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DO - hypoxia

Dissolved oxygen is critical to the survival of Chesapeake Bay's aquatic life. The amount of dissolved oxygen needed before aquatic organisms are stressed, or even die, varies from species to species.

Indicator Details

DO - hypoxia

Largest hypoxic volume on record for July

Overall, summer dissolved oxygen conditions were poor in 2011. Hypoxic (dissolved oxygen ≤ 2.0 mg l^-1) volume was the largest in late July, coinciding with the largest anoxic volume. This was a result of the high spring flows and hot air temperatures that set up strong stratification in the mainstem, as described in the anoxia section.

Similar to anoxia this year, hypoxia increased throughout the summer until Hurricane Irene and Tropical Storm Lee in late August. Winds associated with these storms mixed DO-rich surface waters with DO-poor bottom waters, leading to very little hypoxia in late August. There is some evidence that, following the increased flow (and therefore nutrients) resulting from Hurricane Irene and Tropical Storm Lee, that hypoxia was increasing again in September. 

July hypoxia

In June 2011, scientists forecasted that the 2011 July hypoxic volume would be 9.7 km³, based on January to May total nitrogen loads. The observed July hypoxic volume was 11.47 km³, which is higher than the forecasted number and also above the forecasted range of 8.6 to 11.1 km³. The average hypoxic volume for 2011 is the highest on record (since monitoring began in 1985), slightly higher than the previous record of 11.38 km³ in 1993. For more information, visit University of Michigan's hypoxia forecast website.

 

Summer (June through September) hypoxia

In 2010, a new method for forecasting hypoxia was used to forecast July + August hypoxic volume. The model used 2010 January to May river flow, January to April chlorophyll a biomass, and January to April east-west wind speed to forecast a July + August hypoxic volume. A similar method was used again in 2011 to forecast summer (June through September) hypoxia.

In June 2011, the summer (June through September) hypoxic volume was forecasted to be 6.8 km³ with a range from 5.7 to 8.0 km³. The forecast was very close to the observed hypoxic volume of 7.1 km³ and within the range.

Acknowledgements:
July hypoxia forecast courtesy of Don Scavia (University of Michigan) and Mary Anne Evans (University of Michigan).
July-August hypoxia forecast courtesy of Younjoo Lee (UMCES-CBL). Monthly cruise data provided by the Chesapeake Bay Program.