Aragonite saturation states and nutrient fluxes in coral reef sediments in Biscayne National Park, FL, USA

Some coral reefs, such as patch reefs along the Florida Keys reef tract, are not showing significant reductions in calcification rates in response to ocean acidification. It has been hypothesized that this recalcitrance is due to local buffering effects from biogeochemical processes driven by seagrasses. We investigated the influence that pore water nutrients, dissolved inorganic carbon (DIC) and total alkalinity (TA) have on aragonite saturation states (Ω_aragonite) in the sediments and waters overlying the sediment surfaces of sand halos and seagrass beds that encircle Alinas and Anniversary reefs in Biscayne National Park. Throughout the sampling period, sediment pore waters from both bottom types had lower oxidation/reduction potentials (ORP), with lower pH relative to the sediment surface waters. The majority (86.5%) of flux rates (n = 96) for ΣNO_x^–, PO₄^3–, NH₄⁺, SiO₂, DIC and TA were positive, sometimes contributing significant concentrations of the respective constituents to the sediment surface waters. The Ω_aragonite values in the pore waters (range: 0.18 to 4.78) were always lower than those in the overlying waters (2.40 to 4.46), and 52% (n = 48) of the values were