CHARACTERIZATION AND QUANTIFICATION OF DISSOLVED ORGANIC PHOSPHORUS IN AQUATIC SYSTEMS

The dissolved organic phosphorus (DOP) fraction of the marine phosphorus (P) pool has been recognized as a significant, biologically available source of P for phytoplankton. Yet an incomplete understanding of DOP composition and cycling has hindered efforts to understand nutrient limitation and its subsequent impacts on the marine food web. Recent work suggests the combined approach of electrodialysis (ED) and reverse osmosis (RO) is highly effective for isolating dissolved organic matter (DOM) from seawater and making it readily available for compositional analyses. However, the performance of ED/RO DOM isolation has not been specifically assessed for DOP. Our objectives were to determine any isolation bias for various DOP compounds and to confirm compositional integrity, post-isolation. Individual isolation experiments were conducted using estuarine seawater spiked with an individual, representative DOP compound (6 compounds chosen, covering a range of molecular size and mass/charge ratio) and isolated using ED/RO. High-resolution time-series measurements of total dissolved and soluble reactive phosphorus were taken to determine DOP recovery and mass balance over the course of desalting, concentrating, extracting, and cleaning stages. Similar measurements were taken for dissolved organic carbon and total dissolved nitrogen on a few number of experiments for DOM isolation comparisons. Nuclear magnetic resonance spectroscopy (³¹P NMR) was used to determine compound integrity following isolation. Near complete mass balance of DOP (96.5 +/- 15.30%) was calculated for the compound-specific experiments with moderately-high DOP recovery (66.1 +/- 8.23%). High-resolution sampling of the isolation process shows the majority of DOP being removed from the ED component during the final stages of ED/RO (~20%) and minimal residual DOP in ED (3.4 +/- 0.79), RO (2.8 +/-1.36), and RO permeate (0.9 +/- 0.65%) components.