Temporal variation in sediment C, N, and P stoichiometry in a plateau lake during sediment burial
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Variation in C/N/P stoichiometry during sediment burial is related to elemental biogeochemistry cycles from the hydrosphere to the lithosphere. However, C/N/P stoichiometry change in lakes is still unclear although lakes are an important burial site of terrestrial matter. The purpose of this study was to determine the variation in C/N/P stoichiometry and its influencing factors in the burial processes of lake sediments.
Materials and methods
Two sediment cores (cores 4 and 5) were collected from a plateau lake (Dianchi Lake, China) in July 2014. The CRS 210Pb dating model of was used to estimate the vertical chronological distribution for each layer. Total, organic, and inorganic carbon (TC, TOC, TIC), nitrogen (TN, TON, TIN), and phosphorus (TP, TOP, TIP) were analyzed to determine variation patterns in the C/N (RCN, ROCN, RICN), C/P (RCP, ROCP, RICP), and N/P ratios (RNP, RONP, RINP) in lake sediments.
Results and discussion
The results showed that TOC, TON, and TIP were the main constituents of TC, TN, and TP in both sediment cores, respectively. After 1960, the burial rates of TOC and TON in core 4 exhibited rapidly increasing trends, coincident with TC and TN. In core 5, the increase occurred after 1980. Significant differences in C/N/P stoichiometry were observed in cores 4 and 5, dominated by allochthonous and autochthonous sources, respectively. RCP and RNP in core 4 were higher than in core 5; the difference in RCN was insignificant. RCN exhibited irregular large fluctuations in the middle layer, with mean values of 20.9 ± 4.0 and 17.3 ± 8.1 for cores 4 and 5, respectively. RCP and RNP declined rapidly with time, indicating that the losses of C and N might be higher than that of P. ROCN, ROCP, and RONP followed the same vertical decreasing pattern as RCN, RCP, and RNP, but RICN and RINP did not. Mineralization could be the primary driver and different sources played a regulatory role in the temporal variation of stoichiometry.
Sediment stoichiometry (RCN, RCP, RNP) decreased with time might be mainly due to selective outcome of mineralization and be regulated by different organic matter sources. RCP, ROCP, RNP, and RONP showed significantly decreasing trends with age, whereas RCN and ROCN were relatively consistent. Vertical distribution of inorganic ratios differed from that of organic and total proportions. Further research is needed to determine influencing factors on these ratios and to clarify the role of C/N/P stoichiometry in freshwater ecosystems.
KeywordsAutochthonous and allochthonous sources Dianchi Lake Lake sediments Sediment stoichiometry
We would like to thank Editage (www.editage.cn) for English language editing.
This study was financially supported by the National Natural Science Foundation of China (Grant nos. 41773097, 41673108), a project funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions, the State Key Laboratory of Lake Science and Environment (2016SKL005), and the Jiangsu Planned Projects for Postdoctoral Research Funds.
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