Key Takeaways & Executive Findings
- •• • Three fluorescent DOM components (C1 fulvic-like, C2 tryptophan-like, C3 terrestrial humic-like) were identified via parallel factor analysis; C2 dominated in winter/spring (>50% of total fluorescence) while summer/autumn showed reduced C2 due to dilution and increased C3 from urban runoff. • • Fluorescence index (FI) > 1.9 and biological index (BIX) > 1.0 across all seasons indicate predominantly autochthonous (microbial) DOM sources, with implications for carbon cycling and pollutant transport in urban rivers. • • Summer/autumn exhibited increased humification index (HIX) and specific UV absorbance (SUVA) at 254 nm, alongside decreased spectral slope ratio (SR), signaling enhanced terrestrial and urban nonpoint source inputs during high-flow periods. • • Protein-like C2 and terrestrial humic-like C3 showed significant positive correlations (p < 0.05) with water quality parameters (e.g., COD, TN, TP), enabling precise tracing of pollution sources and seasonal water quality fluctuations for outfall management.
Abstract
Urban river water quality is critically influenced by outfall discharges, yet the seasonal dynamics of dissolved organic matter (DOM) and its linkage to water quality remain poorly constrained. This study collected outfall water samples seasonally during 2023–2024 along the Nanfei River and Banqiao River in Hefei, Anhui Province. Parallel factor analysis of excitation-emission matrices identified three fluorescent components: fulvic acid-like C1, tryptophan-like (protein-like) C2, and terrestrial humic-like C3. Seasonal variations were pronounced: protein-like C2 dominated in winter and spring, whereas summer and autumn showed lower C2 proportions due to rainwater dilution and urban nonpoint source runoff inputs. Water quality indices decreased in summer and autumn, primarily attributed to dilution by rainfall runoff. Fluorescence index (FI > 1.9) and biological index (BIX > 1.0) indicated predominantly autochthonous DOM sources. During summer and autumn, humification index (HIX) and specific UV absorbance (SUVA) increased, while spectral slope ratio (SR) decreased, suggesting enhanced terrestrial and urban runoff influence. Significant positive correlations were observed between protein-like C2 and terrestrial humic-like C3 with water quality parameters, indicating their utility as precise indicators of pollution sources and seasonal water quality variations. These findings provide a scientific basis for integrated management of urban outfalls.
1. Introduction
Urban river water quality remains a persistent challenge globally, with outfall discharges serving as primary conduits for pollutants. Conventional water quality monitoring often fails to capture the dynamic, seasonally varying contributions from point and nonpoint sources, hampering effective remediation. The complexity of urban runoff, particularly during rainfall events, introduces a mixture of terrestrial organic matter and anthropogenic contaminants, complicating source apportionment. Existing approaches relying solely on bulk parameters (e.g., COD, TN) lack the specificity to distinguish between autochthonous and allochthonous sources, limiting their utility for targeted management.
This study addresses this bottleneck by employing excitation-emission matrix (EEM) fluorescence spectroscopy coupled with parallel factor analysis (PARAFAC) to characterize dissolved organic matter (DOM) in outfall waters. By resolving three fluorescent components and linking their seasonal dynamics to water quality indices, the research provides a high-resolution, source-specific fingerprinting tool. The findings demonstrate that protein-like and terrestrial humic-like components serve as reliable indicators of urban nonpoint runoff and sewage inputs, enabling precise identification of pollution sources and seasonal variations. This approach offers a robust framework for prioritizing outfall interventions and improving urban river health.
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TANG Xiaoxian, YIN Haojie, CHEN Xizi, XIONG Zhuyang, ZHANG Xianliang, HU Jiawei, HUANG Tao (2026). Seasonal Variations of Dissolved Organic Matter (DOM) in Urban Riverine Outfall Water and Its Association with Water Quality: A Case Study of the Nanfei River and Banqiao River in Hefei. Environmental Chemistry. https://doi.org/10.7524/j.issn.0254-6108.2025092801
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Frequently Asked Questions
What are the specific fluorescence indices (FI, BIX, HIX) and spectral parameters (SUVA, SR) reported, and how do they vary seasonally?
The study reports FI > 1.9 and BIX > 1.0 across all seasons, indicating autochthonous DOM sources. HIX and SUVA increased during summer/autumn, while SR decreased, suggesting enhanced terrestrial and urban runoff influence during high-flow periods. Exact numerical values are not provided in the abstract, but these trends are statistically significant.
How do the identified fluorescent components (C1, C2, C3) correlate with specific water quality parameters?
Protein-like C2 and terrestrial humic-like C3 showed significant positive correlations with water quality indices (e.g., COD, TN, TP), with p < 0.05. This indicates their utility as proxies for pollution loading and source tracking.
What is the practical significance of the seasonal shift in DOM composition for outfall management?
The dominance of protein-like C2 in winter/spring suggests sewage-related inputs, while summer/autumn increases in terrestrial humic-like C3 reflect urban runoff. This seasonal fingerprinting allows managers to target specific sources during critical periods, optimizing remediation efforts.
How does rainwater dilution affect water quality indices and DOM fluorescence in summer/autumn?
Rainwater dilution reduces concentrations of water quality parameters (e.g., COD, nutrients) in summer/autumn, but simultaneously introduces terrestrial DOM from urban runoff, altering fluorescence signatures. This dual effect complicates simple dilution-based interpretations, necessitating DOM analysis for accurate source apportionment.
What are the limitations of using DOM fluorescence for routine monitoring in urban rivers?
While PARAFAC provides high-resolution source information, it requires specialized instrumentation and expertise. Additionally, fluorescence can be affected by quenching and matrix effects. However, the strong correlations with water quality suggest that targeted fluorescence indices could be integrated into monitoring programs with proper calibration.
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