Identifying organic matter fractions and revealing its dynamic spatial-variation within riparian soil profiles along an urbanized river by solid-phase SFS with moving window 2-dimentional correlation spectroscopy

Abstract

Solid-phase fluorescence with synchronous fluorescence spectroscopy (SFS) is a relatively innovative method for characterizing soil organic matter (SOM), by which dynamic spatial-variation and source of SOM fractions from riparian soils could be elucidated along an urbanized river in this study. Composite soil samples of four depths were collected from six land-uses, i.e., eco-conservation area (ECA), industrial area (INA), urban area (URA), town area (TOA), rural area (RUA) and agricultural area (AGA). Based on synchronous fluorescence spectra coupled with Gaussian band fitting, SOM predominantly contained tyrosine-like (TYLF), tryptophan-like (TRLF), microbial humic-like (MHLF), fulvic-like (FLF1 and FLF2) and humic-like (HLF) substances within each soil profile, among TYLF and TRLF (39.69%-57.07%) are the representative components. The decreasing order of the content of fluorescence materials within the six soil profiles was TOA > RUA > AGA > INA > URA > ECA. According to 2-dimensitonal correlation spectroscopy and moving window, SOM within the ECA soil profile could be mainly derived from the degradations of terrestrial plant metabolites and residuals, while SOM within the INA soil profile could be associated with treated/untreated industrial wastewater, which penetrated the river and partially flew into the riparian. SOM in both the URA and TOA soils might be concerned with scattered domestic sewage and livestock wastewater, whereas the SOM in the RUA and AGA soils might be relative with crop metabolites and residuals. Noticeably, variations of SOM fractions within the ECA, RUA and AGA soil profiles virtually occurred in 20-80 cm, while almost in 20-40 cm within the INA, URA and TOA soil profiles. Based on SEM, humification degree of SOM within the former three soil profiles might be more indirectly affected by MHLF on HLF, while the latter were directly affected by MHLF. This study can provide technical support for ecological restoration of riparian zone.