Quantification of macrobenthic effects on diagenesis using a multicomponent inversemodel in salt marsh sediments

Abstract

Using a multicomponent inverse model, we quantified the rates of organic matter (OM) remineralization and the relative importance of major terminal electron acceptors [Fe(III)-(oxy)hydroxides and SO ] in salt marsh sediments 2Ϫ 4 with varying degrees of bioturbation and vegetation at Skidaway Island, Georgia. The model determined the rates of OM diagenesis by seeking simultaneous agreement between measured and model-calculated depth-concentration profiles of multiple major redox species while using the biological transport parameters determined from direct field observations. The OM degradation rates are found to be greater and penetrate deeper in sediments with vegetation or bioturbation than in sediments with limited macrobenthic components, in which organic matter degradation is restricted to the immediate vicinity of water-sediment interface. The results also confirmed previous observations that Fe(III)-(oxy)hydroxides are much more important than sulfate as terminal electron acceptors in the heavily bioturbated station and provided the numerical values to the depth-dependent relative importance. Solid-phase Fe is recycled as a terminal electron acceptor Ն30 times in the bioturbated station, because biological mixing repeatedly moves reduced Fe(II) back into the aerobic environment, where it is reoxidized to form Fe(III)-(oxy)hydroxides and is reused as a terminal electron acceptor. Vegetation appears to have little influence on net solute transport, but it stimulates microbial activities and significantly enhances the remineralization of OM at depths.

Effects of the dominant SW Atlantic intertidal burrowing crab Chasmagnathus granulatus on sediment chemistry and nutrient distribution

“…To quantify the rates and pathways of OM remineralization, the 1-dimensional inverse diagenetic model formulated by Furukawa et al (2004) was applied to the Mar Chiquita sediments using the experimental depth profile data. The inverse model determines OM degradation rates by searching for simultaneous agreement between measured and model-calculated depth profiles of electron acceptor concentrations.…”

“…For this estimate, radial O 2 concentration was calculated from Eh and pH radial profiles. All pore water species were assigned the same α. Molecular diffusion coefficients at infinite dilution D O were taken from Furukawa et al (2004) and corrected for sediment porosity ϕ (see Table 1). Model calculations were performed using 100 sets of randomized initial values for OM degradation rate (for each C+B, B and NBC treatment) to ensure that optimization leads to a global minimum.…”

Natural-abundance radiocarbon as a tracer of assimilation of petroleum carbon by bacteria in salt marsh sediments

“…Among these, iso-and anteiso-branched monoenoic and saturated C 15 and C 17 acids, 10-methyl-C 16 (10-Me-C 16 ) and monoenoic C 16 (e.g., C 16:1ω7c ) and C 18 (e.g., C 18:1ω7c ) acids are characteristic of many bacteria (Ratledge and Wilkinson, 1988;Kaneda, 1991), especially Gram-negative sulfate-reducing bacteria (Taylor and Parkes, 1983;Edlund et al, 1985;Dowling et al, 1986;Kohring et al, 1994;Vainshtein et al, 1992), and iron(III)-reducing bacteria (Moule and Wilkinson, 1987;Nichols et al, 1992;Coleman et al, 1993;Teece et al, 1999;Venkateswaran et al, 1999;Zhang et al, 2003). In salt marsh sediments inhabited by the tall form of Spartina, sulfate-and Fe(III)-reducing bacteria are abundant (10 6 to 10 8 cells/ml) and anaerobic decomposition predominates over aerobic decomposition (Lowe et al, 2000;Kostka et al, 2002a,b;Gribsholt et al, 2003;Furukawa et al, 2004).…”

Biogeochemical consequences of infaunal activities

“…Modeling such conditions can provide reaction and transport parameters that are distinctively different from those obtained for environments at steady state or unidirectionally changing redox regimes. For example, redox oscillations promote the formation of poorly-crystalline Fe(III) minerals such as ferrihydrite, that are more rapidly utilized as terminal electron acceptors (TEA) than crystalline Fe(III) [Furukawa et al, 2004;Jensen et al, 2003]. Furthermore, the rate of aerobic degradation is significantly higher for OC kept under an anaerobic conditions until recently, compared to OC that has been under a continuously oxic conditions [Hulthe et al, 1998].…”

“…However, burrow walls are quantitatively significant as they can account for a considerable portion of the available interface between advectively circulated overlying water and sediments in addition to the WSI at the seabed. For example, at a salt marsh bioturbated with Uca pugnax in Skidaway Island, over 50% of the interface is accounted for by burrow walls [Furukawa et al, 2004]. Burrows of Nereis diversicolor population increase the interface several fold in a shallow mudflat in Limfjorden, Denmark [Nielsen et al, 20041.…”