Depth-dependent variations of dissolved organic matter composition and humification in a plateau lake using fluorescence spectroscopy.

In aquatic systems, dissolved organic matter (DOM) plays an important role in regulating the reactivity and transport of environmental pollutants. Fluorescence excitation-emission matrix (EEM) analysis combined with fluorescence regional integration (FRI) and parallel factorial analysis (PARAFAC) were applied to investigate the composition, humification degree and depth-dependent variation of DOM in Lake Baihua, China. The results showed that humic-like materials with more than 60% of percentage fluorescence response (Pi,n) were dominant in DOM. The molecular complexity and structural condensation of PARAFAC components showed the order of C1 (humic-like components) > C3 (protein-like components) > C4 (fulvic-like components) > C2 (fulvic-like components). The lower maximum fluorescence intensities (Fmax) of components in surface layers were attributed to photo-oxidation of DOM by radiation. With depths less than 16 m, the Fmax increases and decreases were attributed to accumulation of recalcitrant humic substances and microbial/abiotic degradation of particulate DOM, respectively. A combination of biological and humification indices could be used as indicators for distinguishing different degrees of humification and sources of DOM. DOM from Lake Baihua mainly originated from an aquatic bacterial source that consisted of an important/intermediate autochthonous component with a weak humic character. The fluorescence indices of PI,n/PII,n, PI+II+IV,n/PIII+V,n, C2, C1/C2 and C2/(C3+C4) were more suitable to determine the humification degree. Stronger humic characters and higher humification degree for DOM were present at depths of 10-13 m. The fluorescence spectroscopy combined with fluorescence indices is convenient to investigate depth-dependent DOM characteristics and to assess water quality or pollution risk in lake systems.

Song F ，Wu F ，Feng W ，Liu S ，He J ，Li T ，Zhang J ，Wu A ，Amarasiriwardena D ，Xing B ，Bai Y ... -  《-》

Characterizing variations in dissolved organic matter (DOM) properties in Nansi Lake: a typical macrophytes-derived lake in northern China.

Nansi Lake is the largest lake along the eastern route of China's South-to-North Water Diversion Project (SNWDP). It is divided into the upper lake and the lower lake by a dam. By using UV-Vis spectroscopy, synchronous fluorescence (SF) spectroscopy, excitation-emission matrix and parallel factor analysis (EEM-PARAFAC), spatial, and temporal differences in the properties of dissolved organic matter (DOM) were found in the 2 areas of Nansi Lake under different hydrological conditions. A total of 5 fluorescence components were obtained by EEM-PARAFAC, which included 3 humic-like components (C1-C3) and 2 protein-like components (C4 and C5). On the spatial scale, the fluorescence intensities (Fmax) of humic-like substances and the ratio of the fluorescence intensity of humic-like components to the total fluorescence intensity (%Fmax) and degree of humification (HIX) in the upper lake were higher than those in the lower lake. This indicated the strong contributions of terrestrial sources to the upper lake, while DOM properties in the lower lake were more endogenous than those in the upper lake. On the temporal scale, protein-like substances played a more important role in DOM properties in April (Fmax=0.72±0.03 in the upper lake and 1.84±0.13 in the lower lake) and July (Fmax=1.10±0.05 in the upper lake and 1.49±0.04 in the lower lake) than in October. This result might be related to the water transfer of the eastern route of the SNWDP and to the death of submerged plants. However, the contents of humic-like substances (ranging from 55.61±1.23% to 66.56±0.58% for the upper lake and 29.98±1.56% to 61.98±0.99% for the lower lake) and degree of humification (from 2.23±0.06 to 3.10±0.05 for the upper lake and 1.06±0.05 to 2.62±0.08 for the lower lake) in Nansi Lake showed an increasing trend from April to October. In addition, significant correlations and good linear relationships between humic-like components, a254, and DOC in the 3 months reflected the continuous contribution of humic-like substances to DOM properties in Nansi Lake. Rapid changes in the fluorescence signal were largely dependent on changes in water quality. The fluorescence signal could be a tool for the management of water quality in Nansi Lake.

Ren H ，Yao X ，Ma F ，Fan T ，Deng H ，Zhang Y ... -  《-》

The effect of anthropogenic impoundment on dissolved organic matter characteristics and copper binding affinity: Insights from fluorescence spectroscopy.

Excitation-emission matrix fluorescence spectroscopy combined with parallel factor analysis (EEM-PARAFAC) and two-dimensional correlation spectroscopy (2D-COS) were applied to evaluate the effects of anthropogenic impoundment on the characteristics of dissolved organic matter (DOM) and its heavy metal binding affinity. Three field-sampling cruises conducted in Hongze Lake from 2015 to 2016 were classified as early impoundment and late impoundment cruises according to the hydrological conditions. Five fluorescence components were derived from EEM-PARAFAC, including three humic-like components (C1C3) and two protein-like components (C4 and C5). The results show a higher dissolved organic carbon concentration, humification degree, molecular size, and level of terrestrial humic-like substances (C1C3) for early impoundment DOM compared with late impoundment DOM, which were derived from the relatively high inflow discharges present before impoundment. Meanwhile, the relatively high autochthonous contribution and level of protein-like substances found in late impoundment DOM suggested that anthropogenic impoundment can influence the DOM composition in Hongze Lake. Increases in the binding affinities (log Km) of humic-like substances (C1 and C3) and decreases in the log Km of tryptophan-like substances (C4) were observed during the impoundment period. Additionally, 2D-COS results suggested that the preferential Cu(II) binding ligands in early and late impoundment DOM were tryptophan- (C4) and humic-like (C1) substances, respectively. These results indicated that impoundment-derived DOM composition alteration can decrease the bioavailability and toxicity of Cu in Hongze Lake. The results reported here will improve the understanding of DOM and heavy metal cycling in impoundment lakes.

Hu B ，Wang P ，Wang C ，Qian J ，Hou J ，Cui X ，Zhang N ... -  《-》

Characteristics of Dissolved Organic Matter in Sediments of Typical Lakes in Southeastern Hubei Province, China.

Wu C ，Wu X ，Ge X ，Feng L ，Tan Y ，Yang J ，Ren W ，Zou M ... -  《-》

[Spectral Characteristics of Dissolved Organic Matter in Sediments from Poyang Lake].

Luo YQ ，Wan ZW ，Yan CX ，Nie MH ，Ding MJ ，Ju M ，Liu Y ... -  《-》