In this work research the variability on geochemical and sedimentological characteristics of San Simón Bay intertidal and subtidal areas have been studied. Sedimentary evolution has been described from sediment architecture characterization and interpretation for the last 6000 years. This showed an alternation between estuarine channel facies and intertidal flat facies, related to climatic changes and autocyclic processes.

Sedimentation rates and metal pollutant chronology inputs have been established from isotopic dating techniques. It has been pointed out that geochemical analyses have to be performed parallel to Pb-210 and Cs-137 dating in order to get reliable sedimentation rates in non-homogeneous texture-sandy sediments.

Different metal inputs (lithogenic, biogenic, anthropogenic) have been identified in the intertidal and subtidal areas. The main anthropogenic impacts happened from middle 20th century related to urban and industrial development of the Ría de Vigo and its peripheral area. Such a development generated an increase in the inputs of fine-grained particles, wastewater and typical anthropogenic trace metals. The degree of pollution is classified from low to moderate by Cr, Cu and Zn, and from high to very high by Pb, for the recent sedimentary record. A ceramic factory constituted the main Pb input, whereas vehicle exhaustions are the second one. Most of trace metals are retained into the residual fraction, not representing a high environmental risk, except for Pb. This metal concentration into the most bioavailable fractions exceeded the background level in several magnitude orders for the study area.

Sediment postdepositional diagenetic evolution has been established from studying the C-S-Fe system variability and the related relationships, together with the evaluation of the organic matter provenance influence on the observed diagenetic processes. Early diagenetic processes are intense, related to the high sediment organic matter contents. This is consequence of the continental inputs, the marine flora richness (seaweeds, algae), the biological productivity (marine cultures, upwellings) and the wastewater inputs. Also, it has been determined the utility of several geochemical indexes, such as the degree of pyritization (DOP) and the degree of pyritization of trace metals (DTMP) as indicators of the sediment redox status and quality. In particular, it is highlighted the pyrite role as trace metal reservoir and these trace metal potential mobility in marine culture areas. It has been established a diagenetic zonation model for inner ría areas from these indexes and the C-S-Fe relationships. The following diagenetic zones have been identified: (1) oxic, (2) suboxic, (3) anoxic-sulphidic and (4) anoxic-non sulphidic. Their extent (cm-m) depends on sediment texture (zone 1), water column depth and those processes which generate sediment remobilization (zone 2), organic matter reactivity (intertidal area) or sulphide ions exhaustion with depth (subtidal area) (zone 3) and metabolizable organic matter prevalence (zone 4).

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