Surface hydrology and soil movement in an arid karst: the Nullarbor Plain,Australia

The Nullarbor Plain is the largest karst area in Australia (220,000 km²) and one of the largest in the world. Its climate is arid (Köppen BWk and BWh), and the surface relief is less than 10m. The landscape is divided into extensive closed karstic depressions separated by low rocky ridges, and the dominant vegetation is chenopod shrubland. The extent and severity of soil degradation has been assessed using remote sensing. GPS rectified images from 1972–1973, 1979, 1983, 1988, and 1991 have been compared for two sites on the Nullarbor. Over the 19 years the total extent of bare soil has reduced significantly, but some areas around water points have degraded and there is some disturbance due to fossorial wombats. Sheet-flow processes occur during intense rainfall events, which happen two or three times per decade. Runoff only occurs after the 10– or 50– year return frequency events, and at these times turbid water ponds in depressions and enters caves. Surface soil sorptivity and hydraulic conductivity differ markedly between ridges and depressions; the ridges are clearly zones of groundwater recharge, while ponding is evident in most depressions. Sorptivity is influenced by the extent and nature of ground cover and cryptogam crusts on the soil. The landscape has been divided into classes on the basis of vegetation type and percentage of foliage cover. In each class the activities of fallout radionuclides will be determined by high resolution spectroscopy. Preliminary results suggest that in undisturbed sites little sediment movement has occurred over the time scale of cesium-137 (the last 35 years) but that the landscape has been well sorted over a much longer time scale. Future work will investigate disturbed sites to estimate relative soil loss during the pastoral period.     

The application of caesium-137 measurements to estimate recent sedimentation rates in a typical karst depression of Guizhou Plateau,China

The existing traditional methods of assessing the rates of soil loss have many limitations and are difficult to apply in the karst areas of Southwest China. Karst depressions comprise geomorphologically important sources and sinks for sediments and associated pollutants, yet the sedimentology of many depressions is not well understood. In this paper, the 137Cs technique was employed to investigate recent sedimentation rates in a Chinese polygonal karst depression. The results indicated that the sediment deposition rates ranged from 0.91 to 1.97 mm?a?1 in the period from 1963 to 2007, and the average sediment deposition rate and specific deposit yield of the catchment were estimated to be 1.47 mm?a?1 and 20 t?km?2?a?1, respectively. The results obtained were consistent with the local monitoring data of runoff plots, confirming the validity of the overall approach. It was shown that soil loss rates were very low in some karst areas of Southwest China. Above all, the approach appears to offer valuable potential to study surface erosion by estimating sediment deposition rates of karst depressions, rather than the assessment of complicated soil erosion in stony soils of carbonate rock slopes. In addition, the spacial distribution of surface soil and 137Cs inventories was affected remarkably by the inhomogeneous dissolution of limestone under the soil. It may be an important phenomenon which exists widely in the karst areas and is significantly different from other places.     

Leaf N/P ratio and nutrient reuse between dominant species and stands: predicting phosphorus deficiencies in Karst ecosystems,southwestern China

Variation of vegetation coverage and canopy height may reflect the complex spatial heterogeneity of nutrient storage and supply capacity, soil moisture, and surface hydrology in the karst terrains suffering from severe land degradation. To assess the patterns of nutrient limitation under different vegetation covers in the subtropical karst ecosystems from Guizhou province, southwestern China, topsoil and leaf samples of dominant tree species were collected in forest stand (FO), shrub stand (SH) and shrub-grass stand (SG), respectively. Nutrient concentrations of both soil and leaf were determined, and ratios of N to P and vegetation nutrient reuse capacity (VNR) calculated as well as vegetation coverage, vegetation canopy height and tree density measured across the three stands. Mean leaf N/P ratio was lowest (16.1 ± 1.4) in FO and highest (33.5 ± 3.2) in SG. Vegetation nutrient reuse increased with the decline in N and P availability in soils for these three stands. VNR of N and P ranged from 8.5 to 25.2 mg N g⁻¹ and from 0.4 to 1.1 mg P g⁻¹, respectively, and appeared lowest in SG (10.4 mg N g⁻¹ and 0.5 P mg g⁻¹ on average, respectively) and highest in FO (22.4 mg N g⁻¹ and 0.9 mg P g⁻¹ on average, respectively). Although there was no substantial difference in phosphorus reuse efficiencies between plant species and vegetation stands, concentrations of N and P of senesced leaves (SLs) were, respectively, found in positive correlation with the concentrations of mature leaves. The variation of VNR with elements indicated that P is cycled within vegetation much more efficiently than N across the stands. This study demonstrated that the karst vegetations were generally at P-limited or N- and P- co-limited stresses and that N/P ratio could be an effective indictor for nutrient limitation in the karst ecosystems at vegetation community level rather than at tree species level. It is proposed that phosphorus reuse by mature leaves could be an adaptation strategy by the dominant species to the low P availability in the karst soil.     

Carbon isotopic records from stalagmites and the signification of paleo-ecological environment in the area of Guangxi—Guizhou, China

High resolution carbon isotopic records in millennial, centennial and decadal timescales from three stalagmites from three different caves under a similar monsoon climate in Guangxi–Guizhou, China, provided detailed information on the paleo-ecological environmental conditions in the past 15,000 years. The results indicate that during the glacial period, or cold-dry period, such as Heinrich event H1 and Younger Dryas event karst development was poor as was pedogenesis, C3 vegetation didn’t grow well, resulting in C4 plants dominating and with heavy δ¹³C values in stalagmites. In a warm-humid stage, C3 vegetation grew well and predominated with negative δ¹³C values. The δ¹³C records from stalagmites could be indicative of sensitive vegetation changes and reflective of climate changes in precipitation, temperature, etc. The δ¹³C records may also be used to distinguish different effects from nature or human activity. Particularly since the late Holocene, human activities have increased disturbances to environment, even more than natural factors. Forest vegetation was destroyed, C4 plants became dominant, and rock desertification was aggravated because of severe water and soil loss, all resulting in sharply increasing δ¹³C values of stalagmites that are heavier than pre-middle Holocene δ¹³C values.     

Soil moisture dynamics under different land uses on karst hillslope in northwest Guangxi,China

Temporal and spatial dynamics of soil moisture are little known on karst hillslope with shallow soil in subtropical region. The objectives of this paper were (1) to investigate the temporal dynamics of soil moisture at depth of 0–10 cm under different land uses; and (2) to understand the relationship between mean and coefficient of variation (CV) of moisture contents on karst hillslope in northwest Guangxi, China. Soil moisture contents had a moderate variation (CV 17.5–30.3%) over an 8-month period and they had a significant difference among different land uses at the 0.01 level with a decreasing order: native scrubland > abandoned cropland and sloping cropland > economic forestland. There were higher mean and lower CV of moisture contents in rainy season than those in drought season. Mean and CV of moisture contents had a significant negative linear relationship except in abandoned cropland with higher soil and vegetation heterogeneity. This suggested that spatial variability of soil moisture within sampling sites would decrease when soils were wet and increase when soils were arid. Compared with rainy season, more soil samples may be needed and the interval for sampling should be shortened in drought season. Such information provided some insights to better understand the dynamics and variability of soil moisture at a larger scale in karst region of southwest China.     

Assessment of sediment and erosion rates by using the caesium-137 technique in a Chinese polygonal karst depression

Karst depressions comprise geomorphologically important sources and sinks for sediments and associated pollutants; yet the sedimentology of many depressions is not well understood in the world. In this paper, the ¹³⁷Cs technique was employed to estimate recent sedimentation rates in a Chinese polygonal karst depression. The results indicate that the sediment deposition rates ranged from 0.91 to 1.97 mm year⁻¹ from 1963 to 2007, and the average sediment deposition rate and specific deposit yield were estimated to be 1.47 mm year⁻¹ and 20 t km⁻² year⁻¹, respectively. These results are consistent with the local monitoring data of runoff fields, which confirms the validity of the overall approach. This shows that the soil loss rate is very low in some karst areas of Southwest China. Above all, the approach appears to offer valuable potential to study surface erosion by estimating sediment deposition rates of karst depressions, rather than the assessment of complicated soil erosion in stony soils of carbonate rock slopes. In addition, the space distribution of surface soil and ¹³⁷Cs inventories are affected remarkably by the inhomogeneous dissolution of limestone under the soil. It may be an important phenomenon, which exists widely in karst areas, and it is significantly different from other places.     

Stable carbon isotopic composition of soil organic matter in the karst areas of Southwest China

This study dealt with the distribution characteristics of soil organic carbon （SOC） and the variation of stable carbon isotopic composition （δ^13C values） with depth in six soil profiles, including two soil types and three vegetation forms in the karst areas of Southwest China. The δ^13C values of plant-dominant species, leaf litter and soils were measured using the sealed-tube high-temperature combustion method. Soil organic carbon contents of the limestone soil profiles are all above 11.4 g/kg, with the highest value of 71.1 g/kg in the surface soil. However, the contents vary between 2.9 g/kg and 46.0 g/kg in three yellow soil profiles. The difference between the maximum and minimum δ^13C values of soil organic matter （SOM） changes from 2.2‰ to 2.9‰ for the three yellow soil profiles. But it changes from 0.8‰ to 1.6‰ for the limestone soil profiles. The contrast research indicated that there existed significant difference in vertical pattems of organic carbon and δ^13C values of SOM between yellow soil and limestone soil. This difference may reflect site-specific factors, such as soil type, vegetation form, soil pH value, and clay content, etc., which control the contents of different organic components comprising SOM and soil carbon turnover rates in the profiles. The vertical variation patterns of stable carbon isotope in SOM have a distinct regional character in the karst areas.     

Stable carbon isotope characteristics of different plant species and surface soil in arid regions

The stable carbon isotope composition in surface soil organic matter (δ¹³Csoil) contains integrative information on the carbon isotope composition of the standing terrestrial plants (δ¹³Cleaf). In order to obtain valuable vegetation information from the δ¹³C of terrestrial sediment, it is necessary to understand the relationship between the δ¹³C value in modern surface soil and the standing vegetation. In this paper, we studied the δ¹³C value in modern surface soil organic matter and standing vegetation in arid areas in China, Australia and the United States. The isotopic discrepancy between δ¹³Csoil and δ¹³Cleaf of the standing dominant vegetation was examined in those different arid regions. The results show that the δ¹³Csoil values were consistently enriched compared to the δ¹³Cleaf. The δ¹³Cleaf values were positively correlated with δ¹³Csoil, which suggests that the interference of microorganisms and hydrophytes on the isotopic composition of surface soil organic matter during soil organic matter formation could be ignored in arid regions. The averaged discrepancy between δ¹³Csoil and δ¹³Cleaf is about 1.71%in Tamarix L. in the Tarim Basin in China, 1.50% in Eucalytus near Orange in Australia and 1.22% in Artemisia in Saratoga in the United States, which are different from the results of other studies. The results indicate that the discrepancies in the δ¹³C value between surface soil organic matter and standing vegetation were highly influenced by the differences in geophysical location and the dominant species of the studied ecosystems. We suggest that caution should be taken when organic matter δ¹³C in terrestrial sediment is used to extract paleovegetation information (C₃/C₄ vegetation composition), as the δ¹³C in soil organic matter is not only determined by the ratio of C₃/C₄ species, but also profoundly affected by climate change induced variation in the δ¹³C in dominant species.     

岩溶土壤的生态地球化学特征及其指示意义——以贵州贞丰—关岭岩溶石山地区为例

岩溶石山地区土壤退化与恢复的成因和机理一直是近年来土壤学和生态学研究的热点。以贵州西南部贞丰—关岭岩溶石山区为对象，选择了区内退化地、农用地、恢复地等生态样块以及与未退化地为对照，采集了其中的表层和亚表层土壤，分别进行了土壤的养分库量、微生物活性与功能和土壤酶活性等化学分析。研究表明土壤养分库是土壤中微生物活性基础，微生物量碳随土壤养分库容的退化或恢复而相应变化，退化岩溶地植被恢复3~6年后，主要养分总库容得到明显恢复(恢复程度55%~65%)，因而带动了微生物量碳的恢复（平均恢复程度60%以上），但养分的活性（有效磷）、微生物的功能（呼吸熵及土壤脲酶和磷酸酶活性）并没有得到相应程度的恢复（平均恢复程度仅在25%~40%）。这些结果提示，限制性养分活性和微生物功能的恢复是植被恢复下生态系统健康水平的重要指示。因此，在分析岩溶土壤和生态系统退化过程的本质以及评价生态恢复的效应时，不仅应将微生物量碳和总养分库指标作为岩溶土壤退化恢复的指标，更应将微生物区系的质量和功能指标纳入关键评价内容。      

退化喀斯特植被恢复过程中土壤微生物活性研究——以贵州花江地区为例

退化喀斯特植被的恢复机理一直是近年来土壤学和生态学研究的热点。通过分析退化喀斯特植被恢复过程中土壤微生物数量、土壤生化作用强度、土壤微生物生物量,研究了贵州花江喀斯特高原生态综合治理示范区内土壤微生物活性的变化。结果表明:退化喀斯特植被恢复过程中土壤的微生物活性存在较大差异。随着退化喀斯特植被的恢复,土壤细菌、真菌、放线菌三大微生物数量及微生物总数明显上升,表现为乔木群落阶段〉灌木群落阶段〉草本群落阶段〉裸地阶段,且细菌较真菌和放线菌相比占绝对优势,其在微生物总数中分别占95．95％,93．49％,92．32％和92．48％;各主要生理类群的数量呈上升趋势,且氨化细菌〉固氮菌〉纤维素分解菌〉硝化细菌,土壤生化作用强度增强;土壤微生物生物量碳明显增加,微生物生物量碳与土壤有机碳（P〈0．01）呈显著正相关关系。土壤微生物是表征退化喀斯特植被恢复过程中土壤质量的重要特征之一,反映出随着退化喀斯特植被的恢复土壤质量也在逐渐恢复。      

Vertical patterns of stable carbon isotope in soils and particle-size fractions of karst areas, Southwest China

Taking limestone soil and yellow soil, the two major soil types in karst areas as examples, analyzing stable carbon isotope composition (δ¹³C value) of soil organic matter (SOM) in bulk soils and particle-size fractions of four soil profiles under three vegetable forms, the following results are reached: in the limestone soil profile, soil organic carbon contents are all above 1.0%, the highest value is 7.1% in the surface soil; however, they are between 0.3% and 4.6% in the three yellow soil profiles. From the surface to the bottom of the soil profiles, the variation of δ¹³C value of soil organic carbon for limestone soil profile is only between −24.1‰ and −23.0‰, however, it’s between −24.8‰ and −21.1‰ for yellow soil profiles. The variation range of δ¹³C value of soil organic carbon associated with particle-size separates is slight for limestone soil but is considerable for yellow soil. The contrast research indicates that the changes between the contents and the δ¹³C value of soil organic carbon with depth are complex. The vertical patterns of stable carbon isotope in soil organic matter have a distinct regional characteristic in karst areas.     

Transition from arid to hyper-arid environment in the southern Levant deserts as recorded by early Pleistocene cummulic Aridisols

The time at which deserts established their current arid or hyper-arid conditions remains a fundamental question regarding the history of Earth. Cosmogenic isotope exposure ages of desert pavement and welded, calcic–gypsic–salic Reg soils that developed on relatively flat alluvial surfaces ～2 Ma ago in the Negev Desert indicate long geomorphic stability under extremely dry conditions. Over a short interval during their initial stage of development between 1–2 Ma, these cumulative soils are characterized by calcic soils reaching maximum stage III of carbonate morphology. This interval is the only period when calcic soil horizons formed on stable abandoned alluvial surfaces in the southern Negev Desert. Since ～1 Ma pedogenesis changed toward more arid soil environment and the formation of gypsic–salic soil horizons that were later followed by dust accumulation. The dichotomy of only moderately-developed calcic soil (stages II–III) during a relatively long time interval (10⁵–10⁶ years) indicates an arid environment that does not support continuous development but only occasional calcic soil formation. The very low δ¹⁸O and relatively high δ¹³C values of these early pedogenic carbonates support soil formation under arid climatic conditions. Such an environment was probably characterized by rare and relatively longer duration rainstorms which occasionally allowed deeper infiltration of rainwater and longer retention of soil moisture. This, in turn enabled the growth of sparse vegetation that enhanced deposition of pedogenic carbonate. At ～1 Ma these rare events of slightly wetter conditions ceased and less atmospheric moisture reached the southern Negev Desert leading to deposition of soluble salts and dust deposited in the soils. The combination of long-term hyperaridity, scarcity of vegetation and lack of bioturbation, salts cementation, dust accumulation and tight desert pavement cover, has protected the surfaces from erosion forming one of the most remarkably stable landscapes on Earth, a landscape that essentially has not eroded, but accumulated salt and dust for more than 10⁶ yr.     

Morphometric comparisons between automated and manual karst depression inventories in Apalachicola National Forest,Florida, and Mammoth Cave National Park,Kentucky, USA

Karst depression catalogs are critical to assessing the hydrology and geohazards of an area; yet, the delineation of these features within a landscape can be a difficult, time-consuming and subjective task. This study evaluates the efficacy of karst depression inventorying using an automated fill-difference method operating on high-resolution lidar-derived digital elevation models (DEMs). The resulting catalog is compared with existing karst depression inventories for two low-development areas of the USA, Mammoth Cave National Park (MACA) and Apalachicola National Forest (ANF), where karst depressions have been mapped previously using a manual closed-contour approach. The automated fill method captures 93 and 85 % of these previously mapped karst depressions at MACA and ANF, respectively. Field observations and topographic analysis suggest that the omitted features were likely misclassified within the existing catalogs. The automated routine returns 797 and 3377 additional topographic depressions, at MACA and ANF, respectively, which are not included in the existing catalogs. While the geology of ANF is mostly homogenous Quaternary deposits, the newly identified, typically smaller-scale depressions found within MACA tend to be disproportionally located in non-carbonate-dominated formations, where the development of karst may be restricted by geologic heterogeneity. Within both areas, the size distributions of the two inventories are statistically identical for features larger than ~10³ m² in area or ~3 m in depth. For individual depressions captured by both methods at MACA, the automated fill-difference routine tends to return a slightly larger estimate of depression size and aggregate small depressions into larger ones. Conversely, at ANF, some low-relief depressions may be disaggregated by the fill-difference technique, with a trend toward smaller estimated depression areas when the automated method is employed. The automated fill-difference method, operating on high-resolution lidar-derived DEMs, can reproduce and expand the existing inventories of karst depressions, while minimizing false detections that may be inherent within pre-existing catalogs.     

土地石漠化概念与分级问题再探讨

针对前人研究中将石漠化发生的地域限定在亚热带,将发生的时间限定在人类历史时期,将发生的原因均归结为人为不合理的经济活动,而忽视了石漠化可能发生的其它地域、其它时期和其它成因等问题,对土地石漠化概念作了修正。认为土地石漠化是在湿润、半湿润气候环境和岩溶环境中,由于人类活动和/或气候变化等因素作用,造成地表植被退化、土壤侵蚀、地表水流失、基岩裸露,形成类似石质荒漠景观的土地退化过程,并对其内涵作出释义。在此基础上依据生态基准面的理论,以坡面形态、溶蚀岩溶地貌形态、基岩出露率、土壤厚度和土被覆盖度、土壤侵蚀程度、植被覆盖率和植物种群、土地利用类型等为景观指征,将石漠化土地分为轻度、中度、重度和极重度4个等级,并以粤北岩溶山区为例,拟定了区域性石漠化土地分级及其综合景观指征。      

Combinatorial analysis on spatial information statistics for the karst water environment in Guiyang, China

The karst groundwater system is extremely vulnerable and easily contaminated by human activities.To understand the spatial distribution of contaminants in the groundwater of karst urban areas and contributors to the contamination,this paper employs the spatial information statistics analysis theory and method to analyze the karst groundwater environment in Guiyang City.Based on the karst ground water quality data detected in 61 detection points of the research area in the last three years,we made Kriging evaluation isoline map with some ions in the karst groundwater,such as SO4 2-,Fe 3+,Mn 2+and F -,analyzed and evaluated the spatial distribution,extension and variation of four types of ions on the basis of this isoline map.The results of the analysis show that the anomaly areas of SO4 2-,Fe 3+,Mn 2+,Fand other ions are mainly located in Baba’ao,Mawangmiao and Sanqiao in northwestern Gui- yang City as well as in its downtown area by reasons of the original non-point source pollution and the contamination caused by human activities(industrial and domestic pollution).     

花江喀斯特峡谷地区石漠化成因初探

花江喀斯特峡谷区地下水埋藏深,地表干旱,存在显著的人为加速土壤侵蚀过程,植被次生性明显,生境干热特征显著,是已石漠化和半石漠化的生态系统。其中地质构造、地貌演化、岩溶形态、可开发利用的水资源、植被群落可能是石漠化过程的主要自然成因,以土地利用为表现形式的强烈人类活动是石漠化的驱动力。基于此,提出了石漠化地区的土地利用方式和生态恢复过程的建议,旨在为石漠化的演化研究及生态重建提供参考。     

Mechanism of cultivation soil degradation in rocky desertification areas under dry/wet cycles

Karst rocky desertification is a process of land degradation involving serious soil erosion, extensive exposure of basement rocks. It leads to drastic decrease in soil productivity and formation of a desert-like landscape. In this regard, changes in climatic conditions are the main origin of the soils degradation. Indeed, soils subjected to successive dry/wet cycling processes caused by climate change develop swelling and shrinkage deformations which can modify their water retention properties, thus inducing the degradation of soil–water capacity. The ecological characteristics of cultivation soils in karst areas, Southwest of China, are extremely easy to be affected by external environmental factors due to its shallow bedding and low vegetation coverage. Based on the analysis of the climate (precipitation) of this region during the past decades, an experimental study has been conducted on a cultivated soil obtained from the typical karst area in southwestern China. Firstly, the soil–water properties have been investigated. The measured soil–water retention curve shows that the air-entry value of the soil is between 50 and 60 kPa, while the residual saturation is about 12%. Based on the experimental results, three identifiable stages of de-saturation have been defined. Secondly, a special apparatus was developed to investigate the volume change behavior of the soil with controlled suction cycles. The vapor equilibrium technique was used for the suction control. The obtained results show that under the effect of dry/wet cycles, (1) the void ratio of the cultivated soil is continuously decreasing, leading to a gradual soil compaction. (2) The permeability decreases, giving rise to a deterioration of water transfer ability as well as a deterioration of soil–water retention capacity. It is then obvious that the long-term dry/wet cycling process caused by the climate change induce a continuously compaction and degradation of the cultivated soil in karst rocky desertification areas.     

喀斯特石漠化的形成背景、演化与治理

喀斯特石漠化是青藏高原隆升在其东南翼所诱发的重要地质生态灾害问题,是制约中国西南地区社会经济发展的关键因素.它不是一种纯自然过程,而是与人类活动密切相关,不仅造成土地资源丧失,干旱缺水,生态系统退化,而且使该区的贫困问题加剧,具有明显的自然和社会学属性.本文着重从地质和生态的角度,阐述喀斯特石漠化的形成特点和演化方式,及其对综合治理的指导意义.对西南岩溶山地而言,土壤和植被是生态环境中最为敏感的自然环境要素,与非岩溶区相比,具有明显的脆弱特征.它们在干扰下发生迅速演替,诱发地表水文条件的改变,导致石漠化的形成.文中特别强调岩溶山区碳酸盐岩基底岩性的不同、生态环境类型与植被演替的方式和进程的多样性对于岩溶生态系统的影响作用.基于上述认识,对石漠化地区的土地利用方式和生态恢复过程以及可能发展的方向提出了一些建议和看法.     

Erosion-creep-collapse mechanism of underground soil loss for the karst rocky desertification in Chenqi village,Puding county,Guizhou, China

Carbonate rocks distribute widely in China. The total area of the carbonate rocks is about 3,430,000 km², and the exposed area of the carbonate is approximately 13 % of China’s territory. In 2003, soil loss in Yunnan, Guizhou, and Guangxi provinces reached 179,600 km², which is almost 40.1 % of the total area, causing rocky desertification. In this study, the erosion-creep-collapse mechanism of underground soil loss for the karst rocky desertification in Chenqi village, Puding county, Guizhou province is proposed. The mechanism occurs under the following geological environment: slope surface undulation, underlying bedrock surface fluctuation and thin and inhomogeneous soil overlying, overlying soil generation by bedrock weathering, underground karst development, and large groundwater depth and lying water table under the bottom of soils. The erosion-creep-collapse mechanism of underground soil loss in the karst slopes is explained as follows: power loss due to human cultivation activities that destroy the soil structure, hydraulic force formed by rainfall infiltration, wet–dry cycle generated by rainfall, erosion effect caused by rainfall penetration, creeping and flowing of plastic-stream soil, and collapse. The erosion-creep-collapse mechanism of underground soil loss has seven steps: disturbance of soils filled in underground karst cave by human activities, internal soil erosion and partial collapse caused by hydraulic power, internal free surface formation within the soil in the filled karst cave, internal soil creeping, soil pipe formation, soil pipe collapse, and ground surface collapse and filling. Soil loss develops slowly, and sudden transportation occurs by collapse. Soil loss can be explained by the proposed mechanism, and soil loss can be prevented by controlling soil collapse.     

Soil erosion determinations by using 137Cs technique in the agricultural regions of Gediz Basin, Western Turkey

Gediz Basin is one of the regions where intense agricultural activities take place in Western Turkey. Erosion and soil degradation have long been causing serious problems to cultivated fields in the basin. This work describes the application of two different ¹³⁷Cs models for estimating soil erosion rates in cultivated sites of the region. Soil samples were collected from five distinct cultivated regions subject to soil erosion. The variations of ¹³⁷Cs concentrations with depth in soil profiles were investigated. Soil loss rates were calculated from ¹³⁷Cs inventories of the samples using both proportional model (PM) and simplified mass balance model (SMBM). When PM was used, erosion and deposition rates varied from −15 to −28 t ha⁻¹ year⁻¹ and from +5 to +41 t ha⁻¹ year⁻¹, respectively; they varied from −16 to −33 t ha⁻¹ year⁻¹ and from +5 to +55 t ha⁻¹ year⁻¹ with SMBM. A good agreement was observed between the results of two models up to 30 t ha⁻¹ year⁻¹ soil loss and gain in the study area. Ulukent, a small representative agricultural field, was selected to compare the present data of ¹³⁷Cs techniques with the results obtained by universal soil loss equation (USLE) applied in the area before.