查看更多>>摘要：Among the buried urban Anthrosols and Technosols, urban Dark Earth composes a major challenge to urban archaeologists and soil scientists. These homogeneous units are often the result of a complex formation history, involving human actions and natural processes. In order to understand the significance of the late medieval to pre-industrial urban Dark Earth observed on the site of Mundaneum in the historical centre of Mons (Belgium) an integrated soil micromorphological and phytolith study has been performed. The aim of this study is to understand how the urban Dark Earth formed and to identify the major natural and human processes that are involved in its formation. The results show that major natural processes are bioturbation, sedimentation, humification, alkalinisation and clay translocation. These processes are mainly human induced. Main human activities include cereal cultivation, horticulture, dumping of waste and trampling. Phytoliths proved to be an important witness of the presence of plant material, in a context where organic remains tend to decompose rapidly. The integrated approach allowed to come to a better understanding of the taphonomical history of the phytoliths, hence permitting to distinguish plant remains related to manure, cereal processing and in situ cultivated plants. The study further permitted the authors to gain insight in part of the biography of the site and its surroundings, hence showing changes in spatial organisation and the progressive urbanisation of the area. As such, this analysis provides an important stepstone to the further geoarchaeological study of town development in Medieval and Modern periods.
查看更多>>摘要：Karst slopes have thin soil layers covering bedrock and feature multiple near-surface soil-rock interfaces (SRIs), which can produce hydrological processes that differ from those of nonkarst slopes. This study investigated the differences in the proportions of rainwater transformed into surface and belowground runoff and measured soil loss on soil-mantled karst slopes with different hydrological situations: bedrock with fissures (HS-1) and without fissures (HS-2). The rainfall intensity was 50 mm/h. Three slope gradients (5 degrees, 15 degrees and 25 degrees) were applied, and surface runoff (SR), subsurface flow (SF), underground fissure flow (UFF) and soil-rock interface flow (SRIF) were collected during rainfall. No SR was produced on 5 degrees slopes in either treatment. The proportion of rainwater absorbed by soil (RH) was approximately 34%-46% of the rainwater, with no significant differences (p > 0.05) between HS-1 and HS-2. On the 5 degrees and 15 degrees slopes, 28%-61% of the rainwater was transformed into UFF under HS-1, and 29%-50% of the rainwater was transformed into SRIF under HS-2. On the 25 degrees slope, the SRIF and UFF proportions were<18%. Bedrock fissures greatly affected the type of runoff but had little effect on the nearsurface soil water. The SR and SF amounts were 29%-67% and 3%-38% higher in HS-2 than in HS-1, respectively. Due to bedrock fissures, on average, 6% of rainwater was lost as underground flow during rainfall, and the extra rainwater, 30% on average, flowed along the SRI underground, potentially forming UFF. This difference occurs because the infiltrating rainwater that reaches the SRI can freely drain through bedrock fissures in HS-1 but not in HS-2. The soil loss via SF, SRIF and UFF was very low (<0.05 g/L). Therefore, slope gradients and bedrock fissures both have major effects on rainwater transformation, and soil loss via rainfall impact is very slow on soil-mantled karst slopes.
查看更多>>摘要：Investigations of the evolution of naturally and anthropogenically driven hydrology in arid regions are of great significance for hydrological forecasts. Here, we built the past ~500-year history of lake area and discharge of Lake Tuosu in the northeastern Qaidam Basin. We found that the lake area and inflow variations were sensitive to westerly-forced winter-spring precipitation and showed long-term decreasing trends after 1850. Enhanced local human activities (e.g., agricultural irrigation) led to further rapid shrinkage of Lake Tuosu during 1990-2000, and the lake size reached its minimum in the past ~ 500 years in approximately 2000. Our integrated moisture indices for mountains and basins in southern arid Central Asia showed opposing trends, and the humidity gradient from mountains to basins successively increased after 1850, which may be linked to the migration of the boreal westerlies, global warming, and human activities. After 1950, the humidity increased further, reaching its maximum value in approximately 2000, which likely resulted from the excessive utilization of water resources from anthropogenic activities. Therefore, the mountain-river-basin hydrological system in arid Central Asia has changed significantly, beyond the natural variation pattern, after CE 1950. Therefore, integrated management and rational utilization of water resources are important for ecological protection and sustainable development in the future.
查看更多>>摘要：Soil shear strength (SS) is an important parameter for evaluating soil erosion sensitivity and precision tillage activity. This study is ascertains how the cultivated layer SS of sloping farmland varies with soil erosion and management measures. The typical purple soil sloping farmland in the Three Gorges Reservoir Area of China was selected, and in situ tests of five erosion degrees were performed on sloping farmland using the shovel erosion simulation test method. No fertilizer (CK) was established as the control measure, and two types of restorative management measures, chemical fertilizer (F) and biochar + chemical fertilizer (BF), were established to measure SS and other soil physicochemical properties for each treatment. The results showed that cultivated layer SS had a significant response to interactions between soil erosion and management measures (P < 0.01) and was more sensitive to soil management measures than erosion. According to single-factor analysis, surface soil SS was lower than bottom soil SS; with erosion intensification, surface soil was lost, bottom soil with high SS was retained, and the SS of residual soil, following surface erosion, was 13.99% higher than that of noneroded soil. Concurrently, BF can significantly reduced topsoil SS and was 8.44% and 5.79% lower than CK and F, respectively. After correlation analysis, seven physicochemical factors significantly related to SS were retained; stepwise linear regression determined that soil bulk density and water content were the key factors affecting cultivated layer SS. Our study also showed that coarse ossification and sterility of purple soil sloping farmland could indicate the occurrence of soil erosion in the Three Gorges Reservoir Area, and biochar could restore the soil quality of erosive cultivated land to a certain extent.
查看更多>>摘要：Footpaths are of the oldest and most widely distributed forms of human imprint on the landscape. These elongated features are the result of continuous usage of a certain route for walking, at time scales ranging from days to centuries or millennia. In this qualitative investigation, we take a holistic approach combining micromorphology (including voids analysis), chemical soil parameters (such as selective iron oxide dissolution), and remote sensing (spatial distribution and orientation of footpaths in the landscape) to evaluate the long-term residues and environmental effects resulting from the formation of footpaths. Our diverse case studies incorporate footpaths used for recreational and transport purposes in temperate and sub-humid climates from both recent and historical perspectives. A reduction of the large pores was observed down to 3 cm below current and historical surfaces compared to control areas without footpaths. The lower porosity subsequently hinders of the supply of oxygen and/or water into the sub-surface and encourages water stagnation on the compacted footpath surface. These processes result in higher amounts of pedogenic Fe oxides and, at times, macro-organic residues under footpaths and hindering of soil formation. As an additional result of compaction, surface runoff is promoted. The latter may either trigger the initiation of gullies directly downslope from footpaths or lead to incision of the footpaths themselves. Incised footpaths are more likely to occur when the footpath is oriented parallel to the stream network. Once an incised footpath is formed, it may reduce gully erosion susceptibility downslope as the incised footpath acts as a channel that decreases a footpath's 'overbank' flow. With a better understanding of footpaths as landscape units we can (1) pose archaeological questions related to human environmental interaction, (2) assess carbon storage potential under footpaths and (3) use incised footpaths as possible measures against gully erosion.
查看更多>>摘要：Ecohydrological processes such as evapotranspiration (ET) and streamflow are highly variable after fire in Mediterranean systems and require accurate assessments to improve long-term risk mitigation of erosion and peak flows and revegetation strategies, especially at the small catchment scale. Using the case of the 2018 Holy Fire in southern California, we characterized 1) pre-fire rainfall and evapotranspiration conditions and 2) recovery of ecohydrological processes using a paired analysis between an unburned (Santiago) and burned (Coldwater) catchment. ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS), Operational Simplified Surface Energy Balance Model (SSEBop), vegetation indices, and local rainfall runoff data were used to characterize the sites and investigate spatial and temporal patterns of post-fire ET. Consistent with the drought conditions in California, we observed low precipitation and ET prior to the fire. Additionally, compared to other vegetation types, montane hardwood species were more likely to be classified as high soil burn severity. We also found that the high spatial and temporal resolution of ECOSTRESS provided more information about the general ET patterns. After the fire, ECOSTRESS ET was sensitive to parameters such as slope aspect, soil burn severity, and vegetation species, which has implications for post-fire vegetation recovery and water storage. This work demonstrates opportunities to apply ECOSTRESS ET across globally diverse ecoregions and small catchment scales to identify potentially high-risk areas and improve fire risk and vegetation recovery assessments.
查看更多>>摘要：It is proposed that an extremely warm, humid climate existed in the Tibetan Plateau (TP), including the currently hyper-arid Qaidam Basin (QB), during Marine isotope stage 3 (MIS 3). A detailed luminescence study of aeolian, fluvial and aeolian-fluvial records from the Tiekui Dunefield (TKD) and its margins in the eastern QB reveals paleoenvironmental and paleoclimatic changes during the MIS 3 (ca. 60-32 ka). The records, dated by post -Infrared Infrared Stimulated Luminescence (pIRIR), provide the first aeolian MIS 3 ages in the QB thanks to preservation by overlaying fluvial deposition in the dunefield margins and demonstrate the aeolian expansion of the TKD compared to its modern extent. Complemented by aeolian records in nearby regions, these deposits reflect intensified dune activity in an arid and windy climate and with adequate glacier-derived alluvial -domi-nated sand supply. These results do not support a significant increase in precipitation from the Asian Summer Monsoon (ASM). Comparisons of new ages derived from pIRIR and Optically Stimulated Luminescence (OSL) of quartz in this study suggest that some published quartz OSL ages of the QB may be underestimated, even below 90 Gy (ca. 30 ka, with normal dose rates of 2.8 Gy/ka). The revised chronology questions previously suggested hypotheses of the existence of a mega Qaidam Lake in the upwind reaches of the basin, under an extremely strong ASM during the MIS 3. We propose a conceptual aeolian-fluvial geomorphic model that demonstrates the paleoclimatic value of aeolian-fluvial records and where and how fluvial process can erode or preserve ancient and previously untapped aeolian records.
查看更多>>摘要：Few data are available on how soil erosion rates compare between surfaces of different ages because short-term processes often overprint the longer-term erosion signal. This study investigated the soil dynamics among two end-member sites, a formerly glaciated ('young', maximum glacial extent at 22-30 ka BP) and a non-glaciated ('old') area at the Serra da Estrela (Portugal). To disentangle soil distribution rates over different timeframes, isotopes for long-term (10Be), mid-term (delta C-13) and short-term (239+240Pu) periods were applied together with principles of the percolation theory.& nbsp;The formerly glaciated area has soils with a lower degree of weathering and lower carbon content compared to soils of the 'old', non-glaciated area. The selected isotopes and their distribution along the soil profiles revealed temporal differences in soil mixing process. It is hypothesised that the slightly higher elevation and formerly glaciated sites experienced cryoturbation effects over a longer period, while being less active or absent for the last few decades at the older, non-glaciated soils.& nbsp;The average long-term (millennia) soil erosion rates correspond to the expected higher rates at the younger surface and lower rates at the older surface. Once the formerly glaciated area became ice-free, soil erosion rates were high and decreased giving rise to average long-term rates of 101-140 [t km(-2) yr(-1)] for the older surfaces and 176-248 [t km(-2) yr(-1)] for the younger surfaces. In addition, seasonal freeze-thaw of the soils has persisted over a long period and affected the younger soils more intensively than the older soils. The current (last decades) soil redistribution rates, however, are up to one order of magnitude higher than the millennia rates and are controlled by surface angle and vegetation cover and less by soil texture. The more undulated, non-glaciated older surface had the highest short-term (decades) soil erosion rates in the range of 900-1700 [t km(-2 & nbsp;)yr(-1)], exhibits degrading conditions and relatively shallow soils. The younger soils, however, showed short-term (last few decades) average soil deposition rates of ~ 230 [t km(-2) yr(-1)]. Human impact (bush fires, grazing) is the cause for the currently strong soil degradation at the non-glaciated area.
查看更多>>摘要：Soil carbon (C) sequestration plays a vital role in mitigating global climate change. Human activities have vastly increased nitrogen (N) deposition rate in China, which in turn influences belowground C cycle processes. We performed a meta-analysis based on 61 published studies on N addition experiments, including 4072 observations across China, to quantify the responses of belowground soil C dynamics and sequestration to N enrichment in Chinese forest ecosystems. The results showed that, on average, N enrichment significantly enhanced C dynamics in boreal and temperate forests by an average of 24% and 10% while it reduced in subtropical and tropical forests by 11% and 19%. The response of C pools and C input to N addition were more pronounced in boreal forests with +17% and +10% while it was lower in subtropical forests with-0.4% and-19% respectively. The N enrichment enhanced soil C output by in boreal (6%) and temperate (7%) forests and a negative effect in subtropical (-30%) and tropical forests (-10%). This can be explained by the higher reduction levels in C respiration, despite the slightly lower litter and root-derived C inputs. Notably, N addition specifically increased belowground C sequestration, at low N addition rates (< 30 kg N ha-1 yr-1) and during a short-term period (< 1 year). These C sequestration effects were reversed at higher N deposition levels and /or during a longer time period. This implies that soil C sequestration is currently most likely not enhanced in (large) parts of China, as forests are characterized by long-term elevated N deposition levels.
查看更多>>摘要：Wind erosion is a typical natural hazard in arid and semiarid regions. In recent decades, China has shown significant changes of greening trend due to a range of several ecological restoration projects (ERPs), Meanwhile, the wind erosion in northern China changed significantly. The debate about whether climatic change or ERPs dominated the variations in wind erosion was never truly resolved, which seriously affect the deployment of ERPs in the future, and it is a concerns of both academia and the Chinese government. To address this debate, we distinguished the ERPs' effects on wind erosion from the climate change background by modeling the wind erosion under the different surface vegetation scenarios with the revised wind erosion equation (RWEQ) that was validated by our field observations. The simulated results shown that relative to the benchmark year (2000), the ERPs caused a rate of decrease of 17.77% of wind erosion modulus (WEM) in northern China during the period of 2001 to 2019, which occupied approximately 61% of the total decrease of WEM by ERPs and climatic fluctuations. This result means that the ERPs played the dominant role in wind erosion decreasing overall. Considering the effects of ERPs to wind erosion, the wind erosion intensity, the climatic fluctuation, and vegetation carrying capacity, this study concluded that the Gurbantunggut Desert, the Otindag Sandy Land, the Lop Nor, the Gashun Gobi Desert, the Mongolia Gobi Desert and the Hexi Corridor are the potential regions for ERP deployment in the future. We believe this study should provide robust evidence to resolve the debate on what dominates the variations in wind erosion processes in northern China, and give the valuable suggestions for ecological restoration project deployment in the future.
NSTL
Elsevier