REMINERALIZATION VS REDUCTIVE DISSOLUTION PATHWAY OF PHOSPHORUS CYCLING: A CASE STUDY IN THE CHESAPEAKE BAY

Abstract:

Coastal hypoxia have spread exponentially worldwide due to increased anthropogenic loading of nutrients in coastal waters. Hypoxia exerts an influence on the stability of minerals and organic debris, direction of nutrient flux at the sediment-water interface, and the extent of benthic-pelagic coupling. This study aimed to address fundamental questions related to sediment phosphorus (P) dynamics in response to transient bottom water hypoxia particularly on P effluxes at the sediment-water interface and P burial (as authigenic/vivianite P) under two pathways: remineralization of organic P (coupled C−P pathway) and reductive dissolution of ferric Fe-bound P (coupled Fe−P pathway). Authigenic phosphate isotope data suggest that the regeneration of inorganic P in the sediment from organic matter degradation (remineralization) is the predominant, if not sole, pathway for authigenic P precipitation in the sediments. Interestingly, ferric Fe-bound phosphate oxygen isotopes are heavier than equilibrium. This means that the ferric Fe-bound P pool in these sediments is largely composed of particulate P from terrestrial sources composed primarily of Fe phyllosilicates plus potentially vivianite that are largely resistant against dissolution in the anoxic sediment column. These results collectively support the predominance of coupled C−P pathway of P cycling, rather than Fe−P coupling, in hypoxic environment in the Chesapeake Bay.