Assessing extracted organic matter quality from river sediments by elemental and molecular characterization: Application to the Tietê and Piracicaba Rivers (São Paulo, Brazil)

Abstract

Urban river pollution causes serious problems to the environment, human health, and water scarcity. Developing tools to identify and assess the health of aquatic river systems is essential for monitoring the quality of rivers and implementing actions. This study assesses the elemental and molecular characteristics of organic matter (OM) extracted from river sediments and associates them with river quality. To assess the quality of sediment cores, the most reactive and available OM from two urban rivers (Tietê and Piracicaba Rivers, São Paulo, Brazil) was isolated with alkaline and water solutions. It was then characterized by elemental composition, ultraviolet–visible spectroscopy, and fluorescence excitation-emission matrix with parallel factor analysis. The average yield of alkaline extraction was 40.71% ± 5.52% of OM present in the bulk sediments. Extracted organic matter from sediments (EOMSed) from the Tietê River presented the highest average concentrations of non-purgeable organic carbon (NPOC) and total organic nitrogen (TON), and the lowest average NPOC/TON molar ratios and specific UV absorbance at 254 nm (SUVA254). Considering the high degree of eutrophication in the Tietê River, these results suggest a greater input of simple OM with nitrogenous structures. The humic-like component in EOMSed was the most abundant in both rivers. The aromaticity of EOMSed from the Piracicaba River was evidenced by the greater contribution of complex structures in the form of aromatic and polyaromatic moieties and higher SUVA254. EOMSed from the Tietê River also featured enhanced biological activity due to the greater contribution of microbial-derived products and the presence of small molecules and nitrogenous structures. As this combination of elemental and spectroscopic techniques successfully identified the characteristics of extracted OM, it can be used as a tool to assess the global river quality.