Abstract
The lagoon complex of Cispatá (old Sinú river delta) located at the Northwestern coast of the Colombian Caribbean, encloses one of the biggest mangrove areas in this region. This area has changed during the last 330 years because of several environmental and climatic causes, mainly changes in the position of the delta (Sinú River), which is the main freshwater source in this area, and sea level rise. We hypothesized that the climatic and geomorphologic dynamics has caused changes in the extension and composition of mangrove vegetation, especially during last 150 years. The dynamics of mangroves during the last 900 years was reconstructed based on the changes in the stratigraphy, pollen record, calcite concentrations (CaCO3) and C/N ratio, along two sediment cores from La Flotante and Navio lagoons, located in Cispatá complex. The age model was built based on lineal interpolation of 210Pb ages and changes in granulometry. Establishment and expansion of mangrove forests during the last 900 years were related to fluviomarine dynamics in the area and the lagoon formation. During the period encompassed between 1064 and 1762 A.D., the Mestizos spit was formed when marine conditions predominated in the surroundings of La Flotante Lagoon. At the site of Navío, a river dominated lagoon, terrigenous conditions dominated since 1830. Although the colonization of herbaceous pioneer vegetation started between 1142 and 1331 A.D., mangrove colonization only took place since 1717 A.D. Mangrove colonization was a result of the delta progradation. In 1849 A.D. the Sinú river delta migrated to the Cispatá bay. The eustatic sea level rise, the increase in river discharges and sedimentation rates produced the establishment of mangrove forests dominated by Rhizophora since 1849. Since 1900 a marine intrusion was recorded in both lagoons. In 1938, the migration of the delta toward its actual location in Tinajones gave place to the formation of the present lagoon system and to the expansion of mangrove forests, which reflects the balance between the high alluvial sediment input and the current sea level rise as has been recorded in similar ecosystems.
Highlights
Los manglares ocupan la cuarta parte de las costas tropicales del mundo y se consideran entre las reservas ecológicas y forestales del planeta (Field 1995)
Las investigaciones en manglares han establecido que desde el Holoceno medio al tardío los niveles del mar se incrementaron gradualmente y los manglares permanecieron en muchas áreas, en donde se logró mantener la elevación del sustrato por el aporte de sedimentos desde las áreas continentales y de detritos orgánicos para contrarrestar este efecto (Parkinson et al.1994, Ellison 2008)
Esta expansión de los manglares en Cispatá desde 1850 es el resultado del efecto combinado de los cambios geomorfológicos, que involucran altas tasas de acreción gobernadas por las descargas de sedimentos aluviales y el incremento en el nivel del mar, tal como se ha registrado en otros sitios (Woodroffe 1990, 1999, Parkinson et al 1994, Snedaker 1995, Alongi 2008)
Summary
Area de estudio: Las secciones de sedimentos se obtuvieron de las lagunas La Flotante (9o23’37” N, 75o48’49” O) y Navío (9o24’19” N, 75o51’41” O); localizadas en la zona baja de la cuenca del río Sinú, en El Complejo Lagunar Cispatá, Noroeste de Colombia (Fig. 1). En la parte superior de los dos núcleos, donde se obtuvieron fechas de Pb, se utilizó la tasa de acumulación de polen para construir el modelo de edad según el método propuesto por Traverse (1988). Para la sección profunda del núcleo La Flotante se estimó una fecha en la base a partir del cambio en la granulometría de lodos a arenas, teniendo en cuenta la granulometría actual del Golfo de Morrosquillo (Molina et al 1994) y el modelo de evolución deltaica de Serrano (2001). Las zonas en las cuales se dividieron los diagramas se definieron con base en los grupos obtenidos con los análisis de Cluster y el análisis de correspondencia (DCA), los cuales fueron coincidentes
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