NH 4+ turnover in intertidal sediments of Marennes-Oléron Bay (France): effect of sediment temperature

Abstract

NH 4 + turnover plays an important role in benthic compartment as source of nutrient for primary production. The intertidal mudflats of the Marennes-Oléron Bay are characterized by high fluctuations of sediment temperature that generally ranges from 10 to 30 °C during emersion periods. Influence of sediment temperature on NH 4 + processes was investigated. Gross ammonification and NH 4 + incorporation kinetics were studied using the 15N isotope dilution method. The method was first adapted to these very fine sediments and applied to 2 upper sediment layers (0–2 and 2–4 cm) at different incubation times of up to 120 h. The effect of sediment temperature on gross ammonification and NH 4 + incorporation rates was investigated at 10, 20 and 30 °C. There was a strong increase of both rates as a function of temperature, gross ammonification rates ranged from 0 to 17 μg NH 4 +-N.g –1 dw.d –1 and NH 4 + incorporation rates from 2 to 13 μg N.g –1 dw.d –1 between 10 and 30 °C. This study showed that short-term temperature variations during the emersion period should be taken into account in quantifying NH 4 + turnover in intertidal sediments and that benthic regeneration of NH 4 + significantly supports benthic and planktonic primary production in Marennes-Oléron Bay. It suggests also that there is no N-limitation for benthic primary production in this bay and that there is up to 44 % of NH 4 + produced in surface sediments, which can diffuse to the water column and become available to phytoplankton.