Nutrient contents in bottom sediment samples from a southern Brazilian microbasin

The nutrients, carbon, nitrogen and phosphorus, significantly affect the quality of aquatic environments, especially when present at concentrations above natural levels. In this context, the sedimentary column can act as an environment for storage or accumulation of these nutrients and for the reprocessing of such substances in the water column and aquatic biota. In this context, this study aimed to estimate the concentration of total organic carbon (TOC), total nitrogen (TN), total phosphorus (TP), inorganic phosphorus (IP) and organic phosphorus (OP) in seven sediment samples that were collected from the Marrecas Stream microbasin (Caxias do Sul, Rio Grande do Sul State, Brazil). The relationships among the sediment nutrient concentrations and the levels of organic matter (OM), fine material (silt-clay) and the concentration of the metal species, Al, Fe and Mn, as well as the possible nutrient sources to the stream studied were also evaluated. The data set suggest that the TOC and IP appear to have a direct correlation with the vast riparian vegetation present in areas adjacent to the sampling points and to the physico-chemical properties of the water and sedimentary column. Moreover, the results obtained for TN suggest that its concentration possibly suffers interference from the temperature of the water and its oxygenation, in addition to other biological activities. On the other hand, one cannot rule out human interference, mainly in the levels of OP, possibly due to the inflow of domestic sewage to the stream.