Geochemical phases of Fe and degree of pyritization in sediments from Ría de Pontevedra (NW Spain): Implications of mussel raft culture

Abstract

585Fases geoquímicas del Fe y grado de piritización en sedimentos de la Ría de Pontevedra (NO de España):Implicaciones del cultivo del mejillón en bateas ResumenSe analizaron seis testigos de sedimento de la Ría de Pontevedra para valorar la influencia que ejercen los sistemas de bateas sobre las propiedades texturales y geoquímicas del sedimento (contenido de carbonatos, materia orgánica, fases geoquímicas del Fe y grado de piritización). Cuatro de los testigos se extrajeron en zonas dedicadas al cultivo de mejillón en bateas y los otros dos en áreas adyacentes no sometidas a dicha actividad. El grado de piritización (DOP) osciló entre 11.89% y 67.30%, con un valor medio de 46.36 ± 13.15%. Los valores máximos se obtuvieron en los sedimentos de las zonas con bateas (biodepósitos) que presentaron, a su vez, mayores contenidos de Fe pirítico, fango y materia orgánica que las zonas libres de bateas. Por el contrario, en estas últimas zonas predominó el Fe asociado con los silicatos, junto con las fracciones más gruesas (arena y grava) y elevados porcentajes de carbonatos. Estos resultados muestran un predominio de condiciones más reductoras en los biodepósitos, que favorecen la formación de una mayor cantidad de pirita frente a las áreas donde no hay maricultura. Los valores del DOP indican que el Fe reactivo no se ha convertido en su totalidad en Fe pirítico. La materia orgánica se confirma como el factor limitante en la formación de pirita por la correlación significativa (r = 0.61) encontrada entre ésta y el DOP. Los resultados permiten concluir que el cultivo del mejillón en bateas modifica sustancialmente la textura del sedimento e influye, significativamente, en las formas químicas del Fe, con las consecuentes implicaciones geoquímicas y ambientales.Palabras clave: grado de piritización, Ría de Pontevedra, hierro reactivo, hierro pirítico, bateas. AbstractTo assess the influence of mussel raft systems on several geochemical and sedimentological properties (carbonate and organic matter contents, fractions of Fe and degree of pyritization), six sediment cores were collected from the Ría de Pontevedra area. Four of those cores were collected in mussel raft areas (biodeposits) and the other two in adjacent areas where mussel rafts do not operate. The degree of pyritization (DOP) varied between 11.89% and 67.30%, with a mean value of 46.36 ± 13.15%. The maximum values of DOP were obtained in sediments from the mussel raft areas, which in turn showed higher values of pyrite Fe, organic matter and mud than the areas without mussel rafts. On the contrary, in the latter areas, coarser sediments with high carbonate content and Fe bound to silicates were the predominant phases. The results show a dominance of more reducing conditions in the biodeposit areas than in the adjacent areas. The DOP values indicate that reactive Fe was not totally converted to pyrite Fe. The significant correlation (r = 0.61) between DOP and organic matter confirmed that the latter is the limiting factor in pyrite genesis. These results allow...

Palaeoclimatic changes in the NW Iberian ­Peninsula during the last 3000 years inferred from ­diagenetic ­proxies in the Ría de Muros sedimentary record

“…Similar processes have been described in other Galician Rías (León et al 2004, Álvarez-Iglesias & Rubio 2008) and in similar coastal environments with high concentrations of Fe and Mn and high input of labile organic matter (Sørensen & Jørgensen 1987, Hines et al 1991, Canfield et al 1993, Haese et al 2000. Fig.…”

Influence of mussel aquaculture on sediment organic enrichment in a nutrient-rich coastal embayment

“…, and reduced particulate compounds such as FeS and pyrite formed by sulfate reduction are oxidized by oxygen (Leon et al 2004). With increasing organic matter input sulfate reduction in subsurface layers will be stimulated (Dahlbäck & Gunnarsson 1981) and since vertical oxygen supply is limited, reduced S compounds will accumulate closer to the sediment surface.…”

Sulfur, Iron, and Manganese Speciation in Anoxic Sediments with Methane (Ría de Vigo, NW Spain)

“…In the outer zone (C10‐NO and C11‐GO), Fe and Mn bound to OM tend to decrease with depth. According to León et al , this is due to diagenetic processes in which a portion of Fe reacts with the OM and is incorporated into its structure. In fact, negative correlations were found only in the inner zone of the ría (C8‐GI, with the highest OM content) between TOC and Fe and Mn weakly bound to OM ( r = −0.551 and r = −0.659, respectively, for Fe and Mn); positive correlation between TOC and Fe strongly bound to OM was found ( r = 0.833).…”