Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
  • BCO-DMO Processing Description
• Data Files
• Supplemental Files
• Related Publications
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

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. 

The literature data reported here were obtained by digitizing the figures in the original papers using MATLAB R2020 and can only be considered approximations (except for Li et al. 2019, for which the original values are reported). In brief, data in scatter plots were digitized by referencing the the pixel locations of the data points to those of the coordinates (e.g., x and y axes) using linear interpolation; Values associated with color (e.g, data in colormaps) were obtained by referencing the RGB values of the data points to those of the colorbar using least square approximation.

Imported data from source file "GreatLakes_PolyP.xlsx" into the BCO-DMO data system.
- Corrected latitude and longitude values and site names

Imported supplemental file "GreatLakes_CTD.xlsx"
- Added sampling dates based on Site ID
- Renamed S-240 to S232 as they are same site location

Imported supplemental file "GreatLakes_Phytoplankton.xlsx"
- Rounded Biovolume and Biovolume_perind values to 2 decimal places
- Taxonomic names in the dataset were checked using the World Register of Marine Species (WoRMS) taxa match tool. Added WoRMS information (including AphiaID and source) to phytoplankton data.

NSF Award Abstract:
This project will study the effects of invasive zebra and quagga mussels on the biology and chemistry of the Great Lakes. These mussels have caused unprecedented changes to lake ecosystems, including large shifts in water quality, altered fisheries and diminished recreational opportunities. The mechanisms by which the invasion has affected ecologically important aspects of lake chemistry remain uncertain, making it difficult to predict future changes. This project will quantify how mussels affect sediment and water nutrient chemistry in Lakes Michigan and Huron. Important missing data on altered chemical exchange between sediments and water will be collected to quantify the processes controlling nutrient cycles in the Great Lakes as water moves to the coastal ocean. Development of improved numerical models from this work will allow evaluation of other freshwater and marine systems affected by similar mussel invasions and other stressors. The project will train a post-doctoral researcher and several graduate and undergraduate students in highly interdisciplinary research. Educators and the public at large will be served through creation of freely available, online multimedia content, as well as outreach events at the Duluth Great Lakes Aquarium, the Shedd Aquarium in Chicago, and the Discovery World Science Museum in Milwaukee.

Benthic communities can have large impacts on benthic-pelagic chemical exchanges, but the ecosystem-scale effects of benthos on coupled transformations of carbon, nitrogen, and phosphorus (C-N-P) are rarely addressed and virtually unquantified in freshwaters. The recent invasion of the Laurentian Great Lakes, the world's largest freshwater ecosystem, by dreissenid (zebra and quagga) mussels coincided with massive changes to ecology and water chemistry. Consequences of the invasion include a large and unexplained decline in phosphorus levels, enigmatic reversal of past trends in nitrate levels, and the near-disappearance of native bioturbating Diporeia amphipods. Modeling suggests that nutrient fluxes from sediments could have been strongly affected by shifts in benthic community. Mechanisms explaining these changes, however, remain obscure and thus hamper model predictions of future ecosystem trajectories. Researchers from the Large Lakes Observatory - University of Minnesota Duluth will determine the effects of established dreissenid populations on sediment geochemistry and nutrient dynamics in the Great Lakes by conducting detailed studies in dreissenid-invaded Lakes Michigan and Huron and dreissenid-free Lake Superior. A team of biologists and geochemists will (1) obtain field data to characterize sediment geochemistry of C-N-P, asses rates of biogeochemical processes, and dreissenid effects on chemical and physical properties of sediments, (2) conduct lab experiments to determine how functional traits of sessile dreissenids vs. burrowing Diporeia affect sediment characteristics and chemical fluxes, and (3) use reactive-transport and mass-balance models to understand the whole-lake geochemistry of carbon and nutrients in dreissenid-invaded lakes. This work will advance understanding of the ecology of the great lakes and generally improve models of sediment - water column interactions in aquatic ecosystems.