Abstract. Spatiotemporal variations in the characteristics of fluorescent dissolved organic matter (FDOM) components from 63 lakes across the Tibet Plateau, China, are examined using excitation-emission matrix spectra (EEM) and fluorescence regional integration (FRI) from 2014 to 2017. Freshwater (N = 135) and brackish water (N = 109) samples from 63 lakes were grouped according to salinity or electrical conductivity. In order to compare results between the lakes, cumulative volumes beneath the EEM values (φi, i = I, II, III, IV, V) were normalized to a DOC concentration of 1 mg/L. EEM-FRI identified tyrosine-like (φI), tryptophan-like (φII), fulvic-like (φIII), microbial protein-like (φIV), and humic-like (φV) fluorescence regions, as well as their proportions (Pi). Chromophoric dissolved organic matter (CDOM) absorption parameters, fluorescence indices, average fluorescence intensities of the five fluorescent components and total fluorescence intensities (φT) differed under spatial variation among brackish and freshwater lakes (ANOVA, p < 0.05). Principal component analysis (PCA) was used to assess and group five normalized FDOM components for all of the water samples. These results show that microbial protein-like (φIV), fulvic-like (φIII) and humic-like (φV) have positive correlations (R2 > 0.79, t-test, p < 0.01), indicating that these FDOM components may originate from similar sources. A correlation also exists between normalized φi (i = I, II, III, IV, V) and DOC concentrations with a salinity > 19 ‰ (averaged EC, 23 764 μs cm −1) (t-test, p < 0.01), of which R2 f regression analysis showed a decreasing tendency with EC. Similar correlations between a(254) and DOC concentrations (t-test, p < 0.01) are also evident for sunshine hours > 2900 h. Redundancy analysis (RDA) indicates that a(254) and a(350) have a correlation with CDOM in brackish lakes. a(254), HIX and a(350) were also correlated with water quality. Strong evapoconcentration, intense ultraviolet irradiance and landscape features of the Tibet Plateau may be responsible for the FDOM characteristics identified in this study.
Received: 01 Jun 2018 – Discussion started: 21 Aug 2018
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Inland lakes are a direct link among the land, atmospheric and oceans (via rivers). Little is currently known about colored dissolved organic matter and its relationship with water quality in lakes across the Tibet Plateau. For these brackish and saline lakes, a high salt content with accumulation of carbon and low organic colored dissolved matter in brackish lakes, indicating the influence of strong evapoconcentration, intense ultraviolet irradiance and landscapes.
Inland lakes are a direct link among the land, atmospheric and oceans (via rivers). Little is...
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