Quantitative assessments of organic matter uncoupling from clay surfaces in presence of salinity

Most terrestrial organic matter (OM) is released from clay surfaces when the clay-OM complex enters saline ocean margins and is replaced with ocean OM. However, it remains uncertain how salinity would affect the decoupling of adsorbed OM on clay surfaces. Here we show that the specific location of OM on clay mineral surfaces made a difference on OM migration. The OM trapped on the outer surface of the clay was further consolidated in the presence of salinity, while the OM in the interlayer was exchanged with sodium ions and desorbed. The desorbed OM was further analyzed by Raman spectroscopy and three-dimensional excitation emission matrix fluorescence spectroscopy, which analyses revealed that the aromatic protein, fulvic acid-like organics, microbial byproduct, and humic acid-like substances were likely to adsorb on the clay surface under saline conditions. These results indicated that the clay-terrestrial OM association is strong in saline estuaries, with the terrestrial OM unlikely to break away from clay surfaces.