Comparison of the absorption characteristics of coloured dissolved organic matter between river and wave dominated distributaries of Godavari estuary, India,Journal of Earth System Science

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Comparison of the absorption characteristics of coloured dissolved organic matter between river and wave dominated distributaries of Godavari estuary, India
Journal of Earth System Science ( IF 1.9 ) Pub Date : 2021-05-27 , DOI: 10.1007/s12040-021-01582-6
N V H K Chari , Ch Venkateswararao , P Shyamala

Abstract

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_CDOM350) 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 ± SD = 1.19 ± 0.14) and ESM (1.47 ± 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 ± 0.11) and ESM (1.08 ± 0.17) were low, which indicates higher molecular weight organic matter formation due to biological production driven by local anthropogenic inputs or aquaculture effluents.

Research highlights

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.
Seasonal variation in the molecular weight characteristics of CDOM were studied in the Gautami and Vasishta Godavari estuaries.
High molecular weight terrestrial derived organic matter was more pronounced in the river dominated Gautami Godavari estuary during post southwest monsoon season.
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.

中文翻译：

印度戈达瓦里河口和波浪控制的支流之间有色溶解有机物吸收特征的比较

摘要

有色溶解有机物（CDOM）的吸收光谱及其推导参数，例如吸收系数和光谱斜率，对于研究DOM的分子量分布非常有用。在这里，通过哥达瓦里河口的两个分支[Gautami（GGE）和Vasishta（VGE）]对CDOM的吸收特性进行了评估，以参考西南季风后（PSM）期间的地貌特征检查CDOM的分子量特征及其来源的差异。，东北季风后期（LNM）和西南季风初期（ESM）的季节。在VGE中，由于局部人为输入，吸收系数（_CDOM 350）与PSM和LNM期间的总悬浮物（TSM）和盐度呈显着负相关。在GGE中，光谱斜率的值在PSM期间，S _275-295和S _350-400分别为低和高，表明存在明显的陆地衍生有机物。在VGE中，S _350–400在LNM期间分别从地表水和底水的上游到下游呈现出增加和减少的趋势，这表明有机物是通过原位微生物过程起源的。光谱斜率S _R（S _275–295 / S _350–400）在LNM（Avg±SD = 1.19±0.14）和ESM（1.47±0.27）期间的GGE较高，这表明通过微生物和光降解过程形成的分子量较低的有机物。然而，在VGE中，LNM（1.04±0.11）和ESM（1.08±0.17）期间的S _R值较低，这表明由于当地人为输入或水产养殖废水驱动的生物生产，形成了更高分子量的有机物。