Caracterización preliminar de los sedimentos de un embalse tropical: represa La Fe (El Retiro, Antioquia, Colombia)

Abstract

With the aim to investigate possible differences among zones of the body of water, in May and August of 2006, the interface water-sediment and three sections of sediment column were analysed in two sampling stations (dam and tail end) in La Fe reservoir (Antioquia), Colombia. In situ measurements of pH, temperature, electric conductivity and dissolved oxygen of overlying water were carried out. Later in the laboratory, the chlorophyll a and phaeopigments content, diversity and density of phytobenthic, organic matter, nutrients, heavy metals (Cd, Pb, Ni, Cr), bentic demand, and texture of sediments were quantified. Exploratory and descriptive analyses of the data indicated a mean temperature of 19 ◦C, acid pH, low concentration of ions in solution, and significant differences of dissolved oxygen among stations. A silt texture was dominant in the entrance to the reservoir and a clay one in the sediment of the dam. Nitrates concentrations were low in the sediment sections and high in the overlying water; the concentration of dissolved inorganic phosphate had a tendency to low concentrations in liquid and solid samples. The so-called “short-circuit metabolism” would explain the quick mineralization of the organic matter in the water column and the low percentage found in the sediments. The concentration of dissolved inorganic silica in both stations would be related to the high density of the diatom genera Cyclotella, Navicula and Gomphonema. Similar values of benthic demand were established for the sampling stations, being slightly higher in the dam (2.84 g·m−2 ·day−1) than in the tail (2.09 g·m−2 ·day−1). The mean concentrations of trace metals were higher for Cr (tail end) and Ni (reservoir dam), but only the latter was outside the limits reported by the available sediment literature. These results provide preliminary information about the dynamic of the sediments in La Fe reservoir, which is regulated by the granulometric composition and available dissolved oxygen, besides the quantity, type and speed of aloctonous material sedimentation and that originated from resuspension. Furthermore, the higher anthropic activity in the entrance to the reservoir (Los Salados Park) in comparison to that of the dam, promotes the interaction between the sediments and the water column.