Dataset: PP Bioassay Experiments

Sampling and analytical procedures:

Bioassay experiments were conducted at station 1 and stations 3. At each station, inorganic and organic phosphate amendments were performed on seawater with and without nitrogen enrichment  (NH4Cl, NaNO3). Bioassay Experiments consisted in incubating, over an incubation period of 48h, surface seawater (5m) with inorganic or organic phosphate compounds (20 µM; final concentration of P) including, polyphosphate (polyp), inorganic phosphate (Pi), nucleotides (ATP or AMP) and methylphosphonate (Mepn). In each incubation experiment, a control treatment (surface seawater without amendment) was included.

In bioassay experiments, subsamples were taken for particulate phosphate (PP, 50 mL) from each experimental incubation bottle and then filtered through pre-combusted (450°C, 4.5 h) and acid washed (1N HCl) GF/F syringe filters (25 mm). PP filters were wrapped in pre-combusted (450°C, 4.5 h) aluminum foil, and kept frozen (-20°C) until analysis. PP concentrations were determined after high-temperature combustion (450°C, 4.5 h) and HCl extraction (0.5 N) (Strickland and Parsons, 1972). This method relies on the release and the subsequent extraction of organically bound P compounds as SRP. SRP was then analyzed spectrophotometrically using a conventional spectrophotometer (10 cm cuvette). The efficiency of the procedure was tested on apple leaves (standard reference material 1515) and resulted in a yield of 83±19% (n=20).

Instrument: Measurements of PP were performed using a conventional spectrophotometer (Genesys®,10 cm cuvette) after a high temperature combustion (450°C, 4.5h).

Location:  Northwestern Atlantic surface waters. Depth: surface-50 m.