2 research outputs found
Synthesis and Detection of Oxygen-18 Labeled Phosphate
Phosphorus (P) has only one stable isotope and therefore tracking P dynamics in ecosystems and inferring sources of P loading to water bodies have been difficult. Researchers have recently employed the natural abundance of the ratio of 18O/16O of phosphate to elucidate P dynamics. In addition, phosphate highly enriched in oxygen-18 also has potential to be an effective tool for tracking specific sources of P in the environment, but has so far been used sparingly, possibly due to unavailability of oxygen-18 labeled phosphate (OLP) and uncertainty in synthesis and detection. One objective of this research was to develop a simple procedure to synthesize highly enriched OLP. Synthesized OLP is made up of a collection of species that contain between zero and four oxygen-18 atoms and, as a result, the second objective of this research was to develop a method to detect and quantify each OLP species. OLP was synthesized by reacting either PCl5 or POCl3 with water enriched with 97 atom % oxygen-18 in ambient atmosphere under a fume hood. Unlike previous reports, we observed no loss of oxygen-18 enrichment during synthesis. Electrospray ionization mass spectrometertry (ESI-MS) was used to detect and quantify each species present in OLP. OLP synthesized from POCl3 contained 1.2% P18O16O3, 18.2% P18O216O2, 67.7% P18O316O, and 12.9% P18O4, and OLP synthesized from PCl5 contained 0.7% P16O4, 9.3% P18O316O, and 90.0% P18O4. We found that OLP can be synthesized using a simple procedure in ambient atmosphere without the loss of oxygen-18 enrichment and ESI-MS is an effective tool to detect and quantify OLP that sheds light on the dynamics of synthesis in ways that standard detection methods cannot
Understanding phosphorus mobility and bioavailability in the hyporheic zone of a chalk stream
This paper investigates the changes in
bioavailable phosphorus (P) within the hyporheic
zone of a groundwater-dominated chalk stream. In
this study, tangential flow fractionation is used to
investigate P associations with different size fractions
in the hyporheic zone, groundwater and surface
water. P speciation is similar for the river and the
chalk aquifer beneath the hyporheic zone, with
âdissolvedâ P (<10 kDa) accounting for ~90% of
the P in the river and >90% in the deep groundwaters.
Within the hyporheic zone, the proportion of
âcolloidalâ (10 kDa) and âparticulateâ
(>0.45 ÎŒm) P is higher than in either the groundwater
or the surface water, accounting for ~30% of
total P. Our results suggest that zones of interaction
within the sand and gravel deposits directly beneath
and adjacent to river systems generate colloidal and
particulate forms of fulvic-like organic material and
regulate bioavailable forms of P, perhaps through coprecipitation
with CaCO3. While chalk aquifers
provide some degree of protection to surface water
ecosystems through physiochemical processes of P
removal, where flow is maintained by groundwater,
ecologically significant P concentrations (20â30 ÎŒg/L)
are still present in the groundwater and are an
important source of bioavailable P during baseflow
conditions. The nutrient storage capacity of the
hyporheic zone and the water residence times of this
dynamic system are largel