a graduate, suggests that early spring hypoxia is becoming more common, due to the warming observed in May in recent years.
VIMS and DNR note that their 2018 hypoxia ratios are generally the same, with some variations due to slightly different reporting periods.
-Meg Walburn Viviano
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