Seasonal dynamics of microbial sulfate reduction in temperate intertidal surface sediments: controls by temperature and organic matter

Abstract

The role of microbial sulfate reduction on organic matter oxidation was studied quantitatively in temperate intertidal surface sediments of the German Wadden Sea (southern North Sea) on a seasonal base in the years 1998-2007. The sampling sites represent the range of sediments found in the back-barrier tidal area of Spiekeroog Island: sands, mixed and muddy flats. The correspondingly different contents in organic matter, metals, and porosities lead to significant differences in the activity of sulfatereducing bacteria with volumetric sulfate reduction rates (SRR) in the top 15 cm of up to 1.4 μmol cm −3 day −1 .Depth-integrated areal SRR ranged between 0.9 and 106 mmol m −2 day −1 , with the highest values found in the mudflat sediments and lower rates measured in sands at the same time, demonstrating the impact of both temperature and organic matter load. According to a modeling approach for a 154-km 2 large tidal area, about 39, 122, and 285 tons of sulfate are reduced per day, during winter, spring/ autumn, and summer, respectively. Hence, the importance of areal benthic organic matter mineralization by microbial sulfate reduction increases during spring/autumn and summer by factors of about 2 and 7, respectively, when compared to winter time. The combined results correspond to an estimated benthic organic carbon mineralization rate via sulfate reduction of 78 g C m −2 year −1 .

Imprint of past and present environmental conditions on microbiology and biogeochemistry of coastal Quaternary sediments

“…Modeled net sulfate reduction rates from pore water sulfate profiles are ten to hundred times lower compared to gross rates reported for highly active surface sediments in the study area (Al-Raei et al, 2009;Beck et al, 2009). Modeling the top 6 m of core JS-A and the top 2.7 m of core JS-B yields depth-integrated sulfate reduction rates of 0.1 and 0.3 mmol m −2 d −1 , respectively (considering a pelagic sulfate concentration of 26 mM).…”

“…The studies focused on surface sediments (e.g. Böttcher et al, 2000;Llobet-Brossa et al, 2002;Billerbeck et al, 2006;Al-Raei et al, 2009;Jansen et al, 2009) as well as on deeper sediment layers down to 5 m below the seafloor (mbsf) (e.g. Köpke et al, 2005;Wilms et al, 2006b;Beck et al, 2008b;Gittel et al, 2008;Røy et al, 2008).…”

Increased temperature causes different carbon and nitrogen processing patterns in two common intertidal foraminifera (<i>Ammonia tepida</i> and <i>Haynesina germanica</i>)

“…The temperatures chosen for this experiment correspond to experimentally determined values that cover optimum or tolerance ranges of physiological processes in intertidal foraminifera (Bradshaw, 1957(Bradshaw, , 1961Lee and Muller, 1973). Further, they lie in the range of seasonal and diurnal temperature amplitudes measured on intertidal surface sediments close to the sampling area (Al-Raei et al, 2009). Simulated variations in temperature were assumed to influence the food uptake efficiency of the species due to potential temperature stress.…”

Functioning of intertidal flats inferred from temporal and spatial dynamics of O2, H2S and pH in their surface sediment

“…Aerobic respiration could not drive the pH down and induce a pH minimum due to the very high DIC levels in the seeps that, at pH 7, act as an effective pH buffer. DIC reached concentrations up to or even exceeding 20 mM in the seep fluids and less than 5 mM DIC in the pore water of central areas (Billerbeck et al 2006b;Al-Raei et al 2009). Carbon isotope measurements indicate that the oxidation of methane contributes significantly to the enhanced DIC contents at the seeps (Böttcher et al 2007).…”

“…As the skin circulation efficiently drives infiltration and mineralisation of dissolved organic carbon (DOC) and particulate organic carbon (POC), it promotes high primary productivity. The deep circulation and anaerobic degradation processes produce a sulphate-depleted and methane-enriched plume under the tidal flat surface (Beck et al 2008), and (the development of) sulfidic and nutrient-rich seeps at the low water line (Billerbeck et al 2006b;Al-Raei et al 2009). How the organic material is transported from the sediment surface to a depth of several metres in the tidal flat needs further investigation.…”