Soil is one of the principal substrates of human life and can serve as a reservoir of water and nutrients. Humic substances, indicators of soil fertility, are dominant in soil organic matter. However, soil degradation has been occurring all over the world, usually by soil salinization. Sustainable soil productivity has become an urgent problem to be solved. In this study, fluorescence excitation-emission matrices integrated with parallel factor analysis (PARAFAC) and canonical correlation analysis (CCA) were applied to characterize the components of fulvic acid (FA) and humic acid (HA) substances extracted from soils from the Liaohe River Delta, China. Along the saline gradient, soil samples with four disparate depths were gathered from four aboriginal halophyte communities, i.e., the Suaeda salsa Community (SSC), Chenopodium album Community (CAC), Phragmites australis Community (PAC), and Artemisia selengensis Community (ASC). Six components (C1 to C6) were identified in the FA and HA substances. The FA dominant fractions accounted for an average of 45.81% of the samples, whereas the HA dominant fractions accounted for an average of 42.72%. Mature levels of the HA fractions were higher than those of the FA fractions, so was the condensation degree, microbial activity, and humification degree of the FA fractions. C1 was associated with the ultraviolet FA, C2 was referred to as visible FA, C3 and C4 were relative to ultraviolet HA, C5 represented microbial humic-like substances (MH), and C6 referred to visible HA. C1, C2, C5 and C6 were latent factors of the FA fractions, determined using the CCA method and could possibly be used to differentiate among the SSC, CAC, PAC and ASC samples. C3, C4, C6 and C5 were latent factors of the HA fractions, which might be able to distinguish the ASC samples from the SSC, CAC and PAC samples. Fluorescence spectroscopy combined with the PARAFAC and CCA is a practical technique that is applied to assess the humic substance content of salinized soils.

This study aimed to analyse the spatiotemporal evolution of phytoplankton community dynamics and its underlying mechanisms in the Liaoning section of the Liao River Basin in 2010, 2015, and 2020. Phytoplankton species diversity increased significantly, with an increase from three phyla and 31 species in 2010 to six phyla and 74 species in 2020. Concurrent increases in α-diversity indicated continuous improvements in habitat heterogeneity. The community structure shifted from a diatom-dominated assemblage to a green algae–diatom co-dominated configuration, contributing to an enhanced water purification capacity. The upstream agricultural zone (Tieling section) had elevated biomass and low diversity, indicating persistent non-point-source pollution stress. The midstream urban–industrial zone (Shenyang–Anshan section) emerged as a phytoplankton diversity hotspot, likely due to expanding niche availability in response to point-source pollution control. The downstream wetland zone (Panjin section) exhibited significant biomass decline and delayed diversity recovery, shaped by the dual pressures of resource competition and habitat filtering. The driving mechanism of community succession shifted from nutrient-dominated factors (NH₃-N, TN) to redox-sensitive factors (DO, pH). These findings support a ‘zoned–graded–staged’ ecological restoration strategy for the Liao River Basin and inform the use of phytoplankton as bioindicators in watershed monitoring networks.