Metabolism of a stretch in the lower basin of the Cesar River, department of Cesar, in a dry season, Colombia

Abstract

The functionalities of aquatic systems are the result of biological interactions, the physicochemical conditions of water and the terrestrial environment, these relationships are affected by anthropic actions, such as: deforestation, mining, agriculture, solid waste discharges and domestic and industrial liquids, general harmful practices for aquatic ecosystems. This investigation was carried out with the purpose of estimating the variation of the metabolism and physicochemical variables in the lower basin of the Cesar River, during the period of maximum dry season, the trophic state of the lower basin of the aquatic ecosystem was determined by observations in the changes of the O2 consumption and CO2 accumulation, the processes of photosynthesis and respiration were quantified. Two samplings were carried out in four stations, between February-April 2013, equivalent to the dry period. Physicochemical variables in situ and some nutrients were measured. The metabolism protocol was applied, using the Winkler method (clear and dark bottles), with measurements every hour for 24 h (daily curve). The net metabolism was -10732.23 O2/m3-h, the dark one of -10731.41 02/m3-h and the gross primary production of the entire aquatic community of -10736.91 02/m3-h. These results suggest that the variations in the net and dark metabolism, as well as the primary productivity of the community were almost nil. Additionally, the oxygen produced during the day was consumed quickly at night. Our data show that the trophic state of the lower basin of the Cesar River is eutrophic-heterotrophic, the respiration exceeds the production of O2, which generates deficit of the same and a decrease in the quality of this ecosystem, results that are corroborated with the analyzes of the physicochemical variables measured at the site.