Production and consumption of dimethylsulfide (DMS) and dimethylsulfoniopropionate (DMSP) in a diatom dominated intertidal sediment

Intertidal sediments usually contain a high amount of dimethylsulfoniopropionate (DMSP) and therefore represent environments with a potentially high emission of dimethylsulfide (DMS). However, knowledge on production and release of DMSP in intertidal sediments is limited. Here, we present data on the diel variation of the total DNIS and DMSP content (DMS[P](total)) and the DMS(P) concentration in the porewater (DMS[P](porewater)) in an intertidal sediment covered by diatoms. Measurements were made at low tide during the day and during the night. Both DNIS(P)(total) and DMS(P)(porewater) were constant and did not respond to the changing conditions of light and oxygen in the sediment, indicating that production and consumption processes were in equilibrium. Incubation of diatoms under light/oxic, dark/oxic and dark/anoxic conditions suggested that no large amounts of DMSP were excreted under the different conditions applied. DMS(P)(porewater) was around 100 nM, which was about 3 orders of magnitude lower than DMS(P)(total). Only after the onset of a heavy rainfall DMS(P)porewater in the sediment suddenly increased above 1 muM, which was explained by excretion of DMSP by DMSP-containing microorganisms in response to the osmotic shock. Both DMSP and DMS were rapidly degraded in sediment slurries, especially under oxic conditions, and degradation closely followed first order kinetics. We conclude that although intertidal sediments contain high total amounts of DMSP, a relatively low amount of DMSP is released by the microphytobenthos under naturally fluctuating light and oxygen conditions, and once released, DMSP and DNIS are rapidly degraded in the upper oxygenated sediment. This explains the low flux of DNIS from intertidal sediments to the atmosphere reported in the literature. [KEYWORDS: dimethylsulfoniopropionate (DMSP) dimethylsulfide (DMS), intertidal sediment, diatoms, degradation rates, Diel variation]