Factors controlling the concentration of particulate carbohydrates and amino acids in the Paran� River

Abstract

Particulate carbohydrates and particulate amino acids were determined in a set of samples from the Parana River, Argentina, covering a stretch of over 1300 km. To gain an understanding of the factors which control the concentrations of these organic compounds, a multivariate statistical approach was used (R-mode varimax factor analysis). This technique separated the influence of various sources of organic matter. The floodplain of the middle reach (about 900 km long and 20–30 km wide) was the most significant source controlling the concentrations of particulate carbohydrates (PCH), providing angiosperm debris, phytoplankton and grasses. Particulate amino acids (PAA) concentrations were determined markedly both by contributions from the Paraguay basin, and the lotic and lentic environments of the floodplain. Sugars single out forested tributary basins as sources of bacteria while amino acids point toward the Paraguay River as a major source of biodegraded material; heterotrophic processes, however, appear more clearly depicted with PAA than with PCH. A downstream increase of the PCH/PAA ratio suggests a larger consumption of PAA in the lowermost reaches.