Northwest Guizhou Research Articles

Human and Natural Activities Effects on Soil Erosion in Karst Plateau Based on QAM Model: A Case Study of Bijie City, Guizhou Province, China

The Karst plateau region has a unique natural erosion environment and sharp human–land conflicts. This study selected Bijie City, Northwest Guizhou, as the study area. To quantitatively analyze the human and natural impacts on soil erosion in this area, this paper evaluated the anthropogenic and natural soil erosion based on the Revised Universal Soil Loss Equation (RUSLE) coupled with the Quantitative Analytical Model (QAM). The results showed the following: (1) the total soil erosion modulus in the study area showed an increasing trend: 37.86 t/(ha·a) in 2010, 42.12 t/(ha·a) in 2015, and 48.67 t/(ha·a) in 2020; (2) human activities reduced soil erosion, with an anthropogenic soil erosion modulus of −13.79 t/(ha·a) in 2015 and −17.36 t/(ha·a) in 2020, indicating that human activities, such as projects of returning farmland to forests and rocky desertification control, played a key role in decreasing soil erosion in the study area.; and (3) the percentage of the area of soil erosion deterioration dominated by natural factors (AGN) is gradually decreasing, 89.47% in 2015 and 81.85% in 2020; the percentage of the area of soil erosion deterioration dominated by human activities (AGH) is increasing from 6.17% in 2015 to 13.80% in 2020; and the percentage of the area of soil erosion mitigation caused by human activities (ALH) and the area of soil erosion not affected by natural and human activities (NNH) showed no significant change. This result suggests more attention should be paid to the area of AGH to control soil erosion. This study analyzed the roles of natural factors as well as human activities in the Karst plateau, enriched the application scope of the QAM, and provided new ideas for theoretical research in this field.

Effect of Rice Biochar on Typical Cadmium, Lead and Zinc Form in Contaminated Soil in Northwest Guizhou Province, China

This study was conducted in Hezhang County, Bijie City, Guizhou Province. The soil in the zinc smelting area has been contaminated with cadmium, lead, and zinc. Therefore, these elements are the focus of this research. Rice husk biochar was used as the passivation material. The Fourier infrared spectrum was utilized to study the biochar’s morphology, element content, mineral composition, structure, and surface functional groups. Moreover, the physical and chemical properties of the biochar were analyzed to explore its passivation effect. Biochar is beneficial in the cleaning of cadmium, lead, and zinc minerals and can be used for the passivation of heavy metals in contaminated soil. This study aims to understand the detailed mechanism behind this process and provide experimental data and ideas for pollution control. The results indicate that the biochar contains many functional groups, including -OH, C-H, C-O, C=O, C=C, and C-O-C. It also consists of a significant quantity of potassium salt, calcite, and quartz. Biochar has a noticeable pore structure, and as the pyrolysis temperature increases, the pore structure becomes more developed and thinner, with a smooth surface. The main minerals in the soil are quartz, mica, zeolite, illite, and chlorite. The aromatic degree of biochar increased with pyrolysis temperature. In contrast, the aromatic degree and polarity first increased and then decreased. The 0.2-0.45 mm biochar exhibited the best passivation effect on cadmium, lead, and zinc.

Traditional culture of settlements associated with the natural environment: the case of Yi minority Southwest China

ABSTRACT Traditional culture of settlement is an important medium to record the process of balance between human and nature, and it was passed down from generation to generation in different forms (e.g. sacrificial culture, social structure, belief worship). With the intensification of global multicultural integration, the integration relationship between culture and nature has become an important approach for the protection and inheritance of traditional culture. Now, the relationship between artistic creation and ecological environment has been extensively studied. The scientific consensus regarding the influence of ecological environment on artistic creation has gained widespread recognition. Nevertheless, previous research neglects the relationship of traditional culture and natural environment, as well as different spatial characteristics, which are closely related to agricultural production and living. Based on the in-depth investigation of 23 traditional settlements of Yi minority in Southwest China, this paper conducted spatial analysis based on aerial photography, satellite maps and field investigation to analyze the relationship of culture-environment-space. Our results showed that there are significant differences in settlement space (e.g. landscape pattern, landscape space, architectural form) of Yi minority distributed in different areas. Under the same cultural background, the dispersed layout appears in Liangshan with high altitude and cold climate; the mountain foot layout appears in Central Yunnan and Northwest Guizhou with flat terrain and mild climate; the centralized layout appears in Honghe with narrow valleys and hot climate. These results shows that traditional culture comes from the natural environment, and the settlement space built under the guidance of the traditional culture must be in harmony with the natural environment. Therefore, protecting the traditional culture plays an important role in the sustainable development of urban and rural settlements. In addition, our findings may serve to inheritance and protection of traditional culture in other area all over the world.

Population Structures and Dynamics of Rhododendron Communities with Different Stages of Succession in Northwest Guizhou, China.

To explore the population structures and dynamics of Rhododendron shrub communities at different stages of succession in northwest Guizhou, China, this study examined the populations of Rhododendron annae and Rhododendron irroratum shrub with two different stages. A space-for-time substitution was employed to establish the diameter class/height structures, static life tables, and survival/mortality rate/disappearance rate curves of both Rhododendron populations with different orders of succession. Their structural and quantitative dynamics were analyzed, and their development trends were predicted. The results showed that, quantitatively, the populations of R. annae and R. irroratum in the two Rhododendron communities with different orders of succession were dominated by age classes one, two, and three as well as height classes i, ii, and iii. The number of Rhododendron plants at the three age classes and the three height classes accounted for 97.61-100% of the total. The quantitative dynamic indices of R. annae and R. irroratum were both greater than 0, with and without considering external interference. In terms of age class and height structures, both Rhododendron populations were expanding populations, presenting "inverted-J-shaped" and irregular pyramid patterns. There was a sufficient number of young individuals, but few or no old individuals. Both survival curves of the populations of R. annae and R. irroratum in the two Rhododendron communities with different orders of succession belonged to the Deevy-II type. In the late stage of succession, the mortality curves and disappearance curves of both Rhododendron populations in these communities presented a trend of increasing first and then decreasing with increasing age class. This result indicates that at each age class, R. annae and R. irroratum showed a trend of gradual increase after two, four, and six years. In brief, the populations of R. annae and R. irroratum have rich reserves of seedlings and saplings, but high mortality and disappearance rates. In this context, it is necessary to reduce human interference and implement targeted conservation measures to promote the natural renewal of Rhododendron populations.

Mineralogy and lithium enrichment states of lithium-rich aluminous rocks in the Bijie area, Northwest Guizhou

Mineralogy and lithium enrichment states of lithium-rich aluminous rocks in the Bijie area, Northwest Guizhou

The Cultural Connotation in the Agricultural Proverbs of Northwest Guizhou

The Cultural Connotation in the Agricultural Proverbs of Northwest Guizhou

Effects of clearcutting on species composition and community renewal of Rhododendron shrubs in northwest Guizhou Province, China

Tree base sprouting is the main reproduction and expansion mode of Rhododendron plants. By leveraging the plot survey method, the species composition, community renewal, and species diversity in three Rhododendron shrub communities in control, and before and after clearcutting (CK, D3yr, and D6yr, respectively) were studied. Moreover, the dissimilarity of Rhododendron communities in CK, D3yr and D6yr were analyzed. The results showed that there were 26 plant species belonging to 14 families and 22 genera, in 3 communities in total, with 19 species of shrub plants and 7 species of herbaceous plants. The number of species increased from 13 in CK to 23 in D3yr and then decreased to 20 in D6yr. The height and coverage of D3yr and D6yr reached 39.3% and 58.9% of that of CK, respectively. The relative height of CK, D3yr, and D6yr was 43.79%, 65.4%, and 58.54%, respectively. The coverage of D3yr and D6yr reached 60.8% and 114.70% of that of CK, respectively. The relative coverage of CK, D3yr, and D6yr was 19.05%, 83.24%, and 77.32%, respectively. The important value of Rhododendron plants in the communities increased from 0.42 in CK to 0.74 in D3yr, and then decreased to 0.67 in D6yr. The α diversity in the shrub layer of D3yr and D6yr were generally lower than those of CK except Pielou evenness index. The β diversity indicates that the similarity between CK and D3yr was lower, that between CK and D6yr was moderate, and that between D3yr and D6yr was higher. The sprouting height and coverage of Rhododendron plants was significantly correlated with age and sprouting time. The sprouting ability of Rhododendron plants increased first and then decreased with age, while the sprouting ability of Rhododendron plants with age of 10–12 years was the strongest. Clearcutting measures can improve the dominance of Rhododendron plants in the communities, promote the sprouting and renewal of Rhododendron population, and accelerate the succession rate of communities.

Accumulation Pathway of Cd, Pb, and Zn in Chinese Cabbage under the Condition of Exogenous Pollution Superposition in High Geological Background Area

Northwest Guizhou is a karst area with a high geological background. Affected by historical soil zinc smelting, the heavy metal content of atmospheric dust in the region is high, and soil pollution is severe. In order to explore the accumulation pathway of heavy metals in leafy vegetables, Chinese cabbage was used as the test crop, and the geological high background soil and zinc smelting-contaminated soil with the same contents of Cd, Pb, and Zn were selected. A pot experiment was carried out in the polluted area of zinc smelting and the non-polluting control area. The heavy metal content, enrichment coefficient (BCF), and transport coefficient (TF) of Chinese cabbage were studied under open-air, plastic mulching film, and greenhouse cultivation conditions. The results showed that the contents of Cd, Pb, and Zn in Chinese cabbage in the polluted area and the control area were 0.10-1.01 and 0.10-0.91 mg·kg-1, 0.31-0.62 and 0.23-0.37 mg·kg-1, and 7.50-32.74 and 4.88-21.79 mg·kg-1, respectively. Overall, the contents of heavy metals in the polluted area were relatively high. The contents of Cd and Pb in Chinese cabbage planted in soil with a high geological background met the requirements of the national food safety standard limits. Affected by atmospheric deposition, the contents of Pb and Zn in Chinese cabbage in the polluted area were significantly higher than that in the control area, and the difference in Cd was insignificant. The proportions of weak acid-soluble Cd, Pb, and Zn in the contaminated soil were 48%, 3.0%, and 16%, respectively, which were 3.15, 1.01, and 1.57 times higher than those in the control soil with a high geological background. Affected by the activity of heavy metals, the contents of Cd and Zn in Chinese cabbage planted in the contaminated soil exceeded the national standard and were significantly higher than those in the control soil. The root-soil BCF of Cd, Pb, and Zn in polluted soil was significantly higher than that in the control soil, and the BCF of Cd and Zn was higher than that of Pb. The TF aboveground root Cd and Zn in Chinese cabbage was significantly higher than in the control soil, whereas the TF aboveground root Pb in the polluted area was significantly higher than that in the control area. The Pb content of Chinese cabbage in the two study areas showed open field>plastic mulching film>greenhouse cultivation. In conclusion, the content of Cd and Zn in Chinese cabbage was greatly affected by the activity of heavy metals in soil, and the main accumulation pathway was root absorption and transportation. In addition to root absorption, atmospheric deposition was an important accumulation pathway of Pb. Therefore, in areas with high geological backgrounds, attention should be paid to controlling the exposure risk of Cd and Zn in leafy vegetables planted on exogenously polluted soils. Additionally, greenhouse cultivation could effectively reduce the accumulation of Pb.

Source apportionment of heavy metal(loid)s in sediments of a typical karst mountain drinking-water reservoir and the associated risk assessment based on chemical speciations.

As important place for water storage and supply, drinking-water reservoirs in karst mountain areas play a key role in ensuring human well-being, and its water quality safety has attracted much attention. Source apportionment and ecological risks of heavy metal(loid)s in sediments of drinking-water reservoir are important for water security, public health, and regional water resources management, especially in karst mountain areas where water resources are scarce. To expound the accumulation, potential ecological risks, and sources of heavy metal(loid)s in a drinking-water reservoir in Northwest Guizhou, China, the surface sediments were collected and analyzed based on the combined use of the geo-accumulation index (Igeo), sequential extraction (BCR), ratios of secondary phase and primary phase (RSP), risk assessment code (RAC), modified potential ecological risk index (MRI), as well as the positive matrix factorization methods. The results indicated that the accumulation of Cd in sediments was obvious, with approximately 61.9% of the samples showing moderate to high accumulation levels, followed by Pb, Cu, Ni, and Zn, whereas the As and Cr were at low levels. A large proportion of BCR-extracted acid extractable and reducible fraction were found in Cd (72.5%) and Pb (40.3%), suggesting high bioavailability. The combined results of RSP, RAC, and MRI showed that Cd was the major pollutant in sediments with high potential ecological risk, while the risk of other elements was low. Source apportionment results of heavy metal(loid)s indicated that Cd (75.76%) and Zn (23.1%) mainly originated from agricultural activities; As (69.82%), Cr (50.05%), Cu (33.47%), and Ni (31.87%) were associated with domestic sources related to residents' lives; Cu (52.36%), Ni (44.57%), Cr (34.33%), As (26.51%), Pb (24.77%), and Zn (23.80%) primarily came from natural geological sources; and Pb (47.56%), Zn (22.46%) and Cr (13.92%) might be introduced by mixed sources of traffic and domestic. The contribution ratios of the four sources were 18.41%, 36.67%, 29.48%, and 15.44%, respectively. Overall, priority control factors for pollution in relation to agricultural sources included Cd, while domestic sources are primarily associated with As. It is crucial to place special emphasis on the impacts of human activities when formulating pollution prevention and control measures. The results of this study can provide valuable reference and insights for water resources management and pollution prevention and control strategies in karst mountainous areas.

Multi-scale pore structure characteristics and main controlling factors analysis of Longtan formation shale in Northwest Guizhou

Marine-continental transitional shale strata are widely distributed in China and have high gas potential. The Longtan shales are a typical marine-continental transitional coal-bearing shale system in Northwest Guizhou. Low-temperature N2 adsorption experiments and high-pressure mercury injection experiments were carried out on the unweathered shale samples from Well JS-1. The multi-scale fractal dimensions were calculated based on the MESP (Menger-sponge) model, MESA (mercury saturation) model, and FHH (Frenkel-Halsey-Hill) model respectively. The macropores (≥100 nm) are mainly inorganic with a fractal dimension D1 between 2.8628–3.2057, indicating the macropore structure is relatively complex. The proportion of the macropores in total pores is not high in comparison to mini-micropores (<50 nm), and the content of brittle minerals and pyrite mainly controls its structure. Among the mesopores (50–100 nm), inorganic pores are still the primary pore type, but the proportion of organic pores increases. The fractal dimension D2 is between 2.2125–2.3016. It has medium complexity, and the proportion in the total pores is slightly higher than that of macropores. The influence of organic matter abundance on mesopore structure is greater than that in macropore because of the increase in the proportion of organic pores, making the controlling mechanism of mesopore structure more complicated. Mini-micro pores are mainly organic pores. The fractal dimension D3 (fractal dimension of mini-micropores under low relative pressure, P/P0 ≤0.5) ranges between 2.6709–2.8648, and D3’ (fractal dimension of mini-micropores under high relative pressure, P/P0 >0.5) ranges between 2.6661–2.9256, indicating complex pore structures and rough surfaces. Mini-micropore accounts for the highest proportion of the total pores and its structure is mainly controlled by the abundance of organic matter. The pore structures of macropores and mesopores greatly influence the proportion of desorption gas in shale, while the structure of mini-micropores can control the maximum adsorbed gas volume of shale.

UPLC-Q/TOF-MS coupled with multivariate analysis for comparative analysis of metabolomic in Dendrobium nobile from different growth altitudes

Dendrobium nobile alkaloids (DNLA) and glycosides are the main active components extracted from Dendrobium nobile Lindl. (D. nobile) used for thousands of years in China. The pharmacological effects of the above chemical components are significantly different. D. nobile is mainly grown at an altitude ranging from 230 to 800 m in Chishui City, Northwest Guizhou Province. However, it is unclear whether the metabolite in D. nobile is influenced by the planting altitude. Hence, to reveal the different metabolite in D. nobile cultivated at the altitude of 336 m, 528 m, and 692 m, ultra-high performance liquid chromatography with Q/TOF-MS couple with multivariate analysis were developed. Using the orthogonal partial least squares-discriminant analysis, 19 different metabolites were discovered and then tentatively assigned their structures as alkaloids and glycosides by comparing mass spectrometry data with in-house database and literature. Moreover, the result of semiquantitative analysis showed the content of dendrobine that was belonged to alkaloids significantly increased at the altitude of 692 m, whereas the content of glycosides demonstrated an accumulation trend at the altitude of 528 m. The results could provide valuable information for the optimal clinical drug therapeutics and provide a reference for quality control.

Contamination Evaluation and Source Analysis of Heavy Metals in Karst Soil Using UNMIX Model and Pb-Cd Isotopes.

Karst terrain is the typical area covered with a high background of heavy metals under geochemical anomaly. This research explored the accumulation of geochemical elements and soil sources in karst terrain from rock and soil exposed in carbonate areas. The comprehensive ecological risk and enrichment of heavy metals from parent rock weathered to soil was investigated in 11 formations in the carbonate and clastic areas of the Weining and Hezhang counties in northwest Guizhou. The single factor pollution index, geoaccumulation index, and the potential risk coefficient were used to assess the environmental risk. The results revealed that the heavy metals in an overall geologically high background level of soil in northwest Guizhou is at a slight risk level. However, except for Cd, the heavy metals did not exceed the standard pollution reference. Moreover, the UNMIX model and Cd and Pb isotopes were used to analyze the source of heavy metals, comprising of cadmium (Cd), arsenic (As), lead (Pb), chromium (Cr), copper (Cu), nickel (Ni), and zinc (Zn), and the geochemical elements of silicon (Si), aluminum (Al), iron (Fe), magnesium (Mg), and calcium (Ca). The study showed that most elements in the soil carbonate area exceed the national standard, and the heavy metals in the soil showed a strong enrichment, while the major elements Si and Mg display strong loss. Heavy metal concentrations in soil in the carbonate area were higher than in the clastic area. Geological sources and atmospheric deposition were the main contributors to heavy metal concentrations in both carbonate and clastic areas, and their concentrations differ according to soils developing in different formations.

Health Risk Assessment and Environmental Benchmark of Heavy Metals in Cultivated Land in Mountainous Area of Northwest Guizhou Province

An extensive investigation of heavy metal (Cd, Hg, As, Pb, and Cr) levels in 137 pairs of soil-maize/rice samples was conducted in cultivated land from a typical karst mountain area in the Northwest of Guizhou Province. A health risk assessment model was used to assess the health risks of those areas, and the environmental benchmarks of heavy metals in soils were evaluated using the species sensitivity distribution (SSD) model. The results showed that the soils of maize and rice were polluted by heavy metals. Cd was the primary pollutant, with an exceeding rate ranging from 87% to 445%. The contaminated level of maize fields was higher than those of rice fields. In contrast, only 3.51% and 13.4% of Cd content in maize kernels and rice grains exceeded the national threshold, and the Cd heavy metal accumulation ability of rice was higher than that of maize. The carcinogenic and non-carcinogenic risks of heavy metals for adults and children in the study area were at a low level. The carcinogenic risk of rice consumption was slightly higher than that of maize, and the health risk to children was higher than that to adults. The results derived from the SSD method showed that the 95% and 5% hazardous concentrations (HC5 and HC95) of maize fields were 0.67 for Cd, 771.99 for As, 40.85 for Pb and 609.88 for Cr mg·kg-1, and HC95were 48.47 for Cd, 159.67 for As, 1735.68 for Pb and 1671.74 for Cr mg·kg-1, respectively. The HC5 values of rice fields were 2.42 for Cd, 8.88 for As, 41.41 for Pb and 27.84 for Cr mg·kg-1, and the HC95 values were 48.47 for Cd, 159.67 for As, 1735.68 for Pb and 1671.74 for Cr mg·kg-1, respectively. The HC5 values of Cd, As, and Cr in maize fields and Cd in rice fields were significantly higher than the soil risk screening values in the current standard, and the HC95 values of the two fields were higher than the soil risk intervened values. The results indicated that the current standard would be too strict to evaluate the actual pollution level of soil heavy metals in this area.

Distribution Characteristics of Heavy Metals in Soils Affected by Different Land Use Types in a Superimposed Pollution Area with High Geological Background

The high geological background and the residual pollution of historical zinc smelting in the karst area of northwest Guizhou has led to serious soil heavy metal pollution. In order to understand the characteristics of soil heavy metal pollution in agricultural land, wasteland, and forestland, 126 surface and profile soil samples were collected from a typical zinc powder factory-polluted small watershed in Weining County, Northwest Guizhou Province. The concentrations and distribution characteristics of Cd, As, Pb, Cu, and Zn in soils were studied. The results showed that the average ω(Cd), ω(As), ω(Pb), ω(Cu), and ω(Zn) in the surface soil were 8.14, 45.07, 263.97, 41.36, and 716.98 mg·kg-1, respectively, which were 1.29-12.33 times higher than the background values. The content of heavy metals in soil of different land uses in descending order was agricultural land, wasteland, and forestland. From the perspective of spatial distribution, the soil with high heavy metal concentration was concentrated around the zinc smelting plant and slag, and the accumulation of heavy metals in soil was greatly affected by the pollution sources of mining activities but less affected by the land use mode. In soil profile, heavy metals in the surface layer were generally higher than those in bottom layers, showing a significant difference (P<0.05) in wasteland. Five heavy metals in 80-100 cm soil were higher than the background value, reflecting the existence of a high geological background value. Correlation analysis and principal component analysis showed that Pb, Zn, and As in the surface soil were mainly affected by human activities such as mining and transportation, whereas Cd and Cu were both affected by high geological background and human activities. The single ecological risk coefficient of Cd in soil was the highest, which reached very strong or very strong risk, whereas As, Zn, Cu, and Pb reached slight or medium risk. The comprehensive potential ecological risk index indicated strong ecological risk, which in agricultural land was higher than that in wasteland and forestland. In the karst high geological background area, the influence of lead and zinc smelting on the distribution and accumulation of heavy metals in soils was greater than that of land use; soil heavy metal pollution was serious, and ecological risk was high in this area. Therefore, strict control of heavy metal-contaminated soil should be strengthened.

Impatiensbijieensis (Balsaminaceae), a new species from karst plateau in Guizhou, China.

Impatiensbijieensis X.X. Bai & L.Y. Ren, sp. nov. from northwest Guizhou Province, China, is described and illustrated. This new species is distributed discontinuously in Jiulongshan, Dafang County and Dajiucaiping, Hezhang County, both of which are in the Wumeng Mountain area, a karst plateau landform. The new species is morphologically similar to I.pterosepala Hook.f., I.lasiophyton Hook.f. and I.leptocaulon Hook.f. in height and flower shape and it especially resembles I.lasiophyton in pilosity. However, it differs in its deep purplish-red flower, 2-lobed lower sepal apex and cylindrical capsule. A detailed description, colour photographs and a provisional IUCN Red List assessment are provided along with discussions of its geographical distribution, ecology and morphological relationships with other similar species.

An inference of the wading depths of the cranes in wintering wetlands through photographic sampling: a case study of black-necked cranes (Grus nigricollis) in Caohai Wetland, China

Several overwintering crane species like Black-necked cranes (Grus nigricollis) mainly depends on wetlands for foraging or roosting, preferring stable water depths. Understating the wading depths of cranes is a pressing concern for the better management of wetlands and robust conservation of the overwintering cranes populations. Yet, practically it is very difficult to precisely measure the wading depths due to several limitations like, inaccessibility and sampling difficulties. In the current study a sample of 1288 wading photographs of cranes, based on the constancy of proportion of tibiotarsus to tarsometatarsus was taken in Caohai wetland situated in the Northwest Guizhou Province of southwest China. Caohai Wetland is the biggest overwintering wetland around the world, and a very promising area to infer the exact ranges of wading depths of these cranes. The ratio of tibiotarsus to tarsometatarsus of the cranes standing on the lands and the ratio of tibiotarsus to the rest of tarsometatarsus of the cranes standing in water were measured; to infer the projection depths of the part of tarsometatarsus submerged in water, which was used to calculate the accurate depth range of the cranes by comparing with the referenced values. According to the results, 89.92% of individuals preferred the water depths from (0–20] cm, 76.11% preferred (0–10] cm% while water depths for 49.04% individuals was (0–5] cm. Thus we conclude that the Black-necked Cranes prefer a depth range of (0–10] cm. This water depth may be relative to the swamps around the lake, which are very important foraging and roosting sites for cranes, For better habitat management, we strongly recommend paying special attention to swamps with specific water depth ranges, particularly when the water level changes.

Spatial Distribution, Food Chain Translocation, Human Health Risks and Environmental Thresholds of Heavy Metals of the Dominant Maize Cultivation Area, Northwest Guizhou Province, China

Spatial Distribution, Food Chain Translocation, Human Health Risks and Environmental Thresholds of Heavy Metals of the Dominant Maize Cultivation Area, Northwest Guizhou Province, China

Trace element compositions of sulfides from Pb-Zn deposits in the Northeast Yunnan and northwest Guizhou Provinces, SW China: Insights from LA-ICP-MS analyses of sphalerite and pyrite

Trace elements in sphalerite and pyrite from six deposits at the Sichuan-Yunnan-Guizhou lead–zinc metallogenic province were analysed to constrain the composition, distribution characteristics and substitution mechanisms of trace elements by LA-ICP-MS analyses. The results show that the sphalerites are characterized by high Fe, Ge, Cd and low Bi, Ni, Co and Tl contents, while pyrites characteristically have high contents of Ni, Co, As and low contents of Ge, Ga, Tl, Bi and In. Iron, Ga, Mn, Cd and Ge in sphalerite and Co, Ni and Tl in pyrite are generally lattice-bound, while Ag, Cu, As and Sb are usually present in both micro-inclusions and solid solution. Significant correlations between some elements in sphalerite suggest the substitution mechanisms: 2Zn2+ ↔ (Ag+, Cu+) + (Ga3+, As3+) and 3Zn2+ ↔ 2(Cu+, Ag+) + Ge4+, and the existence of negative correlation between Fe and Mn implies a competition between both elements. The correlation trends between trace elements in pyrite demonstrate the coupled substitution mechanism of 2Fe2+ ↔ (Tl+, Cu+, Ag+) + Sb3+.Generally, darker sphalerite is relatively rich in Fe and Ge compared to light-color sphalerite, and is deficient in Ga, In and Sn. Regionally, the Cu in sphalerite tends to gradually increase from southeast to northwest, and pyrite from Maoping has significantly higher Co and Ti concentrations and Co/Ni ratios than that from the deposits in northwestern Guizhou. The variation of the Co/Ni ratio in pyrite at the scale of these deposits may provide vectors for the geochemical exploration of Pb-Zn mineralization and the Co/Ni ratios close to 0.1 are more prospective for a larger deposit.

Effect of Freeze-thaw Cycles on Microstructure and Mechanical Properties of Limestone

In studying the effect of freeze-thaw cycles on the microstructure and mechanical properties of limestone, scanning electron microscope, low-field nuclear magnetic resonance, and uniaxial compression tests are carried out on the limestone samples dried and subject to 5, 10, 15, and 20 freeze-thaw cycles. Through analysis and discussion, it was found that the number of freeze-thaw cycles has a significant effect on the microstructure of the limestone samples. Compared to the dry samples, the number of microcracks of the limestone samples subjected to freeze-thaw cycles is increased. Moreover, the crack width is positively correlated to the number of freeze-thaw cycles. With an increase in freeze-thaw cycles, the signal intensity of the T2 spectrum is considerably increased, and the connectivity of the micropores and fissures is increased. In addition, the peak compressive strength and elastic modulus showed a significant negative correlation with the number of freeze-thaw cycles. Again, compared to the dry samples, the peak compressive strength of the samples subject to 5, 10, 15, and 20 freeze-thaw cycles decreased by 14.7%, 22.0%, 28.7%, and 37.5%, respectively. The elastic modulus also decreased by 8.0%, 11.4%, 11.7%, and 21.5%, respectively. Therefore, these findings provide basic parameters for the stability evaluation of rock slopes in Northwest Guizhou.

New Insights into Selenium Enrichment in the Soil of Northwestern Guizhou, Southwest China.

Selenium (Se) is an essential trace element for animals and plants. Se in soil has an important influence on the Se intake by animals and plants. To explore the source of Se in soils of the zinc-smelting area in northwest Guizhou, China, 271 topsoils and 50 deep soil samples were collected, and the concentration, speciation and distribution of Se in soils were analysed. The results showed that the concentration of Se in topsoils ranged from 0.2mg/kg to 1.79mg/kg, with an average of 0.84mg/kg, which was more than 2 times of that in deep soil. These observations indicated that Se was enriched in the surface layer of soil. In terms of spatial distribution, high-Se topsoils (> 1.0mg/kg) were mainly distributed near the zinc smelting area, and topsoil samples with relatively low content of Se were mainly distributed in areas with less human activities influence. The Se occurrence species in topsoils were in the order of residue, organic-binding, humic-acid binding, water-soluble, Fe/Mn/Al oxide-binding, carbonate-binding and ion-exchange. The contribution of residual Se to total Se in topsoil was decisive, and the content of other species of selenium changed slightly. The Se speciation that was residual in soil is difficult for plants to utilize, which is consistent with previous studies on seleniferous soils caused by zinc smelting. These results indicated that the main reason for Se enrichment in the topsoils of northwest Guizhou Province was indigenous zinc smelting.