Narragansett Bay, RI, is considered to be a relatively well-mixed estuary not subject to extensive seasonal stratification and hypoxia. However, results of surveys of dissolved oxygen (DO) for the upper half of Narragansett Bay on August 15, 2001 and on August 6, 2002 have documented evidence of wide-area intermittent subpycnoclinal hypoxia (≤ 3 mg l−1). For the August 2001 survey, severe hypoxic to near-anoxic levels were confined to the Providence River, the western side of Greenwich Bay, and a small area of Mount Hope Bay, but hypoxic levels below 2 mg l−1 were also experienced on the western side of the Upper Bay in an extensive, shallow oxygen minimum. Hypoxic bottom waters (≤ 3 mg l−1) extended from the Upper Bay into the upper West Passage. Hypoxic waters covered approximately 66 km2 (36%) of the survey area for August 15, 2001. A more extensive and severe hypoxic event occurred during the August 2002 survey, when near-bottom waters of the entire Providence River and a large area of the Upper Bay and upper East Passage were severely hypoxic to near-anoxic, while other parts of the Upper Bay, upper East Passage and upper West Passage were hypoxic at depths greater than 5 m. Limited data for Mount Hope Bay in August 2002 documented small hypoxic areas of the southern end of that subembayment. The total hypoxic area for August 6, 2002 was approximately 93 km2 (65%) of the total area surveyed. Decreased estuarine circulation due to a severe drought may have contributed to the wider extent of hypoxic and near-anoxic waters in large areas of the upper half of Narragansett Bay recorded in the August 6, 2002 survey as compared with the August 15, 2001 survey. Results of the oxygen surveys affirm sediment profile camera work and limited benthic studies that previously suggested parts of the Mid Bay have become subject to increased organic loading impacts. These impacts can take place even under drought conditions, when only point source nutrients are the major contributors to nutrient loadings entering the upper half of Narragansett Bay.
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