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September Hypoxia Report

Map of Chesapeake Bay dissolved oxygen results from September 2019Maryland Department of Natural Resources monitoring data show that dissolved oxygen conditions in the Maryland portion of the Chesapeake Bay mainstem were higher than average in September. The hypoxic water volume — waters with less than 2 mg/l oxygen — was 0.73 cubic miles in September, down from the 1.06 cubic miles seen in late August, but greater than the historical 0.41 cubic mile average for September. No anoxia — waters with less than 0.2 mg/l oxygen — was detected. This ranked as the fifth-largest Maryland September hypoxia volume since monitoring began in 1985.  Read more…


Late August 2019 Hypoxia Report

Image of Late August 2019 Chesapeake Bay Dissolved Oxygen monitoring mapMaryland Department of Natural Resources monitoring data show that dissolved oxygen conditions in the Maryland portion of the Chesapeake Bay mainstem were near average in late August. This is a significant improvement from hypoxia results observed earlier this summer. The hypoxic water volume (waters with less than 2 mg/l oxygen) was 1.06 cubic miles in late August, down from the 1.77 cubic miles seen in early August. A small volume (0.006 cubic miles) of anoxia (waters with less than 0.2 mg/l oxygen) was detected. Read more…


Early August 2019 Hypoxia Report

Photo of Maryland Department of Natural Resources monitoring vessel in the Chesapeake BayMaryland Department of Natural Resources monitoring data show that dissolved oxygen conditions in the Maryland portion of the Chesapeake Bay mainstem were larger than average in early August. The hypoxic water volume (areas with less than 2 mg/l oxygen) was 1.77 cubic miles in early August, down from the 2.01 cubic miles seen in late July, but significantly higher than the 1985-2018 early August average of 1.19 cubic miles. The hypoxic volumes ranked third-largest since 1985 for the early August time period. Read more…


July 2019 Hypoxia Report

Photo of DNR crew on a Chesapeake Bay monitoring cruiseMaryland Department of Natural Resources monitoring data show that dissolved oxygen conditions in the Maryland portion of the Chesapeake Bay mainstem were larger than average in July, as the result of many factors. The hypoxic water volume (areas with less than 2 mg/l oxygen) was 1.92 cubic miles in early July and 2.01 cubic miles in late July. The early July 1985-2018 average hypoxic volume is 1.36 cubic miles, and late July is 1.34 cubic miles. The most recent hypoxic volumes were respectively the fourth-largest for early July and second-largest for late July since 1985.

Larger than average hypoxia was predicted for this summer in part due to massive rainfall causing high flows into the Chesapeake Bay the past year, which delivered higher nutrient loads. Those nutrients fuel algal blooms, which die and are consumed by bacteria, which then deplete oxygen in bottom waters. Also, average winds were generally low in July, which prevented oxygen from mixing into deeper waters. Read more…


Late June 2019 Hypoxia Report

Photo of staff monitoring water data on a monthly hypoxia cruiseMaryland Department of Natural Resources monitoring 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. Read more…


Early June 2019 Hypoxia Report

Photo of Research Vessel Kehrin during hypoxia cruise

The Maryland Department of Natural Resources Research Vessel Kehrin is used for summer hypoxia monitoring.

Dissolved oxygen conditions in the Maryland portion of the Chesapeake Bay mainstem were slightly above the long-term average in early June. The hypoxic water volume — areas with less than 2 mg/l oxygen — was 1.14 cubic miles, which is slightly above the early June 1985-2018 average of 0.93 cubic miles and similar to levels in 2017 and 2018. 

A significant amount of hypoxia was also observed during May. Hypoxia was not observed in Virginia’s portion of the bay, and no anoxic zones — areas with less than 0.2 mg/l oxygen — were detected in the mainstem bay in either Maryland or Virginia. 

The observed early June and May hypoxia conditions are likely attributable to near record high flows in 2018 that continued into the spring of 2019.

Read more…


Summer 2018 Hypoxia Report

Average Year for Chesapeake Bay Dissolved Oxygen

Photo of Terrapin Park by Mark Dignen

Terrapin Park Driftwood Sunset by Mark Dignen

Dissolved oxygen conditions for the Maryland portion of Chesapeake Bay for the summer of 2018 were average compared to the long-term average from 1985-2017, reports the Maryland Department of Natural Resources. Low dissolved oxygen volume averaged 0.97 cubic miles from June through September.

Crabs, fish, oysters and other creatures require oxygen to survive. Scientists and natural resource managers study the volume and duration of bay hypoxia to determine possible impacts to bay life. Each year from June through September, the department computes these volumes from data collected by Maryland and Virginia monitoring teams. Read more…


August 2018 Hypoxia Report

Photo of sailboat on Chesapeake Bay by Toni Quigley

Sunset Sailing on the Chesapeake Bay by Toni Quigley

Dissolved oxygen conditions for Maryland’s portion of Chesapeake Bay returned to near average for the month of August, reports the Maryland Department of Natural Resources. The department tracks hypoxia throughout the summer during twice monthly monitoring cruises.

Low dissolved oxygen volume was at a record low (0.26 cubic miles) in late July, due to sustained winds and high flows from torrential rainfalls in mid-to-late July. As stormy weather subsided, and warmer days returned, hypoxic water volume (areas with less than 2 mg/L oxygen) rose to 1.08 cubic miles in early August, and 1.26 cubic miles in late August. Warmer waters hold less oxygen, and as freshwater flows subsided, water column stratification increased, making it more difficult for oxygen to mix into lower depths.

The hypoxic zone appeared to recede northward from early-to-late August, but it should be noted that the station at the Maryland/Virginia line was not sampled in late August due to high winds, which could result in a lower estimate of hypoxic volume for bay waters. Read more…


Late July 2018 Hypoxia Report

Heavy Rainfall and Sustained Winds Helped Produce Best Recorded Results Ever

Photo of the Research Vessel KerhinDue to extreme summer weather, dissolved oxygen conditions in Maryland’s portion of the Chesapeake Bay mainstem were the best ever observed in late July, reports the Maryland Department to Natural Resources. The department tracks hypoxia throughout the summer during twice monthly monitoring cruises.

The hypoxic water volume (areas with less than 2 mg/L oxygen) was 0.26 cubic miles.*

Read more…


Early July 2018 Hypoxia Report

Photo of Chesapeake Bay

Dissolved oxygen conditions in Maryland’s portion of the Chesapeake Bay mainstem improved in early July, according to the Maryland Department of Natural Resources. The department tracks hypoxia throughout the summer during twice monthly monitoring cruises.

The hypoxic water volume (areas with less than 2 mg/l oxygen) was 1.05 cubic miles, nearly 0.6 cubic miles less than in late June, and 0.33 cubic miles less than the early July average. No additional hypoxic volume was observed in Virginia’s portion of Chesapeake Bay, and no anoxic zones (areas with less than 0.2 mg/l oxygen) were detected in the mainstem. Read more…


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AccessDNR November 2019

The November 2019 edition of a monthly video newsletter hosted by Gregg Bortz.

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