1 research outputs found
Organic matter sources for tidal marsh sediment over the past two millennia in the Minho River estuary (NW Iberian Peninsula)
Environmental changes during the last 2 millennia in the Minho River tidal
marsh (NW Portugal-Spain border) were reconstructed. Changes in the sources
of organic matter (OM) delivered to the marsh were evaluated from elemental,
isotopic and molecular composition using a 1 m sediment core. Carbon isotopic
composition (delta13C) and organic carbon to total nitrogen ratio (Corg/N) provided
valuable information concerning the origin of the OM. These parameters
indicated a major input from land plants, reaching a maximum at 1100–1200
and 1750–1850 AD. These periods match with major flood events in the NW of
the Iberian Peninsula, as reported by several authors. A significant reduction in
the terrestrial signature occurred at 6–4 cm (ca. 1960–1985 AD), which is
contemporaneous with the construction of several major dams on the Minho
River. The distribution of selected lipid biomarkers, including n-alkanes, n-fatty
acids and n-alkan-2-ones and specific parameters derived from the molecular
distributions, were useful for refining bulk geochemical results. Long chain n- alkanes with an odd number of carbons are indicators of soil-and vascular plant derived terrestrial OM and were dominant throughout the core. In addition, a
greater contribution of plankton-derived lipids was observed in the sections
corresponding to ca. 1960–1985 AD (6–4 cm) and ca. 100–200 AD (96–94 cm).
Although different degradation rates for individual compounds might have partly
affected biomarker assemblages, the variations could be attributed to a sharp
decrease in the freshwater contribution to the Minho River Estuary (dam
construction) and a possible marine highstand, respectively. In addition, several
parameters suggested changes in land use (including deforestation and farming) and probably the effects of mining exploitation during the Roman
occupation of the area.We acknowledge the funding by the Foundation for Science and Technology
(FCT) of Portugal for J.M. M’s PhD. Grant (SFRH/BD/45528/2008) and for the
WestLog Project (PTDC/CTE-GIX/105370/2008). E.L. was awarded a Ralph E.
Powe Junior Faculty Enhancement Award. This is a contribution to the IGCP
Project 588 and to the Geo-Q Research Unit (Aranzadi).Peer reviewe