Abstract
Chromophoric dissolved organic matter (CDOM) is a key component with a critical role in the littoral zones of eutrophic shallow lakes; yet the characteristics of CDOM in these zones remain seldom systematically reported. In this study, the differences in sources, biogeochemical characteristics, and fates of CDOM between the littoral zones of eutrophic lakes Taihu (LLT; frequently occurring algal blooms and longer lake residence time) and Hongze (LLH; no obvious algal blooms and shorter residence time) were compared during the algal bloom season using ultraviolet-visible spectra and excitation and emission matrix spectroscopy combined with parallel factor analysis. Three humic-like fluorescent dissolved organic matter (FDOM) components (C1, C3, and C4) and one protein-like component (C2) were identified. Results showed that FDOM components were dominated by protein-like fluorescent substances in LLT, and humic-like materials in LLH, respectively. The CDOM in LLT had a lower relative aromaticity and molecular weight, humification degree and a higher autotrophic productivity because of algal blooms. Furthermore, CDOM depletion rates in LLT were higher than those in LLH due to a longer lake residence time in LLT. In addition, CDOM shifted from high molecular weight to low molecular weight as the humification degree decreased during the CDOM depletion process. This comparative study showed that algal blooms and lake residence time were the significant factors for distinguishing characteristics of CDOM between littoral zones of shallow lakes on a similar trophic level. This study provides field-based knowledge for remote sensing CDOM measurement and serves as a reference for lakeshore aquatic environmental management.
Highlights
Chromophoric dissolved organic matter (CDOM), the colored fraction of dissolved organic matter (DOM), consisting of aromatics, carbohydrates, and humic, fulvic and proteinaceous materials, is an optically active substance in the water column that plays a momentous role in lake ecosystems [1,2,3].It affects the underwater light field [4], carbon and nutrient cycling [5], metal migration and transformation [6], and contaminant biotoxicity [7] in lakes and the drinking water treatment distributed along a lakeside [8]
The results show that there were significant differences in total phosphorus (TP) concentrations (p < 0.01) between the two lakeshore zones; there were no obvious differences in Total nitrogen (TN) concentrations (p = 0.44, NS)
During the changing process from the a(350)-enriched zone (Tin and had no significant loss from upstream (Hin)) to an a(350)-depleted area (Tout and Hout), the molecular weight and humification degree decreased correspondingly. This indicated that CDOM shifted from high molecular weight (HMW) to low molecular weight (LMW)
Summary
Chromophoric dissolved organic matter (CDOM), the colored fraction of dissolved organic matter (DOM), consisting of aromatics, carbohydrates, and humic, fulvic and proteinaceous materials, is an optically active substance in the water column that plays a momentous role in lake ecosystems [1,2,3]. It affects the underwater light field [4], carbon and nutrient cycling [5], metal migration and transformation [6], and contaminant biotoxicity [7] in lakes and the drinking water treatment distributed along a lakeside [8]. Optical indicative information by means of ultraviolet-visible (UV-Vis) absorption spectroscopy and excitation-emission matrix fluorescence spectroscopy (EEMs) has been widely applied and provide more insight into CDOM fractions and their chemical characteristics because the methods are sensitive, timesaving, informative and require a small sample volume [11,12,13]
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