Southern Regions Of China Research Articles

Quantifying the contributions of climate change and human activities to vegetation dynamic in China based on multiple indices

Distinguishing the respective roles of climate change and anthropogenic activities can provide crucial information for sustainable management of the environment. Here, using the residual trend method (RESTREND), which measures the residue of the actual and potential trends of vegetation, we quantified the relative contributions of human activities (e.g., ecological restoration, overgrazing, and urbanization) and climate change (the warmer and wetter trend) to vegetation dynamics in China during 1988–2018 based on multiple vegetation indices, including the vegetation optical depth (Ku-VOD, C-VOD), normalized difference vegetation index (NDVI), and gross primary productivity (GPP). The results showed that the VOD, NDVI, and GPP exhibited overall increasing trends during 1988–2018. Human activities contributed >70% to the increases in NDVI and GPP in China, whereas a counterbalanced contribution of human activities and climate change was identified for the VOD dynamics (51% vs. 49%). Regions with high contributions from human activities to NDVI, GPP, and VOD were located in northeastern, southern, central, and northwestern China. In northern China, the positive impacts of human activities on NDVI (78%) and BEPS-GPP (83%) were greater than those of climate change. In contrast, human activities contributed 96% to the decrease in Ku-VOD over the same period. Before 2000, climate change promoted increases in GPP and NDVI in most regions of southern China. The increasing rates of GPP and NDVI accelerated after 2000 due to afforestation. However, human activities like overgrazing and urbanization have led to decreases in Ku-VOD in northern and southwestern China, and in C-VOD in northeastern, eastern, central, southwestern, and southern China. In all, the relative roles of climate and human factors varied in different regions when NDVI, GPP, or VOD were individually considered. Our results highlighted that the regional-scale vegetation conditions should be taken into full account to achieve sustainable management of ecosystems.

Voyage of Ben Cao, Part II: Development of Chinese Medicinal Specimens in the British Museum

Voyage of Ben Cao, Part II: Development of Chinese Medicinal Specimens in the British Museum

Two new species of Dugesia (Platyhelminthes, Tricladida, Dugesiidae) from the subtropical monsoon region in Southern China, with a discussion on reproductive modalities

BackgroundFreshwater planarians of the genus Dugesia (Platyhelminthes, Tricladida, Dugesiidae) are distributed in a major part of the Old World and Australia, although until recently only very few species were known from China.ResultsTwo new species of Dugesia from Southern China are described on the basis of an integrative taxonomic approach. BI and ML phylogenetic trees based on the independent genes and on the concatenated dataset had similar topologies, only differing in some nodes that were weakly supported. Phylogenetic trees based on the concatenated dataset revealed that D. adunca Chen & Sluys, sp. nov. and D. tumida Chen & Sluys, sp. nov. are not closely related and belong to different clades. The two new species occupy separate long branches with high support values and, thus, are well-differentiated from their congeners. Separate species status of D. adunca and D. tumida is supported also by the genetic distances between the species included in our analysis, albeit that COI distances varied greatly among species. Dugesia adunca from Guangxi Province is characterized by the following features: living mature animals rather small; asymmetrical openings of the oviducts into the bursal canal; penis papilla with shape of an aquiline bill, albeit with a blunt tip; asymmetrical penis papilla, with a large antero-dorsal lip and a much smaller ventro-posterior lip; very large seminal vesicle, provided with trabeculae; small diaphragm; mixoploid karyotype with diploid complements of 2n = 2x = 16 and triploid complements of 2n = 3x = 24, with all chromosomes being metacentric. Dugesia tumida from Guangdong Province is characterized by a penis papilla provided with a large, symmetrical penial valve from the middle of which arises the small, distal section of the papilla; a duct intercalated between the seminal vesicle and the small diaphragm; ventrally displaced ejaculatory duct curving upwards before opening to the exterior; penis papilla highly asymmetrical, having a slim and long ventral portion and a short and stubby dorsal part; vasa deferentia separately opening into antero-dorsal portion of seminal vesicle; oviducts openings symmetrically into ventral portion of the bursal canal, near its opening into the atrium; mixoploid karyotype, with diploid chromosome portraits of 2n = 2x = 16, and triploid complements of 2n = 3x = 24, with all chromosomes being metacentric. In the context of the various kinds of mixoploidy and the sexualization of specimens, reproductive modalities within the genus Dugesia are shortly discussed.ConclusionMolecular, morphological, and karyological markers show that the two populations examined represent members of the genus Dugesia and constitute two new, distinct species.

Ammonia oxidizing bacteria dominate soil nitrification under different fertilization regimes in black soils of northeast China

Although autotrophic ammonia oxidizing archaea (AOA) and bacteria (AOB) and comammox coexist in soils, their abundances and contributions to nitrification are not well addressed, especially in arable black soils. In this study, using the nitrification inhibitors acetylene and octyne, the contributions to nitrification potential provided by different ammonia oxidizers and heterotrophic nitrifiers in four long-term fertilization treatments, i.e., no fertilization (NoF), manure fertilization (M), chemical fertilization (CF), and chemical fertilization plus manure (CFM), were investigated in samples collected from the northern, middle and southern black soil regions of northeast China. The amoA gene abundances of AOA, AOB, comammox Clade A and comammox Clade B in these soils were quantified by qPCR. The results showed that the amoA gene abundances of the three ammonia oxidizers tended to increase from the northern to southern sites, while the opposite trend was observed in the ratios of AOA/AOB and comammox Clade B/Clade A; the different fertilization treatments significantly influenced the amoA abundances, and the effects varied with the ammonia oxidizers and across the sites. Autotrophic ammonia oxidizers accounted for 62%–100% of the gross soil nitrification potential across all soils. Among them, AOB dominated soil autotrophic nitrification in the fertilized soils, while no fertilization may have increased the nitrification potential provided by AOA plus comammox. Pairwise analysis showed that the amoA gene abundances of AOA and AOB were significantly and positively correlated with their respective nitrification-driven potentials. Correlation heatmaps indicated that soil pH and inorganic nitrogen content were the main soil factors related to nitrification activities and the abundances of the ammonia oxidizers. Our findings highlight that AOB are the dominant ammonia oxidizers contributing to nitrification in arable fertilized black soils, although AOA and comammox are highly abundant.

Determination of terrestrial γ-radiation dose rate and soil radon concentration in a river region of Southern China

Determination of terrestrial γ-radiation dose rate and soil radon concentration in a river region of Southern China

Essential Oil Composition Anti-inflammatory Activities and Distribution of Fruits of Alpinia oxyphylla Miq.

The perennial herb Alpinia oxyphylla Miq. (Zingiberaceae) is an important traditional medicinal plant in China. The present study evaluated the chemical composition of A. oxyphylla essential oil (AOEO) using GC-MS. The AOEO contained 55 compounds, including nootkatone (20.12%), valencene (12.26%), and ethyl-p-methoxycinnamate (5.00%). Previous studies have shown that AOEO possesses significant antioxidant and antibacterial activities. However, the anti-inflammatory effect of AOEO on tissue plasminogen activator (TPA)-induced ear edema is yet to be reported. In this study, TPA-induced ear edema was used to investigate the anti-inflammatory activity of AOEO. Hematoxylin and eosin staining of mouse tissue sections indicated that AOEO reduced the degree of edema, and immunohistochemistry experiments revealed that AOEO inhibited the expression of tumor necrosis factors, such as cyclooxygenase 2 (COX-2), interleukin-6 (IL-6), and nuclear factor-kappa B (NF-κB). A. oxyphylla is a commonly used traditional Chinese medicine with good biological activity. Analysis of the species potential geographical distribution and diversity indicated that the species can be rationally protected and exploited. Based on the chemical composition and biological activity of AOEO, further research and development should effectively promote the development of medicine, food, and cosmetics industries. The potential distribution of A. oxyphylla under current climatic conditions was predicted using DIVA-GIS and geographic information from herbarium specimens and other documents. The species predicted distribution spanned more than 12 provinces in China and was the most extensive in Hainan. Under current climatic conditions, A. oxyphylla is suitable for growing and expanding its population in the warm, humid regions of southern China.

Comparison of the Spatial and Temporal Variability of Cloud Amounts over China Derived from Different Satellite Datasets

Various cloud cover products have been developed over the past few decades, but their uncertainties have not been sufficiently assessed, especially at a regional scale, which is vital for the application of satellite products to climate studies. In this study, we compare the spatial–temporal variability of the cloud amount over China from the 11 datasets provided by the Global Energy and Water Cycle Experiment (GEWEX) cloud assessment project at a horizontal resolution of 1° × 1° from the 1980s to 2000s, using the site data as a reference. The differences among these datasets are quantified in terms of the standard deviations and the correlation coefficients between different datasets. Most of the datasets show a similar spatial distribution of total cloud amounts (TCAs), but their magnitudes differ. The standard deviations of the annual, winter, and summer mean TCA are approximately 9–18% for the regional mean TCAs over the four typical regions of China, including the northwestern region (NW), northeastern region (NE), Tibetan Plateau region (TP), and southern China region (SC), with the largest standard deviations of 13–18% in the TP. By analyzing the factors that influence the satellite inversion data, such as the observation instrument, inversion algorithm, and observation time, we found that the difference caused by the observation instrument or algorithm is greater than the effect of the observation time, and the satellite cloud datasets with better recognition capability for cloud types show lower uncertainties when compared with the station observation. In terms of seasonal cycle, except HIRS and MODIS-ST, most satellite datasets can reproduce the observed seasonal cycle with the largest TCA in summer and the smallest TCA in autumn and winter. For the interannual variation, ISCCP-D1, MODIS-CE, and MODIS-ST are most consistent with the site data for the annual mean TCA, and two of the remaining datasets (PATMOSX and TOVSB) show more consistent temporal variations with the site observation in summer than in winter, especially over NW and NE regions. In general, MODIS-CE shows the best performance in reproducing the spatial pattern and interannual variation of TCA amongst the 11 satellite datasets, and PATMOSX, MODIS-ST, CALIPSO-GOCCP, and CALIPSO-ST also show relatively good performance.

Spatial Patterns of Soil Organic Matter, Nitrogen, Phosphorus and Potassium in a Subtropical Forest and Its Implication for Forest Management

Total nitrogen (TN), total phosphorus (TP), total potassium (TK), and soil organic matter (OM) can significantly affect forest growth. However, these soil properties are spatially heterogeneously distributed, complicating the prescription of forest management strategies. Thus, it is imperative to obtain an in-depth understanding of the spatial distribution of soil properties. In this study, soils were sampled at 181 locations in the Tropical Forest Research Center in the southwestern Guangxi Zhuang Autonomous Region in southern China. We investigated the spatial variability of soil OM, TN, TP, and TK using geostatistical analysis. The nugget to sill ratio indicated a strong spatial dependence of soil TN and a moderate spatial dependence of soil OM, TP, and TK, suggesting that TN was primarily controlled by intrinsic factors (e.g., soil texture, parent material, vegetation type, and topography), whereas soil OM, TP, and TK were controlled by intrinsic and extrinsic factors (e.g., cultivation practices, fertilization, and planting systems). Based on the spatial variability determined by the geostatistical analysis, we performed ordinary kriging to create thematic maps of soil TN, TP, TK, and OM. Model validation indicated that the thematic maps were reliable to inform forest management.

Spatial and Temporal Variations in the Atmospheric Age Distribution of Primary and Secondary Inorganic Aerosols in China

The aging timescale of particles is a key parameter in determining their impacts on air quality, human health, and climate. In this study, a one-year simulation of the age distributions of the primary and secondary inorganic fine particulate matter (PM2.5) components was conducted over China using an age-resolved Community Multiscale Air Quality (CMAQ) model. The results indicate that primary PM2.5 (PPM) and ammonium mainly originate from fresh local emissions, with approximately 60%–80% concentrated in 0–24 h age bins in most of China throughout the year. The average age is about 15–25 h in most regions in summer, but increases to 40–50 h in southern region of China and the Sichuan Basin (SCB) in winter. Sulfate is more aged than PPM, indicating an enhanced contribution from regional transport. Aged sulfate with atmospheric age > 48 h account for 30%–50% of total sulfate in most regions and seasons, and the concentrations in the > 96 h age bin can reach up to 15 µg·m−3 in SCB during winter. Dramatic seasonal variations occur in the Yangtze River Delta, Pearl River Delta, and SCB, with highest average age of 60–70 h in winter and lowest of 40–45 h in summer. The average age of nitrate is 20–30 h in summer and increases to 40–50 h in winter. The enhanced deposition rate of nitric acid vapor combined with the faster chemical reaction rate of nitrogen oxides leads to a lower atmospheric age in summer. Additionally, on pollution days, the contributions of old age bins (> 24 h) increase notably for both PPM and secondary inorganic aerosols in most cities and seasons, suggesting that regional transport plays a vital role during haze events. The age information of PM2.5, provided by the age-resolved CMAQ model, can help policymakers design effective emergent emission control measures to eliminate severe haze episodes.

Ecosystem Service Assessment of Soil and Water Conservation Based on Scenario Analysis in a Hilly Red-Soil Catchment of Southern China

Soil and water conservation (SWC) practices on agricultural watersheds have been the most effective practices for preventing soil erosion for several decades. The ecosystem services (ES) protected or enhanced by SWC practices include the comprehensive effects of protecting and conserving water sources, protecting and improving soil, carbon fixation, increasing agricultural production, and so on. Due to the lack of ES evaluation indicators and unified calculation methods in line with regional characteristics, this study proposes a framework of scenario analysis by using ES mapping, ES scoring, and economic analysis technology for ES and economic-benefit trade-offs under different scenarios. The study area was the Xiaoyang catchment located in Ningdu County, Jiangxi Province, which is a typically hilly red-soil region of southern China. From the results of scenario analysis, an obvious phenomenon is that some SWC practices can affect the value of some ES indicators, while some have no clear trend. By computing the ES scores for the four scenarios, the ranking was S3 (balanced), S1 (conservation), S2 (economic), and S0 (baseline). S3 ranks second in net income (with CNY 4.73 million), preceded only by S2 (CNY 6.36 million). Based on the above rankings, S3 is the relatively optimal scenario in this study. The contributions of this study are the method innovation with the localization or customized selection of ES indicators, and scenario analysis with ES scores and economic-benefit trade-offs in different scenarios.

Impact of Soil Freezing‐Thawing Processes on August Rainfall Over Southern China

AbstractThe impact of soil freezing‐thawing processes on August rainfall in Southern China (SC) during 1979–2008 and related physical mechanisms are investigated using the coupled land‐atmosphere model Grid‐Point Atmospheric Model version 2.0—Community Land Model version 2.0 (GAMIL2.0‐CLM2.0). The moisture‐budget analysis is employed to quantify the contributions of different factors to the change of precipitation in SC. The results indicate that the vertical moisture advection and its dynamic component play an essential role in the long‐term trends of August rainfall. The possible physical mechanism is that the model which includes the supercooled water simulates much higher soil/air temperature in August, especially in the north of 40°N, which is not only weakened the meridional thermal contrast but also induced an anomaly “north high–south low” circulation pattern in the middle and high latitude of Eurasia. Both resulted in the 200 hPa zonal winds weakening, and 850 hpa northerly wind southward moved. Meanwhile, a convergence anomaly cyclone is initiated in the lower troposphere over SC regions, accompanied by enhanced ascending and strong moisture flux convergence, which is beneficial to the increased precipitation. This study provides a new interpretation of the “southern flooding” during 1979–2008 from the point of frozen soil changing.

The Eco-Environmental Changes in Typical Coastal Zones of Southern China From 1987 to 2020: A Case Study of Guangdong Coastal Counties

Population growth, socioeconomic development, and rapid urbanization have exacerbated the deterioration of coastal ecosystems, particularly in the coastal region of southern China, which has experienced significant urbanization. A precise and timely insight into the ecological changes is indicative of economic and environmental harmonization in southern coast of China and other regions of the world. This study applied 731 Landsat images to assess quantitatively the spatial and temporal evolution of ecological environment quality in the coastal zone of South China during 1987─2020 based on the remote sensing ecological index (RSEI). The results show that 1) the correlation between the RSEI calculated using Landsat data and the parameters is more than 75%, and the results were significant when applied to assess the ecological environment of the coastal zone in South China. ​2) The ecological quality of the coastal zone in South China as a whole showed a slight initial degradation during 1987─2020, followed by a gradual improvement trend and then a slight degradation; the area with good ecological quality decreased from 38.96 to 7.97%, and then gradually recovered to 56.61% in 2010. Subsequently, the regions with good ecological quality showed a significant decline, reducing to 1.72%, and then increasing to 38.46% until 2020. In addition, regional differences persisting during the study period are caused by the impact of human activities on the land use types of different landscapes. 3) Good and moderate ecological quality classes occupy most of the coastal zones in South China, but the pressure on the coastal zone is still not optimistic due to the sensitivity of the coastal zone and the accelerated urbanization in South China. As a large-scale, long time series of coastal zone ecological monitoring, this study can provide support for planning, ecological monitoring, environmental protection policy formulation, and integrated regional management of coastal zones and similar areas in South China.

Tylopilus yangzhuliangii (Boletaceae, Boletales), a new bolete from tropical China

Tylopilus yangzhuliangii (Boletaceae, Boletales) is described as a new species, based on morphological and phylogenetic evidence, from Hainan Province, a tropical region of southern China. A detailed description, color photos of fresh basidiomes, and line-drawings of microstructures of the new species are presented as well as comparisons with related species.

Characteristics of runoff and sediment yield for two typical erodible soils in southern China

Granite red soil (GRS) and Quaternary red clay (QRC) are two typical erodible soils in the red-soil region of southern China. Analytical and comparative studies of the characteristics of runoff and sediment yield for the two soils at various slopes are currently needed. The purpose of the current study was to clarify the characteristics of runoff and sediment yield for GRS and QRC at different slopes and to establish models for estimating sediment yield for the two soils. Forty-eight runoff microplots with four slopes (5°, 15°, 25°, and 35°) and two soils (GRS and QRC) were established and exposed to natural rainfall. Runoff and sediment yield were measured 10 times during the study period. Runoff and sediment yield for the two soils under the various slopes had similar temporal variations, and both increased with prior cumulative erosive rainfall. Runoff for GRS and QRC was moderately temporally variable, with coefficients of variation (CVs) from 46.2% to 60.6%, and sediment yield for QRC was strongly temporally variable, with CVs from 114.8% to 145.8%. Sediment yield for GRS increased with slope, but sediment yield for QRC first increased and then decreased, with a calculated inflection point of 18°, but runoff for both soils decreased with slope. The CVs of both runoff and sediment yield with slope for the two soils ranged from 3.6% to 88.0%, lower than the temporal variabilities, indicating that rainfall may have a larger impact than slope on runoff and sediment yield for QRC and GRS. Under the various slopes, runoff and sediment yield for both soils increased with rainfall and sediment yield increased with runoff, but the proportions of effective rainfall and runoff differed. Pedotransfer-function models based on rainfall, runoff, and slope accurately estimated sediment yield for the two soils, with the model fit coefficient of determination (R2) > 0.81 and the R2 for verification >0.79. These results improve the understanding of the laws governing erosion for different soil types in the red-soil region of southern China and are important for managing the erosion of collapsing gullies and sloping farmland in the region.

Heavy Metal Pollution and Soil Quality Assessment under Different Land Uses in the Red Soil Region, Southern China.

The influences of different land uses associated with human activities on soil quality and the redistribution of heavy metal in soil have been widely concerned. Surface soil samples were obtained to assess comprehensive soil quality in a typical red soil region of southern China, combining the heavy metal pollution evaluation with fertility evaluation. It can be learned from the results that the overall level of soil fertility was at medium and lower level, and soil heavy metal pollution risk in the study area in a few regions had reached warning line and slight pollution line, and there was a risk of potential pollution. TOPSIS evaluation results showed that the comprehensive soil quality was mainly good quality and moderate quality, accounting for 31.7% and 29.0% of the total land area, respectively. Positive matrix factorization (PMF) model results showed that transportation source contributes a lot in terms of Cd and Pb. As for Cr, natural source contributes 53.8%. In terms of Cu and Zn, agriculture source contributes 50.7% and 38.7%, respectively. In a word, the comprehensive soil quality assessment in red soil region of southern China provides an important basis for the scientific management and sustainable utilization of soil resources.

Quantification of physical soil crust thickness and its effects on runoff and sediment yield

AbstractPhysical soil crusts will form on most soils during and after rainfall and it has important effects on the runoff and sediment on slopes. However, objective and effective methods for quantifying the characteristics of physical soil crusts (such as the thickness) are not currently available. A new method was used for determining the thickness of physical soil crusts based on X‐ray computed tomography (CT) in order to quantify the thickness of the structural crust (SC) and depositional crust (DC) for two typical erodible soils comprising granite red soil (GRS) and Quaternary red clay (QRC) in the red soil region of southern China. The pores in the GRS and QRC were characterized as finely and densely spatially distributed, with an average porosity of 15.47% and a range of 1.66–28.83%. The soil porosity increased rapidly in the 0‐to‐3‐mm depth, but the porosity of the SC and DC soil samples generally decreased or was stable in the 3‐to‐30‐mm depth. The average thickness of the soil crust was 1.31 mm, and the average thicknesses of SC and DC were 1.16 and 1.46 mm, respectively. The thickness of SC of GRS decreased with the slope, whereas the thickness of DC of QRC generally increased with the slope. The thickness of SC increased with runoff yield and its contribution rate to the runoff and sediment yield cannot be neglected. The study provides a method for the objective quantification of physical soil crust and can deepen the research on slope erosion process and influencing factors.

A novel hybrid clustering model of region segmentation to fuse CMAQ simulations with observations

The Community Multiscale Air Quality (CMAQ) model can predict air pollutant concentrations at every pre-determined location but usually suffers from considerable systematic bias. By post-process the CAMQ simulations with ground observations, K-means-cluster-Observation-examiner-Boundary-denoiser (KOB) model was developed as an unsupervised hybrid model, to segment regions by capturing spatial dependencies of CMAQ time-series and systematically reduce the bias of CMAQ simulations. The KOB model was then applied in 2019 to improve the CMAQ predictions of respirable suspended particulates (RSP) concentrations in the Pearl River Delta (PRD) region of southern China. Compared to the CMAQ simulations, the KOB model is implemented with hourly CMAQ simulations and significantly improves the 1-h predictions of RSP at all stations, with the index of agreement (IOA) increasing from 0.70 to 0.86 and average root mean square error (RMSE) reducing from 28.4 to 20.0 μg/m3. A better agreement was also achieved between the monthly average RSP from predictions using the KOB model and ground observations, with IOA increased from 0.87 to 0.93 and RMSE decreased from 12.4 to 8.2 μg/m3. In addition, the capability of the KOB model to predict extreme pollution was greatly improved, with the RMSE reduced from 76.3 to 50.8 μg/m3. Furthermore, the improvement was identified not only for the next 1-h predictions, but also for the predictions in the next 6 h and after 6 h the SBC method outperforms the KOB model. Through data fusion, our hybrid clustering model can achieve robust real-time air quality forecasting.

Does joint structure promote the development of gully erosion?

Gully erosion is a growing environmental problem around the world, and limits ecological and economic development. Collapse gullies in the granite mountainous region of southern China are unique gully erosion occurrences known locally as Benggang, and its erosion gully is made up of a main gully and multiple branch gullies that form a runoff and sediment drainage channel system. Joint structure is the product of geological movement. To investigate the internal relationship between the morphological development of gullies and joint structure, we measured and recorded morphological parameters, including the area, strike, quantity and depth of gullies and the strike, dip angle, density and wall distance of joints, in four typical granite gully erosion regions. Our findings are as follows: (i) as a unique gully erosion phenomenon, the development intensity of Benggang increases from north to south, and erosion becomes more severe; (ii) the average joint area densities range from 19.41/m2 to 21.85/m2, while the average joint ratios range from 7.40 to 10.32. Overall, joint development gradually increases from north to south, characterized by a high density, clear dominant direction, high dip angle (mostly ranging from 50 to 80°), and high inheritance and considerable influence on the resulting soil structure; (iii) correlation analysis reveals that the erosion gully development direction and dominant joint strike basically coincide, and are significantly positively correlated (P < 0.001); (iv) the average depths of the main gullies in Tongcheng (TC), Ganxian (GX), Changting (CT) and Wuhua (WH) along the dominant joint strike are greater than those along other joint strikes, and deeper main gully depths correspond to more high-angle joints along the same strike. The dip angles of joints along the strike of the branch gully with the maximum depth are greater than 60°, and some branch gullies follow the dominant joint strike. This study concludes that the joint strike controls the development direction of erosion gully and that the depth of erosion gully is greater than that of other strikes in the dominant strike direction where the number of joints is concentrated. Joints aggravate soil erosion and promote the development of gully erosion.

The Whole-Aperture Pore Structure Characteristics and Their Controlling Factors of the Dawuba Formation Shale in Western Guizhou

Since shale gas mainly occurs in shale pores, research on pore structure characteristics is the key to understanding the shale gas accumulation mechanism. The pore structure of the Lower Carboniferous Dawuba Formation shale in the Qianxi area, represented by the well QSD-1, which obtains a daily shale gas flow of 10,000 m3 and represents an important breakthrough in the investigation of marine shale gas in the Upper Paleozoic region of southern China, is characterized by high-pressure mercury compression experiments and low-temperature gas adsorption (N2 and CO2) experiments with whole pore size. The main controlling factors affecting the pore development of the shale are discussed. (i) The micropores and mesopores are more developed in the shale, and the macropores are the second most developed in the shales of the Dawuba Formation in the Qianxi area, among which the mesopores and macropores contribute most to the pore volume and the micropores and mesopores contribute most to the pore-specific surface area. (ii) The microfractures and interlayer pores of clay minerals are developed in the shales of the Dawuba Formation, which are the main storage spaces for hydrocarbon gases. (iii) The main factors affecting the adsorption capacity of the shales of the Dawuba Formation in the Qianxi area are the organic carbon content and clay mineral content of the shales, both of which have an obvious positive correlation with the variation of pore structure.

Effects of tillage-induced soil surface roughness on the generation of surface–subsurface flow and soil loss in the red soil sloping farmland of southern China

The role of tillage-induced soil surface roughness (SSR) in altering surface–subsurface flow and soil loss needs to be investigated in the red soil region of southern China. In this study, two different roughness conditions (smooth surface and rough surface), produced by plowing with and without flattening, were employed to assess the effects of surface roughness on rainfall redistribution, surface and subsurface flow generation, and soil loss. In-situ rainfall simulations with three different rainfall intensities (30, 60, and 90 mm h−1) during 180 min of rainfall were tested for a steep farmland sloped at 15°. The results showed that the rough surface had a higher capability for improving subsurface flow, whereby 34% of the rainfall changed into surface flow, and 24% changed into subsurface flow; whereas the proportions of surface and subsurface flow on the smooth surface were 40% and 16%, respectively. The rough surface exhibited a faster initial generation of surface flow and subsurface flow, and the progress of erosion from sheet erosion to rill erosion was more rapid than on the smooth surface, leading to a higher sediment yield from the rough surface under stronger rainfall events. However, the rough surface demonstrated enhanced infiltration behavior and prevention of soil loss under low-intensity rainfall events. The difference in soil crusts on smooth and rough surfaces was the dominant factor affecting surface–subsurface flow generation and soil loss from the red soil sloping farmland. The roughness decreased on the rough surface and increased on the smooth surface during rainfall events. The interactions between surface and subsurface flow should be considered to evaluate soil loss; hence, this research provides a comprehensive understanding of the impact of tillage activities on soil erosion.