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During the past few years, an observing system has been established for the waters of Narragansett Bay that provides real- time measurements of the pulse of the Bay. An ecosystem such as the Bay can be viewed as having a pulse (or actually a series of pulses) that reflects its general health and the interplay of processes that make up its "metabolism." Some of the pulses we see in Narragansett Bay relate to its seasonal cycle, to changes between day and night, and to the effects of the tides. Even the phases of the moon cause a pulse in the Bay that is due to variations in the tidal range. Measurements of seawater temperature, salinity, dissolved oxygen, pH, chlorophyll, and water level are being obtained from a set of instrumented buoys and shore-based systems in the Bay. We use automated sensor systems to measure water properties in the Bay every 15 minutes.
      This work is designed to provide a record of the changes occurring in the waters of the Bay. From this information, we will be able to determine how the Bay and its ecosystem are affected by changes in climatic conditions, pollutant inputs, and human uses of the Bay and its resources.
      This work began in 1995 with a project supported by the Office of Naval Research to investigate the processes occurring in coastal waters. The automated sensors provide much greater temporal resolution than the conventional methods of collecting samples and bringing them back to the laboratory for analysis. We established a time-series station in the lower West Passage of the Bay at the GSO pier. In 1997, we deployed a prototype buoy in the mid-Bay region between Quonset Point and Prudence Island with instruments located at the surface and at depths of 4m and 14m. The buoy provided information on vertical gradients and stratification in the Bay. In 1999, we deployed two buoys with greater capabilities near the north and south ends of Prudence Island with funding provided by the National Oceanic and Atmospheric Administration (NOAA) as part of a Bay monitoring project involving GSO, the NOAA National Marine Fisheries Service (NMFS) laboratory in Narragansett, and the RI Department of Environmental Management (DEM). Similar shore-based measurement systems have been established on the east side of Prudence Island by the Narragansett Bay National Estuary Research Reserve System managed by DEM and near the mouth of Mount Hope Bay by Roger Williams University. This year DEM is installing a measurement system at the Mobil Oil pier in the Providence River. The Narragansett Bay Commission (NBC), GSO, and Applied Science Associates, Inc. (ASA), received funding from the U.S. Environmental Protection Agency Environmental Monitoring for Public and Community Tracking (EMPACT) program to add three additional monitoring systems in the urban areas of upper Narragansett and Mount Hope Bays.
      There have been several other efforts to increase the observation capabilities in the Bay. The Physical Oceanography Real-Time System (NOAA PORTS) has been established to measure water currents and levels, wind, and other properties to support ship navigation in the Bay. (This system and its data are described at http://co-ops.nos.noaa.gov/nbports/.) The NMFS laboratory has been conducting monthly surveys along transects through the Bay with a set of physical, chemical, and biological sensors on an undulating oceanographic recorder. This instrument collects data continuously from near the sea surface to near the seafloor as the instrument is towed through the Bay. The Massachusetts Coastal Zone Management Office has established three water column measurement systems in Mount Hope Bay and the Taunton River. Their work is being coordinated with and enhanced by EMPACT-funded research at NBC. Chris Kincaid of GSO has been measuring currents from the sea surface to the seafloor using Acoustic Doppler Current Profilers at fixed sites near the Claiborne Pell Newport Bridge, GSO, and Beavertail Point.
      The locations of 12 measurement systems that are being coordinated into an observing system are shown on the map of Narragansett and Mount Hope Bays (see Fig. 1). Sensors at each location measure the same properties at 15-minute intervals. Sites 6 and 12 are close to shore in relatively shallow water and measure at one depth only, but the other sites have instruments near the surface and near the seafloor. The buoys consist of a 1.2 meter foam discus with a watertight compartment in the center for the electronics and batteries (see Fig. 2). The sensor sondes (sets of sensors and their controlling electronics) are connected by cables about 0.5m below the surface and 1m above the seafloor. Three solar panels recharge the batteries. A flashing beacon warns boats of the buoy's presence at night. A cellular telephone or radio transmitter is used to relay the data to a shore-based computer. The buoys located at positions 4 and 10 report measurements daily. The systems at locations 1, 2, 3, and 7 report their data every 15 minutes. In the near future it will be possible for scientists, environmental managers, educators, fishermen, and the public to access the data in near real time through an Internet website. Sensors are mounted on two types of measurement sondes (see Fig. 3).
      Science teachers and students will find access to the measurements in the Bay useful for many purposes. Teachers can use the day-night changes in oxygen and pH in the Bay to illustrate the processes of photosynthesis, respiration, and the bacterial decomposition of organic matter. They can show the importance of seasons and weather on these processes. The ways in which major rain storms and runoff affect the Bay are also seen in the data. Students can use the measurements for projects to enhance their understanding of physics, chemistry, and biology. They can explore different ways to examine the data graphically and numerically. They can develop ideas of how certain events are likely to affect the Bay and then test their expectations by seeing how the Bay responds. People who fish in the Bay will be able to see when the near-bottom temperatures and salinity (salt content) change favoring the migration of different types of fish into the Bay from offshore. The general public will find the changes in the Bay throughout the year and from one year to the next informative and useful.
      While the automated instruments are able to make frequent measurements over long periods and report their observations on an hourly or daily basis, there is a considerable amount of work required to assure that the data are reliable. The sensors must be calibrated periodically to correct for changes in their response to properties in the Bay. Biofouling occurs on the surface of the sensors, and this can change their ability to make valid measurements. This fouling is most rapid during the warm periods of the year. We need to service the instruments about once a week during the summer and about every two weeks during the rest of the year. For the buoys, this servicing is done by going out in a small boat to work on the instruments. There is also a significant amount of data analysis and management that must be done to make the results useful. We monitor the performance of the instruments on a daily basis. At times, the real-time data must be corrected for changes in sensor calibration. The data files need to be organized in ways that make them most useful for people to analyze and work with. The acquisition of the data can be automated, but skilled personnel are needed to maintain the system, track the quality of the measurements, and analyze and interpret the results.
      Our measurements at location 12 in the lower West Passage have been made since 1995 (see Fig. 4). We can see the differences from year to year in temperature, salinity, and phytoplankton blooms in this portion of the Bay. The summers of 1995 and 1999 had the warmest surface waters of recent years. The early summer of 1998 was unusual due to the large amount of freshwater input. The winter and summer of 2000 were the coolest of the past six years.
      The time-series data have revealed many aspects of the processes occurring in Narragansett Bay. They are useful in evaluating the importance of natural and anthropogenic influences in the Bay. Stratification of the waters occurs when the surface layer becomes less dense than the bottom waters. The input of freshwater from rivers, rain, or runoff and heating from solar radiation decrease the density of surface waters, thereby enhancing stratification. High winds, storms, and periods of large tidal amplitudes break down the stratification and mix the surface and bottom waters. We find that photosynthetic growth of algae and phytoplankton is greatest during periods of stratification. These conditions also lead to depletion of oxygen concentrations in the bottom waters. The amount of oxygen in the water is an important determinant of water quality. Low oxygen levels can make the waters and the sediments on the seafloor uninhabitable by fish, shellfish, and other organisms.
      This type of information will be used by scientists and environmental managers to understand the factors that affect the health of the Bay ecosystem. We will also be able to detect changes in water quality and identify ways in which we can sustain and enhance the resources of the Bay.