A rapid assessment of the sedimentary buffering capacity towards free sulphides

Abstract

Combined field surveys and laboratory studies were conducted in two Italian coastal lagoons, which differ for geomorphology, hydrodynamics and eutrophication degree (Sacca di Goro and Lesina lagoons, Adriatic Sea). Research aimed at assessing with a rapid technique the potential buffering capacity of sedimentary iron towards sulphides. In Spring and Summer 2004, the main pools of iron and sulphides were analysed in the uppermost sediment horizon (0-5 cm) at four stations in each lagoon. In parallel, experiments with laboratory incubations of sediment slurries were carried out at two sites in each lagoon in order to assess the sediment capacity of binding and retaining sulphides. Sediment slurries were kept stirred and anoxic with N 2 purging. Aliquots of dissolved sulphides (DS) were then added and DS concentrations were monitored until they were undetectable. On average, the total reactive iron (RFe), extracted with 6 N HCl, ranged from 170 to 400 lmol cm -3 in the Sacca di Goro stations, and comprised between 40 and 150 lmol cm -3 in the Lesina sites. The labile iron ferric quota (LFe: extractable with 0.5 N HCl) is considered representative of the microbially reducible iron fraction and was highest in spring in Sacca di Goro (up to 20 lmol cm -3 ). Differences among stations evidenced by PCA analysis, can be inferred from RFe, LFe and AVS, which represent the iron buffer and its saturation status, respectively. The sedimentary DS uptake was 6 lmol cm -3 of fresh sediment in Lesina and 8-12 lmol cm -3 in Sacca di Goro, indicating a direct relationship between DS removal and iron availability.

Metabolic threshold and sulfide-buffering in diffusion controlled marine sediments impacted by continuous organic enrichment

“…availability, and is consistent with accumulation of TH 2 S near the surface of the same sediments in a parallel experiment (Valdemarsen et al, unpublished results). Similarly, Giordani et al (2008) found that TH 2 S is present for several hours after addition to sediment slurries containing RFeII, which indicates that Fe x S yprecipitation is limited by Fe 2? generation.…”

“…However, estimates of buffering capacity are in many cases derived from anoxic sediment slurries (e.g. Giordani et al 2008), which may overestimate the importance of Fe x S y precipitation compared with diffusion controlled sediments, where precipitation is restricted to a narrow surface and may be limited locally by availability of Fe 2? .…”

“…However, above a certain threshold SOU becomes limited by factors such as O 2 -concentration in the water column and water flow (Jorgensen and Marais 1990) and TH 2 S may escape to the overlying water column (Morrisey et al 2000). Fe-containing sediments may have significant TH 2 S buffering capacity Giordani et al 2008), where TH 2 S precipitates with dissolved Fe 2? to form Fe x S y (e.g.…”

Sulfur, carbon, and nitrogen cycling in faunated marine sediments impacted by repeated organic enrichment

“…Alternatively, TH 2 S is removed from solution by precipitation with dissolved Fe 2+ to form reduced Fe sulfides (e.g. FeS and FeS 2 ) as long as Fe 2+ is available (Rickard 1995, Rickard & Morse 2005, Giordani et al 2008). Fedriven TH 2 S buffering has been shown to significantly hamper TH 2 S buildup and reduce sediment oxygen uptake (SOU) in eutrophic coastal sediments (Heijs et al 1999, 2000).…”

Reactive iron and its buffering capacity towards dissolved sulfide in sediments of Jiaozhou Bay, China

“…Although sedimentary total buffering capacity towards sulfide is a combination of chemical removal and microbial oxidation, it has been suggested that biological buffering capacity becomes effective only after chemical buffering capacity is exhausted. Therefore, chemical buffering is a critical process for dissolved sulfide removal and the last protection against sulfide accumulation in porewater (Kanaya and Kikuchi, 2004;Giordani et al, 2008;Valdemarsen et al, 2009).…”