Geochemical and micropaleontological evidence of recent hydrological changes in sedimentary records of Jiquilisco Bay, El Salvador

Abstract

The geochemical, mineralogical, and micropaleontological (Foraminifera, Ostracoda, Bacillariophyta) spatial and temporal variations in marshland sediments from the Jiquilisco Bay Biosphere Reserve, El Salvador, are described. The sedimentary characteristics of two marsh sites reveal contrasting sedimentary environments: site Los Cedrones depicts a high energy environment with sandy sediments, low organic matter content, and no microfossils, while site El Gimidor represents a lower energy environment with muddy sediments rich in organic matter and more abundant and diverse microfossils. ²¹⁰Pb-dated sedimentary cores showed changes over time (last 100 years) in the mineral and elemental composition, as well as in the accumulation rates, suggesting changes in the type and magnitude of sediments delivered to the sites. Sediment accumulation rates were similar at both sites, ranging from 1.2 ± 0.9 to 3.4 ± 0.5 mm yr^–1 at Los Cedrones and from 0.8 ± 0.2 to 4.0 ± 0.5 mm yr^–1 at El Gimidor. Even though both marshes are located 13 km apart, and depict different sedimentary environments, elemental composition, and microfossil assemblages, both sedimentary records show the influence of hydrological changes, probably due to the damming of the Lempa River and the sea-level increase during the last 100 years.