Effects of land use changes in the biogeochemistry of fluvial systems of the Ji-Paraná river basin, Rondônia.
In this article we present the results of the effects of land use change on the river biogeochemistry of the Ji-Paraná basin (Rondônia). In this region, the spatial distribution of deforestation and soil properties result in different biogeochemical signals, allowing the division of the fluvial systems into three groups: rivers with low ionic concentration and low impact; rivers with intermediate ionic content and medium impact; and rivers with high ionic content and anthropogenic impact. River biogeochemical characteristics present a significant correlation with pasture area, the best predictor for electric conductivity (r2 = 0,87), sodium (r2 = 0,75), chloride (r2 = 0,69), potassium (r2 = 0,63), phosphate (r2 = 0,78), and dissolved inorganic nitrogen (r2 = 0,52), inorganic carbon (r2 = 0,81) and organic carbon (r2 = 0,51). For calcium and magnesium, both soil properties and pasture explained most of the observed variability. Our results indicate that the changes observed at the micro-scale constitute \'biogeochemical signals\' generated by the material processing at the riparian zones. As the rivers evolve to higher orders, the persistent signals in the fluvial channels are very closely related to the drainage basin characteristics (soils and land use), which, in turn, become the determinant of these systems dynamics. While at the macro-scale (the whole basin) the effects of land use changes are not yet detectable in the Amazon, the disruption of the structure and functioning is occuring at the micro and meso scales, with significant alterations of nutrient cycling in fluvial ecosystems