Iron biogeochemistry in Holocene palaeo and actual salt marshes in coastal areas of the Pampean Plain, Argentina.

OSTERRIETH, M.; NUTO NOBREGA, G.; BORRELLI, N.; ALVAREZ, F.

Enviromental Earth Sciences

Springer

Año: 2016 vol. 75 p. 671 - 672

In salt marshes, the hydrodynamics and theavailability of iron, organic matter and sulphate, influencethe formation and/or dissolution of iron sulfides and ironoxyhydroxides. Therefore, they constitute key factorsaffecting the iron biogeochemical processes in these environments.The aim of this work is to evaluate the physicochemicaland mineralogical variations associated to ironbiogeochemistry in palaeo and actual salt marshes in thearea of influence of the Mar Chiquita coastal lagoon,Pampean Plain, Argentina. In soils of exhumed palaeomarshes, the iron contents are 56?95 lmol g-1, whereasthese contents decrease to 36?75 lmol g-1 in actual marshsoils. The presence of framboidal and poliframboidal pyritesassociated with gypsum, barite, calcite, halite and ironoxyhydroxides defines the conditions of the pedosedimentarysequences of the Holocene paleomarshes.Sequences of pyrite formation (sulfidization) and degradation(sulfuricization) were observed. These processeswere evidenced by a sequential extraction, reflecting thatthe largest proportion of iron is in the form of crystallineiron oxides (28?76 %) and lepidocrocite (6?16 %); whilethe proportion associated with ferrihydrite and pyrite is low(0?9 and 1?17 %, respectively). These facts could be partlyexplained by the complex redox processes characteristic ofthese environments, such as aeration generated by therhizosphere and intense bioturbation by invertebrates.These iron biomineralizations have been useful becausethey allow paleoenvironmental interpretations and characterizationof paleomarshes, and environmental inferencesrelated to the management of actual salt marshes.