Dataset: Chlorophyll d15N in Lake Erie

Methodology:
Detailed sampling and analytical procedures can be found in the published paper (Kharbush et al. 2019). Briefly, nitrogen isotopes were measured in bulk organic matter and chlorophyll collected on 142mm GF/F filters (0.7 µm pore size), over the course of the summer harmful algal bloom in Lake Erie. δ15N values were corrected for a N blank originating from the HPLC solvent and from the oxidizing reagent, according to Higgins et al. (2009). Phytoplankton community composition was determined using a submersible FluoroProbe (bbe Moldaenke GmbH, Germany), which monitors in situ chlorophyll fluorescence. Isotope values were then compared with phytoplankton community composition.

Instrumentation details: 
A submersible FluoroProbe, manufactured by bbe Moldaenke GmbH, Germany, was used to monitor in situ chlorophyll fluorescence and to estimate algal community composition. Used with factory calibration settings. 

Chlorophyll was purified using an Agilent 1200 series HPLC equipped with multi-wavelength UV/Vis detector and two Zorbax C18 columns (dimensions 4.6 × 250 mm, 5 μm).

δ15N of chlorophyll was measured using the denitrifier method (Sigman et al., 2001), on a Delta V Advantage isotope ratio mass spectrometer with a custom built purge and trap system. Isotopic measurements were standardized to the N2 reference scale using standard reference materials IAEA N3 and USGS 34. 

δ15N of biomass collected on GF/Fs was analyzed on a Thermo Scientific Flash IRMS Elemental Analyzer with EA Isolink, coupled to a Delta V Advantage IRMS through a Conflo IV universal interface. Sample δ15N values were calculated using in-house laboratory standards as well as standard reference materials USGS40 and USGS41a.

Problems reported: For samples 6/17/2017, 6/27/2017, and 7/6/2017 no Fluoroprobe community data are available because of an issue with calibration.