Phytoplankton Monitoring

Plankton are drifting organisms or organisms with limited swimming ability present in the aquatic environment, in both fresh and salt water.  Plankton can be plants, called phytoplankton, or animals, called zooplankton.  Phytoplankton are microscopic and range in size from about 2 µm to 2 mm.  These organisms are the base of the food chain in waters throughout the world.  Phytoplankton, since they are plants, use sunlight and carbon dioxide to make food in a process called photosynthesis.  Plants and phytoplankton use chlorophyll to absorb the energy from the sunlight.  This allows scientists to measure chlorophyll levels and use this information as a proxy to estimate phytoplankton populations.  Since these organisms are the base of the food chain in the Bay, they are very important to the overall health of the Bay. 

The initial focus of the NBC plankton monitoring initiative is to collect data on the phytoplankton community in the upper Bay.  The NBC is collecting samples from the surface of the water at Bullock’s Reach water quality station.  The Bullock’s Reach station was selected as the plankton monitoring location because it is the site of one of NBC’s fixed site near real-time water quality monitoring stations.  With chlorophyll concentrations constantly monitored at the site, the NBC can collect routine planned samples, but also collect special sampling when chlorophyll concentrations escalate, indicating a phytoplankton bloom is present.  Routine phytoplankton samples are collected every two weeks, in conjunction with the collection of nutrient samples and water quality profiles (see the water quality monitoring page for more information on these programs). 

Two phytoplankton samples are collected on each of the sample days.  The NBC sampling procedure is based upon the methods utilized by the University of Rhode Island – Graduate School of Oceanography (  One of the samples is collected using a plankton net, which will be deployed at the surface for 30 minutes, while other water quality samples are being collected.  The plankton net captures the plankton floating at the surface and concentrates them in a sample bottle.  The other plankton sample is a whole water sample, again collected from the surface.  Back at the NBC laboratory, a sub-sample of the plankton net sample is reviewed under the microscope to identify all of the types of phytoplankton present in the sample.  From the whole water sample, a specific volume of water (1 mL) is examined under the microscope to determine the genus and number of each type phytoplankton present in the sample.  Through this complete analysis, the NBC will be able to track changes in the phytoplankton population and community structure as nutrient reductions occur in the upper Bay.  Also, through aligning the NBC methods with those of the University of Rhode Island – Graduate School of Oceanography, who collects data in the lower Bay, comparisons can be made between the phytoplankton variation in the Providence River and upper Bay with that present in the lower Bay.

The Providence River and upper Bay receives approximately 85% of the wastewater treatment facility effluent in Narragansett Bay (Oczkowski et al 2008).  With nutrient reduction facility upgrades underway at both NBC facilities, Field’s Point and Bucklin Point, it is presumable that the most measurable effects of the nutrient reductions would be present in this region.  Since phytoplankton are highly reliant on nutrients, it is unknown what effect these nutrient reductions in the Providence River estuary and upper Bay will have on the phytoplankton community.  This data will provide a valuable data set that will assist managers and researchers in determining the effects of the dramatic wastewater treatment facility nutrient reductions in the Providence River estuary. 

The NBC would like to thank the Rhode Island Bays, Rivers and Watersheds Coordination Team for their financial support to get this project running and Dr. Rynearson and her lab at the University of Rhode Island – Graduate School of Oceanography for their intellectual support of this project.

Data for the 2012 season will be posted in the near future.

Oczkowski, A., Nixon, S., Henry, K, DiMilla, P., Pilson, M., Granger, S., Buckley, B., Thornber, C., McKinney, R., Chaves, J.  2008.  Distribution and Trophic Importance of Anthropogenic Nitrogen in Narragansett Bay: An Assessment Using Stable Isotopes.  Estuaries and Coasts.  31:53–69.