Search

The concentration and sources of organic nitrogen (ON) in lake sediment significantly affect the lake nitrogen cycle. However, the influencing factors and contributors to the ON accumulation rate (ONAR) are unclear. In this study, tree sediment cores from northern, eastern, and southern Dianchi Lake (DC-N, DC-E, and DC-S, respectively), sampled in July 2014, were used to study the effects of autochthonous and allochthonous sources on ON. The results showed that ON and the ONAR increased 2.4–5.1 and 2.6–4.8 times, respectively, from1900 to2000, especially since the 1980s, at which point algal blooms occurred more frequently. The ON contents decreased in the order: DC-S > DC-N > DC-E, whereas the ONAR values followed the order: DC-N > DC-S > DC-E, suggesting that the ONAR was influenced by ON content as well as depositional environmental conditions. The total concentrations of n-alkanes (n-C12 to n-C34) ranged from 4719.4 ng g− 1 to 61,959.6 ng g− 1 in the three sediment cores, each of which exhibited different n-alkanes characteristic variation with vertical depth. The sources of ON were mainly allochthonous (soil erosion and terrestrial plants) and autochthonous (algal and aquatic plants) in DC-S and DC-N, respectively, whereas they were primarily mixed planktonic and terrestrial sources in DC-E. Using the stochastic impacts by regression on population, affluence, and technology model to further examine the ONAR values revealed that 1% increase in temperature and nitrogen fertilizer can increase the ONAR by 73.8–86.2% and 73.2–151.3% in all sediments, especially in DC-S and DC-E. However, a 1% increase in construction area could reduce the ONAR by 2.4–14.2%, especially in DC-N. Overall, climate change and human activities determine the spatial and temporal ONAR variation in Dianchi Lake.

The regulation of lacustrine organic carbon (OC) burial by nutrient is an outstanding knowledge gap in the current understanding of lake carbon cycles. In this study, we determined how nutrients quantitatively correspond with OC burial using the parallel factor analysis (PARAFAC) method in Dianchi Lake, southwest China. Factors were classified into three types according to their historical sedimentation characteristics: the background factor (BF), response factor (RF), and contingency factor (CF). The BF represented the original OC input combination in the lake and was insensitive to nutrient changes. The RF represented the OC input combination that was induced or promoted by nutrient changes in the lake. The CF represented short-term discontinuous factors in sedimentary history, which may be related to unique historical events. The results indicate that changes in the total nitrogen (TN) to total phosphorus (TP) ratio correlated with changes in the BF contribution; whereas the quantity of OC was mainly correlated with TN. The90% of OC buried in sediment was quantitatively simulated by BF and RF; the driving effect of RF on OC burial was approximately 13 times higher than that of BF. It was observed that a 1 mg kg

Particulate organic carbon (POC) sources, which regulate dissolved organic carbon, sediment organic carbon, and inorganic carbon via deposition, degradation, and mineralization, play an important role in lake ecosystems. Linear or Bayesian algorithms on isotope and n-alkanes have been widely used to identify the source proportion of organic carbon. However, the applicability of these methods is ambiguous because of the unilateral advantages of each model and trace factors. To test the applicability of the various methods for identifying POC sources, we analyzed dual isotopes and n-alkanes in surface water samples of Lake Taihu, and Multi-source mixing model and Bayesian mixing model were used to distinguish between endogenous and exogenous contributions. Carbon isotope presented a clear advantage in West Taihu (-21.85 ± 0.78‰) and Southwest Taih (-22.61 ± 1.35‰); nitrogen isotope also showed high values in Meiliang Bay (9.76 ± 0.92‰). The majority of the lake was dominated by short-chain n-alkanes, except for East Taihu Lake (dominated by medium-chain n-alkanes) and areas with riverine input (dominated by long-chain n-alkanes). Different principles between the Bayesian mixing model (based on the Markov Chain Monte Carlo algorithm) and the Multi-source mixing model (based on linear estimation) caused discrepancies in the estimations of source contributions. But the fraction of chemical compounds during the migration process, and the overlap of potential sources play important role in the inconsistency of results. The estimations from the different models were consistent in indicating the dominance of endogenous organic carbon in Lake Taihu (mean of 60.18 ± 20.26%), particularly in the north and western regions (West Taihu, Meiliang Bay, and Southwest Taihu). This was likely due to algal aggregation influenced by human activities and climatic factors.

Two sediment cores were collected from Dianchi Lake, a plateau lake in Southwest China, to study the temporal trends and to investigate the sources of sedimentary deposited polycyclic aromatic hydrocarbon. The ΣPAH16 concentration in the two sediment cores ranged from 172.5 to 2244.8 ng/g and from 211.4 to 1777.8 ng/g, with mean values of 1106.2 and 865.1 ng/g, respectively. Three temporal trends for the ΣPAH16 concentration and the composition of PAHs in Dianchi Lake all showed three typical changing stages: (1) slight changes in deeper segments before the 1950s; (2) a rapid increase in PAH concentrations between the 1960s and 1990s; and (3) a slight reduction from the 1990s onward. These trends differ from those observed in developed countries due to differences in the timing of industrialization and urbanization processes. According to the results of the molecular ratios and principal component analysis, the PAH deposition was dominated by coal combustion, wood combustion, and vehicle emissions before and after the 1960s, respectively.

Lakes are important organic carbon (OC) traps in the global carbon cycle. Recent studies have shown that the rate of OC burial in lacustrine sediments is influenced by factors such as climate change, land-use change, and eutrophication. In this study, we use multiproxy methods to reveal the mechanisms of lacustrine sediment OC burial in an alpine lake (Cuopu Lake), in southwest China. Combined with the dating from 210Pbex and n-alkanes distribution analysis using the Positive Matrix Factorization model, the sedimentary history was divided into five stages: religious activity (the 1840s–1880s), earthquake (the 1880s–1910s), garrison (the 1910s–1960s), transition (the 1960s–1990s), and ecotourism (the 1990s–2010s). During the earthquake stage, OC burial was dominated by terrestrial solids (>40%) and co-precipitated algae (>30%), with a rapid deposition rate (>4 mm a−1) and low OC concentration (

A layer of flower-like super-hydrophobic film was fabricated on pure Mg surface by chemical etching in H(2)SO(4), H(2)O(2) and subsequent immersion in stearic acid (CH(3)(CH(2))(16)COOH) ethanol solution. The superhydrophobic surface showed a static water contact angle of 154 degrees with the sliding angle of about 3 degrees. With scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and Fourier-transform infrared (FT-IR) spectrometer, the microstructure and composition of the sample were analyzed. Results showed that the flower-like structure and the bonding of the CH(3)(CH(2))(16)COO on Mg surface can be responsible for the superior water-repellent property. Electrochemical impedance spectroscopy revealed that the transfer resistance of super-hydrophobic surface was increased about four times than bare Mg after one-hour immersion in 0.1 mol/L NaCl solution. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved.