The Narragansett Bay Long-Term Plankton Time Series is one of the world's longest-running plankton surveys. Beginning in 1959, weekly samples have been collected to assess phytoplankton biomass with chlorophyll a and to characterize the chemical and physical parameters of Narragansett Bay (i.e., water temperature, salinity, chlorophyll a, silicate, phosphate, ammonium, nitrate/nitrite, water clarity, and light). Samples are collected once per week - regardless of tidal stage - for temperature, salinity, turbidity, chlorophyll a, and nutrients. This dataset provides weekly discrete surface concentrations for all parameters from 1959-2019 with support from the University of Rhode Island by the U.S. Department of Fish and Wildlife.

Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Data Files
• Related Publications
• Related Datasets
• Parameters
• Instruments
• Project Information
• Funding

Methodology:
Surface water temperature, salinity, chlorophyll a (chl a), silicate (SiO4), phosphate (PO4), ammonium (NH4), nitrate/nitrite (NO3/2), water clarity (Secchi depth) and light (irradiance) were collected weekly at the NBPTS location from 1959-2019.

The detailed methodology will be included in an upcoming manuscript: Thibodeau, P.S., Puggioni, G., Strock, J., Borkman, D., and Rynearson T.A., Using one of the world’s longest plankton time series to identify long-term changes in phytoplankton biomass and phenology. In prep, Target journal: Global Change Biology.

Sampling and analytical procedures:
Weekly surface water temperature and salinity were determined using a bucket sample. Total surface chl a was determined weekly at the NBPTS location from May 1968 to 2019, by filtering whole seawater over 25 mm diameter GF/F filters and measured fluorometrically using three protocols, either following Yentsch and Menzel (1963) as outlined in Li and Smayda (1998) after frozen storage at -20°C (1959-1997), or following Strickland and Parsons (1972) after frozen storage at -20°C (1997-2007), or following Graff & Rynearson (2011) with no filter storage (2008-2019). We expanded an existing, corrected chl a data set (1999-2007) (Graff & Rynearson 2011) by applying the same correction factor to historical chl a measurements (1968-1997) to account for pigment loss on frozen filters.

From 1959 to 2003, water samples for nutrients were collected with a plastic bucket and stored in 20 L polyethylene carboys until returned to the laboratory for analysis (within 90 minutes) (Furnas 1983) and then filtered through pre-rinsed GFC glass fiber filters (Furnas et al. 1976). Between 1969 and 1997, PO4, SiO4, and NO3 were determined via either manual colorimetric methods (Strickland & Parsons 1972) or automated colorimetric methods using a Technicon autoanalyzer following the methodologies of (Furnas et al. 1976; Furnas 1983) and references therein (Armstrong 1951; Grasshoff 1966; Wood et al. 1967). NH4 concentrations were determined via the Witting-Buch method (Barnes 1959) from 1972 to 1980.

Post 1980, NH4 measurements were made via automated colorimetric methods using an autoanalyzer following the methodologies of Furnas et al. (1976), Furnas (1983), and (Solórzano 1969). Since only surface NO3 data were available before 1994, and only surface NO3/2 data were available in 1995 & 1996, a correction factor of 1.04 was determined through regression analysis by comparing observed NO3/2 measurements from 2003 to 2019 with NO3 concentrations measured during the same period. Methods of analysis of PO4, SiO4, and NO3 from 1959 to 1963 were not described in the historic archives but were likely similar to methods used from 1969 to 1997 (colorimetric). From 2003 to 2019, surface nutrient samples for PO4, SiO4, NH4, and NO3/2 were collected weekly at NBPTS and kept on ice and filtered within one to three hours of collection.

Samples were run following Grasshoff (1976) for all nutrients as well as and EPA Method 353.4 for NO3/2, EPA Method 365.3 for NH4, EPA Method 365.5 and Murphy and Riley (1962) for PO4, and Parsons et al. (1984) for SiO4. Light, measured as irradiance (W m-2), was collected weekly at NBPTS from 1959 to 1996. Photosynthetically active radiation (PAR) data were obtained from the National Estuarine Research Reserve, Narragansett Bay station (41° 38.22’ N, 71° 20.34’ W) (http://cdmo.baruch.sc.edu/) to provide light data from 2003 through 2019. A conversion factor (2.1) was used to convert irradiance (W m-2) data from 1959 to 1996 into comparable data in the form of µmol m-2 s-1 (Sager & McFarlane 1997). Secchi depth (i.e., water clarity) was measured weekly at NBPTS from 1972 to 1996 and then again from Dec. 2003 through 2019.

No data were collected for the following parameters during the following years:
- Temperature: 1997-1999; 2012
- Salinity: 1964-1970; 1997-1999; 2012
- Secchi Depth: Collection did not begin until 1972, 1997-2003; 2012
- Light: 1997-2003
- Phosphate: 1964-1970; Biweekly or no sampling 1988; Biweekly sampling only 1990-1993; 1997-2003
- Ammonium: Collection did not begin until 1972; Biweekly or no sampling 1988; Biweekly sampling only 1990-1993; 1997-2003
- Nitrate/nitrite: 1963-1970; Biweekly or no sampling 1988; Biweekly sampling only 1990-1993; 1997-2003
- Silicate: 1964-1970; Biweekly or no sampling 1988; Biweekly sampling only 1990-1993; 1997-2003; 2010-2013
- Chlorophyll: Collection did not begin until 1968; 1970-1971; Biweekly sampling only 1990-1994; 1995-1999; 2012

Data Processing:
Data processed via Excel Version 2202 and R Version 4.1.2.

BCO-DMO Processing:
- renamed fields to comply with BCO-DMO naming conventions;
- replaced "NA" with "nd" (no data);
- rounded all numeric fields to the 100th decimal position (0.00).

Website: https://web.uri.edu/gso/research/plankton/

The Narragansett Bay Long-Term Plankton Time Series is one of the world’s longest-running plankton surveys. Beginning in 1957, weekly samples have been collected to assess the phytoplankton community and characterize the physical parameters of Narragansett Bay.

Samples are collected once per week -regardless of tidal stage- for temperature, salinity, turbidity, size-fractionated chlorophyll a and nutrients. Microplankton community composition (size range >10μm, both species identification and abundance) is determined using a light microscope to quantify live samples. The species list for the >10μm size fraction includes 246 different species or species complexes of protists. Samples are also collected for the determination of copepod and ctenophore concentrations.

Funding for the time series has come from the University of Rhode Island since 1999. Ship time is frequently provided by the U.S. Department of Fish and Wildlife.

This Time Series is related to the following projects at BCO-DMO:

• Connecting local, regional and global scales of gene flow in planktonic marine diatoms (https://www.bco-dmo.org/project/511708)
• Dimensions: Collaborative Research: Genetic, functional and phylogenetic diversity determines marine phytoplankton community responses to changing temperature and nutrients (https://www.bco-dmo.org/project/712787)
• LTER: Linking Pelagic Community Structure with Ecosystem Dynamics and Production Regimes on the Changing Northeast US Shelf (https://www.bco-dmo.org/project/747769)
• Quantifying Temperature Dependence In Growth & Grazing Rates of Planktonic Herbivores (https://www.bco-dmo.org/project/739232)
• RII Track-1: Rhode Island Consortium for Coastal Ecology Assessment, Innovation, and Modeling (https://www.bco-dmo.org/project/836631)