Search Results (228)

Inland waters, serving as crucial carbon sinks and pivotal conduits within the global carbon cycle, are essential targets for carbon assessment under global warming and carbon neutrality initiatives. However, the extensive spatial distribution and inherent sampling challenges pose fundamental difficulties for monitoring dissolved organic carbon (DOC) in these systems. Since 2010, remote sensing has catalyzed a technological revolution in inland water DOC monitoring, leveraging its advantages for rapid, cost-effective long-term observation. In this critical review, we systematically evaluate research progress over the past two decades to assess the performance of remote sensing products and existing methodologies in DOC retrieval. We provide a detailed examination of diverse remote sensing data sources, outlining their application characteristics and limitations. By tracing uncertainties in retrieval outcomes, we identify atmospheric correction, spatial heterogeneity, and model and data deficiencies as primary sources of uncertainty. Current retrieval approaches—direct, indirect, and machine learning (ML) methods—are thoroughly scrutinized for their features, effectiveness, and application contexts. While ML offers novel solutions, its application remains nascent, constrained by limited waterbody-specific samples and model constraints. Furthermore, we discuss current challenges and future directions, focusing on data optimization, feature engineering, and model refinement. We propose that future research should (1) employ integrated satellite–air–ground observations and develop tailored atmospheric correction for inland waters to reduce data noise; (2) develop deep learning architectures with branch networks to extract DOC’s intrinsic shortwave absorption and longwave anti-interference features; and (3) incorporate dynamic biogeochemical processes within study regions to refine retrieval frameworks using biogeochemical indicators. We also advocate for multi-algorithm collaborative prediction to overcome the spectral paradox and unphysical solutions arising from the single data-driven paradigm of traditional ML, thereby enhancing retrieval reliability and interpretability. Full article

This study used Xinxin 2 (Juglans regia L. ‘Xinxin2’), a major cultivated walnut variety in Xinjiang, China, to clarify the response and adaptation mechanisms of the anatomical structures of walnut related to source–sink–flow under altered source–sink relationships. We anatomically observed the leaves, fruit stalks, and fruit of bearing branches by artificially adjusting the leaf-to-fruit ratio (LFR). The LFR substantially affected the leaf structure and thickness of the fruit-bearing branches obtained via girdled (p < 0.05). The results of the analysis of the leaf anatomy revealed that a low LFR impeded leaf growth and internal structural development while accelerating senescence, whereas a high LFR promoted leaf growth and delayed senescence. The same trend was observed for the phloem area (PA) of the fruit stalk with the increase in fruit load when the number of leaves on the fruit branch was the same. The maximum PA was reached when the number of fruits was high (except for 4L:3F). This indicates that the micro-anatomical structure of the fruit stalk is more developed under the treatment of a higher number of pinnate compound leaves and fruit level of LFRs. The cells of the 1L:3F and 2L:3F were considerably smaller in the green peel and kernel of the fruit on the branches obtained via girdled than those of 5L:1F plants (p < 0.05). No significant difference was found in the number of cells per unit area or the cross-sectional area of cells in the pericarp and kernel of the fruit under LFRs (p > 0.05); however, a large difference was noted in the microanatomical structure of the pericarp and kernel of fruit. Changes in the structural adaptation characteristics of walnut leaves (source), fruit stalk (flow), and fruit (sink) are related to source–sink regulation. A change in the LFR affects the carbohydrate synthesis in the leaves (source), transport in fruit stalks (flow), and the carbohydrate reception in fruits (sink). Full article

Non-structural carbohydrates (NSCs), the main substrates and energy carriers of plants, play an important role in mediating the source-sink balance of carbon (C). However, the trade-offs in the allocation of NSCs remain unclear at critical stages of fruit development. In this study, we evaluated the dynamic and allometric partitioning characteristics of NSCs at the key stage of fruit development in Camellia oleifera. The seed NSCs pool was the highest in the middle stage of rapid fruit expansion, and an inverted “V” shape appeared from July to September and peaked in August. Notably, although the NSC pool of twigs was the smallest and did not change significantly at each stage, the starch pool was the largest. Significant correlations existed between the NSC content of different organs in C. oleifera in the early stage of slow development and the middle stage of rapid fruit expansion. In particular, NSC components, both of the twigs in the early stage and of the twigs and seeds in the middle stage, showed significant allometric partitioning relationships. In summary, seeds are the main carbon sink for fruit development trade-offs of C. oleifera, and twigs may play an important role in transferring C to seeds at the early and middle stages of fruit development. In the future, attention should be paid to controlling the factors affecting the balance of plant C during the rapid fruit expansion period to ensure high yield. Full article

A lake is a sink, source, and converter of phosphorus, and its ability to intercept phosphorus in water bodies is receiving increasing attention. In this study, the Nanyi Lake sediment in the middle and lower reaches of the Yangtze River basin was taken as the research object, and the phosphorus adsorption capacity and influencing factors of the sediment in the basin were investigated through a control variable experiment. The adsorption capacities of sediments at the sample points are L₁ > L₃ > L₂, with maximum values of 372.41 mg/kg, 332.53 mg/kg, and 346.27 mg/kg, respectively. Equilibrium adsorption is reached at approximately 5 h for L₁ and L_2, and 10 h for L₃. The interaction between sediment and phosphorus involves physical adsorption and mono-layer adsorption. The increase in temperature does not promote phosphorus migration from overlying water to sediments, but instead triggers phosphorus release from sediments, indicating an exothermic process for phosphorus adsorption on sediments. When the phosphorus concentration in overlying water is below and above 1 mg/L, increasing disturbance intensity results in enhanced phosphorus adsorption and release in sediments, respectively. The presence of humus in the overlying water, especially humic acid compared with fulvic acid, causes stronger adsorption of phosphorus on sediments. Overall, this study contributes to our understanding of phosphorus adsorption characteristics and mechanisms in Nanyi Lake sediments, providing valuable insights for managing and conserving this freshwater ecosystem. Full article

The Upper Triassic Xujiahe Formation in the western Sichuan Basin is rich in natural gas resources and is one of the main tight sandstone gas-producing layers in the Sichuan Basin. Taking the tight sandstone of the second member of the Xujiahe Formation (Xu-2 Member) in the western Sichuan Basin as the study target, based on the analysis of the rock sample, a thin section, scanning electron microscopy, inclusion, the carbon and oxygen isotope, the petrological characteristics, the reservoir properties, the diagenetic sequences, and the pore evolution processes were revealed. The tight sandstones are composed of litharenite, sublitharenite, and feldspathic litharenite with an average porosity of 3.81% and a permeability mainly ranging from 0.01 to 0.5 mD. The early to late diagenetic stages were revealed, and the diagenetic evolution sequence with five stages was constructed. The Xu-2 sandstones were subdivided into three different types, and each type has its own tightening factors and processes. In the quartz-rich sandstone, the compaction and pressure solution were the primary causes of reservoir tightening, while late fracturing and dissolution along fractures were the main factors improving reservoir properties. In the feldspar-rich sandstone, early dissolution was a primary factor in improving porosity, while carbonate and quartz cements generated by dissolution contributed to a decrease in porosity. In the rock-fragment-rich sandstone, chlorites formed in the early stage and dissolution were the main factors of reservoir quality improvement, while the authigenic quartz formed in the middle diagenetic stage was the primary cause of reservoir tightening. Four major source-to-sink systems were identified in the western Sichuan Basin and they have different reservoir characteristics and reservoir quality controlling factors. This study will contribute to a deeper understanding of the characteristics, diagenetic evolution, and tightening process of tight sandstone reservoirs, effectively promoting scientific research and the industrial development of tight sandstone gas in the Xu-2 Member of the Sichuan Basin. Full article

Natural gas hydrates are a promising alternative energy source for oil and gas in the future. However, geomechanical issues, such as wellhead instability, may arise, affecting the safe and efficient development of hydrates. In the present work, a sensitivity analysis was performed on sediment subsidence and wellhead instability during the development of marine hydrates using a multi-field coupled model. This is accomplished by adjusting the corresponding parameters based on the basic data of the default case. Meanwhile, the corresponding influencing mechanisms were explored. Finally, design recommendations for operation parameters were proposed based on the research findings regarding wellhead stability. It was found that the wellhead undergoes rapid sinking during a certain period in the early stage of hydrate development, followed by a slower, continued sinking. The sensitivity analysis found that when the depressurization amplitude is small, the wellhead sinking is also minimal. To maintain wellhead stability during the development process, it is recommended that neither the depressurization amplitude or drawdown pressure exceed 3.0 MPa. Although a high heating temperature can increase gas production to some extent, the accompanying excessive hydrate dissociation may compromise the stability of both the formation and wellhead. To balance gas production and wellhead stability, it is recommended that the heating amplitude does not exceed 50 °C. In addition, the permeability influences the distribution of pore pressure, which in turn affects sediment subsidence and wellbore stability. Wellhead stability deteriorates as permeability increases. Therefore, it is crucial to accurately determine the reservoir characteristics (such as permeability) before developing hydrates to avoid wellhead instability. Finally, the investigation results reveal that using different versions of the investigation model can impact the accuracy of the results, and neglecting certain physical fields may lead to an underestimation of the wellhead sinking. Full article

Understanding the contributions of source–sink relationships to photosynthesis will help achieve high wheat grain yields. A single-factor field experiment was conducted to quantify the regulatory effects of different sink–source ratios on wheat photosynthetic characteristics, including two wheat cultivars with different source–sink relationships as materials for detailed source–sink manipulations through flag leaf removal (LR) and removal of spikelets on one side of each spike (SR). Compared with a control (CK), LR increased the sink–source ratio (23.84%) and significantly reduced the yield (16.17%), 1000-kernel weight (11.73%), and kernels per spike (7.33%). LR increased the leaves’ net photosynthetic rate (Pn) (4.27–15.82%), the electron transfer rate (3.97–14.93%), and the Rubisco activity (2.16–12.25%) in the short term, and LR increased sucrose synthesis-related enzyme activities (3.96–19.95%) and gene expressions (SPS1, SUS1, CIN1, and SUT1). Compared with CK, SR reduced the sink–source ratio (44.12%) and significantly increased the 1000-kernel weight (10.02%) but reduced the yield (43.93%) and kernels per spike (49.31%). SR reduced the leaves’ Pn (8.54–21.41%), the electron transfer rate (3.51–16.71%), and the Rubisco activity (5.96–21.51%), and the photosynthetic process was limited. SR decreased sucrose synthesis-related enzyme activities (5.12–29.09%) and gene expressions (SPS1, SUS1, CIN1, and SUT1). Therefore, a higher sink–source ratio is an important indicator of high photosynthetic efficiency, which can be used as a screening and judgment index in variety selection and cultivation regulation. Full article

The rural population shrinkage caused by China’s imbalanced regional development poses challenges to infrastructure configuration and operation. Traditional centralized sewage treatment models face issues in cost-effectiveness, facility utilization rates, and sustainable maintenance, necessitating the exploration of adaptive governance technologies under new demographic conditions. The utilization-driven governance approach is recognized as an emerging method for rural domestic sewage management. This study selects Heyang County, a representative agricultural area in Guanzhong Plain, as a case study. Through mixed-methods research integrating qualitative and quantitative approaches, we analyze the correlation between the Population Shrinkage Index (PSI) and facility operational efficiency, investigate the impact of resident population dynamics on rural sewage treatment patterns, and establish a theoretical “Source–Transmission–Sink” framework. Synthesizing local traditional governance practices with modern technological solutions, we propose a resource-oriented treatment system adapted to population shrinkage trends, comprising three technical components: source process reduction, transmission process interception, and sink process attenuation. This research emphasizes adjusting green water infrastructure (GWI) spatial configurations according to village characteristics in production–living–ecological spaces, forming a hierarchical attenuation mechanism through circular transmission pathways. This facilitates the transition from gray-infrastructure-dependent models to holistic pollution control systems with resource recovery capabilities. The findings provide theoretical foundations for policymaking and infrastructure planning in rural sewage management, offering significant references for sustainable rural water resource governance. Full article

In this study, based on high-resolution online monitoring data of CO₂ concentration in Nanning City in the spring of 2024, we analyzed the characteristics of diurnal and monthly changes of CO₂ concentration in Nanning City and explored the influencing factors through the background sieving method and Lagrangian Particle Dispersion Model (LPDM) traceability simulations combined with meteorological factor analysis. The results demonstrates that the diurnal variation of CO₂ concentration in Nanning City exhibits a bimodal pattern of peak in the afternoon and trough in the early morning, with a mean concentration of 460 ± 15 ppm. Transportation emissions were identified as the dominant source of this variation. The trend of monthly concentration changes was first increasing and then decreasing, with an increase in February–March and a decrease in April, indicating that it was affected by the combined effect of vegetation photosynthesis and urban human activities. The results of the background sieving method and traceability simulation analysis showed that the CO₂ concentration in Nanning City was more affected by local emission sources than sinks, and the industrial sources and transportation sources in the north–south direction had a significant effect on the CO₂ concentration. This research provides critical data support for formulating carbon reduction strategies and coordinated atmospheric environment management in subtropical cities. Full article

Global warming caused by the increase in the atmospheric CO₂ content has become a focal environmental issue of common concern to the international community. As a key resource support for achieving the “dual carbon” goals in Western China, Sichuan Province requires a deep analysis of its carbon sources, carbon sinks, and its characteristics in terms of atmospheric environmental capacity, which is of great significance for formulating effective regional sustainable development strategies and responding to global climate change. In view of the unique geographical and climatic conditions in Sichuan Province and the current situation of a low and uneven distribution of atmospheric environmental capacity, this paper uses three forms of multi-source satellite data, OCO-2, OCO-3, and GOSAT, combined with other auxiliary data, to generate a daily XCO₂ concentration dataset with a spatial resolution of a 1km grid in Sichuan Province from 2015 to 2022. Based on the Optuna optimization method with 10-fold cross-validation, the optimal hyperparameter configuration of the four base learners of Stacking, random forest, gradient boosting decision tree, extreme gradient boosting, and the K nearest neighbor algorithm is searched for; finally, the logistic regression algorithm is used as the second-layer meta-learner to effectively improve the prediction accuracy and generalization ability of the Stacking ensemble learning model. According to the comparison of the performance of each model by cross-validation and TCCON site verification, the Stacking model significantly improved in accuracy, with an R², RMSE, and MAE of 0.983, 0.87 ppm and 0.19 ppm, respectively, which is better than those of traditional models such as RF, KNN, XGBoost, and GBRT. The accuracy verification of the atmospheric XCO₂ data estimated by the model based on the observation data of the two TCCON stations in Xianghe and Hefei showed that the correlation coefficients were 0.96 and 0.98, and the MAEs were 0.657 ppm and 0.639 ppm, respectively, further verifying the high accuracy and reliability of the model. At the same time, the fusion of multi-source satellite data significantly improved the spatial coverage of XCO₂ concentration data in Sichuan Province, effectively filling the gap in single satellite observation data. Based on the reconstructed XCO₂ dataset of Sichuan Province, the study revealed that there are significant regional and seasonal differences in the XCO₂ concentrations in the region, showing seasonal variation characteristics of being higher in spring and winter and lower in summer and autumn; in terms of the spatial distribution, the overall spatial distribution characteristics are high in the east and low in the west. This study helps to deepen our understanding of the carbon cycle and climate change, and can provide a scientific basis and risk assessment methods for policy formulation, effect evaluation, and international cooperation. Full article

Silicon (Si) is one of the biogenic elements in lake aquatic ecosystems. Sediments are both sinks and sources of Si, but little is known about its influence on the biogeochemical cycle of Si in lakes and its relationship to other biogenic factors such as carbon and nitrogen. Examining Caohai Lake, a typical macrophytic lake in China, this study systematically examined the different Si forms and biogenic silica (BSi) distribution characteristics and their coupling relationships with total organic carbon (TOC) and total nitrogen (TN) in surface sediments. Iron–manganese-oxide-bonded silicon (IMOF-Si) and organic sulfide-bonded silicon (OSF-Si) jointly accounted for 95.9% of Valid-Si in the sediments, indicating that the fixation of Si by organic matter and iron–manganese oxides was the main mechanism underlying the formation of the different forms of Valid-Si in sediments. The release and recycling of Si in sediments may be mainly driven by mineralized degradation of organic matter and anoxic reduction conditions at the sediment–water interface. The content of biogenic Si (BSi) in the sediments was relatively higher in the southern and eastern areas, which could be explained by the intensification of eutrophication and the increased abundance of diatomaceous siliceous organisms in these areas seen in recent years. The TOC and TN contents in the sediments were generally high, and the sources of organic matter in the sediments included both the residues of endophytes (main contributors) and the input of terrigenous organic matter. TOC and TN both had highly significant correlations with OSF-Si and Valid-Si, which demonstrated that Valid-Si had excellent coupling relationships with C and N in the sediments. The good correlation between BSi, TOC and TN (p < 0.01), as well as the high C/Si, N/Si mole ratio of TOC and TN to BSi, respectivelny, indicating that the dissolution and release rate of BSi may be much higher than the degradation rate of organic matter from the sediments, especially in the areas with a higher abundance of siliceous organisms. Full article

Highlighting the importance of artificial intelligence and machine learning approaches in engineering and fluid mechanics problems, especially in heat transfer applications is main goal of the presented article. With the advancement in Artificial Intelligence (AI) and Machine Learning (ML) techniques, the computational efficiency and accuracy of numerical results are enhanced. The theme of the study is to use machine learning techniques to examine the thermal analysis of MHD boundary layer flow of Eyring-Powell Hybrid Nanofluid (EPHNFs) passing a horizontal cylinder embedded in a porous medium with heat source/sink and viscous dissipation effects. The considered base fluid is water ($H_{2}O$) and hybrid nanoparticles titanium oxide (${TiO}_2$) and Copper oxide ($CuO$). The governing flow equations are nonlinear PDEs. Non-similar system of PDEs are obtained with efficient conversion variables. The dimensionless PDEs are truncated using a local non-similarity approach up to third level and numerical solution is evaluated using MATLAB built-in-function bvp4c. Artificial Neural Networks (ANNs) simulation approach is used to trained the networks to predict the solution behavior. Thermal boundary layer improves with the enhancement in the value of $Rd$. The accuracy and reliability of ANNs predicted solution is addressed with computation of correlation index and residual analysis. The RMSE is evaluated [0.04892, 0.0007597, 0.0007596, 0.01546, 0.008871, 0.01686] for various scenarios. It is observed that when concentration of hybrid nanoparticles increases then thermal characteristics of the Eyring-Powell Hybrid Nanofluid (EPHNFs) passing a horizontal cylinder. Full article

Average global temperatures have risen by approximately 1.1 °C above pre-industrial levels, prompting South Korea and many other countries to set a carbon neutrality goal by 2050. Expanding green spaces has been proposed as a landscape-based approach to achieving urban carbon neutrality. However, the dense development of urban areas presents spatial and economic constraints in securing new green spaces. As a result, street trees, an existing urban green infrastructure, are increasingly regarded as a practical solution to enhancing carbon storage. Nevertheless, concerns have been raised that street trees planted without a systematic management plan may suffer from reduced vitality, leading to diminished carbon storage capacity. Ultimately, these conditions can result in increased tree mortality, turning what should be carbon sinks into sources of emissions. Such tree mortality not only results in the loss of carbon storage but also degrades the urban landscape, making systematic street tree management essential. This study aimed to address these challenges by developing an effective diagnostic approach to assess street tree growth conditions and identify methods to improve their carbon storage capacity. The methodology included identifying diagnostic indicators through a review of prior research and conducting field surveys on 72 Ginkgo biloba in Dalseo-gu, Daegu Metropolitan City. Correlation and regression analyses were performed, taking into account both growth diagnostic indicators and environmental variables. The results revealed that traffic volume and service population were the main environmental factors affecting the carbon storage capacity of Ginkgo biloba. Among the individual growth characteristics, tree height (β = 0.514), chlorophyll content (β = 0.26), and stem vigor (β = 0.216) were found to have significant influences. Based on these findings, this study proposed a management strategy to enhance the growth and carbon storage potential of urban street trees. These results are expected to serve as a vital foundational resource, contributing to the development of practical street tree management guidelines that support sustainable urban environments and climate change mitigation efforts. Full article

Net ecosystem productivity (NEP) is a crucial metric for quantifying carbon storage, exchange, and cycling across global atmospheric and terrestrial ecosystems. This study examines the spatiotemporal patterns of NEP in China’s Zoigê alpine grassland and its response to climate variability, phenological changes, and soil conditions from 2000 to 2020. The results show a statistically significant increase in the annual NEP of the Zoigê Plateau, with an average rate of 3.18 g C/m²/year. Spatially, NEP displays strong heterogeneity, with higher values in the southwestern and northeastern marginal areas (>80 g C/m²) and lower values in the central region (<0 g C/m²). In alpine meadows (standardized total effect coefficient [STEC] = 0.52) and alpine steppes (STEC = 0.43), NEP is primarily regulated by soil moisture modulation, influenced by both water and temperature factors. This study accurately assesses NEP by incorporating regional soil characteristics, providing a more precise evaluation of changes in vegetation carbon sink sources in high-altitude areas. Full article

Recent breakthrough exploration wells in the Huagang Formation in the Y-area of the central anticlinal zone of the Xihu Sag have confirmed the significant exploration potential of structure–lithology complex hydrocarbon reservoirs. However, limited understanding of the provenance system, sedimentary facies, and microfacies has hindered further progress in complex hydrocarbon exploration. Analysis of high-precision stratigraphic sequences and seismic facies data, mudstone core color, grain-size probability cumulative curves, core facies, well logging facies, lithic type, the heavy-mineral ZTR index, and conglomerate combinations in drilling sands reveals characteristics of the source sink system and provenance direction. The Huagang Formation in the Y-area represents an overall continental fluvial delta sedimentary system that evolved from a braided river delta front deposit into a meandering river channel large-scale river deposit. The results indicate that the primary provenance of the Huagang Formation in the Y-area of the Xihu Sag is the long-axis provenance of the Hupi Reef bulge in the northeast, with supplementary input from the short-axis provenance of the western reef bulge. Geochemical analysis of wells F1, F3, and G in the study area suggests that the prevailing sedimentary environment during the period under investigation was characterized by anoxic conditions in nearshore shallow waters. This confirms previous research indicating strong tectonic reversal in the northeast and a small thickness of the central sand body unrelated to the flank slope provenance system. The aforementioned findings deviate from conventional understanding and will serve as a valuable point of reference for future breakthroughs in exploration. Full article