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Abstract A mechanistic understanding of dissolved organic phosphorus (DOP) utilization, and its role in the marine P cycle, requires knowledge of DOP molecular composition. In this study, a recently developed approach coupling electrodialysis and reverse osmosis with solution31P‐NMR analysis was used to examine DOP composition within a tidally dominated salt‐marsh estuary (North Inlet, South Carolina) over seasonal and tidal time frames. The isolation technique allowed for near complete recovery of the DOP pool (90% ± 13%;n= 12) with six broad compound classes quantified: phosphonates, phosphomonoesters, phosphodiesters, pyrophosphate, di‐ and tri‐phosphate nucleotides (nucleoPα), and polyphosphate. Our results indicate that phosphomonoesters (ca. 61%) and phosphodiesters (ca. 31%) comprise the majority of the DOP pool, with relatively small contributions from pyrophosphates (ca. 4%), phosphonates (ca. 2%), nucleoPα(ca. 1%), and polyphosphates (ca. 1%). The study found no significant differences in DOP composition or concentration between tidal stages, despite significant tidal changes in dissolved organic nitrogen (DON):DOP stoichiometry. Significant seasonal variation was observed, with higher concentrations of phosphonates, nucleoPα, and monophosphates and lower phosphomonoester concentrations in Fall relative to all other seasons. We hypothesize that these seasonal variations reflect the balance between specific compound class seasonal production, lability, and local P demands associated with marine vs. terrestrial sources. Our results indicate that DOP composition exists at a dynamic equilibrium that is strongly conserved across diverse marine environments.
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Dissolved organic phosphorus molecular weight fractionation and apparent bioavailability quantified via coupled sequential ultrafiltration and enzyme hydrolysis
Abstract Aquatic organisms utilize dissolved organic phosphorus (DOP) when phosphate levels are insufficient to satisfy their P‐demand. Its critical role in supporting primary production has motivated efforts to characterize DOP composition and gain insight into its bioavailability.31P nuclear magnetic resonance (31P‐NMR) spectroscopy, the principal tool currently used by aquatic geochemists to identify compositional aspects of the bulk marine DOP pool, has provided limited compositional detail beyond the immediate P‐bonding environment, and does not provide quantitative information on potential bioavailability of DOP. As a result, the DOP pool remains poorly characterized, limiting predictive power relative to DOP bioavailability. We have developed a sequential ultrafiltration (SUF) method to segregate the DOP pool into four distinct molecular weight ranges. The concentrated molecular weight fractions are then incubated with phosphohydrolytic enzymes to determine the potential bioavailability of monoester‐ and diester‐bound P. DOP molecular weight segregation was verified using commercially available DOP compounds of known molecular weight as analogues for naturally occurring DOP. We have applied the SUF method to surface water samples from a nearshore transect in Kāne'ohe Bay, Hawai'i, and surface waters from oligotrophic Station ALOHA (Hawai'i Ocean Time Series). Results of these field tests indicate that the coupled SUF‐bioavailability method reveals greater compositional complexity of the marine DOP pool than has been resolved by31P‐NMR studies. Notably, the SUF‐bioavailability method does not require expensive, technically complicated instrumentation (e.g.,31P‐NMR), and thus is readily accessible to researchers wishing to probe marine DOP composition who do not have access to or expertise in31P‐NMR.
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- PAR ID:
- 10369669
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Limnology and Oceanography: Methods
- Volume:
- 20
- Issue:
- 8
- ISSN:
- 1541-5856
- Page Range / eLocation ID:
- p. 467-481
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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