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2016 Chesapeake Bay Summer Review

Moderate hypoxia and near-absence of anoxia highlight the summer of 2016

• Below-average loads during spring and summer led to below-average hypoxia (dissolved oxygen ≤ 2.0 mg l-1)
• Unusual seasonal cycle of hypoxia, where early summer volumes were low and late-summer volumes were high
• Almost no anoxia (dissolved oxygen ≤ 0.25 mg l-1) observed during summer
• The late-summer anoxic volume in 2016 was the lowest observed since modern monitoring began in 1985.

2016 forecast and observed hypoxia and anoxia dials

Summer conditions for 2016 were influenced by slightly below average winter and spring river flow into the Bay. Low dissolved oxygen conditions, which negatively impact the aquatic organisms that live in the Bay, did not arrive until June, were generally low until late July, and continued at average levels through September. Zero-oxygen zones were almost absent this summer and were short-lived when they did arrive. The main factor for summer dissolved oxygen conditions in 2016 was the generally low river flow and nutrient loads delivered between March and August.

In summer 2016, scientists forecasted that a slightly below average volume of hypoxic waters (dissolved oxygen ≤ 2.0 mg l-1) would occur in the Chesapeake Bay mainstem during July. These forecasts are based on models that predict dissolved oxygen conditions using Susquehanna River flow and nitrogen loads. They also forecast that a smaller than average volume of anoxic waters (dissolved oxygen ≤ 0.25 mg l-1) would occur in the mainstem in the summer. The July hypoxia forecast nearly hit its target, while the forecasted anoxic volumes were higher than observed given the near absence of anoxia.

summer review diagram Chlorophyll a Chlorophyll a Freshwater Flow Freshwater Flow Wind Wind Dissolved Oxygen - Hypoxia Dissolved Oxygen - Hypoxia Dissolved Oxygen - Anoxia Dissolved Oxygen - Anoxia

The conceptual diagram to the left shows how dissolved oxygen in the Chesapeake Bay mainstem is affected by different factors during the summer months.

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The summer forecast and review was produced with contributions from Vyacheslav Lyubchich (UMCES-Chesapeake Biological Lab), Mary Anne Evans (US Geological Survey), Don Scavia (University of Michigan), and Jeremy Testa (UMCES-Chesapeake Biological Lab).