Solid-phase phosphorus pools in highly organic carbonate sediments of northeastern Florida Bay

Currently, few studies have investigated sediment phosphorus (P) pools or i dentified the chemical processes important in the P cycle of fine-grained c arbonate sediments, particularly in coastal estuaries with high organic mat ter. To determine the role of fine-grain calcium carbonate and high organic matter on sedimentary P, we investigated the solid-phase P pools in seagra ss sediments of north-eastern (NE) Florida Bay at the Bay-mangrove ecotone. Sediments were fractionated by sequential extractions into seven chemicall y-defined,groups: exchangeable inorganic and organic P, reducible inorganic and organic P (Fe-bound), acid extractable inorganic and organic P (Ca-bou nd), and residual organic P. Calcium-bound P accounted for approximately 56 % of total P and 96% of inorganic P. Our total calcium-bound P was in the r ange (34-151 mug P g(-1)) reported for coarse-grained low organic sediments , while the organic P associated with this fraction was slightly (similar t o 10%) higher than those reported for other carbonate systems. The second d ominant P fraction was residual organic P (30-71 mug P g(-1)) accounting fo r 42% of TP. This high residual pool suggests the importance of fringing ma ngrove and seagrass detritus in long-term P storage. In contrast to tempera te estuaries, the iron-bound P fraction in NE Florida Bay sediments was low (< 70 <mu>g g(-1)) at the surface and undetectable (< 1 <mu>g g(-1)) below 10 cm. Based on our findings, we hypothesize that carbonate chemisorption reactions, along with potential reactive organic surfaces, and the sequeste ring of P into recalcitrant organic pools, maintain low exchangeable and po rewater P concentrations across the NE Florida Bay estuary, and account for the reported autotrophic P-limitation. (C) 2001 Academic Press.