Diffusional nutrient fluxes at the sediment-water interface and organic matter mineralization in an atoll lagoon (Tikehau, Tuamotu Archipelago, French Polynesia)

Abstract

Fluxes of d~ssolved inorganic N, P and S1 from the sediments were calculated using pore water gradient concentration measured using the peeper technique at 8 stations in the lagoon of Tikehau Atoll, French Polynesia. Nutrient concentrations of pore water reached maximum values of 130 p M NH,, 7 p M PO, and 30 p M S102. Fluxes calculated from concentration gradients were positive at all stations. N and P fluxes represented 6 and 4 % of the N and P deposition rates and between 0.1 and 6.8 % of the N requirements and between 0.1 and 1.7 % of the P requirements of lagoonal primary production. Study of geochernical processes and stoichiometry of the organic matter shows that a great part of deposited organic matter is oxidized in the water column. The amount of organic matter oxidized inside the sediment is estimated to 2.5 mg kg-' in the upper centimeter and 5.2 mg kg" below. Pore water was supersaturated with respect to aragonite and calcite, and the kinetics of carbonate dissolution were faster than the reverse reaction. The dissolution/precipitation of carbonate plays an important role in the composition of the pore water