Abstract Variations in the magnitude of terrestrial and anthropogenic inputs into estuaries, along with their tidal characteristics, might alter the source characteristics of dissolved organic matter (DOM) through microbiological processes and its export to adjacent coastal waters. To investigate this, observations of hydrochemical and fluorescence characteristics of DOM were conducted during the early monsoon (EM), late monsoon (LM), and post-monsoon (PM) seasons in 2018 across four estuaries along the west coast of India. These estuaries exhibit tidal amplitudes ranging from micro (<1 m) to macro (>5 m) and receive significant terrestrial and anthropogenic inputs. Parallel Factor Analysis (PARAFAC) of Excitation-Emission Matrix (EEM) spectra revealed distinct fluorophores (humic-like, protein-like, and unknown) and showed seasonal distribution in each estuary. In the estuary heavily influenced by terrestrial inputs, the presence of UV-humic-like (A) and UV-visible humic-like (C) fluorophores was observed, along with an additional unknown fluorophore (N) derived from biological processes. In contrast, the highly anthropogenically influenced estuary lacked fluorophores A and N contained the tyrosine protein-like (B) fluorophore, in addition to the tryptophan protein-like (T) fluorophore, which was found in all estuaries. Significant negative and positive correlations of humic-like fluorophores with salinity and dissolved organic carbon (DOC) were observed in anthropogenically influenced micro- and macro-tidal estuaries, indicating external sources of DOM. However, in terrestrial-dominated estuaries, the absence of these correlations suggests the predominance of in-situ derived DOM. This led to a significant export of biologically derived DOM into adjacent coastal waters in estuaries with tidal conditions intermediate between micro- and macro-tidal systems. Despite the greater anthropogenic influence in certain estuaries, the export of DOM to adjacent coastal waters was low due to its accumulation in the micro-tidal estuary, whereas in the macro-tidal estuary, labile DOM was formed through in-situ biological processes. Research highlights <UnorderedList Mark="Bullet"> <ItemContent> The source characteristics of dissolved organic matter vary with the magnitude of terrestrial and anthropogenic influences in the estuary. </ItemContent> <ItemContent> Enrichment of refractory organic matter occurs in microtidal estuaries, while labile organic matter is enriched in macrotidal estuaries. </ItemContent> <ItemContent> Significant export of organic matter to the adjacent coastal waters occurs more through mesotidal estuaries than through microtidal and macrotidal estuaries. </ItemContent> </UnorderedList>

Influence of terrestrial and anthropogenic factors on dissolved organic matter dynamics in west coast Indian estuaries: Insights from fluorescence spectroscopy

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发表日期：

2025年10月10日

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N V H K Chari,
B S K Kumar,
C K Sherin,
B Bikram Reddy,
G V M Gupta

摘要

Abstract

Variations in the magnitude of terrestrial and anthropogenic inputs into estuaries, along with their tidal characteristics, might alter the source characteristics of dissolved organic matter (DOM) through microbiological processes and its export to adjacent coastal waters. To investigate this, observations of hydrochemical and fluorescence characteristics of DOM were conducted during the early monsoon (EM), late monsoon (LM), and post-monsoon (PM) seasons in 2018 across four estuaries along the west coast of India. These estuaries exhibit tidal amplitudes ranging from micro (<1 m) to macro (>5 m) and receive significant terrestrial and anthropogenic inputs. Parallel Factor Analysis (PARAFAC) of Excitation-Emission Matrix (EEM) spectra revealed distinct fluorophores (humic-like, protein-like, and unknown) and showed seasonal distribution in each estuary. In the estuary heavily influenced by terrestrial inputs, the presence of UV-humic-like (A) and UV-visible humic-like (C) fluorophores was observed, along with an additional unknown fluorophore (N) derived from biological processes. In contrast, the highly anthropogenically influenced estuary lacked fluorophores A and N contained the tyrosine protein-like (B) fluorophore, in addition to the tryptophan protein-like (T) fluorophore, which was found in all estuaries. Significant negative and positive correlations of humic-like fluorophores with salinity and dissolved organic carbon (DOC) were observed in anthropogenically influenced micro- and macro-tidal estuaries, indicating external sources of DOM. However, in terrestrial-dominated estuaries, the absence of these correlations suggests the predominance of in-situ derived DOM. This led to a significant export of biologically derived DOM into adjacent coastal waters in estuaries with tidal conditions intermediate between micro- and macro-tidal systems. Despite the greater anthropogenic influence in certain estuaries, the export of DOM to adjacent coastal waters was low due to its accumulation in the micro-tidal estuary, whereas in the macro-tidal estuary, labile DOM was formed through in-situ biological processes.

Research highlights

The source characteristics of dissolved organic matter vary with the magnitude of terrestrial and anthropogenic influences in the estuary.

Enrichment of refractory organic matter occurs in microtidal estuaries, while labile organic matter is enriched in macrotidal estuaries.

Significant export of organic matter to the adjacent coastal waters occurs more through mesotidal estuaries than through microtidal and macrotidal estuaries.