喀斯特地貌碳储量研究

Purpose Changes in soil organic carbon (SOC) stock have major impacts on global terrestrial carbon cycling. However, their responses to land use conversions are poorly …

… Afforestation and reforestation projects in the karst regions of … efforts have impacted on carbon stocks and if vegetation … ), and aboveground biomass carbon, which contrasted negative …

… increase in carbon stocks and stabilization of organic carbon in … Since there is a lack of studies on carbon stocks in doline soils, … research on SOC stock in karst landscapes worldwide. …

… C stock and related driving mechanisms in karst areas, intending to provide a scientific foundation for the recovery of fragile ecosystems and to support a regional low-carbon economy. …

… (AG) vegetation carbon stocks and dynamics at a watershed scale. AG carbon density of … % of total AG carbon stock, indicating that carbon pool in karst vegetation was determined …

… While inorganic carbon stocks in tropical karst landscape are … the economic carbon value to support carbon trade program in … carbon stocks value from organic and inorganic carbon in …

… different karst landforms. The proportion of areas with significantly increased carbon stocks in the faulted basin (II) and karst valley (I) regions exceeding 70 %, while the karst trough …

… of a karst area and the accurate estimation of its carbon pool provide a reference to inform regional sustainable development and the accurate estimation of the global soil carbon pool. …

… By treating the SCK as an integrated analytical unit, this research aims to reveal the unique evolution patterns of carbon stocks and provide empirical support for differentiated carbon …

Quantitatively revealing the response of carbon stocks to land use change (LUCC) and analyzing the vulnerability of ecosystem carbon stock (ECS) services are of great significance for maintaining the carbon cycle and ecological security. For this study, China’s Guizhou Province was the study area. Land use data in 2000, 2010, and 2020 were selected to explore the impacts of LUCC on carbon stocks in multiple scenarios by combining the PLUS and InVEST models and then analyzing the vulnerability of ECS services. The results show that forest land plays an important role in improving ECS services in karst plateau mountainous areas. In 2000–2020, forest land expansion offset the carbon stock reduced by the expansion of built-up land, greatly improving the regional ECS function. Following the natural trend (NT), the total carbon stock in Guizhou Province will decrease by 1.86 Tg; however, under ecological protection (EP) measures, the ECS service performs a positive function for LUCC. Focusing on socioeconomic development (ED) will increase the vulnerability of the regional ECS service. In the future, the forest land area size should be increased, and built-up land should be restricted to better improve the service function of ECS in karst plateau mountainous areas.

Soil organic carbon (SOC) contributes the most significant portion of carbon storage in the terrestrial ecosystem. The potential for variability in carbon losses from soil can lead to severe consequences such as climate change. While extensive studies have been conducted to characterize how land cover type, soil texture, and topography impact the distribution of SOC stocks across different ecosystems, little is known about in Karst Region. Here, we characterized SOC stocks with intensive sampling at the local scale (495 representative samples) via Random Forest Regression (RF) and Principal Component Analysis (PCA). Our findings revealed significant differences in SOC stock among land cover types, with croplands exhibiting the lowest SOC stocks, indicating that management practices could play a crucial role in SOC stocks. Conversely, there was little correlation between SOC stock and clay percentage, suggesting that soil texture was not a primary factor influencing SOC at a local scale. Further, Annual Precipitation was identified as the key driving factor for the dynamics of SOC stocks with the help of RF and PCA. A substantial SOC deficit was observed in most soils in this study, as evaluated by a SOC/clay ratio, indicating a significant potential in SOC sequestration with practical measures in the karst region. As such, future research focused on simulating SOC dynamics in the context of climate change should consider the controlling factors at a local scale and summarize them carefully during the up-scaling process.

Investigating land cover patterns, changes in carbon stocks, and forecasting future conditions are essential for formulating regional sustainable development strategies and enhancing ecological and environmental quality. This study centers on Guiyang, a mountainous urban area in southwestern China, to analyze the dynamic changes in land cover and their effects on carbon stocks from 2000 to 2035. A carbon stocks assessment framework was developed using a cellular automaton-based artificial neural network model (CA-ANN), the InVEST model, and the geographical detector model to predict future land cover changes and identify the primary drivers of variations in carbon stocks. The results indicate that (1) from 2000 to 2020, impervious surfaces expanded significantly, increasing by 199.73 km2. Compared to 2020, impervious surfaces are projected to increase by 1.06 km2, 13.54 km2, and 34.97 km2 in 2025, 2030, and 2035, respectively, leading to further reductions in grassland and forest areas. (2) Over time, carbon stocks in Guiyang exhibited a general decreasing trend; spatially, carbon stocks were higher in the western and northern regions and lower in the central and southern regions. (3) The level of greenness, measured by the normalized vegetation index (NDVI), significantly influenced the spatial variation of carbon stocks in Guiyang. Changes in carbon stocks resulted from the combined effects of multiple factors, with the annual average temperature and NDVI being the most influential. These findings provide a scientific basis for advancing low-carbon development and constructing an ecological civilization in Guiyang.

Karst ecosystems are important landscape types that cover about 12% of the world's land area. The role of karst ecosystems in the global carbon cycle remains unclear, due to the lack of an appropriate method for determining the thickness of the solum, a representative sampling of the soil and data of organic carbon stocks at the ecosystem level. The karst region in southwestern China is the largest in the world. In this study, we estimated biomass, soil quantity and ecosystem organic carbon stocks in four vegetation types typical of karst ecosystems in this region, shrub grasslands (SG), thorn shrubbery (TS), forest - shrub transition (FS) and secondary forest (F). The results showed that the biomass of SG, TS, FS, and F is 0.52, 0.85, 5.9 and 19.2 kg m−2, respectively and the corresponding organic cabon storage is 0.26, 0.40, 2.83 and 9.09 kg m−2, respectively. Nevertheless, soil quantity and corresponding organic carbon storage are very small in karst habitats. The quantity of fine earth overlaying the physical weathering zone of the carbonate rock of SG, TS, FS and F is 38.10, 99.24, 29.57 and 61.89 kg m−2, respectively, while the corresponding organic carbon storage is only 3.34, 4.10, 2.37, 5.25 kg m−2, respectively. As a whole, ecosystem organic carbon storage of SG, TS, FS, and F is 3.81, 4.72, 5.68 and 15.1 kg m−2, respectively. These are very low levels compared to other ecosystems in non-karst areas. With the restoration of degraded vegetation, karst ecosystems in southwestern China may play active roles in mitigating the increasing CO2 concentration in the atmosphere.

… carbon (SOC) stocks in territorial ecosystems. However, impacts of land cover on SOC stocks in a karst … of land cover type on SOC stocks in a subtropical karst area. The proportion of …

With few available soil organic carbon (SOC) profiles and the heterogeneity of those that do exist, the estimation of SOC pools in karst areas is highly uncertain. Based on the spatial heterogeneity of SOC content of 23,536 samples in a karst watershed, a modified estimation method was determined for SOC storage that exclusively applies to karst areas. The method is a “soil-type method” based on revised calculation indexes for SOC storage. In the present study, the organic carbon contents of different soil types varied greatly, but generally decreased with increasing soil depth. The organic carbon content decreased nearly linearly to a depth of 0–50 cm and then varied at depths of 50–100 cm. Because of the large spatial variability in the karst area, we were able to determine that influences of the different indexes on the estimation of SOC storage decreased as follows: soil thickness > boulder content > rock fragment content > SOC content > bulk density. Using the modified formula, the SOC content in the Houzhai watershed in Puding was estimated to range from 3.53 to 5.44 kg m−2, with an average value of 1.24 kg m−2 to a depth of 20 cm, and from 4.44 to 14.50 kg m−2, with an average value of 12.12 kg m−2 to a depth of 100 cm. The total SOC content was estimated at 5.39 × 105 t.

Coastal wetlands can have exceptionally large carbon (C) stocks and their protection and restoration would constitute an effective mitigation strategy to climate change. Inclusion of coastal ecosystems in mitigation strategies requires quantification of carbon stocks in order to calculate emissions or sequestration through time. In this study, we quantified the ecosystem C stocks of coastal wetlands of the Sian Ka'an Biosphere Reserve (SKBR) in the Yucatan Peninsula, Mexico. We stratified the SKBR into different vegetation types (tall, medium and dwarf mangroves, and marshes), and examined relationships of environmental variables with C stocks. At nine sites within SKBR, we quantified ecosystem C stocks through measurement of above and belowground biomass, downed wood, and soil C. Additionally, we measured nitrogen (N) and phosphorus (P) from the soil and interstitial salinity. Tall mangroves had the highest C stocks (987±338 Mg ha−1) followed by medium mangroves (623±41 Mg ha−1), dwarf mangroves (381±52 Mg ha−1) and marshes (177±73 Mg ha−1). At all sites, soil C comprised the majority of the ecosystem C stocks (78–99%). Highest C stocks were measured in soils that were relatively low in salinity, high in P and low in N∶P, suggesting that P limits C sequestration and accumulation potential. In this karstic area, coastal wetlands, especially mangroves, are important C stocks. At the landscape scale, the coastal wetlands of Sian Ka'an covering ≈172,176 ha may store 43.2 to 58.0 million Mg of C.

… restoration in a karst area and whether results are similar for soil in a karst area remain unknown. … strategy for SOC stocks in a karst region. Changes in soil OC stock from cropland to …

Little is known on soil organic carbon (SOC) stocks in karst areas worldwide, although many of them have seen long-term application of agroforestry systems with a potential for carbon sequestration. Therefore, our study aimed to assess landscape-level SOC concentration and stock in the Silica Plateau, a part of the Slovak Karst Biosphere Reserve located in the Western Carpathians (Slovakia) with a centuries-long agroforestry record. The most represented local soil units are Chromi-Rendzic Leptosols and Chromic Cambisols with clayey loam texture, C/N ratio 9–12, and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {\text{pH}}_{{{\text{H}}_{2} {\text{O}}}} $$\end{document} 6.6–6.2 in their organo-mineral surface horizons. Mull surface humus form prevails under mixed forest stands dominated by hornbeam (Carpinus betulus L.), oak (Quercus petraea L.), and beech (Fagus sylvatica L.). A total of 2,700 soil samples were collected from 150 soil pits. Both SOC concentrations and stocks were determined for the 0–60 cm mineral soil layer. Soil stoniness was accounted for by means of electrical resistivity tomography. According to the analysis of covariance, cropland SOC concentration (0.026 g g−1) is significantly lower compared to forestland (0.040 g g−1) and pastureland (0.041 g g−1) (P < 0.01). During the period of 130 years after forest clearing, cropland SOC stock has been reduced at an exponential decay rate of ca 0.002 year−1, while the SOC stock in pastureland has increased following land use change from cropland by approximately 30% during the same period of time. Irrespective of land use history, overall SOC stock is high reaching on average 207.4 Mg ha−1, out of which 66% are stored within 0–30 cm and 34% within 30–60 cm soil layers.

… (ETPS) stocks in a karst alpine grassland. A 17 year… carbon stock, whereas RG is beneficial for promoting ecosystem nutrient stock under the condition of pasturing utilisation in the karst …

… zone in China by remedying the data of the northern karst and buried karst regions, and we used a correction coefficient (a=0.65) to eliminate interference from sulfuric acid and nitric …

… Carbon sequestration and stabilization and their regulatory mechanisms are key … carbon cycles, especially in karst areas. Biological carbon pump transforms the timescales for carbon …

Global warming and climate change are becoming the most popular topics among scientists. In this century, the research focusing on the process and mechanism of the carbon cycle, especially the research of reducing the concentration of atmospheric CO2 (carbon sink and carbon sequestration technology), are the core issues of global change. The karst carbon sink was neglected due to the consideration that it was a geological process with a long timescale. Recently, studies have proven that carbonate rock weathering is a rapid and sensitive process, and the Fifth Climate Change Assessment Report of the United Nations Intergovernmental Panel on Climate Change confirmed this. Guizhou, as the center of karst in China, has the unique advantages of the karst carbon sink, and is the core area of the karst carbon sink. On the basis of summarizing the development and evolution trend of karst carbon sinks, through data collection and field research, the Carbon Neutralization Research Group of Guizhou Institute of Technology has conducted an exploratory investigation on karst carbon sinks in Guizhou Province, and basically identified the mechanism, influencing factors and measurement methods of karst carbon sinks in Guizhou karst areas. The results show that the potential of the karst carbon sink in Guizhou is huge. Vegetation restoration, soil improvement, irrigation with external water and the cultivation of aquatic plants are important ways to increase the karst carbon sink by artificial intervention. A series of achievements have been made in the theory, technology and platform construction of the karst carbon cycle geological survey and carbon sink effect evaluation. It is worth noting that there are still great challenges in karst carbon sink measurement and verification, and in the demonstration of artificial intervention in carbon sequestration and sink enhancement, which need to be continuously tackled and improved in the “14th Five-Year Plan” period and beyond, so as to meet the needs of the carbon neutralization target of geological carbon sink services.

… , but its impact on the carbon sequestration capacity of karst ecosystems is not clear. Therefore, in … karst areas in Guangxi are selected as the research object, the carbon sequestration …

… of GTGP in improving carbon sequestration. This evaluation … The ecosystem carbon sequestration in the typical karst area … in ecosystem carbon sequestration in the typical fragile karst …

The karst region of southwest China showed a significant increase in vegetation cover and vegetation carbon stocks under the implementation of a series of ecological restoration projects. However, the relative contribution of ecological restoration projects to terrestrial carbon sequestration in the context of climate change has yet to be well quantified. Here, we used the Community Land Model (CLM4.5) to investigate the trend of net ecosystem productivity (NEP) and attribution to multiple environmental factors in the karst region of southwest China during 2000–2018. The result showed that ecosystems with a significant increasing trend of NEP covered about 46% of the study region, which were mainly located in the peak forest plain region, colliculus region, peak cluster depression region, and middle-high hill region. The simulation experiments suggested that land use change associated with ecological restoration projects caused a large contribution of 53% to the increasing NEP trend, followed by CO2 fertilization (72%), while climate factors and nitrogen deposition showed minor negative effects. Especially, the NEP trend induced by land use change in the 100 pilot counties with the implementation of rocky desertification control project was significantly higher than that in the other karst area. Moreover, moderate and high levels of restoration efforts invested into recovery led to a larger increasing trend (0.66 gC/m2/yr2 and 0.48 gC/m2/yr2) in NEP than the low efforts level (0.22 gC/m2/yr2). Our results highlight the important role of ecological restoration projects in the enhanced terrestrial carbon sequestration in the karst region of southwest China, and recommend a comprehensive assessment of ecological restoration projects for policymaking.

… carbon sequestered in karst systems through dissolution of carbonate minerals is considered to have no net effect on long-term regional and global carbon … of dissolve inorganic carbon (…

… In the southwest karst areas of China, changes in overlying vegetation due to ecological restoration cause considerable carbon sequestration (CS). Assessing the CS potential of …

… autochthonous organic carbon (AOC) burial in the lentic zones. The BCP effect in subtropical deep karst reservoirs buried lots of carbon, increased carbon sequestration and decreased …

… aggregate-associated particulate organic carbon (AAPOC) led … -moss-root interactive effect in this karst area. FG could be a … promoting soil carbon sequestration in deeper soil layers. …

… carbon sequestration during natural restoration process of karst forest vegetation. … ” approach to examine the pattern of carbon sequestration in karst forest ecosystems along the natural …

Carbonate rock weathering coupled with aquatic photosynthesis in karst areas is an important part in the formation of terrestrial carbon sinks. The capacity of photosynthetic carbon sequestration by aquatic microalgae and carbonic anhydrase (CA) is integral in the estimation of carbon sink potential of karst aquatic ecosystems. To date, carbon sequestration by aquatic microalgae in karst areas has been investigated in laboratory experiments. In the present work, the capacity of carbon sequestration by microalgae and CA under natural karst aquatic conditions and the main environmental factors were investigated in field in-situ mesocosms. The Sizhitan Pond of the Huixian karst wetland in Guilin City, Guangxi Province, China, was selected as a typical karst natural water body for this study. The capacity of photosynthetic carbon sequestration varied with microalgal community composition. The microalgal communities with active extracellular CA showed high capacity of carbon sequestration. The average conversion of inorganic carbon to relatively stable organic carbon by microalgae in the Huixian karst wetland aquatic ecosystem was estimated as 4207.5 t C/a. Approximately 28.7% of the bicarbonate fed by the karst underground river was fixed into organic carbon by microalgal photosynthesis. The major environmental factors affecting the capacity of carbon sequestration by microalgae in the karst wetland aquatic ecosystem were the water CA activity, illumination, temperature, total phosphorus and total nitrogen. This study is the first to address the contribution of aquatic microalgae and CA to carbon sequestration under natural karst aquatic conditions. The findings contribute to establishing groundwork for substantiating the carbon sink potential in global karst ecosystems.

Soil erosion is significantly altering the global carbon cycle, leading to considerable soil organic carbon (SOC) loss, which in turn affects carbon redistribution. However, the assessment of SOC loss in complex environments, such as karst regions, and its causal relationships with environmental factors remain underexplored. To fill it, this study proposes a novel approach for evaluating SOC loss in karst regions. This approach integrates rocky desertification factors to refine the Revised Universal Soil Loss Equation (RUSLE) for analyzing dynamic changes in soil erosion and SOC loss in karst regions. Additionally, causal inference theory is applied for the first time to construct a causal network for SOC loss, with the Tree‐Augmented Naive Bayes method used for risk assessment. The findings indicate that the average SOC loss due to soil erosion over the study period was 2.16 × 1010 g C, with SOC loss closely mirroring the spatial patterns of soil erosion. The causal network revealed that rainfall exerted a significant direct causal effect on SOC loss, surpassing vegetation as the dominant factor, with its influence intensifying over time. Exposed bedrock, acting as a moderating factor, added complexity to the SOC loss process in karst regions. High SOC loss areas are mainly found in regions with abundant rainfall, dense vegetation, moderate slopes, high topographic wetness index, and high clay content. These results enhance our understanding of environmental interactions and carbon cycle responses in karst regions, providing a robust scientific basis for regional carbon sink strategies and effective management practices.

Vegetation restoration is an effective strategy for sequestering soil organic carbon (SOC) and restoring degraded ecosystems. However, the effects of different restoration strategies on …

Vegetation restoration measures have been increasingly employed to alleviate rocky desertification in karst ecosystems. However, the comprehensive effects of these interventions on soil properties and soil organic carbon (SOC) remain poorly understood. Herein, we gathered 644 paired observations from 68 studies and conducted a meta-analysis to quantify the performance of different vegetation restoration measures including moss (MS), grassland (GL), cash crop (CP), shrub (SH), and secondary forest (SF) through soil properties and SOC. Our results demonstrated significant effects of MS, GL, CP, SH, and SF on soil biotic and abiotic factors, each with distinct response characteristics. Particularly, MS significantly enhanced all soil properties (excluding a slight decrease in soil pH by 10.8%). Moreover, MS, GL, CP, SH, and SF could elevate SOC by 32.1%, 17.6%, 24.9%, 59.2%, and 48.7% respectively. Utilizing random forest and linear regression models, we identified primary drivers for SOC in MS, GL, CP, SH, and SF as soil moisture content, arbuscular mycorrhizal fungi, soil microbial phosphorus, total nitrogen, and β-1,4-glucosidase, respectively. This meta-analysis underlined the varied effects of vegetation restoration measures on soil properties and advocates for restoration measures that prioritize plant productivity and reduce soil temperature during the karst rocky desertification restoration process. Additionally, this study underscores the pivotal role of vegetation rehabilitation in environmental conservation and carbon sequestration of ecologically vulnerable regions.

The chemical weathering process of carbonate rocks consumes a large quantity of CO2. This has great potential as a carbon sink, and it is one of a significant pathway for achieving carbon neutrality. However, the control mechanisms of karst carbon sink fluxes are unclear, and there is a lack of effective and accurate accounting. We took the Puding Shawan karst water‑carbon cycle test site in China, which has identical initial conditions but different land use types, as the research subject. We used controlled experiments over six years to evaluate the mechanisms for the differences in hydrology, water chemistry, concentrations and fluxes of dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC). We found that the transition from rock to bare soil to grassland led to increases in the DIC concentration by 0.08-0.62 mmol⋅L-1. The inorganic carbon sink flux (CSF) increased by 3.01-5.26 t⋅C⋅km-2⋅a-1, an increase amplitude of 30-70 %. The flux of dissolved organic carbon (FDOC) increase by 0.28 to 0.52 t⋅C⋅km-2⋅a-1, an increase amplitude of 34-90 %. We also assessed the contribution of land use modifications to regional carbon neutrality, it indicate that positive land use modification can significantly regulate the karst carbon sink, with grassland having the greatest carbon sequestration ability. Moreover, in addition to DOC from soil organic matter degradation, DOC production by chemoautotrophic microorganisms utilizing DIC in groundwater may also be a potential source. Thus, coupled studies of the conversion of DIC to DOC processes in groundwater are an important step in assessing karst carbon sink fluxes.

The terrestrial ecosystem in southwestern China has been a long‐term carbon sink, but its spatial–temporal pattern during the previous two decades and its response to karst rocky desertification control measures (KRDC) still merit further quantification, particularly where higher levels of carbon capture by vegetation are proposed in the context of a ‘carbon neutrality’ goal. Satellite datasets, field data from previous studies, and the geostatistical soil respiration model enabled a focus on the karst landscape in Guangxi Province in Southwest China, to probe the spatial–temporal pattern of the ability to capture carbon during 2001–2020 and assess its response to KRDC. The results showed that the interannual variation in the average net ecosystem productivity (NEP) exhibited a remarkable tendency to increase at a rate of 4.15 g C m−2 yr−1 (p < 0.01). A major period of increase was identified from 2006 to 2011, which represented the second stage of the KRDC. The terrestrial ecosystems of karst area have always acted as carbon sinks. Human activity was the dominant factor in the development of NEP and covered an area of 79.30%. The karst area offers climate change characteristics of ‘wetness’ and ‘light stress,’ which can promote the ability of vegetation carbon to serve as a carbon sink (0.18 g C m−2 yr−1). Furthermore, the closing mountains for afforestation is the most effective way to artificially increase the carbon sink. Quantifying vegetation ecosystem carbon sinks and sources in this study is highly significant for understanding regional carbon dynamics and guiding carbon capture policies to design and mitigate land degradation.

The present article reports an assessment of afforestation potential and anticipation of carbon sequestration in the Houzhai River Basin in Guizhou Province in southwestern China. Total of 2755 soil profiles consisting of 22,057 soil samples were collected according to a grid-sampling method at a 150 m scale in the Houzhai River basin, and the SOC contents in soil samples were analyzed using a titration method. General information regarding the geographic characteristics of each sampling grid was recorded in the field. The results indicate that land use in the Houzhai River Basin is very complex. Land use status and land use change in the study area were closely associated with local geographic characteristics and variations in economic structures. There were approximately 15.26 km2 of land that could or should be rearranged as afforestation land in the Houzhai River Basin. The increased SOC storage (0.00-1.00 m soil horizon) would be up to 5.48 × 104 Mg, 6.42 × 104 Mg, 4.77 × 104 Mg and 3.18 × 104 Mg when all of the calculated lands became shrub-grass lands, shrub lands, arbor-shrub forest lands and arbor forest lands, respectively. The increased SOC percentages would be 52.16%, 61.13%, 45.39% and 30.32%, respectively, in comparison with the present SOC storage in these lands.

… karst vegetation is crucial for carbon sequestration and biodiversity conservation. However, research on the carbon … across different geographic types of global karst remains scant. This …

… the karst carbon sink (KCS) is important in understanding its role in the global carbon budget and carbon … Meanwhile, due to the complexity of the karst system and karst carbon cycle, a …

ABSTRACT For the estimation of global karst carbon sink, a few conventional methods usually require the parameters that are difficult to measure, resulting in the big cost. Moreover, under the constraints of incomplete and timeliness issues in the collection of data over a large region, it has remained a challenge for these methods to study global karst carbon sink. Therefore, this paper proposes estimating the global karst carbon sink, and analyzing the suitability of the response surface methodology and the fluctuating variation of karst carbon sink in global karst regions from 1951 to 2050. This paper shows that the proposed method can reduce the time of numerical calculation and is suitable for application in global weathering models; The global karst carbon sink in the future changes not only displays an upward trend but also exposures its fluctuating trend largely. This fluctuation is probably due to global warming.

Two of the most important CO2 sequestration processes on Earth are plant photosynthesis and rock chemical dissolution. Photosynthesis is undoubtedly the most important biochemical reaction and carbon sink processes on Earth. Karst geological action does not produce net carbon sinks. Photosynthesis and karstification in nature are coupled. Karstification–photosynthesis coupling can stabilize and increase the capacity of karstic and photosynthetic carbon sinks. Bidirectional isotope tracer culture technology can quantify the utilization of different inorganic carbon sources by plants. Bicarbonate utilization by plants is a driver of karstification–photosynthesis coupling, which depends on plant species and the environment. Carbonic anhydrase, as a pivot of karstification–photosynthesis coupling, can promote inorganic carbon assimilation in plants and the dissolution of carbonate rocks. Karst-adaptable plants can efficiently promote root-derived bicarbonate and atmospheric carbon dioxide use by plants, finally achieving the conjugate promotion of karstic carbon sinks and photosynthetic carbon sinks. Strengthening karstification–photosynthesis coupling and developing karst-adaptable plants will greatly improve the capacity of carbon sinks in karst ecosystems and better serve the “Carbon peak and Carbon neutralization” goals of China.

… (EC) of the three karst catchments, Banzhai, Huanghou and … Continuous karst-related carbon sink fluxes (CSFs) were … in HCO 3 − for all the karst catchments, because of the chemostatic …

Abstract Research on the carbon source and sink imbalance in global carbon cycle has demonstrated that the mass of CO2 consumed by rock weathering is a portion of the “missing carbon sink.” To further understand the karst carbon sink contributions to atmospheric CO2 emissions, the present study establishes the relationship between the karst carbon sinks and the atmospheric CO2 emissions. We first estimated the mass of CO2 consumed by rock weathering using the Global Erosion Model for CO2 fluxes (GEM-CO2), based on the distribution of different types of rock in Guangxi, China. The rocks were classified using remote sensing imagery, and we estimated the relationship between the mass of CO2 consumed by rock weathering and the CO2 emitted into atmosphere from 2003 to 2012. The analyses reveal that (1) the mass of CO2 consumed by rock weathering could be rapidly estimated using remote sensing imagery, as it not only considers different types of rocks but also simultaneously considers the geological structure and meteorological data, such as rainfall, temperature, and vegetation coverage; (2) the mass of CO2 consumed by rock weathering from 2003 to 2012 displays a “wavy pattern”, which might have been primarily caused by the annual variations in rainfall, whose tendency could be fitted by a straight line at an average annual increasing rate of approximately 8.7%; (3) the mass of emitted CO2 from 2003 to 2012 in Guangxi display a “straight line” at an average annual increasing rate of approximately 12.7%; (4) the mass of CO2 consumed by rock weathering is positively correlated with the mass of emitted CO2 with a correlation coefficient of R2 = 0.62; this implies that an increasing concentration of CO2 in the atmosphere reversely fosters the CO2 consumption by rock weathering; (5) due to different increasing rates, annually 7 × 106 t of CO2 is accumulated in the atmosphere in Guangxi, and a total of 506.42 × 106 t of CO2 is accumulated over a decade; (6) the mass of the karst carbon sinks in Guangxi, China, and globally are estimated to be 1.01 × 106 tC·a−1, 1.49 × 107 tC·a−1, and 0.95 × 108 tC·a−1, respectively. Therefore, the results of this study not only help to understand the relationship between karst carbon sink and the global carbon cycle, but also provide an important basis for predicting the variations in CO2 in the atmosphere and climate change, which could further provide a scientific basis for the rational use of resources and the formulation of environmental protection policies.

It is recognized that karst processes are actively involved in the current global carbon cycle based on twenty years research, and the carbon sink occurred in karst processes is possibly an important part of “missing sink” in global carbon cycle. In this paper, an overview is given on karst carbon cycle research, and influence factors, formed carbon pools (background carbon sink) and sink increase potentials of current karst carbon cycle are analyzed. Carbonate weathering could contribute to the imbalance item (BIM) and land use change item (ELUC) in the global carbon cycle model, owing to its uptake of both atmospheric CO2 (carbon sink effect) and CO2 produced by soil respiration (carbon source reduction effect). Karst carbon sink includes inorganic carbon sink resulted from hydrogeochemical process and organic carbon sink generated by aquatic photosynthetic DIC conversion, forming relatively stable river (reservoir) water body or sediment carbon sink. The sizes of both sinks are controlled by terrestrial ecosystems and aquatic ecosystems, respectively. Desertification rehabilitation and carbon sequestration by aquatic plants are two effective ways to increase the carbon sink in karst area. It is estimated that the rate of carbon sink is at least 381 000 t CO2/a with vegetation restoration and afforestation in southwest China karst area, while the annual organic carbon sink generated by aquatic photosynthesis is about 84 200 t C in the Pearl River Basin. The development of a soil CO2 based model for assessment of regional dissolution intensity will help to improve the estimation accuracy of carbon sink increase and potential, thus provide a more clear and efficient karst sink increase scheme and pathway to achieve the goals of “double carbon”. With the deep investigation on karst carbon cycle, mechanism and carbon sink effect, and the improvement of watershed carbon sink measurement methods and regional sink increase evaluation approaches. Karst carbon sink is expected to be included in the list of atmospheric CO2 sources/sinks of the global carbon budget in the near future.

… carbon sinks in karst ecosystems remain controversial, the contributions of climatic factors to carbon sink … of karst vegetation to climate change have yet to be clearly understood. …

… The δ 13 C value of CO2 emission from soil respiration in the karst area is heavier with … soil/rock interface in karst area.In other words,karst processes in soil was one of the carbon sinks. …

… that the negative feedback of karst-related carbon sinks on future global … carbon sequestration by carbonate liming in non-karst areas will contribute to the realization of the future carbon …

The weathering of carbonate rocks consumes significant amounts of soil CO2, contributing to both direct source reduction and to the enhancement of carbon sinks. This process holds substantial potential as a carbon sink, making it a critical strategy for achieving carbon neutrality and mitigating climate change. However, the control mechanisms for the reverse assessment of karst carbon sinks, with soil CO2 as the core at the input end of karstification, are unclear. By comparing soil respiration and its δ13C values between karst and non-karst regions, we analyzed the impact of karstification on soil respiration. In this study, we examined the karst grassland (KG), woodland (KW), and non-karst woodland (NKW) in the karst region with identical climate conditions as the research subject, analyzing the differences in soil respiration rate (RS), flux (SRF), and isotope δ13C under different land-use types, and comparing them with the non-karst region to reveal the carbon sink potential of karstification in reducing carbon emissions. The results showed that after the land-use change from KG to KW in the karst region, the annual mean values of the RS and SRF increased by 55.50% and 20.94%, respectively. Additionally, the annual mean values of the soil respiration contribution to carbonate weathering in KG were approximately 8.2% higher than those in KW. In contrast, the annual mean values of RS and SRF in KW were 25.14% and 41.80% lower than those in NKW, respectively. Furthermore, the soil respiration participation in carbonate weathering in KW was about 8.9% of that in NKW. Land use change can significantly influence karst carbon sinks, with the KG exhibiting the highest carbon sink capacity. Karst soils play a crucial role in reducing atmospheric CO2 levels and facilitating regional carbon neutralization. Therefore, the karst systems play a pivotal role in mitigating the “land use change term” (source term, ELUC) in the global carbon balance.

Within ecosystems, habitat influences structure, and structure determines function, forming a habitat-structure-function framework (HSFF). Net ecosystem productivity (NEP) is a key indicator for assessing regional or global carbon dynamics. However, the response thresholds of NEP to habitat and structural factors, along with management strategies based on these thresholds, remain under-explored. Therefore, this study examines the response thresholds of NEP to habitat and structural factors in the karst and non-karst regions of southwest China, which exhibit strong surface heterogeneity, based on the HSFF using a restricted cubic spline method. The results are, (1) The interannual NEP increase rate and carbon storage per unit area were notably greater in karst regions than in non-karst ones. However, compared to non-karst regions, karst regions show greater NEP variability and lower stability. (2) Significant nonlinear relationships were identified between NEP and nine habitat factors and six structural factors. NEP thresholds due to habitat and structural factors were smaller in karst regions than in non-karst regions. (3) Habitat factors had greater relative importance and marginal contribution than structural factors in karst and non-karst regions, with energy and water as the main influences on NEP. (4) Using the potential carbon sinks areas determined by the threshold, the karst areas in the entire study will play an important role in carbon sinks in the future. Overall, this study not only deepens the understanding of the differences in ecosystem NEP between karst and non-karst regions, but also provides new perspectives and strategies for optimizing ecosystem management based on habitat and structural characteristics.

… in the vegetation carbon sinks in different karst geographic … its karst area was influenced by the long-term effects of changes in DFMI and VPD. Therefore, the variability of different karst …

In the study of global change, one of the key issues is the global and regional carbon cycle, and estimating the carbon sink magnitude and determining the spatiotemporal pattern of carbon sources have attracted considerable attention from the academic community and are of great scientific significance. The Chinese karst region, which has considerable potential for carbon sequestration, is the principal area for carbon sequestration in China and even in the world. Changes in temperature and precipitation caused by global warming not only affect the hydrological processes in the karst region but also profoundly impact its carbon sink capacity. Nevertheless, no studies have as yet revealed the magnitude and spatial pattern of carbon sinks in the Chinese karst region, as well as the mechanism of the impact of climate change ( CC ) and human activities ( HA ) on the region. Therefore, to elucidate the spatial and temporal patterns of carbon sinks in Chinese karst ecosystems and reveal their responses to CC and HA , this paper employed data on climate, lithology, and ion concentration,

… impacts of recent climate change on the karst-related carbon sink in the SW China for the … the total karst-related carbon sink (TCS) and carbon sink fluxes (CSFs) in the SW China karst …

Southwest China (SWC) holds the distinction of being the world’s largest rock desertification area. Nevertheless, the impacts of climate change and ecological restoration projects on the carbon sinks in the karst area of Southwest China have not been systematically evaluated. In this study, we calculated carbon sinks by utilizing the Carnegie–Ames–Stanford Approach (CASA) model, and the actual measurements, including the net primary productivity (NPP) data and soil respiration (Rs,) were calculated to obtain carbon sink data. Our findings suggest that the carbon sinks in the karst areas are displaying increasing trends or positive reversals, accounting for 58.47% of the area, which is larger than the overall average of 45.08% for Southwest China. This suggests that the karst areas have a greater carbon sequestration potential. However, approximately 10.42% of carbon sinks experience negative reversals. The regions with increasing and positive reversals are primarily located in the western parts of Guizhou and Guangxi, while negative reversals are observed in the eastern parts of Chongqing, Guangxi, and Guizhou. Ecological restoration projects are the main driving factors for the carbon sinks with increasing trends. Increased humidity and ecological restoration management are the main reasons for the positive reversals of carbon sinks. However, warming and drought shift the carbon sinks from increasing to decreasing in Chongqing, east of Guangxi and Guizhou. The findings of this study highlight the significant role of ecological restoration projects and reexamine the impact of climate change on carbon sequestration.

China karst is a global hotspot of increasing vegetation cover, with ecological conservation projects being considered as the main driver. New research using global datasets also indicates that rural outmigration has contributed to increasing biomass at national scale. However, the link between rural outmigration and vegetation cover increase has not been established at regional scale, and it remains unclear as to whether increases in biomass do, in fact, improve the environmental conditions. In this study, we use local field and statistical data on population density and rocky desertification areas to study population movements and changes in aboveground biomass in relation to rocky desertification in South China karst during 2000–2017. Our results show that the urban population in this region increased by 8.3 million people between 2005 and 2015, and the rural population decreased by 4.8 million people. We find that aboveground biomass increased most in rural areas with low human pressure, and that there was an almost linear relationship between increase in biomass and rural outmigration, with the highest increase in aboveground biomass density (1.5 MgC ha−1 yr−1) observed in areas where rural outmigration was highest, and the lowest increase in aboveground biomass density (1.1 MgC ha−1 yr−1) where rural outmigration was lowest. Rocky desertification areas decreased with a higher level of rural outmigration. Using local field data, our study confirmed that rural outmigration can generate a carbon sink at regional scale by reducing rocky desertification.

The research documented here aims to clarify the transport and fate of carbon species that evolved in a typical conical karst system in Gunungsewu. Special interest is attributed to the estimate of carbon flux by considering the conical karst as a whole system. It includes carbon input to karst area, soil respiration, SOC, soil CO2, particulate-dissolved and organic carbon, as well as dissolved organic carbon. The research was conducted between 2012 and 2015. Two study sites were selected to represent different morphological and hydrogeological settings. Carbon input was collected for one year round on the basis of conical hill topo-sequence. Carbon input included in this research was litter fall, plant residue, and organic fertilizer. Incorporated with field measurement, soil samples were also collected for SOC estimation. DIC and DOC were estimated from the underground river of Gilap. The results show that carbon flux in the Gunungsewu karst is favored by the agricultural land uses and practices. Accordingly, the organic carbon input to the karst area is governed by spatial distribution of agricultural land uses and practices. Organic carbon input tends to be in the order of organic fertilizer > litter input > and plant residue. Soil CO2 varies in depth and season. Soil organic carbon also varies seasonally, of which the higher content occurs in the rainy season. Most of the carbon is stored as SOC, 20 % is emitted to the atmosphere through soil respiration, and 9 % is transferred to the deeper zone through a hydrological cycle in the form of dissolved organic carbon and particulate-dissolved organic carbon. The results suggest that carbon sink in the karst area is ten order higher than that previously estimated from DIC. Key words: soil organic carbon, carbon flux, Gunungsewu, Java, karst carbon sink.

… Thus, in this study, the bicarbonate flux is considered to be equal to the inorganic carbon flux from rock weathering, expressed as the total DIC flux per square kilometer in a catchment. …

… flux at the water–air interface in karst aquatic ecosystems is the key to accurately evaluating karst carbon flux … in balancing the CO 2 budget in karst catchments. With the development of …

An effective carbon loading can be calculated from measured alkalinity and pH of karst waters. The carbon loading is independent of the degree of saturation of the water and does not depend on the water being in equilibrium with the carbonate wall rock. A substantial data base of spring water analyses accumulated by students over the past 40 years has been used to probe the CO2 generation, transport, and storage in a variety of drainage basins that feed karst springs. Carbon loading in the water exiting karst drainage basins depends on the rate of CO2 generation in the soils of the catchment areas and on the partitioning between CO2 dissolved in infiltration water and CO2 lost by diffusion upward to the atmosphere. For any given drainage basin there are also influences due to vegetative cover, soil type, and the fraction of the water provided by sinking stream recharge. Losses of CO2 back to the atmosphere occur by speleothem deposition in air-filled caves, by degassing of CO2 in spring runs, and by tufa deposition in spring runs. There are seasonal cycles of CO2 generation that relate growing season and contrasts in winter/summer rates of CO2 generation. Overall, it appears that karst aquifers are a net, but leaky, sink for atmospheric CO2. Keywords: CO2, karst aquifers, springs, carbon loading. DOI: 10.3986/ac.v42i2-3.659

… in karst groundwater is dominantly derived from carbonate dissolution by carbonic acid. However, recently increases in the inorganic carbon flux … fluxes of DIC, and evaluate the carbon …

… in carbon flux in karst regions, yet the underlying carbon sequestration mechanisms remain elusive, and relevant research is particularly scarce in the northern karst … of the karst critical …

… of epigenic karst processes as a major element of the carbon … of dissolved inorganic carbon (DIC) flux in karst landscapes at … a variable rate of DIC flux driven by large fluctuations in …

Abstract Whether carbonate weathering on land represents an important terrestrial carbon sink has long been debated as the CO2 sequestered by the dissolution of carbonate may return to the atmosphere through CO2 outgassing from groundwater-feeding surface waters. In headwater area of karst terrain, the CO2 outgassing frequently happens in spring-fed streams, but its flux and influencing factors still remain under-researched. In this study, we conducted a monthly monitoring of hydrochemical and isotopic compositions of stream water along a karst spring-fed creek at Changliushui, SW China that has a steep gradient and in which tufa deposition occurs, in order to explore the process of CO2 outgassing and elucidate the outgassing flux across space and time and its influencing factors. The analyses of downstream geochemical evolution have revealed that two distinguishable types of CO2 outgassing exist along the flow path: (i) outgassing of physically dissolved soil CO2 during the process of carbonate dissolution, as the primary CO2 outgassing, and (ii) an additional outgassing of the CO2 arising from the precipitation of calcite. At a short distance from the spring, the aqueous CO2 escapes from water to a large degree through molecular diffusion driven by high gradient of partial pressure of CO2 (PCO2) between the water and the atmosphere. Such CO2 outgassing concomitantly causes the saturation index with respect to calcite (SIc) to rise, resulting in subsequent calcite precipitation and thus more CO2 outgassing. Spatiotemporal variations in the mass transfer of CO2 and CO2 outgassing flux show that the rates of both types of CO2 outgassing are significantly influenced by hydrodynamic conditions, such as flow discharge and streambed morphology. In particular, lower rates of CO2 outgassing are observed at higher flow discharge, and vice versa. In the studied reach of stream, the primary and additional CO2 outgassing have caused about 21%–35% and 4%–20% of the total soil CO2 sequestered in DIC of the feeding spring water to be released back to the atmosphere, respectively and the higher flow discharge, the less CO2 return. Based on these findings, we postulate that the CO2 outgassing, especially that induced by calcite precipitation should be relatively smaller in streams which have a lower gradient and elevated discharge rate and where the mixing or dilution of tributaries and increased in-stream metabolism occur. This provides more evidence for the previous conclusion that the H2O-carbonate-CO2-aquatic phototroph interaction could represent a net carbon sink at least over short timescales.

ABSTRACT On the basis of proposing the existence of a karst carbon cycle and carbon sink at a watershed scale, this paper provides four pieces of evidence for the integration of geology and ecology during the carbon cycle processes in the karst dynamic system, and estimated the karst carbon sink effect using the methods of comparative monitoring of paired watersheds and the carbon stable isotope tracer technique. The results of the soil carbon cycle in Maocun, Guilin, showed that the soil carbon cycle in the karst area, the weathering and dissolution of carbonate rocks under the soil, resulted in a lower soil respiration of 25% in the karst area than in a non-karst area (sandstone and shale), and the carbon isotope results indicated that 13.46% of the heavy carbon of the limestone is involved in the soil carbon cycle. The comparative monitoring results in paired watersheds, suggesting that the HCO3- concentration in a karst spring is 10 times that of a rivulet in a non-karst area, while the concentration of inorganic carbon flux is 23.8 times. With both chemical stoichiometry and carbon stable isotopes, the proportion of carbon in karst springs derived from carbonate rocks was found to be 58.52% and 37.65% respectively. The comparison on carbon exchange and isotopes at the water-gas interface between the granite and carbonate rock basins in the Li River showed that the CO2 emission of the karst water is 10.92 times that of the allogenic water from the non-karst area, while the carbon isotope of HCO3- in karst water is lighter by 8.62‰. However, this does not mean that the karst water body has a larger carbon source effect. On the contrary, it means the karst water body has a greater karst carbon sink effect. When the karst subterranean stream in Zhaidi, Guilin, is exposed at the surface, carbon-rich karst water stimulated the growth of aquatic plants. The values of carbon stable isotopes in the same species of submerged plants gradually becomes heavier and heavier, and the 512 m flow process has a maximum range of 15.46‰. The calculation results showed that 12.52% of inorganic carbon is converted into organic carbon. According to the data that has been published, the global karst carbon sink flux was estimated to be 0.53-0.58 PgC/a, equivalent to 31.18%-34.41% of the global forest carbon sink flux. In the meanwhile, the karst carbon sink flux in China was calculated to be 0.051 PgC/a, accounting for 68% of its forest carbon sink flux.

… Paired eddy flux measurement design with grassland site and tree/… Karst (submediterranean climate region) to investigate the effects of secondary succession on ecosystem carbon …

… of the karst carbon budget, offering insights into the carbon response mechanisms of … karst carbon budget, which uncovers a key process mechanism that may influence karst carbon …

… Here, carbon and water exchanges of a spatially … to be a carbon sink but the annual carbon fixation had a … m −3 ) at which evapotranspiration and carbon fluxes started to be limited by …

… The aim of this article is to determine the contribution of the karstic … carbon fluxes exchanged between the main reservoirs: gross fluxes are about 100 GtC/year when net resulting fluxes …

ABSTRACT In order to understand the hydrological changes of groundwater in karst areas, the Xiangxi River Basin in the western Hubei karst area was selected for water sample collection and monitoring. A carbon flux estimation model was established by combining support vector machine regression and sparrow search algorithm to achieve groundwater carbon flux estimation. The results show that the average range of dissolved oxygen in karst groundwater is 9.65~10.79mg · L−1, with an overall high content. The anions in groundwater are mainly HCO3−, and the cations are mainly Ca2+. The pH value of the water sample is mainly between 7.28 and 8.16, showing weak alkalinity. The mineralization value of the water sample is distributed between 81.36~323.41mg/L, and the groundwater hydrochemical types are mainly HCO3 Ca type and HCO3 Ca · Mg type. The carbon flux estimation model for karst groundwater has reduced the regression error value by 43.6% compared to the unimproved support vector machine. This indicates that improving the model can improve the accuracy of carbon flux estimation. By analyzing the hydrochemical characteristics, the resource characteristics, environmental effects, and ecological significance of karst groundwater can be understood, providing scientific basis for management and decision-making in related fields..

Abstract Extensive areas of agricultural land have been abandoned to ecological restoration in recent years in the karst region of Southwest China, which contributes to the greening of the area. However, there has yet no direct observation of carbon, water, and energy fluxes on abandoned land in the region. In addition, because of the coupling between above and below-ground processes, monitoring of the karst ecosystem needs to be conducted from a critical zone perspective. In this study, an integrated vertical observation system through air-vegetation-soil-cave continuums was constructed on abandoned farmland under natural restoration in Puding Karst Ecosystem Research Station. Preliminary results show that: First, vegetation cover restored rapidly after abandonment, and the measured net ecosystem exchange (NEE), soil CO2 efflux, actual evapotranspiration (ETa) and latent heat (LE) in the rainy season are about twice of that in the dry season, this strong seasonal variation relates to the typical subtropical monsoon climate with synchronous water and heat availability during rainy season. Second, high CO2 concentrations and significant CO2 variation in the monitored cave indicate that the exchange of underground carbon pools with the atmosphere cannot be neglected in the carbon budget of the study site.

… atmospheric CO2 sink relating to carbonate weathering might be … is that rock-weathering-related carbon sinks have increased … of rock weathering processes and mechanisms in carbon …

The Carbonate rock weathering Carbon Sink (CCS) and Silicate rock weathering Carbon Sink (SCS) play a significant role in the carbon cycle and global climate change. However, the spatial‐temporal patterns and trends of the CCS and SCS from 1950 to 2099 have not been systematically quantified. Thus, Supported by long‐term hydrometeorological data under the RCP8.5, we use the accepted Suchet and Hartmann models to determine the following. First, we found except for the difference in their weathering rates, the SCS covers 37.2 million km2 more area than the CCS. The CCS Flux (CCSF) and SCS Flux (SCSF) are 5.36 and 1.22 t/km2/yr, respectively. Similarly, the Full CCS (FCCS, 0.3 Pg/yr) is more than the Full SCS (FSCS, 0.08 Pg/yr). Furthermore, the CCS (7.01 kg/km2) and SCS (3.95 kg/km2) are in a state of overall increase. In addition, the mid‐to‐high latitudes of the northern hemisphere are aggravated by warming (0.03°C) and humidity (0.65 mm), while the decrease in runoff in the mid‐latitudes of the southern hemisphere reduces karstification. Specifically, by 2099, the CCSF in the mid‐latitudes of the southern hemisphere will decrease by 5.72%. Instead, the CCSF in the northern hemisphere and lower latitudes of the southern hemisphere will exhibit a gentle upward slope. Particularly, the peak regions of the global FCCS (65.63 Tg/yr) and FSCS (33.01 Tg/yr) are the tropical zone. In conclusion, this study contributes a high‐resolution and long‐time series CS datasets for the CCS and SCS. We provide data and a theory for solving terrestrial carbon sink loss.

… weathering carbon sink (CS) of rocks. However, due to data quality limitations, the magnitude of the CS of rocks … dataset of CS for 11 types of rocks from 2001 to 2018. The results show …

… Some opinions on rock鄄weathering鄄related carbon sinks from the IPCC fifth assessment report[J]. Advances in Earth Science,2015,30(10):1 081鄄1 090,doi:10. 11867 / j. …

The weathering carbon sink (CS) of rocks has a sensitive response to different influencing factors, and it is important to accurately distinguish this response in the global carbon cycle. However, no quantitative analysis of the response mechanism has been performed. In this study, the CS of the 12 types of terrestrial rocks in China from 2000 to 2014 is estimated using the GEM-CO2 model. The relative contribution rates of climate change and ecological restoration to the CS are quantitatively evaluated using the Lindeman-Merenda-Gold model. Results showed that: (1) The CS of terrestrial rocks in China was 17.69 Tg C yr-1, and the CS flux (CSF) was 2.53 t C km-2 yr-1; mixed sedimentary rocks had the highest CS (6.89 Tg C yr-1), and carbonate rocks had the highest CSF (5.8 t C km-2 yr-1). (2) The average annual CSF slightly decreased at a rate of 5.4 kg C km-2 yr-1; the areas of the CSF that decreased in the south were the areas where water budget decreased significantly, and it was the areas with a reduced water budget and ecological deterioration in the north. (3) The relative contribution rates of water budget and precipitation reached 57% and 35%, respectively; the response of the CSF to temperature was evident in areas with low or decreasing temperatures, and the influence of fractional vegetation cover (FVC) on the CSF in low value area was evident. (4) Mixed sedimentary rocks and carbonate rocks displayed a more evident reduction trend in the CSF than other rocks. This research verified the applicability of the GEM-CO2 model in China and presented a scientific basis for quantitative assessment of the impact of climate change and ecological restoration on the CSF.

… a carbon sink was primarily evaluated in terms of the biomass carbon pool and soil organic carbon pool… Plants play a significant role in enhancing the chemical weathering of rocks and …

Rock weathering actively participates in the global carbon cycle on both short and long-time scales. However, considerable debate on the global carbon sink flux, spatial patterns, and controlling factors of rock weathering still exists. In this study, we estimated the carbon sink flux of carbonate rocks (Fcarb) and silicate rocks (Fsil) weathering in global major rivers using hydrochemistry-discharge method and GEM-CO2 model based on the GEMS-GLORI Database, and analyzed the controlling factors affecting the rock weathering. The results show that the Fcarb and Fsil are 3.09 and 1.73 t km-2 yr-1, respectively, and the total amount of weathering carbon sink of carbonate rocks (Tcarb) and silicate rocks (Tsil) are 0.17 and 0.093 Pg yr-1, respectively. The rock weathering carbon sink (RWCS) shows significant differences among different continents, latitudes, and climate zones. The highest values of Fcarb and Tcarb are in Asia and Oceania, and the highest Fsil and Tsil are in Oceania and South America. The RWCS flux has high-value areas near the equator. Both the flux and the total amount of RWCS are high in the tropics and warm temperate zones, while the cold zones also have high total amount of RWCS due to the presence of many large basins. The correlation analysis results indicate that the intensity of RWCS will depend mainly on precipitation, soil pCO2 and LAI. RWCS contributes to constraining the fate of the residual land sink.

The response of carbonate weathering carbon-sink flux (CCSF) to its environmental drivers is still not well understood on the global scale. This hinders understanding of the terrestrial carbon cycle. Here, we show that there is likely to be a widespread and consistent increase in the global CCSF (ranging from + 9.8% (RCP4.5) to + 17.1% (RCP8.5)) over the period 1950–2100. In the coming years the increasing temperature might be expected to have a negative impact on carbonate weathering. However, the increasing rainfall and anticipated land-use changes will counteract this, leading to a greater CCSF. This finding has been obtained by using long-term historical (1950–2005) and modeled future (2006–2100) data for two scenarios (RCP4.5 and RCP8.5) for climate and land-use change in our CCSF equilibrium model. This study stresses the potential role that carbonate weathering may play in the evolution of the global carbon cycle over this century. Carbonate weathering captures CO2 and represents a large sink of terrestrial carbon that is threatened by climate and land-use change. Here the authors build a model that predicts drivers of carbonate weathering into the future, determining that runoff is an overlooked controlling factor.

The accurate determination of the carbon-neutrality capacity (CNC) of a region is crucial for developing policies related to emissions and climate change. However, a systematic diagnostic method for determining the CNC that considers the rock chemical weathering carbon sink (RCS) is lacking. Moreover, it is challenging but indispensable to establish a fast and practical index model to determine the CNC. Here, we selected Guizhou as the study area, used the methods for different types of carbon sinks, and constructed a CNC index (CNCI) model. We found that: (1) the carbonate rock chemical weathering carbon sink flux was 30.3 t CO2 km−2 yr−1. Guizhou accounted for 1.8% of the land area and contributed 5.4% of the carbonate chemical weathering carbon sink; (2) the silicate rock chemical weathering carbon sink and its flux were 1.44 × 103 t CO2 and 2.43 t CO2 km−2 yr−1, respectively; (3) the vegetation-soil ecosystem carbon sink and its flux were 1.37 × 108 t CO2 and 831.70 t CO2 km−2 yr−1, respectively; (4) the carbon emissions (CEs) were 280 Tg CO2, about 2.8% of the total for China; and (5) the total carbon sinks in Guizhou were 160 Tg CO2, with a CNCI of 57%, which is 4.8 times of China and 2.1 times of the world. In summary, we conducted a systematic diagnosis of the CNC considering the RCS and established a CNCI model. The results of this study have a strong implication and significance for national and global CNC determination and gap analysis.

… Global application of our model indicates that CWC generates a carbon sink of 0.27 Pg C … weathering models and reducing uncertainties in future projections of the terrestrial carbon sink…

… the rate of chemical weathering of carbonate rocks and the … process of Carbonate rock weathering Carbon Sink (CCS) to … the rate of chemical weathering of carbonate rocks, and hence …

… This means that the contribution of carbonate rock weathering to the atmospheric CO2 sink increases with the lifting of the atmospheric CO2 content. Therefore, the carbonate rock …

… rock weathering and carbon sink. In this regard, we collected two sample series during both high-water and low-water periods and assessed the chemical weathering … rock weathering …

… However, the soluble carbon loss mechanism through various runoff components occurring … that the karst critical zone structure determines the runoff and soluble carbon loss, and that …

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.

ABSTRACT

Abstract Carbonate terrains (CT) underlie one-fifth of terrestrial, ice-free land and are an important supply of potable water to the world's population, and yet processes endemic to CT critical zones (CZ) and responses of these processes to climatic and anthropogenic pressures are not well understood. Given the rapid dissolution rates and ability to generate well-developed networks of secondary porosity these landscapes can be highly sensitive to impacts from climate change (e.g., modifications of temperature, precipitation, sea level) and human disturbance (e.g., water withdrawal/diversions, changes in land use/land cover). This special issue includes 16 papers focused on CT-CZ processes and potential responses to climatic and human perturbations. Five major themes emerge from these papers, namely: (1) anthropogenic climate and land use changes alter CT-CZ weathering rate and diagenesis, (2) metal and carbon fluxes in CT-CZ will respond to increasing hydrologic variance caused by climate change, (3) endogenous and exogenous processes operating over short time periods (

Abstract The earth is gradually turning green due to afforestation, especially in China. Because the carbon cycle is driven by the groundwater cycle in karstification, the process of water & carbon coupling cycle (PWCC) in karst forest area can not only promote vegetation growth but also enhance chemical weathering processes of carbonate rocks to absorb more CO2. Therefore, carbon sequestration can occur during the process of ecological restoration in karst areas. However, forest respiration also increases with the vegetation growth which can produce extra CO2 back to atmosphere. To study the promotion function of forest vegetation during different succession stages on the PWCC in karst critical zone, three karst groundwater systems with different vegetation coverages (a native forest, a secondary forest during reforestation and a crop area in rural land) are chosen in southwest China. Their long-term monitoring of indicators, including precipitation (P), partial pressure of air CO2 ( P CO 2 ), groundwater discharge (Q), hydrochemical and isotope components, was conducted. The results indicated that part of CO2 produced by forest respiration diffuses into the atmosphere as a carbon source, and the remaining dissolves into the groundwater, thereby increasing corrodibility. The carbon sequestration mechanism differs at different vegetation succession stages. The secondary forest development stage displays an obvious carbon sequestration effect during the process of rocky desertification control. When the succession stage approaches the top-level ecosystem, the carbon sequestration effect descend sharply until the net carbon sequestration can be ignored.

… mechanisms of dissolved carbon transformation and its interaction with the structure of karst critical zone. … The diagram showing the transport of dissolved carbon in karst critical zone. …

… carbon flux estimation, especially regarding carbon exchange between soil and underground cracks or pipes in karst critical zone… of soil CO 2 in karst critical zone. The intensity of water–…

… and time scales of carbon turnover are not the … of carbon input,storage and output in karst critical zone should be carried out. The importance of karst carbon sinks in the global carbon …

Hydrochemical behavior and dissolved carbon dynamics are highly-sensitive to hydrological variations in the monsoon-influenced karstic critical zone which has high chemical weathering rates and experiences strong anthropogenic impact. Continuous high-frequency monitoring in the spring outlet of a karstic catchment in Southwestern China revealed that most hydrochemical variables changed distinctively in response to hydrologic variations, influenced by mixing of different sources and miscellaneous biogeochemical processes. Na+, K+ and SO42- varied significantly with hydrology, showing weak chemostatic behavior controlled by dilution. The flushing effect and random behavior of NO3- and Cl- likely reflect agricultural inputs from high throughflow. Soil CO2 in infiltrated water supports carbonate weathering, enabling DIC (dissolved inorganic carbon) and weathering products (e.g., Ca2+ and Mg2+) to maintain chemostatic behavior. Biogenic DIC exhibited a stronger chemostatic response than carbonate sources and was the foremost control in DIC behavior. Carbon exchange between DIC and DOC (dissolved organic carbon) did not significantly influence DIC concentration and δ13C due to very low DOC concentration. More DOC was exported by flushing from increasing discharge. Hysteretic analysis indicated that the transport processes were controlled by proximal sources mixing and diverse mobilization in various periods responding to rainstorms. NO3- and Cl- presented different hysteresis behavior as sourced from agricultural activities. DOC increased on the hydrograph rising limb and was controlled by a transport-limited regime. However, the hysteresis behavior of most weathering products and DIC were regulated by a process-limited regime in the karstic critical zone. Overall, biogeochemical processes, hydrogeological properties, storm intensity/magnitude and the timing of storms (antecedent conditions) are main factors influencing the response of hydrochemical variables and dissolved carbon to storm events.

Spatial heterogeneity in the subsurface of karst environments is high, as evidenced by the multiphase porosity of carbonate rocks and complex landform features that result in marked variability of hydrological processes in space and time. This includes complex exchange of various flows (e.g., fast conduit flows and slow fracture flows) in different locations. Here, we integrate various “state‐of‐the‐art” methods to understand the structure and function of this poorly constrained critical zone environment. Geophysical, hydrometric, and tracer tools are used to characterize the hydrological functions of the cockpit karst critical zone in the small catchment of Chenqi, Guizhou Province, China. Geophysical surveys, using electrical resistivity tomography (ERT), inferred the spatial heterogeneity of permeability in the epikarst and underlying aquifer. Water tables in depression wells in valley bottom areas, as well as discharge from springs on steeper hillslopes and at the catchment outlet, showed different hydrodynamic responses to storm event rainwater recharge and hillslope flows. Tracer studies using water temperatures and stable water isotopes (δD and δ18O) could be used alongside insights into aquifer permeability from ERT surveys to explain site‐ and depth‐dependent variability in the groundwater response in terms of the degree to which “new” water from storm rainfall recharges and mixes with “old” pre‐event water in karst aquifers. This integrated approach reveals spatial structure in the karst critical zone and provides a conceptual framework of hydrological functions across spatial and temporal scales.

Soil organic carbon (SOC) sequestration in aggregates under land use change have been widely concerned due to intimate impacts on the sink (or source) of atmospheric carbon dioxide (CO2). However, the quantitative relationship between soil aggregation and SOC sequestration under land uses change has been poorly studied. Distribution of aggregates, SOC contents in bulk soils and different size aggregates and their contributions to SOC sequestration were determined under different land uses in the Puding Karst Ecosystem Observation and Research Station, karst Critical Zone Observatory (CZO), Southwest China. Soil aggregation and SOC sequestration increased in the processes of farmland abandonment and recovery. SOC contents in micro-aggregates were larger than those in macro-aggregates in restored land soils, while the opposite results in farmland soils were obtained, probably due to the hindrance of the C-enriched SOC transport from macro-aggregate into micro-aggregate by the disturbance of agricultural activities. SOC contents in macro-aggregates exponentially increased with their proportions along successional land uses. Macro-aggregates accounted for over 80% on the SOC sequestration in restored land soils, while they accounted for 31–60% in farmland soils. These results indicated that macro-aggregates have a great potential for SOC sequestration in karst soils.

The role of bedrock geochemistry in vegetation growth within karst areas has been examined in recent works, implying that the approach of the critical zone (CZ) extending from the canopy to the groundwater bottom enhances the understanding of vegetation ecology. In this paper, the research progress of vegetation ecology associated with bedrock features in the karst CZ in subtropical Southwest China is systematically reviewed. There are great differences in soil formation and soil features (water-holding capacity, particle size, and soil chemistry) between karst and non-karst regions, even between dolomite and limestone within a karst region. Water and soil are easily leached due to the connected underground crevices in karst, particularly in limestone-dominated regions, leading to water deficits in karst CZ plants in subtropical Southwest China. The development of plant roots in crevices affects the water and nutrient absorption by plants and microbial activities in the soil, which form the basis for vegetation distribution and growth in the karst CZ. The organic acids from plants also increase weathering rates. As extensive human activities have accelerated vegetation degradation and soil erosion and further led to rocky desertification characterized by increasing areas of rock exposure, state-of-the-art knowledge about the effects of bedrock-associated belowground and aboveground interactions can guide the implementation of vegetation restoration and the control of further rocky desertification in the subtropical karst CZ.

In the Karst Critical Zone (KCZ), mining and urbanization activities produce multiple pollutants, posing a threat to the vital groundwater and surface water resources essential for drinking and irrigation. Despite their importance, the interactions between these pollutants in the intricate hydrology and land use of the KCZ remain poorly understood. In this study, we unraveled the transformation mechanisms and sources of nitrogen, sulfate, and carbon using multiple isotopes and the MixSIAR model, following hydrology and surface analyses conducted in spatial modelling with ArcGIS. Our results revealed frequent exchange between groundwater and surface water, as evidenced by the analysis of δD-H2O and δ18O-H2O. Nitrification predominantly occurred in surface water, although denitrification also made a minor contribution. Inorganic nitrogen in both groundwater and surface water primarily originated from soil nitrogen (48 % and 49 %, respectively). Sewage and manure were secondary sources of inorganic nitrogen in surface water, accounting for 41 % in urban and 38 % in mining areas. Notably, inorganic sulfur oxidation displayed significant spatial disparities between urban and mining areas, rendering groundwater more susceptible to sulfur pollution compared to surface water. The frequent interchange between groundwater and surface water posed a higher pollution risk to groundwater. Furthermore, the primary sources of CO2 and HCO3- in both groundwater and surface water were water‑carbonate reactions and soil respiration. Sulfide oxidation was found to enhance carbonate dissolution, leading to increased CO2 release from carbonate dissolution in the KCZ. These findings enhance our understanding of the transformation mechanisms and interactions of nitrogen, sulfur, and carbon in groundwater and surface water. This knowledge is invaluable for accurately controlling and treating water pollution in the KCZ.

Abstract Carbonate mineral weathering coupled with aquatic photosynthesis on the continents, herein termed coupled carbonate weathering (CCW), represents a current atmospheric CO2 sink of about 0.5 Pg C/a. Because silicate mineral weathering has been considered the primary geological CO2 sink, CCW's role in the present carbon cycle has been neglected. However, CCW may be helping to offset anthropogenic atmospheric CO2 increases as carbonate minerals weather more rapidly than silicates. Here we provide an overview of atmospheric CO2 uptake by CCW and its impact on global carbon cycling. This overview shows that CCW is linked to climate and land-use change through changes in the water cycle and water-born carbon fluxes. Projections of future changes in carbon cycling should therefore include CCW as linked to the global water cycle and land-use change.

Abstract Carbonate rocks are a peculiarity of the Earth relative to other planets in the solar system. Large terrestrial areas are covered by carbonate lithology, which actively reacts with atmospheric/biospheric CO2. Although carbonate rocks represent a major component of the global carbon cycle, their intensity and rates of chemical weathering have been overlooked. In this study, we examine three global databases of rivers and springs draining carbonate regions under various climate conditions (from −15 °C to +30 °C). Using Ca2+ + Mg2+ concentrations as a proxy, we show that carbonate weathering intensity depends upon land temperature according to a boomerang-type relationship, with maximum dissolution between 10 and 15 °C. We show that this pattern is primarily controlled by thermodynamics if we assume that the partial pressure of CO2 in soil (pCO2) increases from atmospheric-like levels under cold climate up to 100 times the present day atmospheric concentration under hot climate. The link between soil pCO2 and land temperature is still not very well known, but by using three different published predictive soil pCO2 vs. T curves, we show that the boomerang shape can be, at least qualitatively, reproduced. This study shows that more data on carbonate weathering in various environments are needed to predict with more accuracy the role that carbonate lithologies and overlying ecosystems could play in the Anthropocene.

… microflora in carbonate precipitation during silicate weathering, particularly in anoxic subsurface environments, might help explain the problematic missing atmospheric carbon dioxide …

The continental weathering process is driven by environmental factors such as changes in temperature, moisture, and CO2 concentration, which can have natural (climate) or anthropogenic (land‐use) origins. In this paper, we attempt to evaluate the global applicability of different environmental drivers, which can be used to estimate the global carbonate dissolution intensity (bicarbonate concentration, (HCO3−), as a proxy) and the related carbon sink flux (CCSF). We employ three ecological models and a series of satellite‐based databases, which provide estimates on soil CO2‐concentrations (pCO2). By using the three parameterized pCO2, global temperature (T) and runoff (N), we obtain similar global averages for (HCO3−) and CCSF, ranging from 2.73 to 2.81 mmol L−1 and 4.52–5.36 t C km−2 yr−1. We compare our calculated (HCO3−) to observed carbonate spring records. The results indicate that the net primary production based pCO2 (NPP‐pCO2) model is more accurate for simulating (HCO3−) in most boreal and temperate ecosystems, while the soil‐water content based pCO2 (SWC‐pCO2) model may perform better in forests. According to the findings in this study, we stress that natural and anthropogenic factors are strongly intertwined in shaping global (HCO3−) and CCSF patterns. Due to the crucial role of human land‐uses in pCO2 and water yield, future human land‐use changes may be as significant as natural climatic changes for carbonate weathering and thus the relevant carbon sink.

Enhanced weathering is a geoengineering strategy aiming to increase continental weathering rates, thereby increasing the delivery of atmospheric carbon (as HCO3-) to the oceans. Most enhanced weathering studies focus on the capacity of silicate rocks (e.g., basalt) and minerals (e.g., olivine, Mg2SiO4, or wollastonite CaSiO3) to remove atmospheric CO2. However, carbonate minerals (e.g., calcite, CaCO3) could provide an additional, rapid way to increase HCO3- export to the oceans. Recent studies suggest that 0.84 Gt C yr−1 could be removed from the atmosphere through the enhanced dissolution of calcite in soils, provided carbonic acid is the main dissolution agent. What is not clear is whether atmospheric CO2 dissolved in soils can be transported by rivers, which typically have lower [pCO2], to the oceans. This difference in calcite solubility between soils (where weathering occurs) and rivers (where HCO3- is transported) may lead to large amounts of secondary carbonate formation during transport, releasing the CO2 consumed through dissolution. Here, we present a modeling study comparing the estimated soil dissolution capacity (SDC) in 149 of Earth's largest river basins, to the potential transport capacity of carbon (PTCC) in corresponding rivers. We find the SDC can only be exported to the oceans, without secondary carbonate precipitation, if rivers are in disequilibrium with respect to calcite (i.e., SIc = 1). In this instance, 0.92 Gt C yr−1 may be sequestered above background weathering rates, which is ~20% of annual increases in atmospheric carbon. If rivers are at equilibrium with calcite (i.e., SIc = 0), approximately two-thirds of the carbon dissolved in soil waters are lost due to calcite precipitation in rivers, and just 0.26 Gt of additional atmospheric C yr−1 can be transported to the oceans. Overall, the efficacy of enhanced carbonate weathering is a function of the capacity rivers have for transporting the products from carbonate weathering to the oceans, rather than the dissolution capacity of soils. These findings have implications for the efficiency of enhancing silicate weathering for ocean alkalinity enhancement, as secondary carbonate precipitation during transport is not always considered.

Abstract Accurate estimate of carbon sink flux resulted from carbonate weathering in the karst area is of great significance for advancing the current understanding of the global carbon cycle and climate change. However, the carbon sink flux may be overestimated when the natural reaction with carbonic acid is influenced by protons of anthropogenic sulfuric and nitric acids, which can reduce the carbon sink flux during carbonate weathering. Here, we quantitatively evaluated the impact of anthropogenic sulfuric and nitric acids on carbonate weathering and carbon sink flux under base flow condition based on the stoichiometry of chemical compositions of groundwater from a typical karst catchment (Guohua), Guangxi, southwestern China. Seventy groundwater samples were analyzed for the characteristics of hydrochemistry and carbon isotopes of dissolved inorganic carbon (δ13CDIC) during the dry season in 2015. The results show that: (1) Ca2+ and Mg2+ dominate 92.4%-99.7% of the total cations, while HCO3- accounts for 83.0%-97.4% of total anions, indicating that the compositions of groundwater are primarily controlled by carbonate weathering; (2) The [Ca2++Mg2+]/[HCO3−] equivalent ratios (1.00 to 1.41) and the corresponding δ13CDIC values (-16.8‰ to -8.1‰) of groundwater are all distributed between carbonate weathering by carbonic acid, and carbonate weathering by sulfuric and nitric acids. Meanwhile, the [Ca2++Mg2+]/[HCO3-+SO42-+NO3-] ratios of groundwater are about 1, and the [Ca2++Mg2+] equivalent concentrations have a good positive correlation with [HCO3-+SO42-+NO3-] and [SO42-+NO3-], suggesting that sulfuric and nitric acids, in addition to carbonic acid, have been involved in carbonate weathering; (3) The contribution of sulfuric and nitric acids involved in carbonate weathering to (Ca2++Mg2+) and HCO3- in groundwater varies from 0.6% to 58.0% (mean value of 20.9%) and from 0.3% to 40.9% (mean value of 12.2%), respectively. The carbonate weathering rate has increased by 20.9% while the karst carbon sink flux has decreased by 12.2%. Therefore, the carbon sink flux produced by carbonate weathering should be carefully evaluated when anthropogenic sulfuric acid and/or nitric acid are involved and the role of sulfuric and nitric acids in carbonate weathering could not be ignored in the global carbon cycle.

… fluxes (FCO 2 ), and Carbon budgets ( Carbon budget = ( T O C o … systems controlled by carbonate weathering and different … stability of the carbonate weathering-driven carbon sink (DIC…

… human impact upon the carbon budget. Here, we show, by synthesizing recent findings in rock … ecosystems, that the carbon sink produced by carbonate weathering based on the H 2 O–…

… hydrochemical data from three karst catchments in the mountainous … , karst regions in cold climates with vegetation cover will have increasing CO 2 consumption potential, whereas karst …

Abstract. CO2 concentrations of 21 soil profiles were measured in Zhaotong City, Yunnan Province. The varying characteristics of soil profile CO2 concentrations are distinguishable between carbonate and noncarbonate areas. In noncarbonate areas, soil profile CO2 concentrations increase and show significant positive correlations with soil depth. In carbonate areas, however, deep-soil CO2 concentrations decrease and have no significant correlations with soil depth. Soil organic carbon is negatively correlated with soil CO2 concentrations in noncarbonate areas. In carbonate areas, such relationships are not clear. This means that the special geological process in carbonate areas – carbonate corrosion – absorbs part of the deep-soil-profile CO2. Isotope and soil pH data also support such a process. A mathematical model simulating soil profile CO2 concentration was proposed. In noncarbonate areas, the measured and the simulated values are almost equal, while the measured CO2 concentrations of deep soils are less than the simulated in carbonate areas. Such results also indicate the occurrence of carbonate corrosion and the consuming of deep-soil CO2 in carbonate areas. The decreased CO2 concentration was roughly evaluated based on stratigraphic unit and farming activities. Soil pH and the purity of CaCO3 in carbonate bedrock deeply affect the corrosion. The corrosion in carbonate areas decreases deep-soil CO2 greatly (accounting for 5.2 %–66.3 % with average of 36 %) and naturally affects the soil CO2 released into the atmosphere. Knowledge of this process is important for karst carbon cycles and global climate changes and it may be a part of the “missing carbon sink”.

Carbonate minerals comprise the largest reservoir of carbon in the earth’s lithosphere, but they are generally assumed to have no net impact on the global carbon cycle if rapid dissolution and precipitation reactions represent equal sources and sinks of atmospheric carbon. Observations of both terrestrial and marine carbonate systems indicate that carbonate minerals may simultaneously dissolve and precipitate within different portions of individual hydrologic systems. In all cases reported here, the dissolution and precipitation reactions are related to primary production, which fixes atmospheric CO2 as organic carbon, and the subsequent remineralization in watersheds of the organic carbon to dissolved CO2. Deposition of carbonate minerals in the ocean represents a flux of CO2 to the atmosphere. The dissolution of oceanic carbonate minerals can act either as a sink for atmospheric CO2 if dissolved by carbonic acid, or as a source of CO2 if dissolved through sulfide oxidation at the freshwater-saltwater boundary. Since dissolution and precipitation of carbonate minerals depend on ecological processes, changes in these processes due to shifts in rainfall patterns, earth surface temperatures, and sea level should also alter the potential magnitudes of sources and sinks for atmospheric CO2 from carbonate terrains, providing feedbacks to the global carbon cycle that differ from modern feedbacks. Keywords: Global carbon cycle, carbonate terrains, organic carbon fixation, remineralization, carbonate mineral dissolution, carbonate mineral precipitation. DOI: 10.3986/ac.v42i2-3.660

Abstract The karst region in southwestern China is a typical region with fragile ecological environments, and the coordination of regional agricultural development and environmental protection faces enormous challenges. Based on the soil and hydrological characteristics of karst in southwestern China, this study summarized water-related environmental issues caused by agricultural activities in this karst region. Agriculture in the karst hills is more likely to cause soil and nutrient losses due to the fast hydrological flow through special karst structures with high permeability. Thus, this review emphasized the impacts of agricultural development on the riverine biogeochemical cycles of elements based on previous studies. Meanwhile, the carbon cycle is also strongly impacted by agricultural activities in this karst region due to enhanced carbonate weathering by nitric acid from the nitrification of ammonium. This weathering mechanism represents a net source of atmospheric CO2 and might impact regional and global carbon cycling in the Anthropocene. Based on the results summarized in this study, we advocate that in the future, better management of agricultural land, improvement of fertilizer use efficiency, and boosting of nutrient recycling rate should be taken into account for reducing nutrient losses and water quality deterioration. Targeted management of local agricultural practices along with guidance from scientific research results is needed to be devoted to sustainable development of agriculture and economies while protecting water environment.

… the karst groundwater 14C age of dissolved inorganic carbon (… , grassland, shrubland) at a karst simulated test site in SW … , particulate organic carbon (POC), dissolved organic carbon (…

Currently, there is a lack of systematic knowledge concerning carbon (C) biogeochemical cycles in impounded rivers. In this study, we investigated different C species and related …

… global carbon neutrality. The findings also underscore the importance of considering … landscape characteristics and hydrological dynamics in the management of riverine carbon cycles…