Hydrological Seasonality and DOM–Bacteria Interactions Rushan River Basin #pencis #researchawards

Introduction

River ecosystems are dynamic interfaces where hydrology, biogeochemistry, and microbial ecology intersect to regulate water quality and carbon cycling. Dissolved organic matter (DOM) plays a central role in these processes by acting as both an energy source and a regulatory factor for microbial communities. Seasonal hydrological variation, particularly the alternation between dry and wet periods, strongly influences DOM composition, sources, and bioavailability. Understanding how hydrological seasonality controls DOM–microbe interactions is therefore essential for predicting ecosystem responses to climate variability and for developing adaptive river basin management strategies.

Seasonal Dynamics of Dissolved Organic Matter

Hydrological seasonality drives pronounced shifts in DOM quantity and quality within the Rushan River Basin. During the dry season, reduced runoff and longer water residence times favor in situ microbial processing and phytoplankton production, resulting in DOM dominated by protein-like components, particularly tyrosine-like substances. In contrast, the wet season introduces strong allochthonous inputs through rainfall and surface runoff, increasing the contribution of terrestrial-derived humic and fulvic acids alongside tryptophan-like components. These seasonal contrasts highlight the sensitivity of riverine DOM composition to hydrological forcing.

PARAFAC-Based Characterization of DOM Components

The application of 3D excitation–emission matrix spectroscopy combined with PARAFAC analysis enabled the resolution of distinct fluorescent DOM components across seasons. Six components were identified in both dry and wet periods, but with contrasting distributions of protein-like and humic-like substances. Dry-season DOM was characterized by a higher proportion of labile, microbially derived compounds, whereas wet-season DOM exhibited a more balanced mixture of labile and refractory components. This analytical framework provides mechanistic insight into DOM sources and transformation pathways under varying hydrological conditions.

Microbial Community Structure and Seasonal Assembly

Microbial community composition in the Rushan River displayed clear seasonal patterns linked to hydrological regimes and DOM characteristics. Wet-season communities showed higher α-diversity and were dominated by Proteobacteria and Actinobacteriota, taxa often associated with versatile metabolic capabilities and the processing of diverse organic substrates. In contrast, dry-season communities were enriched in Bacteroidota and Verrucomicrobiota, groups known for degrading protein-rich and algal-derived organic matter. These shifts suggest that microbial assembly is tightly coupled to seasonal changes in DOM availability and composition.

DOM–Microbe Interactions Revealed by Structural Equation Modeling

Structural equation modeling (SEM) provided a semi-quantitative assessment of the pathways linking hydrology, DOM components, and microbial communities. The model indicated that microorganisms play a dual regulatory role by preferentially consuming unstable protein-like DOM while simultaneously promoting humification processes that increase DOM stability. This interaction is modulated by seasonal hydrology, with wet-season conditions enhancing external DOM inputs and dry-season conditions favoring internal microbial transformation. SEM thus clarifies the indirect and direct controls governing DOM fate in river ecosystems.

Implications for River Management and Carbon Cycling

The synergistic regulation of DOM and microbial communities by hydrological seasonality has important implications for water quality management and carbon cycling assessments. Seasonal shifts in DOM composition influence microbial metabolism, nutrient dynamics, and the persistence of organic carbon in river systems. Recognizing these patterns can support the development of season-specific management strategies aimed at mitigating pollution, maintaining ecological integrity, and improving predictions of carbon fluxes under changing climate and hydrological regimes.

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Hashtags

#HydrologicalSeasonality, #DissolvedOrganicMatter, #DOMMicrobeInteractions, #RiverEcosystems, #3DEEMs, #PARAFACAnalysis, #MicrobialEcology, #16SrRNASequencing, #SeasonalDynamics, #Biogeochemistry, #CarbonCycling, #WaterQualityManagement, #FreshwaterMicrobiology, #HumicSubstances, #ProteinLikeDOM, #StructuralEquationModeling, #AquaticEcosystems, #EnvironmentalResearch, #RiverBasinStudies, #ClimateHydrology