Dataset: Polyphosphate and associated measurements from water and particulate samples collected from 13 locations in the Great Lakes in July-Aug 2018 on R/V Blue Heron cruise BH18-09

Water samples were collected using Rosette Niskin bottles attached to a Seabird 911plus conductivity-temperature-depth probe (CTD), which also profiled temperature, oxygen, light transmission, and chlorophyll (Chl-a) concentrations. Suspended particles in the water were collected by filtering water through various sizes of filters (0.2 μm and 2.0 μm polycarbonate membrane filters and 0.7 um GF/F). Particulate carbon and nitrogen (PC and PN) were analyzed by using an Elemental Analyzer on the particles collected on the 0.7 μm GFF that have been pre-combusted at 550°C for 6 hours. Particulate phosphorus (PP) was quantified using the persulfate digestion and molybdenum blue method (Suzumura 2008, Grasshoff et al. 1999). Soluble reactive P (SRP) in the water column was also measured using the molybdenum blue method (Grasshoff et al. 1999).

Chl-a was extracted from the 0.2 μm filters using 90% acetone for 12 hours at 4°C in the dark after homogenization and sonication, and determined for Chl-a fluorometrically at an excitation wavelength of 430 nm and an emission wavelength of 663 nm (APHA 1998).  Alkaline phosphatase activity (APase) was determined using a fluorogenic substrate 3-O-methylfluorescein phosphate (MUF-P) (Martin et al. 2018). PolyP in the particles was extracted using an enzyme digestion and boiling method for marine plankton (Martin and Van Mooy 2013). Extracted PolyP was stained using 4’,6-diamidino-2-phenylindole (DAPI) and fluorometrically quantified (Aschar-Sobbi et al. 2008; Diaz et al. 2010). We also used a polyP-specific dye JC-D7 (InvivoChem, USA, # V22869, 87% purity) to quantify polyP (Angelova et al. 2014): the polyP extracts were stained using JC-D7 (25 μmol L-1) dissolved in 5% DMSO buffered with HEPES solution (pH = 7.4, 25 mmol L-1), and quantified for polyP concentrations by measuring fluorescence intensity at an excitation wavelength of 405 nm and an emission wavelength of 535 nm. The colorimetric and fluorescence measurements were conducted using a BioTek microplate reader.

PolyP data from other aquatic ecosystems (lakes and oceans) reported in the literature are also included in the dataset for comparison (Diaz et al. 2016, Hashihama et al. 2020, Li et al. 2019, Martin et al. 2014, Martin et al. 2018). The literature data were obtained by digitizing the figures in the original papers and can only be considered approximations (except for Li et al. 2019, for which the original values are reported).

The data for phytoplankton abundance were originally reported in the Great Lakes Environmental Database (GLENDA) by the US Environmental Protection Agency Great Lakes National Program Office (EPA GLNPO; https://cdx.epa.gov/; Barbiero et al. 2018). In the GLENDA dataset, phytoplankton were identified to species or the lowest practical taxonomic level, counted, and estimated for biovolume (µm³ mL-1) for each identified species using the Utermöhl technique and the EPA Standard Operating Procedure for Phytoplankton Analysis (LG401). We extracted data from stations near our sites and only analyzed the data collected in the summer (August) for the past five years (2014-2019). Biovolume and biovolume per individual cell were averaged for each species identified. The GLENDA phytoplankton data were collected as part of a grant to Euan Reavie from the U.S. Environmental Protection Agency under Cooperative Agreements GL-00E23101 and GL-00E0198. Our data treatment and this document have not been subjected to the EPA’s required peer and policy review and do not reflect the view of the Agency, so no official endorsement should be inferred.