Effects of organic mineral fertiliser on heavy metal migration and potential carbon sink in soils in a karst region

Heavy metal pollution in karst mountainous area of Guizhou has spread due to the long-term exploitation of mineral resources and the improper disposal of environmentally hazardous waste. Heavy metals are characterised by non-degradation, strong toxicity, and constant accumulation, posing a grave threat to karst mountain fragile soil ecosystem. To reduce the harm caused by heavy metal pollution and damage to agricultural products, research was undertaken on the basis of previous work by simulating pot experiments on pak choi cabbage(Brassica rapa chinensis)planted in Cd-contaminated soil: different amounts of organic mineral fertilisers(OMF) compared with chemical fertiliser(CF) were used and by detecting the amount of heavy metal in the mature vegetable, a better fertilisation strategy was developed. The results showed that the Cd content in vegetables grown with CF was 23.70 mg/kg,while that of vegetables grown with OMF and bacterial inoculant was the lowest at 15.13 mg/kg. This suggests that the use of OMF and microbes in karst areas not only promotes plant growth but also hinders plant absorption of heavy metal ions in the soil. In addition, through the collection of pot leachate, the detection of water chemistrycharacteristics, and the calculation of the calcite saturation index, it was found that the OMF method also induces certain carbon sink effects. The results provide a new way in which rationalise the use of OMFs in karst areas to alleviate soil heavy metal pollution and increase soil carbon sequestration.

Interactions between Soil Characteristics, Environmental Factors, and Plant Species Abundance: A Case Study in the Karst Mountains of Longhushan Nature Reserve, Southwest China

The ability to manage and restore plant communities in the face of human-induced landscape change may rely on our ability to predict how species respond to environmental variables.Understanding this response requires examining factors or their interactions that have influence on plant and resource availability.Our objective was to analyze the relationships between changes in plant abundance and the interaction among environmental habitat factors including soil, geological(rock type), and other environmental variables in the Longhushan karst mountains ecosystem.Species density and dominance were examined using ANOVA, ANCOVA,and Generalized Linear Models to establish the single or combined effects of these groups of factors.The results showed that trends in abundance were mainly affected by rock type(related to the percentage content of dolomite and calcite), soil characteristics in association with topography.Both plant indices were higher in dolomite dominated areas and varied positively with moisture, and elevation, but negatively with organic matter, while density also increased with slope degree.The results demonstrate that significant variations in species abundance was produced with the combination of variables from soil, geological, andenvironmental factors, suggesting their interaction influence on plants.We postulate that spatial variations in plant abundance in karst ecosystem depends on the carbonate rock type in addition to water and nutrient availability which are mainly controlled by topography and other factors such as soil texture and temperature.The study suggests that in karst areas carbonate rock type, in addition to local environmental variables, should be taken into account when analyzing the factors that have impact on plant communities.

Hazards and Landscape Changes(Degradations) on Hungarian Karst Mountains Due to Natural and Human Effects

In order to study the karstological processes within the karst ecological system,the geohazards and degradation of karst landscapes on the karst areas of the Bakony mountains(Hungary),we investigated the abiotic elements of the environment,soil and cover deposits,erosion soil decay;the changes in the quantity and quality of karst waters:contamination at swallow holes,contamination of karst springs;and the biogenic factors:surface vegetation coverage by the corine land cover method,plant-ecological examinations,qualification of surface waters with the help of biological water labeling.We recognized that the increasing human activities during the past few centuries have had significant impact on the investigated landscapes of karst areas because of their spatial sensitivity.In the scope of our research we concluded that the landscape changes due to natural and human effects can vary strongly on the different karst areas.These differences can arise from the climatic and geomorphologic situation,the coverlayer's qualities,etc.,but primarily from the different utilization of the investigated karst areas(e.g.the intensity,characteristics and territorial extension of utilization).On the spot investigation we detected traces of new and fast geomorphological processes(gully formation,landslides,collapses,new sinkhole development) and landforms(sinkholes,gullies,swallow holes),which are clear evidences of the effect of climatic changes.

Characteristics and distributions of humic acids in two soil profiles of the southwest China Karst area

Characteristics and distributions of humic acid(HA) and soil organic matter(SOM) in a yellow soil profile and a limestone soil profile of the southwest China Karst area were systematically investigated to reveal their evolutions in different soils of the study area. The results showed that characteristics and distribution of SOM along the two soil profiles were notably different. Total organic carbon(TOC) contents of soil samples decreased just slightly along the limestone soil profile but sharply along the yellow soil profile. TOCs of the limestone soils were significantly higher than those of the corresponding yellow soils, and C/N ratios of SOMs showed a similar variation trend to that of TOCs, indicating that SOM can be better conserved in the limestone soil than in the yellow soil. The soil humic acids were exhaustively extracted and further fractionated according to their apparent molecular weights using ultrafiltration techniques to explore underlying conservation mechanisms. The result showed that C/N ratios of HAs from different limestone soil layers were relatively stable and that large molecular HA fractions predominated the bulk HA of the top soil, indicating that HA in the limestone profile was protected while bio and chemical degradations were retarded. Combined with organic elements contents and mineral contents of two soils, weconcluded that high calcium contents in limestone soils may play a key role in SOM conservation by forming complexation compounds with HAs or/and enclosing SOMs with hypergene CaCO_3 precipitation.

A numerical simulation study on the evolutionary characteristics of the damage process of karst soil cavity under positive pressure effect

Positive pressure effect is the result of rapid urban development in recent years,which leads to over-exploitation of karst groundwater,coupled with the emergence of extreme weather(such as heavy rainfall,the increase in the duration of heavy rainfall),leading to the sharp rise of karst water level,the gas in the karst cavity can not be discharged in time to form a high positive pressure in the soil cavity and promote the destruction of the soil layer,which then induces a series of phenomena,such as karst subsidence.As a new collapse mechanism,the positive pressure effect causes geological disasters that seriously affect the safety of people's lives and properties in karst regions.In order to study the damage characteristics and evolution characteristics of karst soil cavities under positive pressure effect,this study is based on the ASCII text provided by FLAC itself,and the orthotropic simulation computation compilation program,which realizes the finite element analysis in FLAC3D,and focuses on the inhomogeneous change of soil displacement,redistribution of stresses,and plastic damage of karst soil cavities in different evolution stages under the action of positive pressure,and summarizes the characteristics and laws of stress,strain and damage in plastic zone of karst soil cave at different stages of evolution.The results will play a positive role in further investigating the potential mechanical effects,development mechanism and critical warning conditions during the evolution of covered karst soil caves,and also have important scientific research value in deepening the theory of prevention and control of collapse disasters in covered karst soil caves.