Instability in a carbon pool driven by multiple dissolved organic matter sources in a eutrophic lake basin: Potential factors for increased greenhouse gas emissions.

Lakes serve as vital reservoirs of dissolved organic matter (DOM) and play pivotal roles in biogeochemical carbon cycles. However, the sources and compositions of DOM in freshwater lakes and their potential effects on lake sediment carbon pools remain unclear. In this study, seven inflowing rivers in the Lake Taihu basin were selected to explore the potential effects of multi-source DOM inputs on the stability of the lake sediment carbon pool. The results showed the high concentrations of dissolved organic carbon in the Lake Taihu basin, accompanied by a high complexity level. Lignins constituted the majority of DOM compounds, surpassing 40% of the total, while the organic carbon content was predominantly composed of humic acids (1.02-3.01 g kg-1). The high amounts of lignin oxidative cleavage led to CHO being the main molecular structure in the DOM of the seven rivers. The carbon constituents within the sediment carbon reservoir exhibited a positive correlation with dissolved CH4 and CO2, with a notable emphasis on humic acid and dissolved CH4 (R2 = 0.86). The elevated concentration of DOM, coupled with its intricate composition, contributed to the increases in dissolved greenhouse gases (GHGs). Experiments showed that the mixing of multi-source DOM can accelerate the organic carbon mineralization processes. The unit carbon emission efficiency was highest in the mixed group, reaching reached 160.9 µmol∙Cg-1, which also exhibited a significantly different carbon pool. The mixed decomposition of DOM from different sources influenced the roles of the lake carbon pool as source and sink, indicating that the multi-source DOM of this lake basin was a potential driving factor for increased carbon emissions. These findings have improved our understanding of the sources and compositions of DOM in lake basins and revealed their impacts on carbon emissions, thereby providing a theoretical basis for improving assessments of lake carbon emissions.

Particulate organic carbon potentially increases methane emissions from oxic water of eutrophic lakes.

Lakes are hot spots for methane (CH4) emissions and particulate organic carbon (POC) production, which describes the methane paradox phenomenon. However, the current understanding of the source of POC and its effect on CH4 emissions during eutrophication remains unclear. In this study, 18 shallow lakes in different trophic states were selected to investigate the POC source and its contribution to CH4 production, particularly to reveal the underlying mechanisms of the methane paradox. The carbon isotopic analysis showed that the δ13Cpoc ranged from -30.28 ‰ to -21.14 ‰, indicating that cyanobacteria-derived carbon is an important source of POC. The overlying water was aerobic but contained high concentrations of dissolved CH4. Particularly, in hyper-eutrophic lakes, such as Lakes Taihu, Chaohu, and Dianshan, the dissolved CH4 concentrations were 2.11, 1.01, and 2.44 µmol/L, while the dissolved oxygen concentrations were 3.11, 2.92, and 3.17 mg/L, respectively. The intensified eutrophication increased the POC concentration, concomitantly promoting the dissolved CH4 concentration and the CH4 flux. These correlations revealed the role of POC in CH4 production and emission fluxes, particularly as a possible cause of the methane paradox, which is crucial for accurately evaluating the carbon budget and balance in shallow freshwater lakes.

Space-for-time substitution leads to carbon emission overestimation in eutrophic lakes.

Lacustrine eutrophication is generally considered as an important contributor of carbon emissions to the atmosphere; however, there is still a huge challenge in accuracy estimating carbon emissions from lakes. To test the effect of widely used space-for-time substitution on lake carbon emissions, this study monitored different processes of carbon emissions, including the carbon production potential, dissolved carbon concentrations, and carbon release fluxes in eight lakes along the trophic gradients on a spatial scale and the typical eutrophic Lake Taihu for one year on a temporal scale. Eutrophication promoted carbon production potential, dissolved carbon concentrations, and carbon release fluxes, especially for CH4. Trophic lake index (TLI) showed positive correlations with the CH4 production potential, dissolved CH4 concentrations, and CH4 release fluxes, and also positive correlations with the CO2 production potential, dissolved CO2 concentrations, and CO2 release fluxes. The space-for-time substitution led to an overestimation for the influence of eutrophication on carbon emissions, especially the further intensification of lake eutrophication. On the spatial scale, the average CH4 production potential, dissolved CH4 concentrations and CH4 release fluxes in eutrophic lakes were 268.6, 0.96 µmol/L, and 587.6 µmol m-2·h-1, respectively, while they were 215.8, 0.79 µmol/L, and 548.6 µmol m-2·h-1 on the temporal scale. Obviously, CH4 and CO2 emissions on the spatial scale were significantly higher than those on the temporal scale in eutrophic lakes. The primary influencing factors were the seasonal changes in the physicochemical environments of lake water, including dissolved oxygen (DO) and temperature. The CH4 and CO2 release fluxes showed negative correlations with DO, while temperature displayed positive correlations, respectively. These results suggest that the effects of DO and temperature on lake carbon emissions should be considered, which may be ignored during the accurate assessment of lake carbon budget via space-for-time substitution in eutrophic lakes.

Simulation of generation and dynamics of polarization singularities with circular Airy beams.

The generation and dynamics of polarization singularities have been underresearched for years, while the focusing property of the topological configuration has not been explored much. In this paper, we simulated the generation of low-order polarization singularities with a circular Airy beam and explored the focusing property of the synthetic light field during propagation due to the autofocusing of the component. Our work researched the focusing properties of the polarization singularity configuration, which may help to develop its application prospect.

Condition for far-zone spectral isotropy of light transmitted from Young's pinholes scattering on a quasi-homogeneous medium.

The far-zone spectral isotropy of light transmitted from Young's pinholes on scattering from a quasi-homogeneous medium has been discussed. A sufficient condition for the far-zone spectral isotropy has been derived as a new scaling law. Our result not only is analogous with the scaling law for weak scattering in previous works but is also applicable for a more general situation where the incident light has an arbitrary spectral degree of coherence. More discussion about cross-spectral purity of the far field is presented.

Second-order moments of Schell-model beams with various correlation functions in atmospheric turbulence.

The general formulae for second-order moments of Schell-model beams with various correlation functions in atmospheric turbulence are derived and validated by the Bessel-Gaussian Schell-model beams and cosine-Gaussian-correlated Schell-model beams. Our finding shows that the second-order moments of partially coherent Schell-model beams are related to the second-order partial derivatives of source spectral degree of coherence at the origin. The formulae we provide are much more convenient to analyze and research propagation problems in turbulence.

[Endpoint Temperature Prediction of the Basic Oxygen Furnace Based on the Flame Temperature Measurement at the Converter Mouth].

In the basic oxygen steelmaking process, the endpoint temperature of the molten steel is one of the key factors whether the molten steel is qualified for tapping. Currently, it mainly relies on the experienced operators to control the endpoint temperature of the molten steel, and the prediction precision may vary among different operators. In order to realize the effectively end-point steel temperature prediction of the basic oxygen furnace as well as to meet the requirement of different sizes of the converter mouth, a new method based on the flame temperature measurement at the converter mouth was proposed in this paper. Firstly, a fiber-optic spectrometer system in the visible and near infrared spectral range was designed which can real-timely and effectively realize the collection of the flame radiation information at the converter mouth. Secondly, in consideration of the actual temperature of the flame and the distance between the converter and the designed system, an improved calibration method instead of the halogen lamp was adopted, and the two-color method was employed for the flame temperature measurement. Then a regression model based on the support vector machine was built with the flame temperature and several other parameters of the steel-making process as the input variables of the model. Verification experiment was carried out on 68 industrial data collected in the steel-making workshop. The results show that the prediction accuracy of this method is superior to the experienced operators, and close to the sub-lance based method. As a result, the proposed method can provide a feasible and effective solution to the end-point steel temperature prediction for those small-sized and medium-sized converters.

Effect of astigmatism on states of polarization of aberrant stochastic electromagnetic beams in turbulent atmosphere.

The effect of astigmatism on states of polarization of aberrant stochastic electromagnetic beams in turbulent atmosphere is investigated. Using the Gaussian-Schell model source with astigmatism, the analytical formula for the degree of polarization, the orientation angle, and the degree of polarization ellipse are derived. Analytical results show that different strengths of astigmatism have different effects on states of polarization on propagation. It is also shown that when the astigmatic coefficient of sources is large enough, states of polarization are hardly affected by atmospheric turbulence and the free-space diffraction phenomenon. The sufficient conditions for propagating with invariant polarization are derived and discussed.