查看更多>>摘要：? 2022The Younger Dryas (YD) is a roughly 1,100-year cold period marking the end of the last glaciation. Climate modelling for northern Europe indicates high summer temperatures and strong continentality. In eastern Europe, the scale of temperature variation and its influence on ecosystems is weakly recognised. Here, we present a multi-proxy reconstruction of YD conditions from Lake Go?ci?? (central Poland). The decadal-resolution analysis of its annually varved sediments indicates an initial decrease in Chironomidae-inferred mean July air temperature followed by steady warming. The pollen-inferred winter-to-summer temperature amplitude and annual precipitation is highest at the Aller?d/YD transition and the early YD (ca. 12.7–12.4 ky cal BP) and YD/Holocene (11.7–11.4 ka cal BP) transition. Temperature and precipitation were the main reasons for lake level fluctuations as reflected in the planktonic/littoral Cladocera ratio. The lake's diatom-inferred total phosphorus decreased with increasing summer temperature from about mid YD. Windy conditions in the early YD until ～12.3 ka cal BP caused water mixing and a short-lived/temporary increase in nutrient availability for phytoplankton. The Chironomidae-inferred summer temperature and pollen inferred summer temperature, winter temperature and annual precipitation herein are one of only a few in eastern Europe conducted with such high resolution.
查看更多>>摘要：? 2022 Elsevier B.V.Soils from maritime Antarctica store important information about initialization of pedogenesis and role of the major factors of soil formation. Deciphering the interplay among all contributing agents is however challenging and needs involvement of an interdisciplinary approach. The main aim of our study is to contribute to this goal by assessing mineral magnetic signature of a collection of topsoils from Livingston Island and investigate the major contributing factors, determining their magnetic properties. A set of 23 soil samples from Hurd Peninsula at Livingston Island were studied. Magnetic susceptibility and frequency dependent magnetic susceptibility measurements, anhysteretic remanent magnetization, hysteresis measurements at room temperature and low temperatures were carried out. Identification of magnetic minerals was achieved through thermomagnetic measurements of magnetic susceptibility and analysis of Isothermal Remanence acquisition. Magnetic measurements were supplemented by geochemical analyses of total elemental composition by X-ray fluorescence spectrometry and selective Fe- and Al- extractions by Dithionite-Citrate-Bicarbonate and ammonium oxalate. Magnetic results indicate that composition of iron oxides in soils differs significantly from that of bedrocks by the presence of titianomagnetite fractions with high- and medium Ti-content, while rocks’ mineralogy is dominated by paramagnetic minerals or by coarse grained multi-domain magnetite. Titanomagnetite phases were ascribed to the input of tephra additions from the nearby Deception Island. Based on the magnetic susceptibility measurements at low temperatures it was concluded that a fraction of fine grained magnetite is present in soils, in addition to titanomagnetite. Geochemical data reveal differences between the composition of soils and main rock lithologies, which is also assigned to tephra input. Amount of ammonium-oxalate extractable iron and aluminum were higher than that extracted by dithionite, which was attributed to fast tephra weathering in cold polar climate.
查看更多>>摘要：? 2022 The AuthorsGully erosion is one of the most destructive geomorphological processes on relatively flat surfaces. This is exacerbated in the Arctic regions, where gullies are referred to as thermo-erosion gullies because of their unique connection to permafrost. As the surface of the permafrost freezes and thaws, soil particles destabilize, inducing erosion along preferential incisions, giving rise to widespread thermo-erosion gullies. In this study, we present the first thermo-erosion gully inventory in the Svalbard region (Nordenski?ld Land). The inventory was created using a combination of available aerial photographs from 2009 to 2011, direct field observations and measurements. The spatial distribution of thermo-erosion gullies is then exploited to investigate potential threats to the Arctic cultural heritage (CH). Analyses of thermo-erosion gullies are increasingly important for artic administrations, which require more detailed hazard assessments as the effect of climate change becomes increasingly evident across these landscapes. The inventory is comprised of 810 thermo-erosion gullies in Nordenski?ld Land, most of which are located in close proximity to coastlines. We assess the inventory size statistics and correlation with terrain characteristics to investigate potential predisposing factors. No gullies occurs at elevations greater than 200 m a.s.l., but gullies occur up to a maximum steepness of 37 degrees and along the whole topographic profile and, looking at the potential threat to CH, we found 44 of these sites within a 100 m buffer from the gullies. This distance is the reference that local administrations use to prioritize actions and safeguard the existence of artic CH sites. In fact, a 100 m distance implies that future evolution of thermo-erosion gullies, especially enhanced by climate change may eventually erode away soil from the CH surroundings, threatening their stability and existence.
De Girolamo A.M.Lo Porto A.Cerdan O.Grangeon T....
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查看更多>>摘要：? 2022 Elsevier B.V.The present paper contributes to bridging the gaps in modelling post-fire impact and mitigation measures on soil erosion. The specific aims were to predict the effects of forest fires and post-fire mitigation measures on runoff and specific sediment yield (SSY) in a river basin (Celone, S-E Italy). The Soil and Water Assessment Tool model, calibrated with field observations, was used to evaluate runoff and SSY for the current land use (baseline) and six post-fire scenarios. From 1990 to 2011, at the basin scale, the average annual SSY was 5.60 t ha- 1yr?1 (SD = 3.47 t ha-1yr?1). 20% of the total drainage area showed a critical value of SSY (>10 t ha?1 yr?1). The effects of different fire-severity levels were predicted for one year after the fire, acting on a limited area (2.3% of the total basin area). At the basin scale, the post-fire effect on surface runoff was negligible for all scenarios (<0.4%), and the impact on SSY increased from 5.86 t ha?1 yr?1 up to 12.05 t ha?1 yr?1. At the subbasin scale, the post-fire logging scenario showed the highest increase of soil loss (SSY increased from 9.48 t ha?1 yr?1 to 57.40 t ha?1 yr?1). Post-fire mitigation treatments like straw mulching and erosion barriers effectively reduced soil erosion in high- and moderate-severity fires (19.12 t ha-1yr?1 and 20.93 t ha?1 yr?1, respectively). At the hydrological response unit level, the SSY estimated for the forest in the baseline ranged from 1.18 t ha- 1yr?1 to 2.04 t ha?1 yr?1. SSY increased more than one order of magnitude for the high-severity fire scenarios and ranged from 4.33 to 6.74 t ha?1 yr?1 in the very low-severity fire scenario, underlining the scale effect from the HRU to the basin scale.
查看更多>>摘要：? 2022 Elsevier B.V.The delayed response of channel evolution upstream of dams to base-level changes has not yet been thoroughly understood. In this paper, we studied the delayed response of the morphological adjustment at the middle Yellow and lower Wei Rivers upstream of the Sanmenxia Dam, China, based on data of water volume, sediment load, cross-sectional profiles, and erosion/deposition volumes during 1960–2018. Channel evolution upstream of the dam obviously lagged behind the dynamic pool level fluctuation during the first approximately two decades following dam closure, when retrogressive aggradation/erosion phases were identified. The retrogressive aggradation migrated ～200 km upstream to the tributary of the Yellow River, i.e., the Wei River. The impact of base-level rise may propagate backwards behind the beginning of the backwater reach, reflecting indirect backwater effects. The dam has been operated by the controlled release of “storing the clear water during nonflood seasons and discharging the turbid water during flood seasons” since 1974, and the reservoir has generally been eroded during flood seasons and aggraded during nonflood seasons. The erosion center was defined as the subreach between two adjacent cross-sections with the greatest erosion rate during the flood season, and the aggradation center was defined as that with the greatest aggradation rate during the nonflood season. The results showed that the erosion/deposition centers migrated towards the dam by ～50–60 km during 1974–2010 and migrated upstream after ～2010. The location of the erosion/deposition centers was related not only to the water and sediment conditions and backwater length in the current year but also to these conditions in the previous ～4 years, reflecting the delayed response of channel adjustment or the cumulative impact of pervious conditions on channel morphology. This study helps to inform future reservoir management and the delayed channel response to base level change caused by different natural and anthropogenic disturbances.
查看更多>>摘要：? 2022 Elsevier B.V.Snow-affected mountainous areas are highly vulnerable to climate changes in arid and semi-arid regions. Previous studies have put more emphasis on runoff, however, research about snow hydrological processes is still insufficient. Based on the optimization of calibration strategies, this study aims to provide a more realistic simulation of snow hydrology by coupling both a lumped rainfall-runoff model (GR6J) and a semi-distributed snow model (CemaNeige). Compared with calibration using only runoff, the multi-objective calibration with both runoff and snow not only significantly improved the KGE (Kling-Gupta efficiency) of snow from 0.34/0.47 to 0.67/0.69 during the calibration/validation period, but also slightly improved the KGE of runoff from 0.84/0.75 to 0.86/0.78, respectively. Additionally, we also found that the calibration using only runoff may underestimate snow cover (41%) and overestimate snowpack (20%), while there is little discrepancy in snowmelt and runoff. Snowmelt runoff is 57.7 mm accounting for 26% of the annual runoff. In the historical period (1980–2011), the runoff varied with a positive trend of 2.15 mm year?1 (p < 0.1), while its tendency became negative in the future. A 15% to 30% decline in runoff was projected for SSP370 (SSP3-RCP7) and SSP585 (SSP5-RCP8.5) in the 2085s (2070–2100) compared with that in the 1985s (1970–2000). Through further study on seasonal variations, we found that the future runoff decline is probably due to mild rise in rain not enough to alleviate the larger AE (actual evaporation), and for the runoff and AE we also found the variations in summer dominated the annual changes. In response to global warming, SCED (snow cover end date) advances while SCOD (snow cover onset date) recedes in all four scenarios as the year increases. Generally, coupling different hydrological models and multi-objective calibration strategies is vital for understanding the hydrological processes in snow-affected catchments.
查看更多>>摘要：? 2022 Elsevier B.V.Low-frequency heavy rainfall events commonly trigger debris flows. However, it is not currently understood how high-frequency, light rainfall can trigger giant catastrophic debris flow events with return periods of greater than 100 years; for example, the 2014 event in the Erkazi gully (EKZG), Danba County, Sichuan Province, China. This study uses the EKZG debris flow as a case study to determine the main factors controlling the formation of low-frequency debris flows and their generation by high-frequency light rainfall through field investigations, indoor and outdoor experiments, simulated calculations, and statistical analysis. We revealed that the soil mass predominantly controlled the generation of the EKZG debris flow. Moreover, internal geological factors such as earthquakes and external geological factors such as dry-wet cycles and freeze-thaw erosion likely dominated the EKZG debris flow formation process. In contrast, the geomorphological characteristics, basaltic columnar jointing, and earthquakes jointly determined the amplification process of the debris flow. Furthermore, we discussed the critical role of community-based warning systems during debris flow disasters. For example, early identification of the blocking characteristics of the EKZG debris flow by observers enabled the successful real-time evacuation of 651 people. The following recommendations are proposed: (1) future research should focus on the dynamic replenishment process of the soil mass through dry-wet and freeze-thaw cycles, and (2) the effectiveness and applicability of community-based warning systems should be improved for the prevention and mitigation of geological hazards.
查看更多>>摘要：? 2022 Elsevier B.V.Information on Quaternary landscapes and paleoenvironmental changes in the interior of Brazil are scarce. One of such areas, particularly sensitive to these variations, is the modern tropical Pantanal wetland, whose alluvial deposits record paleoenvironmental and paleoclimatic changes during the late Quaternary. Based on detailed pedological and sedimentological descriptions, stimulated optical luminescence dating and analytical data we described a well-exposed sedimentary succession that crops out in slope terraces of the Aquidauana River, located in the southern area of the Pantanal. We interpret environmental changes that have occurred since the beginning of the Upper Pleistocene, and which affected sedimentation and biogeochemical processes. Basal deposits comprise cross-stratified sands, which record active fluvial sedimentation from ～106 to ～70 ka, a period of probable increased river discharge. Fluvial channel facies are overlaid by pedogeneized floodplain deposits, in which we recognized a pedocomplex composed of a sequence of three late Pleistocene truncated paleosol profiles and a Holocene soil profile. The two lower paleosols are Vertisols with mottling, slickensides, rhizolites and septarian glaebules of carbonate. These characteristics indicate prolonged drought periods under semi-arid to arid climates ca. ～70 and ～30 ka. The upper paleosol profile is a Planosol (Ultisol) with block structure, waxiness, iron glaebules, and manganese films, pointing to prevailing humid climates during the terminal Pleistocene (since ～30 ka). Covering this truncated Planosol is a layer of fine to medium-grained Holocene sands, with development of a horizon A of an Arenosol (Entisol). These paleoenvironmental changes correlate with regional changes in precipitation deduced from speleothems in nearby plateaus and in southeastern Brazilian sites.
查看更多>>摘要：? 2022 Elsevier B.V.This study explores climatic influences contributing to apparently unreliable 14C ages from loess organic materials. The relationship between anomalous 14C ages and climate suggests that young/old 14C age deviations correspond to wet/dry climate periods. Based on stepped-temperature combustion results, we found that the ratio of refractory (old)carbon liberated at high temperature (HT)(>900 °C) from loess deposited during a dry period can reach 70% of the total organic carbon (TOC). This high temperature fraction is known to contain aged carbon and can explain age reversals with respect to underlying sediments. Thus, after removing HT fractions, the 14C ages of LT fractions is relatively reasonable. In contrast, the ratio of young carbon from the low temperature fraction (LT) (<400 °C) is as high as 85% during a wet period. Mobile carbon that percolates downward in the sediments may result in younger TOC 14C ages. In our study region, the 14C ages of HT fractions are not absolutely reasonable after removing LT fractions. Once the 14C ages of TOC are used to establish age model, the influence of different climate types on the source of sediment organic matter should be taken into consideration. In summary, Climate and material are the main factors causing the 14C age deviations (unreliability) in loess from the Xinjiang region.
查看更多>>摘要：? 2022 Elsevier B.V.Dinitrogen (N2)-fixing woody plants, mainly alder (Alnus) species, have widely expanded to boreal peatlands. However, little is known about the effect of N2-fixing plant expansion on soil phosphorus (P) dynamics and its potential mechanisms in these ecosystems. To clarify the response of soil P status to N2-fixing plant expansion, we compared the differences in aboveground plant biomass, soil total P pool, acid phosphatase activity, P sorption index, and four bioavailable P fractions (CaCl2, citrate, phosphatase enzyme, and HCl extractable P fractions) in the 0–10 cm, 10–20 cm, and 20–40 cm depths between A. sibirica islands and adjacent open peatlands in a boreal peatland, Northeast China. While alder expansion hardly affected bulk density and associated volume of the peats, it strongly decreased total P pool in the 0–40 cm soil depth because of approximately ninefold increases in aboveground plant biomass and associated P transfer from soils to plants. Soil total P concentration increased in the 0–10 cm depth, but declined in the 10–20 cm and 20–40 cm depths. At each depth, alder expansion increased soil acid phosphatase activity, and CaCl2 and enzyme extractable P fractions, despite unchanged P sorption index and citrate extractable P fraction. Both CaCl2 and enzyme extractable P fractions correlated positively with acid phosphatase activity, indicating that increased P bioavailability was primarily caused by elevated microbial mineralization of organic P. These findings highlight the contrasting responses of soil P pool and bioavailability to N2-fixing tree expansion, and suggest that N2-fixing tree expansion would reduce soil P pool via enhanced P bioavailability and subsequently increased plant P uptake in boreal peatlands.
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