Short-term variability in biogenic sulphur emissions from a florida spartina alterniflora marsh

am44981/%7 s3.00 +o.oo Q 1987 Paganon Journals Ltd. ~~narpkrfc Emironnrnt Voi. 21, No. I. pp. 7-12. 1987 Rimed in Greal Eritrin. SHORT-TERM VARIABILITY IN BIOGENIC SULPHUR EMISSIONS FROM A FLORIDA SP~~~~~~ ~~~~~~~F~O~~ MARSH DE MELLO, WILLIAM J. COOPER*, ROD G. ZIKA, ERIC S. SALTZMAN, JOSEPH M. PROSPERO and DENNIS L. SAVOIE Rosenlo~l University, Miami, Florida 33199, U.S.A. DAVID J. COOPER, WILLIAM 2. (First received 18 November 1985 and infinaljorm 2’7 June 1986) Abstract -Emissions of biogenic sulphur gases from a Florida Sparrina ulfernifloru zone were measured over several tidal and diel cycles using a dynamic flow chamber technique, corroborating recently published i~or~tion in the literature. The flux of hydrogen sulfide from individuaf measurements is shown to vary by over four orders of magnitude, and correhtes primarily with the stage of the tidal cycle. In contrast, the fluxes ofdimethyt sulphide, carbon disulphideand dimethyl disulphide vary by less than an order of magnitudeand correlate primarily with !he diurnal temperature changes in the sediment surface. These diflerences are discussed in terms of the various biological and physical parameters which may regulale the release of reduced sulphur compounds to the atmosphere. Key word index: Bioaenic sulphur emissions, salt marshes, hydrogm sulphide, dimcthyl sulphide, carbon the effect of physical parameters such as tidal inund- ation (Aneja, 1984) and temperature (Hansen et al., 1978). In this paper, we present flux measurements of four reduced S gases which were measured at three different en~ronments within a Spurt~nu u~~er~i~~ra zone on the Gulf coast of Florida. The fluxes of hydrogen sulphide (H2S), dimethyl sulphide (DMS), carbon disulphide (CS,) and dimethyl disulphide (DMDS) are assessed in terms of the relative import- ance of tidal and die1 cycles. INTRODUCTION Rexxnt studies on the problem of acid precipitation have focused largely on the biogeochemical cycling of SuIphur~on~ining ~om~unds. The cont~bution of biogenic reduocd S gases to the atmospheric S burden has been and remains an area of major concern (Marouiis and Bandy, 1977; Adams et al., 1981; Aneja er al., 1981; Cline and Bates, 1983; Andreae and Raemdonck, 1983; Steudler and Peterson, 1984). Oxi~tion of these com~unds leads to the formation of sulphate, which is precipitated as sulphuric acid in rainwater. Tidally influenced marine sediments and salt marshes are a major source of atmospheric H2S (Georgii. 1977; Hansen er al., 1978; Jaeschke et al., 1980; lngvorsen and Jg Aneja. 1984; Will er a/., 1978) as a result of anaerobic bacterial sulphate reduction and decomposition of organic material. Salt marshes have also been shown to be a major source of organosulphur compounds (Adams et al., 1981; Aneja et 01.. 1981; Steudler and Peterson, 1984). The range of reported emission rates is large, and extreme variability at a given sampling site is often found. Consequently, estimates of the annual emissions of H2S and or- ganosulphur compounds are still very uncertain, and are, in fact, the major holdback in attempts to ac- curately quantify the atmospheric S cycle. The spatial and temporal emission patterns of biogenic S compounds reflect the combined effect of numerous biological and physical parameters. Different metabolic pathways produce di#Terent S compounds (Aneja, 1984). and the ultimate release to the atmosphere may depend on both the emciency of remineralization processes (Hansen et al., 1978) and EXPERIMENTAL Study site Emission measurements were made on M-17 May and 7-8 October 1985at St. Mark’s National Wildlife RcJuge,Florida, U.S.A. (Fig. I). A stand of short Sparrina u~rer~~or~ (30-50 cm tali) extended about IS m below the high tide mark. The substrate was fine-grained quartz sand with an organic content of =z 1%. Measurements were made at three different locations; over the S. ahem$ora. on bare sand adjacent to S. alremiflora, and on exposed mudflats below the S. crlrernilyora stand. Sediment temperatures ranged from 23”Cat night to 36°C in the early afternoon in May.and from I9 to 29-C in October. The tidal range was 80-100 cm, exposing about 100 m of mud Rats. The anaerobic zone in the sand, evidenced by black colouration, with the characteristic odour of HIS, WBS typically less than 2 cm below the surface, and occasionally broke the surJace. The depth of this anaerobic region was observed 10 be much deeper within the S. altern#foru stand @@tally 5-10 cm). Emission maasunments were made using a polycarbonate chamber (30.5 cm diameter x 30.5 cm height) lined with a thin film of FEP Teflon. Design and construction of the chamber was similar to Adams er al. (1980), and is described in more