Carbon and nitrogen deposition on the surface of marginal sediments under different land use systems along the Paraopeba river basin (Minas Gerais, State)

The knowledge of the contents of organic compounds in aquatic ecosystems is of great importance, since the dissolved organic matter represents a dynamic component in the interaction between geospheres. The objective of this study was to evaluate the levels of carbon, nitrogen, and carbon-to-nitrogen ratio in the marginal sediments and the carbon content in the waters along the Paraopeba river basin (MG). The samples were collected in five locations (Jeceaba, Brumadinho, Fortuna de Minas, Florestal, and Três Marias) corresponding to the high, medium, and low river segments. The carbon content was determined by the Walkley & Black method and the nitrogen content by the Kjeldahl method. The carbon content ranges from 4.75 to 5.97 g kg-1. Nitrogen ranged from 0.73 to 1.08 g kg-1. Finally, the carbon-to-nitrogen ratio varied from 5.15 to 21.25. The carbon content in the water samples ranged from 0 to 0.25 g L-1. As the values ​​of dissolved organic carbon were very low or even zero, the nitrogen content and the carbon-to-nitrogen ratio were not determined. There was a negative and a positive correlation with the aluminum content (r = -0.70 and r = 0.74, respectively) indicating possible contamination by heavy metals. Therefore, the levels of carbon, nitrogen, and the carbon-to-nitrogen ratio were sensitive indicators of changes in the aquatic ecosystem.