• N V H K CHARI

      Articles written in Journal of Earth System Science

    • Comparison of the absorption characteristics of coloured dissolved organic matter between river and wave dominated distributaries of Godavari estuary, India

      N V H K CHARI CH VENKATESWAR RAO SHYAMALA P

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      Absorption spectra of coloured dissolved organic matter (CDOM) and their derived parameters such as, absorption coefficient and spectral slopes are useful to study the molecular weight distribution of DOM. Here CDOM absorption characteristics were assessed in two distributaries [Gautami (GGE) and Vasishta (VGE)] of the Godavari estuary to examine the differences in molecular weight characterization of CDOM and its origin with reference to the geomorphological features during post southwest monsoon (PSM), late northeast monsoon (LNM) and early southwest monsoon (ESM) seasons. In VGE, absorption coefficient (a$_{CDOM}$) exhibited significant negative correlation with total suspended matter (TSM) and salinity during PSM and LNM due to the local anthropogenic inputs. In GGE, the values of spectral slope S$_{275–295}$, and S$_{350–400 }$, were low and high, respectively during PSM, indicating the presence of pronounced terrestrial derived organic matter. In VGE, S$_{350–400 }$, showed increasing and decreasing trends from upstream to downstream in surface and bottom waters respectively during LNM, indicating that organic matter originated through in-situ microbiological processes. The spectral slope ratio, S$_{R}$ (S$_{275–295}$/S$_{350–400 }$) was higher in GGE during LNM (Avg  $\pm$   SD = 1.19  $\pm$  0.14) and ESM (1.47  $\pm$   0.27), which suggests the lower molecular weight organic matter formation through microbiological and photodegradation processes. However, in VGE, the values of S$_{R}$ during LNM (1.04  $\pm$   0.11) and ESM (1.08  $\pm$   0.17) were low, which indicates higher molecular weight organic matter formation due to biological production driven by local anthropogenic inputs or aquaculture effluents.

      $\bf{Highlights}$

      $\bullet$ This is first of its kind on the absorption characteristics of coloured dissolved organic matter (CDOM) with reference to the different geomorphological features of Godavari estuary.

      $\bullet$ Seasonal variation in the molecular weight characteristics of CDOM were studied in the Gautami and Vasishta Godavari estuaries.

      $\bullet$ High molecular weight terrestrial derived organic matter was more pronounced in the river dominated Gautami Godavari estuary during post southwest monsoon season.

      $\bullet$ High molecular weight in situ produced organic matter was more in the wave dominated Visishta Godavari estuary during late northeast and early southwest monsoon seasons driven by anthropogenic or aquaculture inputs.

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