Rocky desertification is a common phenomenon in karst areas. Soil carbon and nitrogen storage is of great significance to the formation and evolution of ecosystems. Soil leakage is one of the important indicators in evaluating ecosystem stability. There are few studies on the response of carbon and nitrogen leakage below the surface of karst critical zones to forest ecosystems. The karst springs in the study area of Shibing Heichong, Bijie Salaxi and Guanling-Zhenfeng Huajiang in Guizhou, China, were selected to determine the variation characteristics of carbon and nitrogen content and karst spring outputs and their response to soil leakage. The results showed the following: (1) The content and output of carbon and nitrogen in karst springs in the three study areas showed obvious spatial differences. The carbon and nitrogen output of karst spring water was mainly concentrated in the rainy season. The carbon and nitrogen contents and output of karst springs in the Shibing Heichong study area were higher than those in the Bijie Salaxi and Guanling-Zhenfeng Huajiang study areas. (2) The carbon and nitrogen outputs of karst springs were mainly affected by flow. Land cover and land use in forests affect the carbon and nitrogen contents of karst springs and thus affect the output. (3) The higher the soil leakage of the karst spring was, the higher the carbon and nitrogen output. The leakage of the overlying soil in the Shibing Heichong study area was high, but the soil decline was small, and the stability of the forest ecosystem was relatively good. In summary, a lower degree of rocky desertification results in higher leakage from karst springs and higher risks of soil leakage; however, the ecosystem was relatively stable. Evaluating forest soil carbon and nitrogen loss and ecosystem stability in karst areas through the nutrient output of karst springs is of great significance for the prevention and control of rocky desertification areas.

In karst areas, the characteristics of water chemistry and carbon and nitrogen are of great significance to basic research. The contents of Ca²⁺, Mg²⁺, K⁺, Na⁺, HCO₃⁻, SO₄²⁻, NO₃⁻, Cl⁻, dissolved organic carbon (DOC), and total nitrogen (TN) in water samples from 18 rivers and 14 springs in the Huangzhouhe River Basin were determined. The results showed that the water chemistry type in the Huangzhouhe River Basin is HCO₃-Ca-Mg. The chemical composition is mainly affected by dolomite weathering and also by ion exchange and other human activities. The river and spring DIC remain at the same level in the upper and middle reaches and decrease in the lower reaches. The NO₃-N and TN of river water and TN of spring water increase in the middle reaches, while NO₃-N of spring water decreases in the lower reaches. The DOC in the basin increases with the increase of SO₄²⁻ and Cl⁻, mainly due to the human influence of agricultural and domestic sewage. In the basin, the NO₃-N and TN in spring water are larger, and the DOC in river water is larger, mainly because there are more phytoplankton and human activities in the river water. The carbon and nitrogen in the Huangzhouhe River Basin are mainly HCO₃⁻ and NO₃⁻ ions. The evaluation of pH, Cl⁻, NO₃-N, SO₄²⁻, and TDS shows that the water quality is good and the ecological environment is good.

Carbon and nitrogen are among the most important biogenic elements in terrestrial ecosystems, and carbon and nitrogen stable isotopes (δ¹³C and δ¹⁵N) are often used to indicate the sources of carbon and nitrogen elements and turnover processes, and the study of C and N isotopes coupling can provide more precise indications. To this end, this study was conducted to investigate the effects of different land use types on soil organic carbon (SOC), soil organic nitrogen (SON) and the coupling relationship of C-N isotopes, as well as to reveal the seasonal variation characteristics of soil C and N. The results showed that SOC and SON contents of forest land were significantly higher than those of agricultural land and grassland. The soil C/N was significantly higher in the dry season than in the rainy season (p < 0.01), indicating that the decomposition rate of soil organic matter (SOM) was faster in the rainy season, which was not conducive to the accumulation of soil C. Soil δ¹³C and δ¹⁵N coupling showed seasonal characteristics: soil δ¹³C and δ¹⁵N did not have a good linear relationship in the rainy season, but showed a significant positive correlation in the dry season (r² = 0.75, p < 0.05), indicating that there are differences in the soil C-N isotope fractionation coupling under the influence of climatic factors. This study provides a reference for regional land resource management as well as carbon and nitrogen cycle studies in karst areas.

The Shuiluo River Catchment (SRC) is the front zone of the southeast compression and uplift of the Tibetan Plateau, with intense tectonic activity. In the basin, a series of regional large NW–SE trending active faults are developed. Studying clearly the geomorphic evolution of the SRC is conducive to further understanding the uplift and expansion mechanism of the SE edge of Tibetan Plateau. Our research was based on geographic information system, numerical analysis tool, and digital elevation model data, to extract six geomorpic parameters (hypsometric integral, asymmetry factor, basin shape ratio, valley floor width–valley height ratio, normalized channel steepness index and index of relative active tectonics) in SRC. After eliminating the impacts of climate, catchments area, and glacier, the geomorphic evolution of the SRC is mainly affected by geological structure and differential tectonic uplift movement; in the upstream and midstream (upper part), the shape of valleys and stream longitudinal profile shapes are affected by lithology; affected by geological structure and tectonic uplift, the tectonic activity in the midstream and downstream is relatively strong, and the intensity of activity in the downstream is stronger than that in the midstream, which may suggest that the faults’ activity in the downstream is stronger; the index of relative active tectonics values of the SRC are consistent with the regional seismic intensity, field-work and low-temperature thermochronology which indicates it is reasonable to use the fluvial geomorphic parameters to study the regional geomorphic evolution. The morphological parameters we extracted show different values in different regions of SRC, which may be the result of differential uplift in the southeastern of the Tibetan Plateau.

Epikarst is connected with a “binary” geological structure, and the hydrogeochemical processes are complex. Nutrients play an important role in the restoration of the surface ecosystem in the desertification area, which is prone to loss and leakage, and the transport and transformation of nitrogen is crucial to the growth and development of plants in the ecosystem and the safety of drinking water for the residents. In this study, we reviewed nitrogen research in the past 20 years in the “Web of Science (WOS)” and “China National Knowledge Infrastructure (CNKI)”, and we reviewed nitrogen research in the following areas. From the results of the systematic review, (1) We found that nitrogen-related research literature has been growing over time, and the growth has been faster in the past five years, mainly in the fields of agriculture, public health, and environmental science; (2) In karst water systems, researchers are mostly concerned with the sources of nitrate, distribution characteristics, and pollution of karst water, and the dual isotope techniques of δ¹⁵N and δ¹⁸O are used to identify these; (3) In karst water systems, surface water bodies and underground rivers are the main objects of study, relatively few studies have been conducted on karst springs, and NO₃⁻-N, NO₂⁻-N, and NH₄⁺-N are the main forms of nitrogen presence. The study of nitrogen in karst water systems ignores the unique subsurface leakage problem of karst areas, and the study of the relationship between nitrogen and nutrient leakage in karst water systems should be strengthened for karst desertification management and ecological restoration. This review may provide some insights for researchers working in related fields.

Exploring the hydrogeochemistry of cave drip water and its response to precipitation events in karst rocky desertification regions is of great significance to the paleoenvironment reconstruction of the karst desertification process using speleothem. We selected three perennial drip sites in the Shijiangjun Cave, located in Guizhou Province, Southwest China, and carried out high-frequency monitoring and sampling during two rainfalls from 22 to 25 May 2016. The major hydrogeochemical parameters of drip water and their relationships with karst desertification were analyzed. The results show that the hydrogeochemistry of the drip water in the Shijiangjun Cave, characterized by HCO₃-Ca·Mg, was dominated by the dissolution of calcareous dolomite. The three drip sites were classified into the delayed response type (W1) and the rapid response type (W2 and W3) based on the response speed of the drip water indicators to precipitation, which were highly influenced by the piston effect and precipitation dilution, respectively. Furthermore, the response sensitivity of the drip water indicators to precipitation was constrained by the desertification degree in the rainy season, specifically, the faster response appeared in the higher desertification degree area. It is essential to select appropriate drip sites and establish an applicable indicator system for the evolutional history reconstruction of karst desertification using speleothems.