查看更多>>摘要：? 2022 Elsevier B.V.The dendrogeomorphic dating of past landslides can be limited by the speed or magnitude of movements, as they are sometimes too small to induce growth responses in trees standing on unstable slopes. As a result, movements of low magnitude are generally assumed to remain undetectable in standard macroscopic analysis of growth disturbances in tree-ring series. To close this gap and to enlarge the suite of approaches available for the dendrogeomorphic detection of landslide activity in growth-ring records of trees, this study focuses on the detection of wood-anatomical growth responses in trees following low-magnitude landslides. Anatomical growth responses of five individuals of common spruce (Picea abies (L.) Karst.) growing on a monitored landslide have been analyzed in this study on a total of 200 tree rings from 40 increment cores extracted at two vertical levels of tree stems. Analysis included seven anatomical parameters commonly used in quantitative wood anatomy, with a focus on the year 2017 year during which the landslide body moved by 8 mm (prior to the start of the growing season) according to extensometer records. We report that mean tracheid lumen area (TLA) decreased significantly due to landsliding, whereas the mean number of traumatic resin ducts (TRD) and rays increased significantly after the occurrence of the landslide. By contrast, the intensity of stem tilting was visibly too small to induce the formation of compression wood but strong enough to induce larger number of rays, which are known to enhance stability as well. We also realize that the low intensity of the landslide movement also resulted in rather localized anatomical anomalies along the stem, with detected responses decreasing in intensity with increasing distance from the ground. We conclude that anatomical responses of P. abies trees can be used to detect past activity in low-magnitude landsliding and that this new proxy can thus extend the applicability of tree-ring approaches to landslide research and to the detection of events that have hitherto remained unidentified in reconstructions.
查看更多>>摘要：? 2022 Elsevier B.V.Wastewater discharge and salt marsh invasion are two main disturbances in global mangrove wetland ecosystems, but their combined effects on greenhouse gas (GHG) emissions remain unclear. Here, we performed a laboratory incubation experiment by adding wastewater (aquaculture and domestic wastewater) to mangrove and salt marsh sediments. Dissolved GHGs (CO2, CH4 and N2O) and environmental parameters were measured over a time series of 50 days. The nitrification and denitrification rates and corresponding functional gene abundances (AOA, AOB, nirS, and narG) were also quantified. The results show that wastewater addition significantly increased GHG emissions and global warming potential (GWP) in wetland sediments (p < 0.05 for both). Compared with mangroves, salt marsh sediments produced more carbon GHGs (CO2 and CH4) but less N2O after wastewater input. These different stimulatory effects could be explained by the nitrogen and carbon substrate availability, organic matter quality, and functional gene abundances in sediments. Assessing GHG emissions as CO2 equivalents, future scenarios of increasing salt marsh invasion with wastewater addition would increase the GWP caused by CO2 and CH4, decrease blue carbon sequestration potential in wetlands, and decrease the GWP caused by N2O and total GWP, indicating a great impact on global climate change and important implications for managing coastal wetlands.
查看更多>>摘要：? 2022 Elsevier B.V.Soil organic carbon (SOC) on the Qinghai-Tibet plateau is of global significance, due to the high carbon density and potential positive feedbacks to climate warming. Qinghai Lake watershed is an important soil pool in Qinghai-Tibet plateau, but the magnitude and characteristics of SOC stock in the high-altitude basin were not clear. To understand better how much SOC was stored and its spatial patterns in the watershed, this study analyzed the vertical variation of SOC content, quantified its influence by varied environmental factors, and further predict its storage in the entire basin. Results showed that, the SOC content decreased with the increasing depth, and was the highest in the alpine meadow in all depths, following by the alpine steppe and temperate steppe, respectively. It was generally higher in the permafrost region than that in the non-permafrost region at all depths. Soil profile depth, soil water content and NDVI could together explain about 72.6% of total variation in SOC density. The regression-kriging method was the best upscaling approach for the prediction of SOC in the study area. Approximately 317 Tg organic carbon was stored in the entire soil profile of Qinghai Lake watershed, in which 136, 140, and 41 Tg were at 0–30 cm, 30–100 cm, and below 100 cm, respectively. The higher SOC density mainly appeared on the northeast and southern region of Qinghai Lake, while the high-altitude area in the northwest of the watershed had the lower values. Moreover, it increased firstly and then decreased with the increase of altitude, with the maximum values at 3350–3400 m, which was dominated by the elevational variation of soil profile depth and NDVI. Overall, the comprehensive assessment of SOC demonstrated high storage and strong heterogenicity of soil carbon in the Qinghai Lake watershed, and it is critical for the sustainability of regional terrestrial ecosystem with future climate change.
查看更多>>摘要：? 2022 Elsevier B.V.Assessing regional sediment yield variation and their responses to the potential controlling factors are critical to develop specific strategies of soil conservation measures to adapt to future climate change. This study attempted to investigate the spatial–temporal variation of sediment load in the Wei River basin in the midstream of the Yellow River during 1961–2015 at 15 hydrological stations. The results indicated that annual sediment load in the past six decades decreased significantly (P < 0.01) with the changing trends of ?6.43 × 104, ?3.86 × 104, ?4.6 × 104 t/a at Xianyang, Zhangjiashan, and Zhuangtou stations, respectively. Annual sediment load exhibited abrupt changes in the mid-1990s, which were largely attributed to the strong effects of soil conservation measures in the study area. The spatial pattern of soil erosion were characterized by high sediment yield in the north with sparse vegetation cover and well-developed gullies, and low sediment yield in the south with flat plain and good vegetation cover in the Wei River basin. The results of the partial least squares-structural equation model (PLS-SEM) showed that vegetation changes and rainfall variability explained 62.3%, 47.3%, and 40.1% of the variation in runoff at Xianyang, Zhuangtou, and Zhangjiashan stations, respectively, whereas 59.4%, 17.6% and 48% of the variation in sediment load were explained by the combining effects of rainfall variability, changes of vegetation and runoff. This study provides a deep insight for understanding the effects of driving forces on sediment yield changes, and can be useful to regional soil conservation planning in the region.
查看更多>>摘要：? 2022 Elsevier B.V.The Hengduan Mountains are frequently disturbed by high-risk wildfires. However, insufficient information is available on post-fire temporal trends in soil properties and revegetation of areas with various fire severities. To address this gap, two adjacent wildfires that occurred in 2010 and 2018 were selected. The study areas were divided into low (LS), moderate (MS), high (HS) severity fire burned areas and unburned (as control, UB) areas. Temporal trends in soil properties (0–5 cm): soil water repellency, saturated hydraulic conductivity, bulk density, soil moisture content (SMC), and soil organic matter content (SOM) were measured by in-situ and laboratory tests at 1, 7, 19 months (1MAF, 7MAF, 19MAF), and 10 years after the fires (10YAF), respectively. Temporal trends in post-fire revegetation were evaluated via on-ground surveys and remote sensing images. The statistical analysis results showed that the HS and MS fires significantly altered the soil properties and resulted in a remarkable decrease in vegetation coverage, leading to substantial bare soil 1MAF. The soil properties of the HS and MS fire burned areas had not recovered to normal due to the significantly decreased SOM and SMC 7MAF and 19MAF, and they had recovered to the pre-fire level 10YAF. The first three years following the fires were a crucial period for revegetation, during which the shrubs and bryophytes rapidly recovered, causing a rapid increase in vegetation coverage, and a corresponding sharp decrease in the coverage of bare soil. The incompletely recovered pines of the HS and MS areas provisionally resulted in a degeneration of the forest stand within a decade after the fire. We conclude that the fire-affected soil properties can return to normal within 10 years, and complete recovery of the vegetation requires a longer period than a decade. These results may provide scientific guidance for post-fire management of the burned area.
查看更多>>摘要：? 2022 Elsevier B.V.The cover management factor (C-factor) calculation requires the assessment of the intra-annual spatiotemporal variability of biomass cover, owed to the natural growth cycle of vegetation and the impact of agriculture on land cover. However, this is frequently omitted, and the vegetation conditions are approximated by assigning constant values to static classified Land Use/Land Cover (LULC) maps, such as the Coordination of Information on the Environment (CORINE) Land Cover (CLC). Using as test site the Sperchios River catchment, Central Greece, this study introduces a new approach to estimate C-factor in a spatiotemporally exhaustive manner. The goal is to increase estimation accuracy in erosion modelling applications. The C-factor computations are performed on monthly scale, based on LULC maps that portray the basin's agricultural areas in unprecedented detail. The methodology involves the use of a biophysical index, namely Fraction of Vegetation Cover (Fcover) and empirical literature data on crop types. Fcover was developed from Sentinel-2 (S2) imagery in 10-m analysis. Such analysis (compared to the 300-m one provided by the EU) is a major improvement towards a more precise estimation of C-factor. The study identified the monthly C-factor fluctuation at basin scale, and the most susceptible months seasons at localities in terms of land cover/soil loss potential. The higher C-factor values were acquired in October and the lower in May. Mean annual (numerical) C-factor complies with the value of July. All monthly values are significantly higher – almost double – than the mean annual stationary one. The revealed patterns would not have been detected in a lower temporal (e.g., annual) resolution without the incorporation of vegetation density seasonality. The study shows high reproducibility and upscaling potential, as the utilized datasets are available in all European Union (EU) Member States, having similar structure, thus they can be harmonized towards a unified continental approach.
查看更多>>摘要：? 2022 Elsevier B.V.An integrated multiproxy dataset involving both mineralogical and geochemical investigations of the northern Tibetan Plateau helps in assessing regional weathering processes linked to topographic evolution and environmental change. However, changes in landscape and drainage reorganizations caused by active tectonics and remarkable climate change during the Cenozoic characterize the basins in and around the Tibetan Plateau by frequent facies changes and coarse lithologies, which largely limit the reliability of bulk geochemical indicators for revealing the regional weathering history. Here, we present detailed geochemical investigations of clay-sized sediments collected from the Hongliugou section (54–26 Ma) in the northern Qaidam Basin to reconstruct high-resolution chemical weathering records of the northern Tibetan Plateau. To prevent chlorite bias when calculating the chemical index of alteration (CIA) in the clay-sized sediments, we propose a modified CIA formula (CIAMg+), in which Mg is added as a soluble cation that can be removed during weathering, similar to Na, K and Ca; thus, CIAMg+ = Al2O3/(Al2O3 + Na2O + K2O + CaO* + MgO) × 100. The CIAMg+ and illite chemistry indices are generally the highest values in the early Eocene Climate Optimum (～52–49.5 Ma) and a long-term decreasing trend is present from ～ 49.5–26 Ma; the Mg/Al ratios of the clay-sized sediments and hydrochloric acid leachates are the lowest during the EECO and present a long-term increasing trend in the following 49.5–26 Ma, thus collectively indicating a continuous decrease in the regional chemical weathering intensity. The weakening weathering process during the Paleogene is mainly attributed to the decreasing global temperature and decline in precipitation caused by global cooling. Our study suggests that the proposed geochemical index based on clay-sized sediments can serve as an efficient proxy for regional chemical weathering reconstruction, even in thick sedimentary sequences with frequently changing facies and lithology.
查看更多>>摘要：? 2022 Elsevier B.V.A debris flow flowing into a river may cause river blockage and form a dam. When the dam breaks, large floods can occur in the areas downstream, which can lead to fatalities and property damage. In this study, the parameters of river blockage were classified as three types of factors: morphological factors, dynamic factors, and characteristics factors of debris flows. The confluent angle, the dimensionless volume, the unit discharge ratio, and the dimensionless yield stress are important parameters for river blockage. They are all independent and dimensionless parameters. The degree of river blockage was divided into 4 stages: minor blockage, partial blockage, major blockage, and complete blockage. A classification based on the blockage coefficient is proposed to assess the degree of blockage. An experimental study was conducted with a total of 61 experimental runs. Based on the blockage coefficient of each run of the tests, the relationships between the degree of blockage and the key parameters (i.e., the confluent angle, the dimensionless volume, the unit discharge ratio, and the dimensionless yield stress) were obtained. A prediction model of the degree of river blockage is proposed based on these relationships. The area total of 21 debris flow tributaries and their corresponding rivers in China were selected to validate the prediction model. In these 21 tributaries, 24 events involving a debris flow flowing into a river resulted in partial blockage, major blockage, and completely blockage of the rivers. The prediction model was successful validated using the 22 events in China involving partial blockage, major blockage, and complete blockage.
查看更多>>摘要：? 2022 Elsevier B.V.The transitional characteristics of desert grasslands in the Sahel determine the ecosystem's fragility, which is extremely susceptible to the expansion and reversal of land desertification under the influence of climate change and anthropogenic activities. Accordingly, monitoring desertification dynamics is essential to combat this process. Based on Moderate Resolution Imaging Spectroradiometer (MODIS) data, this study analysed the applicability of different feature space models to monitor desertification levels in the Sahel from 2000 to 2020, revealing the optimal monitoring model, analysing the spatiotemporal changes and primary driving factors. The results were as follows: In the Sahel, the albedo-modified soil adjusted vegetation index (MSAVI) based on the point-to-point model is the best for desertification monitoring, with an overall accuracy of 86.78%. Generally, the level of desertification was reduced from 2000 to 2020, the area of extremely severe desertification decreased by retreating northward; and the areas of light, moderate, and severe desertification increased slowly by expanding northward. Light, moderate, and severe desertification lands were more sensitive to climate change and anthropogenic activities, undergoing greater change intensity. Precipitation was the most influential factor determining the spatial distribution of desertification in the Sahel, with anthropogenic activities also having a significant effect on the desertification level. This study comprehensively analysed desertification patterns in the Sahel and identified the primary driving factors, which are essential to inform Sahelian desertification control mechanisms in the future.
查看更多>>摘要：? 2022 Elsevier B.V.Due to global changes and anthropogenic disturbances shrubs are widely encroaching into alpine meadows, which may have profound impacts on the ecohydrological functioning of these key ecosystems. This phenomenon is particularly alarming in the alpine meadows of the Qinghai-Tibetan Plateau, the headwaters for many of Asia's largest rivers. However, little is known about the extant in which shrub encroachment alters the infiltration capacity of those soils. Here we examined the effects of shrub encroachment on the plant community and soil infiltration processes by contrasting vegetation and infiltration variables between three areas: a reference alpine meadow, an alpine meadow lightly encroached by smaller shrubs, and an alpine meadow heavily encroached by larger shrubs. We found that shrub encroachment reduced herbaceous plants aboveground biomass by 10–24 g m?2 and root biomass by 1346–2239 g m?2. The sedge functional group was gradually replaced by forbs. Initial infiltration rates gradually increased with shrub encroachment, and were approximately doubled and tripled at the earlier and later stages of encroachment, respectively. Overall, shrub encroachment improved the soil infiltrability by changing soil conditions and inhibiting herbaceous species due to the reduction of surface mattic epipedon and the formation of dead root channels. These findings suggest that the rapid transformation of alpine meadows into shrublands could have drastic effects on the surface runoff and streamflow dynamics of the Qinghai-Tibetan Plateau.
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