Characteristics of different extractable organic matter in sediments and its hydrogeochemical significance: A case study of the typical study area in hetao basin

Characteristics and reactivity of organic matter (OM) in groundwater systems play very important roles in the formation and evolution of groundwater chemical characteristics. In this study, 70 fluviolacustrine sediments were taken at 10 cm interval near the land surface in the Hetao Basin of Inner Mongolia to characterize sedimentary organic matter properties. The diffuse spectral reflectance of sediments, water soluble organic matter (WEOM) and salt soluble organic matter (SEOM) contents and their spectroscopic properties were measured. Results showed that diffuse spectral reflectance between 530 nm and 520 nm(R530-520) of sediments and TOC content showed the opposite trend: When the R530-520 value was higher, the TOC content was lower. In comparison with fine sand, clay layer had lower R530-520 values, but higher TOC contents. In the same sediment, contents of SEOM were higher than those of WEOM, but WEOM was easier to migrate into groundwater. The spectral index showed that WEOM possesses more biological/microbe-associated materials, but SEOM is representative of terrigenous materials.Excitation-emission matrix spectroscopy analysis showed that the fluorescence intensities were positively correlated with OC contents in sediments (SOC),which were high in clay layer. Moreover, both WEOM and SEOM had similar humic-like components and protein-like components, but the humic-like components in SEOM were higher than those in WEOM. Humic-like OM is considered to be the most important form in sedimentary OM in this study.