Hydrochemical and sedimentological dynamics in a subtropical plain river: assessment by multivariate statistical analysis

Understanding the transport dynamics of sediments and soluble components is critical when ecosystems could be adversely affected. This study examined some environmental factors influencing the spatial and temporal variations of water–sediment interactions in Negro River, northeast of Argentina, a subtropical plain fluvial system with anthropogenic influence. Samples of water and bottom sediments were collected from four sampling stations in four sampling campaigns spread over 2 years. Chemical parameters, including pH, conductivity, major ions, concentration of suspended sediments, extractable major cations and particle size of sediments, were determined. The experimental data were interpreted by classical hydrogeochemical methods and statistical methods. Multivariate statistical tools were applied to reduce the dimensionality of the data set and to evaluate the relative importance of combinations of environmental variables on sediment dynamics. The results showed that the variability of the hydrochemistry and the sediment chemistry is controlled by longitudinal and seasonal factors, whereas differences across the river section were nonsignificant. The concentration of suspended solids and the abundance of fine-grained materials in bottom sediments were inversely correlated with the concentration of some metals with agglutinant and coagulant properties in sediments. This corroborates the presence of fine particle aggregates, also evidenced by classical grain-size analysis. Thus, particle disaggregation by chemical methods is not recommended, as it could lead to misinterpretation when the objective is to evaluate the dynamics of sediments in natural environments. This study highlights the importance of analyzing multiple dimensions (spatial and temporal) to understand the dynamics of fluvial sediments, especially in plain rivers.