Introduction.

The main objective of this work was to determine the Sediment Oxygen Demand (SOD) in four different sections of the Rio Negro (Rionegro, Antioquia) during three climatic seasons in 2014 (dry and rainy seasons and a transition phase).

Materials and Methods.

The sediment samples were taken using an Ekman dredger. Analysis of moisture and organic matter content of the samples was performed later in the laboratory. The measurement of the benthic oxygen demand was made based on the Batch technique. Likewise, at each monitoring point, using a multiparameter sensor, the following environmental variables were measured: pH, conductivity, dissolved oxygen, saturation percentage and temperature.

Results.

It is worth highlighting the behavior of SOD in the Puente Autopista station, where low values of this variable were obtained, ranging from 0.05 - 0.15 g O2 *m2/day. This contrasts with other environmental variables in the same station, such as dissolved oxygen and saturation percentage, whose results were also reported as very low. For the other stations the values ranged from 0.09 - 0.25 g O2 *m2/day, which are typical demands of sediments with low content of organic material.

Conclusions.

This study found that the results obtained for SOD measurement are low when compared to similar national and international-level studies. Additionally, other environmental variables such as pH, temperature and conductivity remained in the typical range of values for mountainous streams.