Groundwater quality and land use change in a typical karst agricultural region:a case study of Xiaojiang watershed,Yunnan

Taking the typical karst agricultural region, Xiaojiang watershed in Luxi of Yurman Province as a research unit, utilizing the groundwater quality data in 1982 and 2004, the aerial photos in 1982 and TM images in 2004, supported by the GIS, we probe into the law and the reason of its space-time change of the groundwater quality over the past 22 years in the paper. The results show： （1） There were obvious temporal and spatial changes of groundwater quality during the past 22 years. （2） Concentrations of NH4^＋, SO4^2- , NO3, NO2^-, Cl^- and the pH value, total hardness, total alkalinity increased significantly, in which NH4^2-, NO3, and NO2^- of groundwater exceeded the drinking water standards as a result of non-point pollution caused by the expansion of cultivated land and mass use of the fertilizer and pesticide. （3） Oppositely, Ca^2＋ and HCO3^- showed an obvious decline trend due to forest reduction and degradation and stony desertification. Meantime, there was a dynamic relation between the groundwater quality change and the land use change.

The impact of land use on soil properties in a karst agricultural region of Southwest China: a case study of Xiaojiang watershed, Yunnan

Supported by RS and GIS, the land use change from 1982 to 2003 were analyzed and the impacts of land use changes on pH value, organic matter, total N, total P, total K, available N, available P, and available K in soil of Xiaojiang watershed, a typical karst agricultural region of Yunnan Province, Southwest China were assessed. The following aspects are concluded. （1） The total land use converted during the past 20 years in Xiaojiang watershed covers an area of 610.12 km^2, of which 134.29 km^2 of forestland was converted into cultivated land, and 210 km^2 of.unused land was converted into cultivated land. （2） The rapid growth of population and the economic development were the main driving forces of land use change. （3） With the change in land use, the soil properties have been changed significantly. The pH, organic matter, total N, total P, total K, available N, available P and available K in soil in 1982 were 6.3, 38.02 g·kg^-1, 1.86 g·kg^-1, 1.63 g·kg^-1, 10.94 g·kg^-1, 114.42 g·kg^-1, 11.65 mg·kg^-1 and 64.69 mg·kg^-1g, respectively; and those in 2003 were 6.73, 25.26 g·kg^-1, 1.41 g·kg^-1, 0.99 g·kg^-1, 12.6 g·kg^-1, 113.43 mg·kg^-1, 11.11 mg·kg^-1 and 151.59 mg·kg^-1, respectively. Pared samples t-test of the tested indices of soil properties indicate that those indices have changed significantly during the last 20 years. But the soil properties changed differently, due to the differences in land use change. （4） Also, with the change in land use and management measures of soil, the modifications in soil properties which developed from carbonate rocks were more sensitive than those in the soil developed from sandstone.

The Impact of Urban Expansion on Plant Diversity Change in Karst Regions of Southwest China

Biodiversity is vital for the integrity and stability of ecosystems and sustainable development.Karst regions of Southwest China is featured for undulating and broken karst terrain as well as high plant diversity.Land use changes induced by the growing population and expanding human settlement have threatened biodiversity preservation in this region.However,the impact of urban expansion on plant diversity remains unclear here.This study focuses on how expanding countryside landscapes affect the recovery rate of plant diversity and demonstrate how urban expansion affects plant diversity conservation in karst regions of Southwest China.In situ biodiversity investigations and multisource remote sensing images were combined to analyze the role of human settlement evolution in the conservation of plant diversity using descriptive statistics and regression analysis.Unmanned vehicle images,historical aerial photographs,and long-term remote sensing images were used to observe the human settlement pattern changes over 40 yr and found that plant diversity is restored faster in countryside ecosystems than in island ecosystems restricted by water.Forests,however,contribute the most to plant diversity conservation in both ecosystems.While the forest area is stable during urban expansion,massive forest patches play an essential role in plant diversity conservation.Arable lands and grasslands shrank but with a fragmenting trend,which was conducive to preserving plant diversity,whereas increased and regularized large patches of built-up areas were not beneficial to plant diversity.Accordingly,forest protection should be prioritized to coordinate future socioeconomic development and plant diversity conservation in karst and broader regions.Furthermore,large built-up patches should be limited,and the irregularity should be improved during urban expansion.Irregular shaped cultivated land and grassland were suggested to promote biological information exchanges as landscape corridors.

Landscape structures of different rural landscape connectivity in typical plateau karst regions: Taking the Houzhai River area of Anshun City, Guizhou Province as an example

Landscape connectivity is important for energy and material flow in ecosystems as well as for the survival of species. The landscape structure influences and reflects the degree of landscape connectivity. In order to study the coupling relationship between landscape structure and connectivity and reveal the succession relationship between its structure and connectivity in the typical karst plateau area. The study analyzed the typical area of Houzhai River in Puding County, Anshun City, Guizhou Province, according to the landscape pattern index and probability landscape connectivity index. The results show:(1) The landscape structure of the study area A is mainly characterized by large patches and uniform distribution. The main land is woodland and cultivated land, and the overall landscape is low fragmentation.(2) The landscape structure of the study area B is mainly characterized by the clustering of a certain type of land cover and the uneven distribution of the patches, for example, cultivated land. Other types of patches are scatteredly distributed, and the overall landscape is highly fragmented.(3) The study area A, B in 100, 500, 1000, 2000, 3000, 5 distance thresholds of landscape connectivity were 1.55, 1.99, 2.26, 2.49, 2.58 and 0.02, 0.10, 0.15, 0.19, 0.20, respectively. The average landscape connectivity is 2. 18 and 0. 13, respectively. Study Area A has a higher degree of landscape connectivity than B. Landscape pattern indicators can represent the landscape structure and probability landscape connectivity index calculates the landscape connectivity in the study area. The results of the study can provide a basis for ecological restoration of plateau karst regions and well-oriented rural development planning.

The comprehensive evaluation of sustainabledevelopment in karst regions-Taking Shishanareas in Guangxi of China as an example

This paper works out a practical evaluation method of sustainable development for theundeveloped the regions and take Shishan areas of Guangxi Zhuang Autonomous Region of Chinaas an example. First of all, according to the actual conditions of the karst regions in Guangxi and thetheory of regional sustainable development this paper estabishes an index system of comprehensiveevaluation, then takes twenty-eight representative cities and counties within the karst regions ofGuangxi as research objects to evaluate the level of sustainable development. It basically illustratesthe state of regional sustainable development of the karst regions in Guangxi.

Aging Characteristics and Influencing Factors of the Sheds of Composite Insulators in Karst Regions of China

In recent years,more and more high-voltage overhead transmission lines were built passing through the karst regions in southwestern China.This type of special landform seems to have an adverse effect on the aging of the sheds of the line suspension composite insulators,which may lead to unexpected flashover and line tripping.In order to find out the particularity of the aging characteristics of insulators operating in the karst regions,samples in operation were selected from both the karst regions and the flatlands.Hydrophobicity,amount of surface contamination,and contaminant composition of the sheds were studied,then a comparison of performance between the two was made,and the possible influencing factors that cause such differences were discussed.The results show that the overall aging of the sheds of the composite insulators operating at the karst regions is more aggravated,which is caused by the combined influence of factors including the special topography,climate,and pollution in the area.The strong wind crossing the col will bring about the mutual scraping on the edges and stress concentration at the root of the sheds,leaving scratches and root cracks;the infiltration from these rupture of acid liquid,if any,will accelerate the aging and corroding of the internal silicone rubber material;moreover,the carbonates enriched on the surface of the sheds will gradually transform into more corrosive sulfates in an acidic environment,leading to further deterioration and chalking of the sheds of the insulators.The research work in this paper can provide guidance for the current operation and maintenance of composite insulators in the karst areas,as well as having important reference values for the layout design and insulation configuration of transmission lines to be built across karst landforms in the future.

Genotype-Specific Microsatellite (SSR) Markers for the Sugarcane Germplasm from the Karst Region of Guizhou, China

Genetic variability among sugarcane genotypes from the Karst region of China was evaluated using genotype-specific microsatellite (SSR) markers. Eighteen sugarcane genotypes including 13 active cultivars and five elite QT-series clones bred locally were screened for genetic variability with 21 SSR primer pairs. All the primer pairs were highly polymorphic and amplified a total of 167 alleles with an average of eight alleles per primer pair. The average polymorphism information content (PIC) value was 0.86 with a range of 0.68 and 0.92. A UPGMA dendrogram categorized the 18 sugarcane genotypes into three major groups containing three, ten and five genotypes, respectively. No geographical affinity was observed among genotypes within the same group. Eight SSR primer pairs produced cultivar-specific alleles, of which five alleles were unique to the QT-series clones, namely, SMC334BS-165 and SMC851MS-145 in QT 08-558, mSSCIR43-229 in QT 4, SM597CS-182 in QT 08-536 and SMC7CUQ-168 in QT 06-212. The clone-specific SSR alleles will be useful in identifying elite QT-series clones for use in the sugarcane crossing programs in China.

Study of soil and water conservation Function on Slope with Different Planting Patterns for a Typical Small Watershed in Karst Region of Guizhou Province

Ten runoff plots with different planting patterns were established for experimental observation in Yangjichong small watershed of Longli County in Karst region of Guizhou Province. Results show that under the same rainfall condition, shrub land, natural grassland and abandoned land presented the best function of soil and water conservation. The function of soil and water conservation was poor for arbor planting pattern, because the shrub layer, herb layer and forest floor were not formed. Because of no-tillage, surface crust and other effects, the function of soil and water conservation in slope farmland was better than that in runoffplots with arbor planting pattern.

Pollution pattern of underground river in karst area of the Southwest China

Investigation of groundwater pollution has been carried out on multiple typical karst underground river systems in recent years in order to reveal the characteristics and mechanism of underground river pollution. Through the summary of the survey results, five characteristics of underground river pollution have been revealed, including directionality, weak hysteresis, easier for reversibility, linear and intermittent(or seasonal); combining with karst geomorphic types, pollution sources(primordial, secondary pollution and compound), pollution ways and pollution receptors, three basic pollution patterns of the underground river were depicted: Recharge area pollution, runoff area pollution and discharge area pollution. At the same time, the study discloses the reality of the underground river pollution is the three basic patterns and their subgenera in combination with super imposition on the space and time. And from the angle of the hydrogeological model, the study expounds the process of underground river pollution. Finally, the study gives naming rules of pollution pattern of the underground river and sets up PISAB method of pattern recognition. The results provide scientific basis for pollution repair and management of underground river in the southwest karst region.

Land cover change in different altitudes of Guizhou-Guangxi karst mountain area, China： patterns and drivers

Topography, especially altitude, will influence the way, process and characteristics of land cover changes in mountainous area, simultaneously, the vertical difference of land cover changes will affect soil quality and regional ecological environment. Therefore, the gradient relationship analysis between land cover changes and altitude is very important for regional sustainability. This study investigated land cover dynamics based on land cover data from a typical mountainous area in the Guizhou-Guangxi karst mountain area, China, in 2000 and 2010, then explored the relationship between altitude and land cover change and analyzed different drivers of land cover change at different altitudes. Our findings are as follows. 1) From 2000 to 2010, the total area of land cover transition was 7167.04 km^2 or 2.8% of the region. The increasing area of build-up land(926.23 km^2) was larger than that of forest(859.38 km^2), suggesting that the urban construction speed was higher than that of reforestation. 2) Intensity of land cover transition in northwestern Guizhou-Guangxi karst mountain area was much larger than that of southeast part and their transition trend was also significantly different, which was consistent with regional population and economy. 3) Human activity was the most dramatic at altitudes between 0–500 m. For 500–1000 m, grassland mainly converted to forest and build-up land. Area of land cover transition was the greatest between 1000–1500 m, while above 1500 m, the transition of grassland was the most obvious. 4) The drivers of land cover change varied. Land cover change was positively correlated with gross domestic product and population density but was inversely related to relief amplitude. There were correlations between land cover change and distance to roads and rivers, and their correlations varied with altitude. By revealing patterns and causes of land cover changes in different altitudes, we hope to understand the vertical dependence of land cover changes, so as to improve land productivity and protect land ecological environment scientifically.

Evolution and Effects of the Social-ecological System in Karst Mountainous Regions:A Case Study of Guangxi,China

Karst regions are the typical areas of interaction between human society and natural ecosystems.Understanding the historical mechanisms of the evolution of social-ecological systems(SES)is crucial for the future sustainable management of karst regions.This study selected Guangxi,a typical karst mountainous region in Southwest China,as the study area,and used population,cropland area,and forest coverage as the SES elements.Based on the framework of SES research in the karst region,it adopted segmented linear regression to identify the stages of the interactions among these elements,to reveal the evolutionary stages of social development from the long-term perspective.In addition,the driving factor indicators were constructed from the aspects of natural environment,social development,government policy,and climate change,and then the feedback changes brought about by the evolution were investigated.The results show that the evolution of SES in Guangxi from 1363-2020 can be divided into seven stages.In the first,second,and early period of the third stages,the government of Guangxi mainly focused on agricultural activities,although the only way to meet the growing demand for food was by expanding the area of cropland,and the timber trade’s pursuit of economic development,resulting in an increase in rocky desertification.In the fourth stage,the ecological environment improved under the implementation of measures such as the control of rocky desertification and the compensation of forest ecological benefits.After the fifth stage,the effect of rocky desertification control has been remarkable.Although the implementation of relevant policies has alleviated the environmental problems to some extent,the continual changes in the structure and function of SES can challenge further progress towards sustainability in karst regions.This study aims to provide a reference for the long-term national spatial planning and the development of environmental policies in karst regions.

Performance of a deep excavation and the influence on adjacent piles:A case history in karst region covered by clay and sand

This paper presents a case study of deep excavation adjacent to an existing bridge in karst region of Guangzhou city,China.The movements of retaining structures,settlements of surrounding ground and pipelines,and the responses of bridge piles were measured and evaluated.A sudden surge of groundwater was recorded at the north pit when excavated halfway.Soil-cement columns using the Metro Jet System(MJS)method was employed along the outer perimeters of the diaphragm wall where water inflow occurred,for the sake of blocking the flow channels.The measured maximum wall deflection dhm in this case ranged from 0.13%H to 0.3%H,with a mean value of 0.2%H(H is the excavation depth),which agreed well with the empirical prediction in mixed ground.During the MJS treatment,the wall and surrounding soils experienced notable lateral deflection and settlement.The bridge piles experienced significant settlement since the excavation commenced,which might be attributed to the inherent deficiency in geological condition and pile length.The soil disturbance induced by the adjacent deep excavation accelerated bridge settlement.The finite element analysis revealed that the excessive settlement of the bridge piles and ground surface resulted from confined-water withdrawal in sand layers.

Human disturbance exacerbated erosion and deposition in the karst peak-cluster depressions during the Ming and Qing dynasties

Under the background of large-scale ecological restoration, China's southwestern karst region has become a hotspot of global vegetation cover “greening” in the past 20 years. However, because of geological constraints, it is difficult to restore the forest landscapes in some areas. It is urgent to understand the impacts of human disturbances during the historical period on the difficult-to-forestation rocky-desertification areas of the karst region in order to guide future afforestation. In this study, we quantified the changes of specific sediment yield in typical karst depressions over the past 500 years by using ^(137)Cs,^(210)Pb, and ^(14)C dating methods in karst depressions, and identified the main human disturbances related to historical erosion and sedimentation by combining with historical data. The results showed that the erosion and sedimentation of the three depressions in 1921–1963 were significantly higher than that in 1963–2021, and the sedimentation rate(0.64–1.33 cm a^(-1)) and the specific sediment yield(2.51–13.11 t ha^(-1)a^(-1)) during Ming and Qing dynasties(1504–1812) were higher than the sedimentation rate(0.26–0.95 cm a^(-1)) and specific sediment yield(0.95–6.99 t ha^(-1)a^(-1)) in the recent century(1921–2021). Reconstruction data and literature from the Ming and Qing dynasties show an empirical link between changes in population, arable land, food, forest area,and deforestation events during the same period. It was found that the population and arable land in Guangxi increased more than three-fold and the forest area decreased significantly in the 17th century after the migration of the Yao ethnic group and the introduction of maize to the region, which may be the main reason for intensifying the erosion of depressions. This study is of great significance to understanding the evolution history of rocky desertification in this region and to answer the potential of afforestation.