Bedeutung gasfoermiger Komponenten an den Grenzflaechen Sediment/Atmosphaere und Wasser/Atmosphaere

Abstract

As a contribution to the SWAP-Project the trace gas fluxes of the three macro elements nitrogen (NO, NO_2, N_2O), carbon (CO_2, CH_4) and sulfur (H_2S, COS, CH_3SH, DMS, CS_2) between the Wadden Sea and the atmosphere were analyzed. The measuring program was designed to determine the spatial and temporal variations of the gaseous C-, N- and S-fluxes. The quantification of atmospheric trace gasfluxes is an essential part to calculate the element balance of the Wadden Sea. The trace gas fluxes were investigated by conducting eleven measuring campaigns between August 1990 and September 1994. Measurements were performed at representative sites mainly in different sediments of the Koenigshafen but also in a wider range of the Sylt-Roemoe tidal flat area. The in situ-fluxes of the different trace gases were determined by using static and dynamic chamber techniques focussing on dry sediment periods. Additional experiments were performed in order to determine gas-concentrations in the sea water (S-gases) as well as in the sediment between the surface and 70 cm depth (S-gases, CH_4). The transfer rates of gaseous nitrogen compounds between the Wadden Sea and the atmosphere were of minor importance compared to the exchange of CO_2 and reduced S-gases. Nevertheless the occurrence of seagrass and green-algal mats caused a distinct increase of the N_2O-fluxes. Highest flux rates between the sediment and the atmosphere were demonstrated for CO_2. The generally observed diurnal cycle of CO_2-exchange (deposition during the daytime and a release from the sediment during nighttime) reflected the amplitude of photosynthetic primary production as well as the respiratory activities of the organisms present in or above the sediment. As found for N_2O-transfer there was only low emissions of CH_4 from uncovered sediment areas, but relatively high CH_4-emissions (up to 90 fold) were found in seagrass beds or green algal-mats. In most cases H_2S was the dominant gaseous sulfur compound emitted from the sediment to the atmosphere, contributing up to 77% of the total S-emission at this interface. The comparison of H_2S-emission and the corresponding sulfur reduction rates showed that depending on season and sediment type between 1600 and 26000 times more H_2S was produced than emitted. These findings demonstrate the efficiency by which sediments retain the H_2S produced during sulfate reduction, and indicate a high H_2S consumption by biological and chemical sediment processes. During the submersion period DMS was, in contrast to the gas exchange between the sediment/atmosphere interface, the predominant S-compound emitted to the atmosphere contributing 40% to 93% to the total S-emission. In summary, the increased input of organic material to the Wadden Sea and the resulting ecological changes like increase of anaerobic sediment areas or increasing green algal mats result in increasing emission rates of different trace gases like N_2O, CH_4, H_2S and with respect to green algae also of DMS. (orig.)SIGLEAvailable from TIB Hannover: F96B1244+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman