Phosphorus release with carbonate dissolution coupled to sulfide oxidation in Florida Bay seagrass sediments
Limnol. Oceanogr., 54(5), 2009, 1753-1764 | DOI: 10.4319/lo.2009.54.5.1753
ABSTRACT: We hypothesized that CaCO3 dissolution, coupled to sulfide oxidation, is an important mechanism by which solid-phase inorganic P (iP) becomes available to seagrass in tropical carbonate sediments. To examine this supposition, we measured field sulfate reduction rates and simulated the acidity (10-50 µmol H2SO4 cm-3 sediment) generated by subsequent sulfide oxidation from high (western) and low (eastern) total P (TP) sediments in Florida Bay. Dissolution experiments were conducted using sediment slurries at field pH (pore-water pH ~6.5-7.5). While CaCO3 dissolution (maximum 1.3% of sediment dry weight) was evidenced at all sites by leaching of Ca2+ into slurries, at three of the four sites PO43- was primarily recovered in the sediment exchangeable pools and at a lower P : Ca ratio than observed in source sediments. In contrast, no PO43- was recovered from an eastern bay site with the lowest TP and finest-grained sediments, suggesting that PO43- was either tightly adsorbed or incorporated into the carbonate matrix post-acidification. The potential for tight PO43- resorption by sediment from the low-TP site was also supported by the rapid rate of isotopic exchange of 33PO43- into the sediment matrix. These adsorptive and incorporation processes may explain the low PO43- in pore waters in the eastern vs. western regions of Florida Bay, even upon dissolution of carbonates. Carbonate dissolution coupled to sulfide oxidation could potentially provide 1.8 and 23.5 µmol iP m-2 d-1 at eastern and western bay sites, respectively, meeting 5% of eastern and 29% of western bay seagrass (Thalassia testudinum) P requirements.