Iron–sulphur–phosphorus Interactions: Implications for Sediment Buffering Capacity in a Mediterranean Eutrophic Lagoon (Sacca di Goro, Italy)

Abstract

The interactions among sedimentary cycles of sulphur, iron and phosphorus were investigated in the eutrophic Sacca di Goro lagoon (Northern Adriatic coast, Italy) in order to assess the iron buffering capacity of the sediment. Three stations were chosen, which represented different primary producer communities, hydrodynamics and sediment characteristics. Station G was close to the outlet of the Po di Volano river, station 4 was in the central part of the lagoon under tidal influence and station 17, in the sheltered zone, was affected by macroalgal blooms. From January 1997 to January 1998, sediment cores were sampled approximately every 2 months. In parallel, temperature, salinity and dissolved oxygen were determined in the water column. Sedimentary profiles of Eh, pH, dissolved sulphide (DS), acid volatile sulphide (AVS), chromium reducible sulphur (CRS), iron and phosphorus pools were determined in the 0-10 cm sediment horizon. Bacterial sulphate reduction rates were measured only at station 17. Iron pools, AVS and CRS followed similar patterns at all the considered stations, with lower values in the 0-2 cm sediment horizon and peaks in the deepest sediment layer (5-10 cm horizon). Overall, the labile Fe accounted for an annual average of 115.6 ± 3.0 lmol cm )3 , with peaks of labile ferric iron up to 40 lmol cm )3 . The great iron availability and reactivity accounted for an efficient buffering capacity against sulphides, with the accumulation of AVS and CRS, specially at station G where the iron buffer was replenished by iron-rich freshwaters. At station 17, in spite of a great iron availability the buffering capacity was less efficient due to macroalgal blooms and accumulation of labile organic matter, whose decomposition stimulated bacterial sulfate reduction and the inherent sulphide production both in the pore-water (DS: 4.0 ± 3.7 mM) and in the deepest water column (DS: 85 lM). The iron and sulphur interactions had also implications for P cycling, since in summer the ferric iron reduction was accompanied by a significant increase of pore-water and exchangeable phosphates. The AVS to labile Fe and AVS to TRIS (AVS + CRS) ratios were used to assess the sediment capacity of precipitating and retaining sulphides. These ratios were then compared with the chemical buffer capacity, demonstrating their suitability as indicators of buffering capacity towards sulphides.

Vertical distribution of Fe and Fe(III)-reducing bacteria in the sediments of Lake Donghu, China

“…Fe is perhaps the most versatile element, and the redox cycling of Fe exerts a wide influence on the biogeochemical cycling of N, S, and P in sediment environments (Azzoni et al 2005;Weber et al 2006;Wilms et al 2007). Pore water and sediment profiles of Fe geochemistry also showed active Fe(III) reduction at depth.…”

“…immediately, and the second subsample was acidified with 1 mL of 0.5 mol/L HCl to prevent precipitation of Fe (Azzoni et al 2005) and was then measured for Fe(II) in triplicate using the 2,2,-bipyridyl assay (Moss and Mellon 1942). Total organic carbon (TOC) of sediment was measured using an Elementar Vario TOC system (China).…”

“…Total organic carbon (TOC) of sediment was measured using an Elementar Vario TOC system (China). Total inorganic phosphorus (TIP) was sequentially extracted from 2 g of sediment with 20 mL of 1.0 mol/L MgCl 2 (pH 7.5) for 2 h and 20 mL of 0.5 mol/L HCl for 1 h (Azzoni et al 2005). Total phosphorus (TP) was extracted from 2 g of fresh sediment with 40 mL of 3.5 mol/L HCl for 16 h. All extracts were analyzed for P by spectrophotometric determination at 700 nm (Ruban et al 2001).…”

In Situ Chemical Transformations of Silver Nanoparticles along the Water–Sediment Continuum

“…The decrease of Fe(II) in the porewaters at depths >35 mm is the result of sulfate reduction which subsequently causes the precipitation of iron-sulfides 46,47 . Dissolved Mn continued to increase, peaking at 60 mm depth, which was also the depth at which the Fe(II) decreased to concentrations similar to those at the SWI.…”

Seasonal steady-state budgets of nutrients and stoichiometric calculations in an Eastern Mediterranean lagoon (Papas Lagoon-Greece)

“…In addition, recent field and laboratory experiments have shown that under anoxic conditions, the build-up of sulphide by the bacterial sulphate reduction induces enhanced release of phosphate from coastal lagoon sediments. The interactions of sedimentary iron and sulphur cycles have implications for phosphorus cycling and its availability to macroalgae (HEIJS et al, 2000;AZZONI et al, 2005). Evidence to show that the sulphide metabolism is critical for the release of non-iron-bound phosphate (organic and/or Ca-bound phosphate) was also obtained however, the responsible mechanism has not yet been elucidated (HEIJS et al, 2000).…”