Characterization and sources of sedimentary organic matter in Xingyun Lake, Jiangchuan, Yunnan, China

Xingyun Lake plays a particularly important role in the retention and processing of organic matter in Yuxi City, China. In this study, geochemical analyses (grain size, OC, N, δ¹³C) were carried out. The April 2014 sediment was finer than the October 2013 sediment. OC content was in the range of 1.07–2.68 % showing a increasing OC content with decreasing percent sand from the October 2013 sediment to the April 2014 sediment. TN distribution in surface sediments followed a similar distribution and was commonly correlated with OC. The correlation of δ¹³C values and N/C ratios in sediment reflected a mixing of soil-derived and terrestrial organic matters. The Ali/Aro ratios from the solid-state ¹³C-NMR spectra exhibited more aliphaticity for April 2014 sediments. The isotopic analyses on the fatty acids of sediments from twenty sampling stations in Xingyun Lake indicated that terrigenous components can be assigned as the major sources of the organic matters in the lake sediments. The low yields in lignin in sediment pointed to nontypical terrigenous inputs to the lake sediments. Ratios of p-hydroxyacetophenone to p-hydroxyl phenols (Pon/P) in the surface sediments (0.08–0.22) over the all sampling stations in Xingyun Lake further demonstrated a contribution from soil-derived organic matters. It was observed a plot of the ratio of S/V versus C/V exhibited an organic input attributed to angiosperm nonwoods. The reworking of surficial sediments may result in a difference in organic input between the October 2013 sediment and the April 2014 sediment. Furthermore, the associated ratios of (Ad/Al)ᵥ, P/(V + S) in sediment indicated that the April 2014 sediments had experienced the lower degree of oxidation of lignin than the October 2013 sediments. This can be attributed to the higher fine particle content in the former sediments protecting organic matter than in the latter sediments, as revealed by the lower alkyl C/O–alkyl C ratio (A/O–A) in solid-state ¹³C NMR spectra of April 2014 samples.