Karst Depressions Research Articles

An inception framework hypothesis for karst development in the Burren, Ireland

The Inception Horizon Hypothesis (IHH) postulates that certain stratigraphic horizons in a limestone sequence, combined with structural surfaces such as joints, provide a framework for cave development. Although subsurface and surface karst landforms are fundamentally linked, the IHH has not yet been extended to surface karstification. We tested this extension of the IHH in the world-renowned Burren karst due to its stratigraphic and structural simplicity. We used very high-resolution remote sensing datasets and detailed fieldwork to develop an updated map of the Burren's surface karst features, combined with a 3D geological model containing over 60 km of mapped cave passages.Our analysis shows that karstic connectivity between the surface and subsurface is primarily provided by a suite of vertically-persistent calcite and silica-rich veins, which form a non-stratabound fracture system across the Burren. The flow pathways provided by these veins then intersect the following inception horizons: (i) boundaries between distinct lithological units in the limestone sequence; (ii) crinoidal cycle tops, and more sporadically chert lenses, within one of those units (the Slievenaglasha Formation); (iii) thin horizons of non‑carbonates (‘clay wayboards’) within another unit (the Aillwee member). At the surface, the same horizons have been preferentially exploited by glacial processes, creating surfaces from which meteoric waters now recharge the subsurface and form new surface karst depressions and other karst landforms. Our new inception framework for karstification thus provides a new basis for understanding surface and subsurface connectivity in the karst critical zone in the Burren landscape, and it provides new geological insight into the functioning of carbonate critical zones more generally.

Burning effects on the soils of the Mexican Maya Lowlands: Current evidence for understanding past events

The slash-and-burn cultivation system is a millenarian practice still used in many countries today, with significant environmental impacts. However, identifying evidence of this agricultural method in soil records is challenging due to natural and human factors that can obscure or alter fire signals. This challenge is particularly evident in the Yucatán Peninsula, where the ancient Maya practiced slash-and-burn agriculture in a dynamic tropical karst environment, making it difficult to pinpoint the origins and consequences of this practice. In this study, we use a recent agricultural burning in a karstic landscape in Chiapas as a model to understand alterations in soil properties. We then apply these insights to identify similar features at a Maya site on the Yucatán Peninsula, specifically at Coyote Quarry. For both cases, we conducted micromorphological analysis, soil physical-chemical characterization, thermogravimetry and differential scanning calorimetry analysis, and radiocarbon dating of mollusk shells, soil organic carbon, and charcoal fragments (the latter exclusively at Coyote Quarry). Our findings reveal significant effects on the soils from the Chiapas site post-burning, including changes in grain size distribution, pH, and total organic and inorganic carbon. These results were compared to those obtained from the Coyote Quarry soils and pedosediments. Key findings include micromorphological features, the presence of charcoal and other burned materials, and pyrogenic carbon identified through thermal analyses. The preservation of these burned features was facilitated by the typical karstic vertical soil erosion and redeposition as pedosediments in karstic depressions. The intrinsic association of the fire signals found in these karstic sinkholes and their radiocarbon dates enables us to link this evidence to the initiation of slash-and-burn agriculture by the Maya in the Yucatán Peninsula during the transition between the Archaic and Early Pre-Classic periods.

Comprehensive Characterization of Karst Depressions in the Northwestern Yucatan Peninsula Using LiDAR and ASTER GDEM Data

Comprehensive Characterization of Karst Depressions in the Northwestern Yucatan Peninsula Using LiDAR and ASTER GDEM Data

Integrating geodiversity in animal spatial ecology: microhabitat selection of Eurasian lynx (Lynx lynx) and European wildcat (Felis silvestris) in a karst landscape

Geodiversity, encompassing various geophysical elements, can have an important impact on species distribution and affect animal behaviour patterns. Although many wild felids are attracted to rugged terrain and conspicuous relief features, most previous research was limited to general topographical characteristics (e.g., slope or terrain ruggedness) and rarely considered the effects of specific microhabitat characteristics. This gap is primarily due to the limited availability of high-resolution digital terrain models (DTMs) and relief features data at larger scales. However, LiDAR DTMs can be used in combination with various automatic methods to detect relief features, enabling non-contact and accurate mapping of large, remote and densely-forested areas. Here, we investigated the selection patterns of various karstic relief features, as well as topographic, anthropogenic and vegetation characteristics, by two sympatric felids, the Eurasian lynx (Lynx lynx) and the European wildcat (Felis silvestris), in the Dinaric Mountains, Slovenia. We used LiDAR DTM to calculate topographic characteristics and detect karst relief features based on automatic methods. We compared the selection of these features between the GPS-collared lynx and wildcats under a use-availability approach. We also investigated the differences in the selection of these features by lynx based on their origin and experience (remnant vs. translocated and naive vs. experienced, respectively). We observed significant impact of relief features on space use by both felids and detected distinct selection patterns between the two species. Lynx selected rugged terrain and proximity of caves, cliffs, karst depressions, ridges, small rocky outcrops, and roads, but avoided human settlements and forest edges. Wildcats selected areas with lower surface slope, closer to main roads, forest edges, caves and ridges, but avoided cliffs, forest roads and human settlements. We observed stronger selection/avoidance patterns among the translocated compared to the remnant lynx, while the differences in experience levels were less important. Our study demonstrates the potential of integrating remote sensing techniques and information on geodiversity into the study of animal spatial ecology. Furthermore, our results indicate that specific relief features provide important abiotic microhabitats for felids and may influence habitat segregation between sympatric species. Our findings provide further evidence for the importance of geodiversity conservation and the need to incorporate abiotic microhabitat features in wildlife habitat selection studies.

Impact of Different Land Use Types on Bacterial and Fungal Communities in a Typical Karst Depression in Southwestern China

Impact of Different Land Use Types on Bacterial and Fungal Communities in a Typical Karst Depression in Southwestern China

Detection of karst depression in Brazil comparing different semantic and instance segmentations and global digital elevation models

This research assessed the efficacy of deep segmentation in identifying and measuring natural karst depressions in the Bambuí Group's carbonate rocks in Western Bahia, Brazil. The investigation used five Global Digital Elevation Models (DEMs) with 30-m resolution: Advanced Spaceborne Thermal Emission and Reflection Radiometer - Global Digital Elevation Model version 3 (ASTER-GDEM v3), Advanced Land Observing Satellite World 3D – 30 m version 3.2 (AW3D30 v3.2), Copernicus 30 m global DEM (GLO-30), NASA Digital Elevation Model version 1 (NASADEM v1), and Shuttle Radar Topography Mission version 3 (SRTM v3). The karst feature detection analysis compared five semantic segmentation architectures: Feature Pyramid Networks (FPN), LinkNet, UNet, UNet++, DVL3+, using an EfficientNet-B7 backbone, one instance segmentation model (Mask-RCNN), and a semantic-to-instance conversion method. This comparison considers different datasets, including one, two, or eleven variables (DEM, DEM-based sink depth, and nine terrain attributes). Besides, we performed a combinatorial analysis of the DEMs to evaluate the improvement in karst feature detection. The methodology involved the generation of geomorphometric attributes, sample labeling from Sentinel-2 and Operational Land Imager-Landsat 8 datasets, training-validation-testing steps with 128 × 128 samples, reconstruction of large images for semantic and instance segmentation, and accuracy analysis. The findings revealed that GLO-30 and AW3D30 data were the most accurate, while ASTER GDEM performed poorly in both segmentation forms. Among the semantic models, FPN showed the highest accuracy. The 11-variable models preferentially outperformed those with fewer in both types of segmentation. The approach of semantic-to-instance conversion with Geographic Information System tools favored individualizing karst depressions and obtaining efficient quantification, consisting of an easy alternative to achieve instance segmentation. Reconstruction of large remote sensing images through sliding windows considering the specifics of instance and semantic segmentation demonstrated that smaller stride enhances object coverage and reduces the risk of losing crucial information, effectively improving the predictions. The combinatorial analysis for semantic and instance segmentation indicates that models incorporating more DEMs (4- and 5-DEM models) and variables achieve generally higher accuracy. The best result in semantic segmentation was combining the five DEM datasets using 11 variables, reaching an F-score of 85.06 and IoU of 74.00. In instance segmentation, the best result for the bounding box was the model that integrates AW3D30, GLO-30, NASADEM, and SRTM with eleven variables reaching Average Precision (AP) of 45.64, AP50 of 88.40 and AP75 of 39.38, while the best result for the segmentation mask was the model that integrates the five models with eleven variables with AP of 42.61, AP50 of 86.79 and AP75 of 35.43. These results demonstrate that integrating a wide range of DEM data, even the lowest performing ones, improves model generalization and accuracy in segmentation, leveraging strengths and mitigating individual weaknesses. Future work could explore high-resolution DEMs and the integration of various deep-learning methods.

Maize Cultivation Three Hundred Years Ago Triggered Severe Rocky Desertification in Southwest China

AbstractUnderstanding the forest evolution is vital to answering the reforestation potential in karst areas. Here, we present the first‐ever pollen record in karst depression sediment, combined with comprehensive dating methods (137Cs, 210Pbex, and 14C) and historical documents, to reveal plant change history in southwest Guangxi, a severe rocky‐desertification region. We inferred three stages of “virgin forest–deforestation–sparse tree planting” over the past three centuries. Before the 1780s, the barren mountains used to be a lush mixed broadleaf forest probably. However, maize cultivation, along with explosive population growth and migration, accelerated mountain reclamation and deforestation, leading to severe rocky desertification since the 1780s, featured by the co‐occurrence of Zea pollen appearance and Dicranopteris spore surge from 0.92% to 12.18%. Since the 1930s, sparse tree planting began, as Cupressaceae/Taxodiaceae pollen abruptly increased by 32%. Our study is significant in understanding the rocky desertification causes and guiding ecological restoration in the region.

Remotely Sensed and Field Data for Geomorphological Analysis of Water Springs: A Case Study of Ain Maarrouf

Tabular Middle Atlas of Morocco holds the main water reservoir that serves many cities across Morocco. Dolomite and limestone are the most dominant geologic formations in this region in which water resources are contained. The recent studies conducted to evaluate the quality of this water suggest that it is very vulnerable to pollutants resulting from both anthropogenic and natural phenomenon. High and very high-resolution satellite imagery have been used in an attempt to gain a better understanding of this karstic system and suggest a strategy for its protection in order to reduce the impact of these phenomenon. Based on the surface reflectance of land cover benchmarks, the karstic system has been horizontally delineated, as well as regions with intense human activities. Using band combination in the portion of the infrared, shortwave infrared, and visible parts of the electromagnetic spectrum, we identified bare lands which have been interpreted as carbonate rocks, clay minerals, uncultivated fields, basalts rocks, and built-up areas. Other classes such as water and vegetation have been identified. Carbonate rocks have been identified as areas with a high rate of water infiltration through their fracture system. Using a Sobel operator filter, these fractures have been mapped and their results have revealed new and existing faults in two major fracture directions, NE-SW and NW-SE, where NE-SW is the preferable pathway for surface water infiltration towards the groundwater reservoir, while the NW-SE direction drains groundwater from the Cause to the basin of Saiss. Over time, the infiltration of surface water through fractures has contributed to a gradual erosion of the carbonate rocks, which in turn developed karst landforms. This karst system is vulnerable due to the flow of pollutants in areas with shallow sinkholes. Using GDEM imagery, we extracted karst depressions, and their analysis shows that they are distributed along the fracture system and many of them were located on curvilinear or linear axes along the NE-SW fracture direction. We found also dolines scattered in areas with a high intensity of fractures. This distribution has been validated by both on-the-ground measurements and very high-resolution satellite images, and depressions of different forms and shapes dominated by dolines, poljes, lapiez, and avens have been identified. We also found many water springs with a highly important water output, such as the Ain Maarrouf water spring. The aim of this study is to enhance the understanding of the hydrogeological system of TMA, to improve the existence of the fracture database in the Cause of Agourai, and to establish a new morpho-structural picture of the Ain Maarrouf water spring.

REE and trace element mobility during the transformation of basalt to laterite and bauxite, Payas Province, Türkiye

The bauxites of the Payas area in the eastern Mediterranean region of Turkey occur as a stratigraphically continuous layer between Early and Late Cretaceous shallow marine carbonates. The laterites represent an in situ formation and mark a key stratigraphic layer in the region. Bauxite pockets are also present in the laterites, formed from the reworking of the laterites and accumulated in depressions in the karst terrain. Therefore, bauxite occurrences are found locally in this stratigraphic layer. The parental rock was a Ti-rich basalt that is compositionally similar to Hawaiian basalts, as indicated by petrographic features and distinctive trace element composition (Zr/TiO2 and Nb/Y). The behavior of elements during the lateritization and bauxitization processes was interpreted using the composition of the Hawaiian basalts with the iron laterite and Ti-rich bauxites of the Payas Region. During lateritization, Fe, Al, Ti, Cr, Nb, and Ta, were largely immobilie while REE and other trace elements, except for Rb, Ni, Co, and Pb were significantly removed. Approximately 75 % of the REE were removed at the end of the bauxitization and/or transportation of the lateritic soil into the karstic depressions. REE were not equally mobile with La to Ce and Lu to Yb having a relatively lower mobility than highly mobile middle REE. During the transformation of laterite to bauxite, low mobility elements such as Ti, Nb, Th, Cr, Hf, and Sn were enriched in the bauxite phase. In comparison to other elements, Rb, As, Pb, Mo, and Ni were strongly removed from the lateritic material during the bauxitization processes. The transfer of MREE during lateritization and bauxitization would have resulted in the enrichment of both light and heavy REE (concave pattern) in contemporaneous seawater. In other words, silicate weathering periods on land should be marked by a concave REE pattern with positive Eu anomaly in marine sediments throughout the geological period.

BAUXITES OF THE TATAR DEPOSIT (YENISEI RIDGE, RUSSIA): THE FIRST EVIDENCE OF CONTACT-KARST GENESIS

The Tatar bauxite deposit on the territory of the Russian Federation was formed as a result of sedimentation in contact-karst depressions of the products of denudation of lateritic weathering crusts of amphibolites. Detailed mineralogical studies of bauxites made it possible to reliably reconstruct the conditions for their formation. As it turned out parent rocks and weathered before rocks occurred due to the close location of the areas of nutrition and accumulation and denudation. At the same time, chemical processes was continuing in karst depressions. For the first time, the presence of nanoparticles of amorphous aluminum oxide was revealed into contact-karst bauxites. This characteristic feature of the form of alumina precipitation is associated with the subsequent cessation of lateritization processes and their attenuation with depth. The presence of amorphous aluminum monohydrate must be taken into account when choosing a scheme for bauxite enrichment.

Soil toposequences, soil erosion, and ancient Maya land use adaptations to pedodiversity in the tropical karstic landscapes of southern Mexico

The soil mantle of the tropical karst landscapes of southern Mexico was a key resource for ancient Maya agriculture and experienced deep transformation due to long-term human impacts under changing environmental conditions. We conducted a comparative analysis of three compound soil toposequences in mountainous (Sierra de Chiapas/Middle Usumacinta Valley, Busiljá, and Chinikihá archaeological sites) and platform (NE Yucatán Peninsula, Yalahau region) karst landscapes to reconstruct general tendencies and regional variations in pedodiversity development and soil–human interactions since the Early Preclassic Period. Toposequence characterization is based on macro- and micromorphological observations, accompanied by a suite of laboratory data. Calcareous upland geoforms of all toposequences have similar soil combinations consisting of shallow Rendzina and deep red clayey Terra Rossa types of profiles. We argue that Rendzinas, now dominant in the upland soil cover, in most cases, are not a product of incipient pedogenesis on limestone; they have developed from the residues of Terra Rossa soils after their advanced erosion. Pedosediments generated by ancient soil erosion have been found in the piedmont and depression positions in the mountainous landscapes of Chiapas, as a result of lateral downslope soil removal, and in the subsurface karstic cavities in the platform of NE Yucatán, indicating vertical “soil piping.” The soils of the lowland domains show contrasting differences between the toposequences: gleyic clay–rich soils and humic alluvial soils prevail in Chinikihá and Busiljá, whereas hydromorphic carbonate soils have formed in Yalahau karstic depressions. These differences in the lowland soil properties led to divergent ancient Maya land use strategies; in Chinikihá and Busiljá, the major agricultural domain was developed in the lowlands, implying largescale artificial drainage. On the contrary, in Yalahau, mostly upland Rendzinas were cultivated, implying “precision agriculture” and “container gardening.”

Characterization and classification of lakes based on geospatial analyses in the karst hydrogeological system of the Bambuí group, Lagoa Santa, Minas Gerais, Brazil

The karst of Lagoa Santa is a protected area located near the city of Belo Horizonte, in Minas Gerais state (Brazil), namely Lagoa Santa Karst Environmental Protection Area (EPA), one of the main research areas related to archeology, paleontology, speleology and hydrogeology in the Brazilian territory. The region is comprised by several lakes, because of its complex water system due to karst evolution. In addition, the karstic nature of the rocks in the region allows the existence of several other typical dissolution morphologies, such as: caves, speleothems, sinkholes, uvalas, among others. The morpho-structural characteristics, combined with the local geology, can provide important information about the behavior of lakes in view of the cycles of expansion and retraction of the water surface. Thus, this work aims to understand the water dynamics of the lakes present in the Karst of Lagoa Santa through analysis of spatial data between the years 1984 and 2020. Based on the surveys, 153 lakes were identified in the study region in the last 35 years: 40 perennial lakes, 89 intermittent lakes, 19 new lakes and 5 lakes that dried up completely. Also, this study compares the relationship of each lake with the type of relief depressions (Sinkhole or Uvala), rock masses and the main negative structural lineaments. The data obtained allowed the identification of which characteristics are diagnostic for perenniality or intermittence of existing lakes in the region, as well as the grouping of existing lakes into subgroups with similar geological and morpho-structural characteristics. The most important characteristics to define the water dynamics on lakes are the evolutionary state in karst depressions and the presence of structural lineaments, in which in more evolved depressions (uvalas) the lakes tend to be intermittent and in less evolved depressions (sinkholes) the lakes tend to be perennial. Finally, the water bodies associated with structural lineaments may be the condition for the permanence of water in some depressions, mainly in lakes over non-carbonate formations existing in the region.

Landscape Evolution in Glacier Valleys of Glaciokarsts

The landscape evolution of the glacier valleys of glaciokarsts is described. Depending on the character of coveredness (quality and thickness of the cover), altitude and the presence of karst features, different ways of geomorphic evolution occur adjacently. Most widespread is the denudation of bare surfaces by karren formation. During this process, beds are denuded, which is primarily controlled by the dip direction of the beds. The denudation of beds may modify the original cross-section of valleys. On terrains covered with caprock, the cover is becoming thinner by erosion processes since the debris is transported into the karst depressions and then from here into the karst. On terrains covered with limestone debris, if the cover is purely limestone debris, denudation is cyclical. The thick cover becomes thinner by dissolution and subsequently, the bedrock is dissolved by karren formation if water with dissolution capacity arrives at the bedrock. Then, the debris that developed on the bedrock makes the cover thicker from below. Reaching an adequate thickness, the process is repeated by the dissolution of the cover debris. In cirques, the superficial deposit is transported into the karst, which is supplied from the slopes, increasing the upfilling of the feature.

Spatial patterns and controlling factors of the evolution process of karst depressions in Guizhou province, China

Spatial patterns and controlling factors of the evolution process of karst depressions in Guizhou province, China

Bauxites of the Tatarka Deposit (Yenisei Ridge, Russia): The First Evidence of a Contact-Karst Origin

The Tatarka bauxite deposit on the territory of the Russian Federation was formed as a result of sedimentation of the products of denudated lateritic weathering crusts of amphibolites in contact-karst depressions. Detailed mineralogical studies of bauxites made it possible to reconstruct reliably the conditions for their formation. As it turned out, the initial rocks and rocks, weathered before, have been denudated due to the close location of the areas of alimentation and accumulation. At the same time, chemical processes have been continued in karst depressions. For the first time, the presence of nanoparticles of amorphous aluminum oxide was revealed in contact-karst bauxites. This specific feature of the form of alumina precipitation is associated with the subsequent cessation of lateritization and their attenuation with depth. The presence of amorphous aluminum monohydrate must be taken into account when choosing a scheme for bauxite enrichment.

Enclosed Karst Depression Identification and Analysis for the Pumped Storage Power Station Reservoir Construction Using DEM

An enclosed karst depression, a typical natural negative terrain, has the advantage of less engineering excavation when constructing a reservoir. In this study, the enclosed karst depression and its range identification technique have been developed. What is more, the geometric parameters and spatial distribution of enclosed karst depressions in Anlong County, Guizhou Province of China, have also been analyzed. Results show that (1) the focus statistic method and local terrain contour tree model were developed to identify enclosed karst depression and its range using regular grid DEM data with 12.5 m spatial resolution, which has been applied to enclosed karst depression identification in Anlong County. (2) 7262 independent and nested depressions with an average density of 3.7/km2 were identified by using the proposed method. The effectiveness and reliability of the proposed model have been verified through comparative analysis and visual recognition comparison. (3) High-density depression areas (5.6 depressions/km2), medium-density depression areas (2.9 depressions/km2), and low-density depression areas (1.1 depressions/km2) were well classified through kernel density analysis. (4) The geometric parameters of enclosed karst depressions (area, perimeter, circularity, depth, elevation, slope, and volume) were all analyzed in the study area. In addition, an indicator called DCK (depression is caused by karstification) was proposed to evaluate the dissolution degree and karstification stage of the enclosed karst depression. Based on the DCK, we determined that around 2.7% of depressions were identified as middle-stage and suitable for reservoir construction with enough volume and good slope stability. The idea and method in this research could provide a technological support for the engineering utilization of enclosed karst depressions.

REE Geochemical Characteristics of the Huri Karst-Type Bauxite Deposit, Irano–Himalayan Belt, Northwestern Iran

The Huri bauxite deposit is located 40 km northwest of Maragheh City, East Azerbaijan province, northwestern Iran. Bauxite horizons at Huri develop within karstic depressions and sinkholes of carbonate footwalls of the Ruteh Formation, overlain by carbonate of the Elika Formation. Powder X-ray diffraction (PXRD) and scanning electron microscope, coupled with energy dispersive X-ray spectroscopy (SEM-EDS) analyses show that the Huri bauxite ores consist of hematite, diaspore, kaolinite, and lesser amounts of halloysite, pyrophyllite, illite, goethite, clinochlore, amesite, rutile, zircon, and monazite. Based on geochemical studies (Eu/Eu* vs. Sm/Nd and U/Th bivariate diagrams), basalt rocks interbedded in limestone of the Ruteh Formation are the possible precursor rocks of the Huri bauxite deposit. The pH variations of weathering solutions, fluctuations in the groundwater table level, the function of carbonate bedrock as a geochemical barrier, simultaneous precipitation of Fe-bearing minerals, and preferential scavenging of light rare earth elements (LREE) by hematite played an important role in the fractionation of LREE from heavy rare earth elements (HREE) in the Huri bauxite ores. Fluctuations in groundwater table level, increasing pH of acidic solutions percolating downward, preferential adsorption of Ce onto hematite at the base of the profile, and the possible presence of Ce-bearing fluorocarbonates played an important role in increasing Ce anomaly from the top of the profile downward.

DEVELOPMENT OF FLOATING KARST MIRES IN THE NORTH-EASTERN PART OF THE MIDDLE RUSSIAN UPLAND, AND CARBON ACCUMULATION IN PEAT DEPOSITS

The floating karst mires are unique natural ecosystems of the Middle Russian Upland, since they are habitats of rare species and communities in the region with low paludification (0.5%), and also participate in the deposition of atmospheric carbon. The study of the genesis of the floating karst mires will allow to develop approaches to their conservation. The purpose of this work is to identify the features of development and to estimate the intensity of carbon accumulation in the peat deposits of the floating mires of the Middle Russian Upland. The objects of the study were the mires Glavnoe and Kochaki-1, located in the north-eastern part of the Middle Russian Upland. To identify the genesis of the mires, the peat deposits were drilled and the botanical composition of peat was studied. The carbon content (%) was determined in peat samples and the rate of carbon accumulation by mire paleocenoses was calculated. The conducted studies have revealed different types of paludification in karst depressions, accompanied by the formation of a float, depending on a hydrological regime. It is shown that the most active vertical growth of peat deposits occurs in conditions of high moisture content of mire biotopes. This contributes to the maximum accumulation of atmospheric carbon by mire paleocommunities (up to 79.3–125 gC/m2/year). The highest carbon deposition rates are characteristic of the sphagnum and herb-sphagnum paleocenoses (up to 151–305 gC/m2/year) formed on the floats in the second half of the Subatlantic Holocene period. The results obtained indicate the diversity of the genesis of the floating mires and characterize these ecosystems as a “depot” of atmospheric carbon.

Using geochemical elements to discriminate sediment sources in a typical karst watershed

Knowledge of temporal variations in sediment sources is necessary to identify the principal sources of sediment for effective implementation of soil conservation measures and to improve the calibration and validation of process-based soil erosion models. Quantitative information on sediment provenance is often limited in karst regions because of their complex surfaces and underground three-dimensional erosion systems. Peak-cluster depressions are typical landforms in karst areas and can well intercept most sediment from hillsides such as dams or reservoirs. Thus, peak-cluster depressions are suitable areas for sediment source identification. The objective of this study was to quantify the contribution of sediment sources in a typical karst watershed and to identify temporal variations in sediment sources in the watershed in the past 60 years. We collected 194 soil samples from three sediment profiles in a karst depression and 58 source samples from cropland, fissure soil, and forestland. We used a composite fingerprinting method based on 45 geochemical properties and an IsoSource multivariate mixed model in a typical karst watershed. The results indicate that cropland was the principal sediment source (89.2 %) in the last 60 years, followed by fissure soil (9.6 %) and forestland (1.2 %). Importantly, compared with the period from 1949 to 1999, the contribution of sediment from fissure soil reached a maximum value of approximately 20 % from 1999 to 2015. This result implies that the “Grain for Green” program, which was implemented in 1999, clearly reduced the amount of soil erosion from cropland. Therefore, the program may greatly affect sediment deposition in karst depressions. Using metal ratios as fingerprint factors, the IsoSource mixed model can be effectively used to study the source of sediments in karst watersheds quantitatively. This study can aid the existing understanding of soil erosion processes and contributes to the sustainable development of agro-ecology in karst watersheds.

Paleoclimatic and anthropogenic impacts on the environment of Southwest China since 33 ka based on multiproxy analysis of karst depression deposits

Paleoclimate change and anthropogenic activities have fundamentally modified the Earth's environmental system since the late Quaternary. Southwest China has one of the largest continuous karst areas in the world, yielding geological records from karst depressions that can improve our understanding of changes in the dominant control on regional environmental conditions. In this study, we investigated a sediment sequence formed over 33,000 years in a typical karst catchment by using combined geophysical, geochemical and biological properties of the depression deposits. The results suggest that paleoclimate change was the main modulator of environmental changes prior to the Late Holocene, and that significant vegetation change related to paleotemperature influences played an important role during the Early (ca. 12–8 ka) and Middle (ca. 8–4 ka) Holocene. During the Late Holocene (ca. 4–0 ka), the impact of anthropogenic activities has overwhelmed paleoclimatic influences on the environment. This study demonstrates the utility of dated karst depression deposits for reconstructing Holocene climate change and the timing of anthropogenic impacts on the landscape.