Composition, source characteristic and indication of eutrophication of dissolved organic matter in the sediments of Erhai Lake

Composition and source characteristics of dissolved organic matter (DOM) in the surface sediments of Erhai Lake were studied by using fluorescence spectroscopy and UV–Vis absorbance. Moreover, the influence factors and the indication significance for eutrophication are also discussed. The results are as follows: (1) The DOC content of Erhai Lake sediments ranges from 0.17 to 0.77 g kg⁻¹, which is higher in dry season than that in wet season. Its DOC content of the sediment from the northern part is higher than that from the southern, and that is the smallest in the central. Moreover, DOM in Erhai Lake sediments comprise of protein- and humic-like substances. The average contents of protein-, fulvic acid-like substances and soluble microbial byproduct-like materials in the wet season are higher than those in the dry season by 25.92, 11.82 and 2.96 %, respectively; while the content of humic-like substance in the wet season is lower than that in the dry season by 6.94 %. As to the spatial distribution, the contents of protein- and fulvic acid-like substances are the highest in the central of Erhai Lake sediments, and that of the humic-like substance is the highest in the southern part. In addition, the humification degree of DOM in the dry season is higher than that in the wet season. (2) The DOM in Erhai Lake sediments mainly originated from terrestrial sources, of which the terrestrial pollutant has a main impact in the dry season, and the terrestrial pollutant input and biogenetic derivation play an equally important part in the wet season. Terrestrial pollutant and aquatic plants are the important factors that influence the DOM composition of Erhai Lake sediments. (3) The characteristic parameter (P₍III₊V,ₙ₎/P₍I₊II,ₙ₎) (the content ratio of humic-like substance to protein-like substances) of the DOM composition of Erhai Lake sediments is positively correlated with the contents of the different nitrogen (N) forms in the sediments (R ² = 0.68–0.83, P < 0.01). The contents of N forms in sediments and its source characteristic can be reflected by the P₍III₊V,ₙ₎/P₍I₊II,ₙ₎ value. So the P₍III₊V,ₙ₎/P₍I₊II,ₙ₎ value can be taken as the indirect indicator of the contents of N forms in sediments. Moreover, the composition characteristic of DOM in sediments can reflect the contents of N forms to some extent, that is, the risk of N release from Erhai Lake sediments can be indicated to some extent.