Vegetation plays an important role in the dry deposition of particles with significant spatial variability, but the magnitude remains unclear at the global scale. With the aid of satellite products, this study estimated the vegetation-related dry deposition of fine particulate matter (PM2.5). Methodologically, dry deposition was first calculated using an empirical algorithm. Then, deposition on the leaf surface was estimated to evaluate the influence of vegetation. Our results showed that the mean deposition velocity (Vd) of global PM2.5 was 0.91×10?3 µg·m?2·s?1, with high velocities observed in sparsely vegetated regions because of the high friction velocity. Under the combined effect of the PM2.5 mass concentration and deposition velocity, the global mean dry deposition reached 0.47 g·m?2·yr?1. Global vegetation absorbed 0.26 g·m?2·yr?1 from PM2.5 pollution sources, contributing 54.98% of the total dry deposition. Spatially, vegetation-related dry deposition was high in the Amazon, Central Africa and East China due to dense vegetation coverage or serious pollution. Temporally, the increasing trends were mainly in Central Africa and India because of worsening air pollution. The results of this study helped to clarify the impact of vegetation on air pollution, which supported related land management and planning for air quality improvement.
Due to the atmospheric nuclear weapon tests carried out, terrestrial environments have been extensively contaminated by global fallout of plutonium (Pu) worldwide. The 249+240Pu inventories in soil profiles from undisturbed and flat forest or grasslands (reference sites) mainly from Europe and Asia are considered as important background for evaluating soil erosion. Thus, we conducted a literature survey over an area extending from 2.6°W to 148.9°E and from 53.2°S to 76.6°N, with the purpose of analyzing the spatial distribution of 239+240Pu inventories and possible controlling factors. The aim of this work was to derive an empirical model of 239+240Pu inventory based on currently available 239+240Pu data, precipitation and latitude. The results show that, in general, the latitudinal distribution of 239+240Pu inventory was consistent with the UNSCEAR reports. However, the 239+240Pu inventories are higher than the UNSCEAR data, especially in the Northern Hemisphere. In addition, close relationships (at the 0.01 significance level) were identified between 239+240Pu inventories and annual precipitation and latitude. An empirical formula was therefore developed to estimate 239+240Pu inventories in soils based on latitude and precipitation data. However, future research may require more data of measured 239+240Pu inventories in soil profiles that can be used to compare, validate and improve upon the accuracy of the inferred empirical equation.
The history of dune landform changes and dust activity at mid-latitudes is a good archive for exploring environmental changes and related landscape response. In this study, the dynamic changes, material sources, dust activity history and the influencing factors of typical sand dunes in the Hexi Corridor were comprehensively analyzed from the aspects of aeolian geomorphology, grain-size sedimentology, geochemistry and climatology. The results show that in the past half century, the typical crescent-shaped dunes and chains of crescent-shaped dunes in the study area have moved or swayed greatly, with an average speed ranging from 0.8 m/a (Dunhuang) to 6.2 m/a (Minqin). The dynamic changes of sand dunes are mainly affected by annual precipitation, annual average wind speed and annual gale days, which indicates that climate is the primary influencing factor of dune landform changes. The three-stage grain-size curve model of dune sands is obviously different from that of gobi sediments (two-stage), revealing the “immaturity” of the latter in sedimentology, while the former has experienced efficiently aeolian differentiation and non-local origin. The comprehensive evidences of paleogeography, sedimentology and geochemistry reveal that the source materials of sand dunes are mainly alluvial/proluvial and palaeo-fluvial sediments, including clastic sediments in the denudation/erosion zones of the north and south piedmonts. Indicators such as the proportion of surface fine particles, the coverage of surface salt crusts, and the content of erodible sandy materials indicate that the western gobi areas are not the main source areas of wind-blown dust in the central and eastern parts of the Hexi Corridor. The spatial distribution of the movement direction of sand dunes is similar to that of the regional dominant wind direction, which indicates that the difference in the dynamic evolution of dune landforms between the east and west of the Hexi Corridor should be controlled by the regional-scale wind system, that is, controlled by the dynamic mechanism rather than the difference in material sources. The warming and humidification of the Hexi climate is a synchronous response to the global warming and the strengthening of the Asian Summer Monsoon. It is also the main reason for the reduction of dust storms in the study area, which means that a potential inverse desertification process exists in the Hexi Corridor during the same period and it is also controlled by climate change. However, the process of desertification in the oasis areas during the period is caused by groundwater fluctuation affected by human activities.
The spatial distributions and variation mechanism of key soil indices in the Qinling-Daba Mountains are important indicators for the identification of the transitional effect and regional characteristics of the north-south transitional zone in China. This manuscript analyzes the spatial variations in soil organic carbon (SOC) and total nitrogen (TN) and corresponding relationships with major geographical factors based on spatial analysis and geostatistics considering data obtained from the Second National Soil Survey. The results indicate that the spatial distributions of the SOC and TN contents are consistent, and three high-content areas, one secondary high-content area and one low-content area are observed. High content values are located in the high-altitude regions of the Qinling-Daba Mountains and mountainous areas to the west of the Jialing River, the low-content area occurs on the north slope of the Qinling Mountains, and the secondary high-content area mainly encompasses both sides of the Hanjiang River and regions in the Qinling-Daba Mountains at altitudes below 1000 m. The SOC and TN contents vary between the above two ranges, with the gradual increase in content revealing a horn-shaped pattern. Considering the spatial variations and functions of vegetation, topography and climate factors, it is found that the SOC/TN range in the secondary high-content area remains consistent along the 1000 m contour line, the upper limit of the transitional mountain altitudinal belt, the 0°C isotherm line in January and the 24°C isotherm line in July. This region constitutes the main body of the transitional zone between the subtropical and warm temperate zones, and the northern boundary is roughly distributed along the Dujiangyan-Maoxian-Pingwu-Wenxian line to the west of the Jialing River and the 1000 m contour line on the southern slope of the Qinling Mountains, while the southern boundary occurs along the Dujiangyan-Beichuan-Qingchuan line to the west of the Jialing River and the 1000 m contour line on the northern slope of the Daba Mountains. SOC/TN spatial variation provides a reference for the demarcation of the subtropical and warm temperate zones, and further identification of the soil processes and ecological effects in typical regions can help reveal multidimensional transitional characteristics and variation mechanisms.
Studying an ecological restoration zoning process under the background of ecological security patterns is of great significance to the rapid adjustment and optimization of a landscape pattern. In this study, a remote sensing ecological index and a morphological spatial pattern analysis method were used to assess the quality of habitats and identify ecological sources in the city of Ningbo; ecological corridors, ecological pinch points, and ecological barrier points were extracted by using a circuit theory to construct ecological security patterns and ecological restoration zones. The results indicate: (1) There were 47 ecological sources, and 83 key ecological corridors in Ningbo, and the ecological land area was about 1898.39 km
Land ecological security (LES) is an important part of China’s ecological civilization construction, which plays a vital role in ensuring the sustainable development of its society and economy. Based on the Driving force-Pressure-State-Impact-Response (DPSIR) framework, this study quantified the spatiotemporal changes of LES in 28 counties of the southern Shaanxi Province from 2009 to 2018. The influencing factors of LES in Yangxian County were explored to clarify the mechanisms that rely on the land ecological advantages to develop organic agriculture and boost poverty alleviation. Results show that the LES of Yangxian always ranked in the top six in 28 counties of the southern Shaanxi region during 2009-2018. The LES in Yangxian increased from 0.385 in 2009 to 0.533 in 2018, and the LES level changed from relatively unsafe to safe. The indicators of rural per capita net income, grain output per unit area of arable land, and grazing intensity could explain 99.8% of the LES variance in Yangxian. Relying on ecological resources, Yangxian increased farmers’ income and boosted alleviation of poverty through innovative land policies, developing organic agriculture, and rural tourism. These findings will provide theoretical support and model reference for balancing ecological protection and poverty alleviation in restricted development zones.
Land use patterns (LUPs) are the form in which various land use types are combined spatially, evidently impacting soil water. However, the influence mechanism by which LUPs form remains unclear. In this study, the soil water content (SWC) in the 0-160-cm soil depth was observed in shrubland (SL), mature forestland (MF), grassland (GL) and young forestland (YF) sites on four slopes with different LUPs in the Yangjuangou catchment of the Chinese Loess Plateau. The SWC in SL-YF-SL (13.28%) was significantly greater than that in YF-MF (9.93%), MF-GL-YF (10.38%) and SL-MF (10.83%) and was temporally stable during the study period. The spatial distribution of SWC along the slope differed among the four LUPs. Vegetation characteristics and soil texture mainly determined the spatial variations in SWC in the shallow soil layers (0-40 cm), while topographic factors were the determinants in the deep soil layers (60-160 cm) as well as in the entire soil profile (0-160 cm). The significance of SWC differences among the various land use patterns increased with decreasing precipitation during the growing seasons. YF-MF (77.8 mm) and SL-YF-GL (73.9 mm) required more rainwater than SL-MF (68.2 mm) and MF-GL-MF (67.5 mm) to compensate for the loss of soil water on the monthly scale during the rainy season. Therefore, vegetation restoration should consider land use patterns on hillslopes for soil water conservation.
During the 21st century, artificial intelligence methods have been broadly applied in geosciences to simulate complex dynamic ecosystems, but the use of artificial intelligence (AI) methods to reproduce land-use/cover change (LUCC) in arid ecosystems remains rare. This paper presents a hybrid modeling approach to understand the complexity in LUCC. Fuzzy logic, equation-based systems, and expert systems are combined to predict LUCC as determined by water resources and other factors. The driving factors of LUCC in this study include climate change, ecological flooding, groundwater conditions, and human activities. The increase of natural flooding was found to be effective in preventing vegetation degradation. LUCCs are sensitive under different climate projections of RCP2.6, RCP4.5, and RCP8.5. Simulation results indicate that the increase of precipitation is not able to compensate for the additional evaporation losses resulting from temperature increases. The results indicate that grassland, shrub, and riparian forest regions will shrink in this study area. The change in grasslands has a strong negative correlation with the change in groundwater salinity, whereas forest change had a strong positive correlation with ecological flooding. The application of artificial intelligence to study LUCC can guide land management policies and make predictions regarding land degradation.
Groundwater resources have always been some of the most valuable resources of human settlements. Climate changes and ever-increasing water demands registered in the last century have led to diminishing levels of groundwater reserves, as well as reduced recharging potential. Therefore, in order to use groundwater aquifers in a sustainable manner, it is required to identify areas with higher replenishing potential. The current study addresses the issue of generating a map for identifying differently ranked groundwater recharging potential values, in the aquifers of the Moldavian Plain region, Romania. For the purpose of conducting the analysis, maps were created through GIS based multi-criteria Analytic Hierarchy Process (AHP) and Catastrophe Theory (CT), with seven relevant, thematic, spatial layers: precipitation distribution, lithological strata, soil texture, declivity, drainage density, land use and the distribution of groundwater level tendencies. The results of the two methods of analysis are similar. Prediction differences are of maximum 3%, in the case of extreme classes (very bad and very good) and in the case of middle classes the deviation is not greater than 0.4%. Following the validation of the results generated by the two methods that were applied, it was observed that the predictions offered by CT are more accurate. This aspect can be based on the fact that the main factors that contribute to the prediction are different. This type of workflow emphasizes the necessity of implementing appropriate groundwater management plans for mitigating reservoir scarcity/depletion, and recommending sustainable solutions for future groundwater exploitation practices.
Water depths and flow velocities decisively influence the damage caused by flash floods. Geographic Information System (GIS) is a powerful and useful tool, allowing the spatial analysis of results obtained by hydraulic modelling, namely from the HEC-RAS/HEC- GeoRAS software. The GIS spatial analysis performed in this study seeks to explain and quantify the spatial relationships between the stream channel features and flow components during flash flood events. Despite these relationships are generically known, there are few studies exploring this subject in different geographic contexts. A 1D hydraulic model was applied in a small watershed in Portugal, providing good results in the definition of floodable areas, water depths and longitudinal velocities. No direct relationship was found between water depths and velocities in the floodable areas; however, negative strong correlations were found between the two flow components along the stream centerlines. Bed slope, channel and flood width, and roughness prove to be highly relevant on the longitudinal variations of water depths and velocities and on the location of maximum values. Increasing peak discharges and return periods (RT) can change the relationships between water depths and velocities at the same location. Results can be improved with more accurate elevation data for stream channels and floodplains.
