OVERVIEW

BACKGROUND

Narragansett Bay is a medium-sized (370 km²), relatively well-mixed temperate latitude estuary located in the northeastern United States. With an average depth of 7.8 m, relatively low input of fresh water, and high tidal and wind mixing, Narragansett Bay is considered to be only moderately susceptible to adverse effects of nutrient loading including low oxygen (hypoxic) conditions (Bricker et al. 1999). During several summers in the late 1980's and early 1990’s, fish kills, thought to be the result of oxygen depleted waters, occurred in the upper sections of Narragansett Bay (Deacutis, 1999). Unfortunately, no data were available to document dissolved oxygen levels that may have been associated with the fish kills. To address this lack of data, Dr. Christopher Deacutis of Narragansett Bay Estuary Program (NBEP) organized a survey team to measure dissolved oxygen throughout the upper Bay and Providence River. This volunteer team, later dubbed "The Insomniacs", was made up of boat groups from various organizations in the Rhode Island and Massachusetts area with an interest in water quality issues in Narragansett Bay and its watershed. We started on a cool summer evening in June of 1999 with 8 boats covering more than 80 stations in upper Narragansett Bay, the Providence River, Greenwich Bay, and Mt. Hope Bay. Since that time we have participated in a total of 13 surveys and have dedicated much effort, with minimal funds, to compile the data and make it available for use in our future studies and by others.

After a year hiatus we reinitiated our DO surveys in the summer of 2005 using new Sea-Bird SBE 19 Plus SEACAT profilers purchased with support from the NOAA Bay Window Project (NOAA Award NA05NMF4721253). We call this new effort the Day Trippers survey because we go out during daylight intervals. Currently we use three boats (Brown, NBEP/DEM, and STB/USDA) to sample about 75 stations covering the Providence River, Greenwich Bay, and the East and West Passages of Narragansett Bay.

STATION LOCATIONS AND WHAT WE MEASURED

Stations were distributed throughout upper Narragansett Bay, the Providence River, Greenwich Bay, and Mt. Hope Bay. The sites were located both in navigational channels that provided maximum depth ranges, and in shoal areas adjacent to the channels. At each station we measured depth profiles of temperature, salinity, and dissolved oxygen. The temperature and salinity measurements were used to calculate density values for each depth.

WHY DID WE GO OUT ON A SUMMER NIGHT DURING NEAP TIDE?

The surveys focused on the warm summer months during neap tides when the risk of hypoxia is greatest. During the summer months, warm waters increase respiration rates and the Bay often has a layer of relatively warm and low salinity surface water overlying colder and saltier deep water. This low density surface layer creates stratification that can isolate the deep waters from sources of oxygen at the surface (the atmosphere or phytoplankton). Biochemical reactions associated with decaying plant matter, remove oxygen from the waters. This oxygen demand coupled with density stratification increases the risk of hypoxic conditions in the summer months, especially during neap tides when tidal mixing is low. At the beginning of our study, we decided to go out at night because the low DO events are expected to be the most extreme during the midnight to 6 am period. This is due to respiration, which consumes oxygen and dominates over daytime photosynthetic production of oxygen. After a few surveys, we realized that the diurnal effects did not play a dominant role in the large-scale spatial changes we observed. However, we continued to go out at night because, except for the loss of sleep, a calm summer evening is one of the best times to enjoy a boat ride on the waters of Narragansett Bay.

THE SURVEY DATA

All data presented on this website has undergone quality control and correction where necessary. For more information about corrections and QA/QC contact David Murray. For each survey, maps of surface, bottom, and minimum dissolved oxygen are displayed on the data page. Linked to these maps are plots of temperature, salinity, density and dissolved oxygen versus depth, for each station. A complete data table including geographic coordinates is also available for download. Accompanying the interactive maps are time series plots of bottom DO, tides, winds, salinity, river flow, and water and air temperature during the interval preceding and following the survey.

REFERENCE

Please use the following citation when referring to the seasonal DO survey data set collected from 1999 through 2003:

Prell, W., Saarman, E., Murray, D., Deacutis, C., 2004. Summer-Season, Nighttime Surveys of Dissolved Oxygen in Upper Narragansett Bay (1999-2003). Data available at http://www.geo.brown.edu/georesearch/insomniacs.

Please use the following citation when referring to the summertime DO survey data set collected since 2005:

Prell, W., Murray, D., Deacutis, C., 2006. Summer-Season survey of dissolved oxygen in upper Narragansett Bay beginning in 2005. Data available at http://www.geo.brown.edu/georesearch/insomniacs

ACKNOWLEDGEMENTS