Hanzhong Basin Research Articles

Assessing the risk of subsoil compaction in croplands using the soil compaction stratification ratio as an indicator

AbstractAccurate prediction of subsoil compaction in cropland areas is important for food security and sustainable agricultural production development. This study evaluated the validity and advantages of the soil compaction stratification ratio (SR) as an indicator for assessing the risk of subsoil compaction and presented a theoretical framework for predicting and evaluating subsoil compaction risk. Geographic information system and remote sensing technologies were utilized in combination with a state‐of‐the‐art ensemble machine learning model to quantitatively predict the spatial distribution and uncertainty of subsoil compaction risk in croplands. The results showed that the subsoil bulk density (BD) was significantly greater than the topsoil BD in Shaanxi Province, China. Compared with that of the subsoil BD, the stratification ratio of the bulk density (SRBD) exhibited greater sensitivity to subsoil compaction, and it accurately reflected spatial variations in subsoil compactness. The SRBD exhibited obvious spatial heterogeneity, and the mean annual precipitation, elevation, and mean land surface temperature substantially influenced its spatial distribution. The critical thresholds of the SRBD for the low‐risk, medium‐risk, and high‐risk groups were 1.01, 1.21, and 1.32, respectively. Low subsoil compaction dominated in the mountainous and hilly areas, whereas the Guanzhong Plain and Hanzhong Basin exhibited medium levels of subsoil compaction. Some croplands in the central Guanzhong Plain experienced severe subsoil compaction issues. In conclusion, the soil compaction SR was found to be an effective indicator of subsoil compaction by effectively eliminating soil background differences. This approach has potential applications in cropland management, digital soil mapping, and early warning of soil compaction risk.

Drainage reorganization and divide migration driven by basin subsidence: An example from the Micang Shan, outskirts of eastern Tibet and its implications for Cenozoic evolution of the Yangtze River

AbstractThe Cenozoic India‐Asia collision has elevated the Tibetan Plateau and produced large strike‐slip faults in the interior and margins of the plateau, which profoundly influenced drainage reorganization and divide migration in Asia. Recent studies have revealed that the drainage divides between the major rivers in and around the Tibetan Plateau have been migrating for tens of millions of years, due to tectonic and/or climatic disturbance or river capture events. Drainage‐divide stability analysis can provide new, independent insights into the Cenozoic evolution of the river systems. In this study, we focus on the Hanzhong Basin and the adjacent Micang Shan (Shan means Mountain(s)) at the tail of the Qingchuan strike‐slip fault in the outskirts of eastern Tibet. We investigated the stability of the Micang Shan drainage divide, which separates the Han and Jialing rivers (two major tributaries of the Yangtze River), using two methods—χ‐plot and Gilbert metrics. The results show that most segments of the Micang Shan drainage divide are either moving south or stable. We further calculated the predicted stable divide location and identified the abandoned river channels and residual planation surfaces. Based on these analyses, we suggest that (1) the migration of the Micang Shan drainage divide is driven by the tectonic subsidence of the Hanzhong Basin; and (2) the upper reaches of the Han River flowed southward to the Sichuan Basin before basin subsidence. This study supports the hypothesis that the Palaeo‐Middle Yangtze River and its tributaries primarily flowed southward. Moreover, the flow direction of the Middle Yangtze River has been, and still is, transitioning from southward to eastward. The change in river network flow direction is driven by regional block tilting towards the east, surface deformation from strike‐slip faulting, regional extension east of the Tibetan Plateau and/or increased influence from the summer monsoon.

Intelligent classification and analysis of regional landforms based on automatic feature selection

AbstractTerrain features are an important basis for realizing high‐precision landform classification, and feature selection is a key step of machine learning and knowledge mining. However, the feature selection process is facing challenges due to the multidimensionality and correlation of multisource terrain feature datasets and factors. Traditional feature selection methods lack enough consideration for the interpretability and transparency of feature factors, but the transparent decision‐making process of feature selection precisely determines the modelling effect and the reliability of model application results. Current research urgently needs to work out the black holes of visual representation during feature selection. In the process of intelligent landform classification, multiple and effective terrain feature is an essential factor in enhancing the performance and generalisation ability of the network. Therefore, we initially selected 40 terrain feature parameters, including basic terrain factors and digital elevation model (DEM) terrain textures, to calculate the feature contribution degree and sort the parameter importance based on the SHapley Additive exPlanations (SHAP) method, then reserved 10%, 20%, 30%, 40% and 50% terrain features in turn for constructing the landform classification dataset. Because the traditional UNet network cannot completely capture abrupt landform features, the convolutional block attention module (CBAM) was integrated into the UNet, and a deep learning model was established for the fine‐grained classification of regional landforms. Considering the calculation rate, even though there are large regional spatial differences and genetic mechanisms, it is appropriate to retain 20% of terrain features for intelligent landform classification. The classification accuracy of typical regions, namely, the Hanzhong Basin, North China Plain, Yunnan–Guizhou Plateau and Tibetan Plateau, reached 98.76%, 97.36%, 96.3% and 92.78%, respectively, and what's more, some accuracies went up to a higher level under other feature combinations. Meanwhile, given the different feature combinations corresponding to regional landform types, the combinative stability and spatial orderliness characteristics were explored to explain the accuracy variation trend.

Is Cultivated Land Increased by Land Consolidation Sustainably Used in Mountainous Areas?

Land consolidation (LC) in China is an important means by which we can increase the quantity and improve the quality of cultivated land. At present, large areas of cultivated land are abandoned in mountainous areas. It is unclear whether the increased cultivated land from LC in mountainous areas is sustainably used. Data from 64 land consolidation zones completed in 2016 in the Qinba Mountain Area were collected. The land-use status was obtained from high-resolution remote sensing images by the method of visual interpretation, and land-use changes were analyzed. According to our results, the increased cultivated land by LC is mainly terrace, accounting for 92.22% of the total area of increased cultivated land. The increased cultivated land is mainly distributed in the Qinba Mountainous Area, and terrace is the main type of increased cultivated land in both the Hanzhong Basin Area and Qinba Mountainous Area. The transformation rate of cultivated land from LC, especially terrace, is small. The transformation rates of terrace in the Hanzhong Basin Area and Qinba Mountainous Area are 0.36% and 0.09%, respectively. The socioeconomic development in mountainous areas is relatively lagging, and the per capita cultivated land area is small. Many farmers are still engaged in agricultural production and earn a basic income. Thus, high-quality cultivated land with convenient transportation is sustainably used. LC remains a key avenue for increasing cultivated land area, improving agricultural productivity, increasing farmers’ incomes, and promoting rural development in the mountainous areas.

Spatial-Temporal Pattern Analysis of Land Use and Water Yield in Water Source Region of Middle Route of South-to-North Water Transfer Project Based on Google Earth Engine

The water source area of the middle route of the South-to-North Water Diversion Project is an important water conservation and ecological protection area in China. Based on remote sensing data, this paper analyzed the evolution process of land use/cover change in water source region in the past 35 years. Then, based on the InVEST model, the spatial-temporal patterns of water yield in the water source region were calculated with land use cover, meteorology and soil data as inputs. The impacts of climate factors such as precipitation and temperature and land use change on water yield were discussed, and the responses of water yield to these two changes were also discussed. The results show that from 1985 to 2020, the average water yield depth in the middle route of the South-to-North Water Diversion Project increases first and then decreases, from 615 mm in 1985 to 738 mm in 2000, and then decreases to 521 mm in 2020. The spatial heterogeneity of the water-producing capacity is obvious. The high value of the water-producing capacity is concentrated in the Daba Mountain area in the south, while the low values are concentrated in the Hanzhong Basin, Ankang Basin and the eastern plain area. The spatial pattern of water producing depth has no obvious change. The average water yield depth of forest, grassland and shrub in the region was the largest, and forest and cultivated land were the main contributors to the total water yield of the region, providing 82% and 14% of the total water yield in 2020. Precipitation has a significant effect on water yield, while land use/cover change has a small effect on water yield.

Diverse floodplain deposits of reworked loess in a monsoon climate (Hanzhong Basin, central China)

AbstractThis paper describes an assemblage of diverse floodplain facies of reworked loess (facies b, c) in a Middle Pleistocene monsoonal setting of the Hanzhong Basin, central China. The vertical and lateral sedimentary sequences show changing energy conditions. Apart from the highest energy in the channel facies (facies a), a relatively high energy floodplain environment (facies b) prevailed in waterlogged conditions, with small, laterally migrating (sub)channels. Facies b generally interfingers with aggrading horizontal sheets of overbank deposits in alluvial pools and swamps in a floodplain with much lower energy (facies c), in which phases of stability (soil formation) occasionally interrupted overbank deposition. Reworked loess forms the main part of the floodplain deposits. The paleosols are considered to have been formed under low hydrodynamic conditions in an interglacial environment. These interglacial conditions follow the commonly assumed glacial conditions of channel facies a. The sedimentary successions in the floodplain show a recurrent composition and cyclicity between wet and dry floodplain sedimentation terminated by stability with soil formation. The cyclic rhythm of stacked high- and low-energy floodplain sediments is attributed to varied intensity of different hydrodynamic flooding events that may have been due to changing monsoonal rainfall or simple intrinsic fluvial behavior.

Identifying the relationships among multiple ecosystem services

Ecosystem services (ES) and relationships among them have temporal and spatial patterns that need to be understood. The purpose of this research was to study the spatial and temporal characteristics of the synergies and trade-offs in ES in Guanzhong Basin (sub-humid area) and Hanzhoung Basin (humid area), as well as to compare the ES differences between the two basins. We use linear relationship between grain output and Normalized Difference Vegetation Index, Carnegie-Ames-Stanford Approach, integrated storage capacity method, and the revised universal soil loss equation model to simulate the four types of ecosystem services: food production (FP), carbon sequestration (CS), water retention (WR) and soil conservation (SC). Our results revealed that ES interactions varied across land use types and climate difference. Trade-off relationship between FP and CS in Guanzhong Basin (R = −0.40, P < 0.01) was stronger than that in Hanzhong Basin (R = −0.31, P < 0.01); synergistic relationship between CS and WR, WR and SC in Hanzhong Basin were stronger than those in Guanzhong Basin, but the synergistic relationship between CS and SC was weaker in Hanzhong Basin than in Guanzhong Basin. This study will help to deepen the understanding of the relationship among ES because of regional differences in temporal and spatial patterns.

Spatial patterns of Pinus tabulaeformis and Pinus massoniana forests in Qinling-Daba Mountains and the boundary of subtropical and warm temperate zones

The Qinling Mountains is not only the geographical boundary between North and South China, but also the boundary between subtropical and warm temperate zones. It plays an important role in the geo-ecological pattern of China. However, there is controversy about the specific location of this geographical boundary in academic community due to the complexity, transition and heterogeneity of the transitional zone, as well as the differences in the delimitation indicators and research purposes. To further reveal the characteristics of the North-South transitional zone and clarify the specific location of the geo-ecological boundary between North and South China, combined with SRTM topographic data, temperature and precipitation data, Pinus massoniana forest and Pinus tabulaeformis forest, which represent subtropical coniferous forest in South China and temperate coniferous forest in North China respectively, were chosen to analyze their spatial distributions in the Qinling-Daba Mountains and the climatic conditions at their boundary with the climatic indexes of annual precipitation, the coldest month (January) average temperature, the warmest month (July) average temperature and the annual average temperature. The results show that: (1) Pinus massoniana and Pinus tabulaeformis forests and the climate indicators of their boundary can be used as one of the vegetation-climate indexes for the delimitation of subtropical and warm temperate zones. The boundary between the subtropical coniferous forest (Pinus massoniana forest) and temperate coniferous forest (Pinus tabulaeformis forest) is located along the south slope of Funiu Mountain to the north edge of Hanzhong Basin (the south slope of Qinling Mountains) at an altitude of 1000–1200 m, where the climatic indictors are stable: the annual precipitation is about 750–1000 mm, the annual average temperature is about 12–14°C, the coldest monthly average temperature is 0–4°C, and the warmest monthly average temperature is about 22–26°C. (2) It can be more scientifically to delimitate the boundary of subtropical and warm temperate zones in China by comprehensively considering the vegetation-climate indicators. Additionally, the boundary between subtropical and warm temperate zones in Qinling-Daba Mountains should be a transitional zone consisting of the boundaries of coniferous forests, broad-leaved forests and shrubs between subtropical and warm temperate zones. The results provide a scientific basis for the selection of delimitation index of subtropical and warm temperate zones.

Discussion on position of China’s north-south transitional zone by comparative analysis of mountain altitudinal belts

The Qinling Mountains has always been regarded as an essential dividing line between the warm temperate zone and the subtropical zone in eastern China and plays a vital role in the geoecological pattern of China. However, there is controversy about the specific location of this geographical boundary in the academic community. As a product of the combined effects of zonal and non-zonal factors, the mountain altitudinal belts (MABs) can reflect both the horizontal zonality and the vertical zonality of vegetation distribution. Using the MAB information, we can not only profoundly understand the complex mountain system of Qinling-Daba Mountains but can also judge its nature as a geographical boundary more scientifically. Therefore, based on the comparative analysis of basal belt, dominant belt characteristics and belt structure characteristics of the MABs in Qinling-Daba Mountains, subtropical and temperate mountains, this paper analyzed the MAB differences and similarities among Qinling-Daba Mountains, subtropical and temperate typical mountains, to reveal the vegetation distribution characteristics in the north-south transitional zone. The results show that: (1) The MABs of the southern part of Qinling-Daba Mountains (southern slope of the Daba Mountains) are the same or similar to those of the Subtropical Mountains, and the MABs of the northern part of Qinling-Daba Mountains (northern slope of the Qinling Mountains) are similar to those of the temperate mountains. While it shows obvious transitional characteristics in the vast area between the northern slope of the Daba Mountains and the southern slope of the Qinling Mountains: the basal belts gradually transit from the evergreen broad-leaved forest belt (basal belt in subtropical mountains) to the evergreen and deciduous broad-leaved mixed forest belt, and the dominant belts also transit from the evergreen broad-leaved forest belt to the evergreen and deciduous broad-leaved mixed forest belt or the deciduous broad-leaved forest belt. (2) The transitional zone between the subtropical zone and the warm temperate zone is located between the northern slope of the Daba Mountains and the southern slope of the Qinling Mountains. The southern boundary of the transitional zone is along the northern slope of Shennongjia Mountain-the northern slope of Micang Mountain-Baishuijiang Nature Reserve, and the northern boundary is along the southern slope of Funiu Mountain-the southern slope of Taibai Mountain-Lianhua Mountain. Additionally, in the transitional zone, the average temperature in January is between -5°C and 1°C, the annual average temperature is between 10°C and 13°C except Hanzhong Basin and Hanshui Valley, and the accumulated temperature above 10°C ranges from 2000°C to 4000°C, the annual rainfall is about 800–1000 mm. The results provide a scientific basis for revealing the characteristics of China’s north-south transitional zone and scientific division of the boundary between the subtropical zone and warm temperate zone in China.

Fluvial or aeolian? Unravelling the origin of the silty clayey sediment cover of terraces in the Hanzhong Basin (Qinling Mountains, central China)

This study is focused on a silty clayey sedimentary sequence on a terrace in the intramontane Hanzhong Basin, located in the Qinling Mountains (QLM), central China. Traditionally, the QLM are considered to have blocked dust transport from northwest to southeast China. However, in recent years, geo-archaeological studies have documented loess-palaeosol sequences at numerous locations in and surrounding the QLM. In the loess deposits overlying the terraces of the Hanjiang River in the Hanzhong-, Ankang- and Yunxian basins, abundant artefacts, flakes, stone tools (e.g., scrapers and choppers) and cores are commonly found. The loess deposits have been deposited with lower sedimentation rates, and they are finer grained and more intensely weathered compared to the loess deposits on the Central Loess Plateau (CLP). The loess deposits overly coarse sandy and gravely fluvial deposits (terraces). Silty fluvial deposits are situated in between them. Discrimination between these two types of deposits could prove difficult because both deposits are fine grained (silt and clay) and can have similar grain size distribution characteristics. This is, however, crucial for palaeo-environmental interpretations during hominin occupation, understanding fluvial morphodynamics, and for pedostratigraphic correlation with the typical loess-palaeosol sequences on the CLP. The aim of this research is to determine and characterize the transition of the fluvial to aeolian depositional environment in a fine grained sequence, based on field observations, organic matter and carbonate content, grain size and shape analyses, mineral content (mica's) and end-member modelling of the grain size dataset. In addition, terrestrial cosmogenic nuclides (TCN) burial dating is used to determine the age of the basal, coarse grained fluvial deposits. The determined age, 0.6 ± 0.14 Ma, allows for a chronological correlation of the deposits to the loess-palaeosol sequence on the CLP independent from the pedostratigraphic correlation. This age also gives insight in terrace abandonment and the fluvial morphodynamics of the Hanjiang River.The result indicates a clear distinction between sediments deposited in a fluvial environment and those formed in an aeolian depositional environment. However, the aeolian (loess) deposits show some atypical characteristics. For example, the end-member model results show a coarsening in the five palaeosol layers. This is in contrast with the fine grained nature of palaeosols on the CLP. The coarsening observed in the studied palaeosol layers is interpreted as the result of local surface runoff processes, eroding fine sediment and/or depositing relatively coarse material during interglacial periods.Because of the known depth of the fluvial-aeolian transition and the absolute age of the TCN burial dated terrace deposits, pedostratigraphic correlation of the palaeosol layers with the Central Loess Plateau is possible. The oldest palaeosol is correlated with S5 (0.625–0.503 Ma). The transition from a fluvial to aeolian environment takes place in L6, between 0.625 and 0.693 Ma. This is consistent with the TCN age of 0.6 ± 0.14 Ma. This age also marks the abandonment of the terrace caused by incision of the Hanjiang River, which is possibly related to an uplift phase of the QLM.

Spatially Explicit Analysis of Trade-Offs and Synergies among Multiple Ecosystem Services in Shaanxi Valley Basins

Understanding the spatiotemporal characteristics of trade-offs and synergies among multiple ecosystem services (ESs) is the basis of sustainable ecosystem management. The ecological environment of valley basins is very fragile, while bearing the enormous pressure of economic development and population growth, which has damaged the balance of the ecosystem structure and ecosystem services. In this study, we selected two typical valley basins—Guanzhong Basin and Hanzhong Basin—as study areas. The spatial heterogeneity of trade-offs and synergies among multiple ESs (net primary production (NPP), habitat quality (HQ), soil conservation (SC), water conservation (WC), and food supply (FS)) were quantified using the correlation analysis and spatial overlay based on the gird scale to quantitatively analyze and compare the interaction among ESs in two basins. Our results found that: (1) Trade-offs between FS and other four services NPP, HQ, SC, and WC were discovered in two basins, and there were synergistic relationships between NPP, HQ, SC, and WC. (2) From 2000 to 2018, the conflicted relationships between paired ESs gradually increased, and the synergistic relationship became weaker. Furthermore, the rate of change in Guanzhong Basin was stronger than that in Hanzhong Basin. (3) The spatial synergies and trade-offs between NPP and HQ, WC and NPP, FS and HQ, SC and FS were widespread in two basins. The strong trade-offs between pair ESs were widly distributed in the central and southwest of Guanzhong Basin and the southeast of Hanzhong Basin. (4) Multiple ecosystem service interactions were concentrated in the north of Qinling Mountain, the central of Guanzhong Basins, and the east of Hanzhong Basin. Our research highlights the importance of taking spatial perspective and accounting for multiple ecosystem service interactions, and provide a reliable basis for achieving ecological sustainable development of the valley basin.

Geomorphic indices and longitudinal profile of the Daba Shan, northeastern Sichuan Basin: Evidence for the late Cenozoic eastward growth of the Tibetan Plateau

The Daba Shan Orocline is located in the northeastern Sichuan Basin, and has undergone foreland propagation and distinct surface uplift owing to the eastward expansion of the Tibetan Plateau since the late Cenozoic. In order to describe and quantify the earth surface processes respond to deep geological mechanisms, and to detect the kind of tectonic deformation in the Daba Shan area during the late Cenozoic, various geomorphic indices were analyzed for study area. The obtained results are: (1) The northeast of the Hanzhong Basin, the Hannan-Micang Massifs, along the Chengkou-Fangxian fault, and the Shennongjia Massif exhibit intense tectonic activity. (2) The spatial patterns of the channel steepness indices indicate that the western segment of the northern Daba Shan (Fenghuang Shan and Paotaizi region) have higher uplift rates than the eastern. (3) The longitudinal profile analysis revealed that the landscape evolution of the Shennongjia Massif is in a transient state, with an uplift amplitude of 1700–1900 m since the end of the Paleogene (25 Ma), and an average uplift rate of 0.072 ± 0.004 mm/a. The paleochannel reconstruction indicate an incision of ~900–1000 m since the late Neogene (3.0–3.4 Ma), with the average uplift rate being 0.3 ± 0.03 mm/a. (4) Three tectonic deformation zones can be distinguished in the Daba Shan (from west to east), the shortening deformation, strike-slip deformation, and vertical uplift zones. These observations suggest that the eastward growth of the Tibetan Plateau has affected the Daba Shan area and shaped the modern landscape.

Long-period ground motion effect in Shaanxi Province of Changning Ms6.0 earthquake

At 22:55 on June 17, 2019, an earthquake of magnitude 6.0 occurred in Shuanghe Town, Changning County, Yibin City, Sichuan Province. In Shaanxi Province, the obvious earthquake sense appeared in some places which are 600 km to 800 km away from the epicenter. Based on the collection, collation and analysis of the data about Weihe Basin, Hanzhong Basin and Ankang Basin in Shaanxi Province, and the analysis of representative seismic network records and seismic wave propagation distance in each basin, the mechanism of the long-period disaster induced by the Changning Ms6.0 earthquake in Shaanxi Province is revealed. This study has a positive significance for the seismic fortification of long-period structures in this area, the scientific popularization of long-term ground motion effect, and the avoidance of earthquake panic.

Investigation on Current Status of Rice Fertilization in the Plain Area of Hanzhong Basin

Scientific fertilization is the key to obtain a high-yield and good quality rice. In order to understand the present situation of rice fertilizer application in the Plain Area of Hanzhong Basin, a survey had been conducted. The investigation results showed that: in the Plain Area of Hanzhong Basin, N application was more higher, P2O5 application was reasonable and K2O application was a little lower. Fertilization was very unbalanced and the application rates were quite different among farmers. The base to dressing ratio was unreasonable. All the P2O5, K2O and most of N were applied as base fertilizer, and only a few farmers use top dressing N fertilizer. In the frame of fertilizer variety, there is a phenomenon that using more ammonium bicarbonate than formula fertilizer, using more chemical fertilizer than organic fertilizer and using more macro element fertilizer than trace fertilizer.

Fluvial terrace formation and its impacts on early human settlement in the Hanzhong basin, Qinling Mountains, central China

The Qinling Mountains (QLM) form the climatic boundary between the temperate north and subtropical south of China. Many important Paleolithic archaeological sites located on fluvial terraces in this area have been reported in recent decades. Abundant artifacts have been excavated in silt layers overlying fluvial gravels and coarse sands. These silt layers have thus far been interpreted as aeolian deposits. However, in principle they could also represent (in part) fluvial (floodplain) deposits, especially near the base of fine-grained sequences. Reconstruction of fluvial terrace formation is crucial for the correct interpretation of the environment of hominin occupation. In this paper, two sediment sequences from two Paleolithic sites, located on different terrace levels of the Hanjiang River in the Hanzhong basin, are studied mainly using grain-size and grain-shape analyses. In addition, grain-size distributions have been unraveled by applying end-member modelling to distinguish different sedimentary environments. The results show that three different units can be discriminated in each section. The lower unit, consisting of gravelly sand mixed with fine silt, is interpreted as shallow-channel-fill sediment deposited during the start of the transition from a channel to a floodplain environment. The middle unit comprises a fine-grained, gradually fining-upward sequence, representative a floodplain environment. At its base, it reflects a high-energy floodplain situation; at its top, the sequence is interpreted as a low-energy floodplain environment with aeolian input (settling in static water). The third, uppermost unit consists of aeolian loess interbedded with paleosol(s) and sediments that are interpreted as the results of episodic surface runoff. The gradual transition between the 3 units and the gradual fining upward trend of the middle unit indicates that there is no considerable age gap (no hiatus) between the fluvial- and aeolian sedimentary environments. Stone artifacts have been found in all 3 units, with difference abundance, indicating that both the aeolian and floodplain depositional environments provided favorable living conditions. For the floodplain environment, the resources of water and raw materials (fluvial gravels) for tool making may have offered fundamental resources for hominin settlement. © 2019 Elsevier B.V.

Temporal and Spatial Changes of Non-Point Source N and P and Its Decoupling from Agricultural Development in Water Source Area of Middle Route of the South-to-North Water Diversion Project

The quantitative estimation of non-point source (NPS) pollution provides the scientific basis for sustainability in ecologically sensitive regions. This study combined the export coefficient model and Revised Universal Soil Loss Equation to estimate the NPS nitrogen (NPS-N) and NPS phosphorus (NPS-P) loads and then evaluated their relationship with Primary Industrial Output Value (PIOV) in the water source area of the middle route of South-to-North Water Diversion Project (SNWDP) for 2000–2015. The estimated results show that: (1) dissolved nitrogen (DN) load increased 0.55%, and dissolved phosphorus (DP) load decreased 4.60% during the 15 years. Annual loads of adsorbed nitrogen (AN) and adsorbed phosphorus (AP) increased significantly before 2005 and then decreased after 2005. Compared with 2000, AN and AP loads in 2015 significantly decreased by 32.72% and 30.81%, respectively. Hanzhong Basin and Ankang Basin are key areas for controlling dissolved pollution, and southern and northern regions are key areas for adsorbed pollution. (2) From 2000 to 2005, NPS pollutants and PIOV showed weak decoupling status. By 2015, NPS pollutants had strong decoupling from PIOV in most counties. (3) Land use has been the main source of NPS-N and NPS-P pollution, accounting for about 75% of NPS-N and 50% of NPS-P based on the average value over the study period. In the future, various measures—such as returning cropland to forest and reducing the number of livestock—could be adopted to reduce the risk of NPS pollution. NPS pollution caused by livestock was grown over the past 15 years and had not yet been effectively controlled, which still needs to be urgently addressed. Collecting ground monitoring data and revising parameters are effective means to improve the accuracy of simulation, which deserve further study. The results will also provide scientific support for sustainable development in similar regions.

Spatial and temporal changes in inter-annual and seasonal NDVI in the Qinling mountains of China

As an important ecological barrier in central China, the Qinling Mountains have received more attention in response to global or regional climate change. Spatial and temporal changes of inter-annual and seasonal NDVI were analysed after extraction of the vegetation growth season, based on MODIS NDVI images and linear trend analysis. The results showed that: (1) the NDVI value and vegetation cover level of the Qinling Mountains were high. The NDVI showed significant annual and seasonal increases, in which the summer value contributed the most to the inter-annual value, followed by spring and autumn. In terms of the change trend, the NDVI showed a linear increase in annual and seasonal data, in which the spring growth rate contributed the most to the inter-annual value, followed by autumn and summer. (2) The spatial distribution of the linear change trend of the NDVI in the inter-annual and seasonal data was mainly increased, but the area of reduction was also large. The area of reduced NDVI was mainly distributed in the middle and western area with middle and high elevations, as well as urban neighbourhoods with intensive human activities, such as the Hanzhong basin, the Ankang basin, and the Shangluo basin. The rate of change in NDVI in human activity areas was higher than in the middle and higher elevation areas. The change may be driven by human activities in the former and by climate change in the latter. Monitoring of the vegetation ecological system in the Qinling Mountains should be strengthened to understand the change process, as well as to provide a scientific basis when making policies for regional ecological environmental protection.

Increasing drought has been observed by SPEI_pm in Southwest China during 1962–2012

Drought is regarded as an environmental disaster that has significantly impacted on economic and social development in recent decades, particularly in Southwest China (SWC). Here, we presented an analysis of spatiotemporal variations of meteorological drought in SWC. We computed the standardized precipitation evapotranspiration index using the Penman–Monteith equation (SPEI_pm) and explored spatiotemporal variational evolution of drought in SWC during 1962–2012 utilizing the Mann–Kendall test, continuous wavelet transform (CWT), and rotated empirical orthogonal function (REOF). We also analyzed the relationship between the rotated principal component time series (RPCs) and the 74 circulation indices. The results showed that (1) SWC displayed a dry trend at annual and seasonal scale with a 2–4-year significant period. The SWC can be divided into six sub-climate regions with different aridity and wetness features. (2) Among the six regions, the Eastern Yunnan Plateau showed an obvious dry trend while Hanzhong Basin and the Eastern Mountain Areas showed a wet trend that was not significant. There were 2–8-year periods of oscillation in general within the variation of the six regions. (3) The indices of the strength of the polar vortex in Asia (APVA) may affect the drought evolution of the whole study area. The change of drought in Eastern Yunnan Plateau and Sichuan Basin may be associated with Tibetan Plateau High.

Early human settlements in the southern Qinling Mountains, central China

China is a key area of early human settlement in East Asia, with numerous Paleolithic localities indicating an early Pleistocene presence of hominins in northern and southern China. Considerable research has been devoted to determining possible migration routes for hominins linking the two areas. In this paper, we report the discovery of several loess-covered Paleolithic sites in the Hanzhong and Ankang Basins along the Hanjiang River in the southern piedmont of the Qinling Mountains (QLM) in central China. A chronology is developed for these sections using a combination of detailed optically stimulated luminescence dating, magnetostratigraphic analyses, and pedostratigraphic correlation with the well-dated loess–paleosol sequence of the central Chinese Loess Plateau. The results indicate that the age of the oldest lithic assemblage at the Longgangsi locality 3 Paleolithic site in Hanzhong Basin is ∼1.20 Ma, thus making this locality as one of the oldest sites in central China. Our work also indicates that hominins occupied the Hanjiang valley at several times: ∼1.2, 0.9, ∼0.6, and ∼0.1 Ma. We propose that the Hanjiang River Valley was a probable hominin routeway through the QLM because many sites corresponding to these different phases were also discovered to the north of the QLM. Future study on the Hanjiang River Valley is important for verifying the hypothesis of an early human migration route between southern and northern China.

Taphonomic and paleoenvironmental issues of the Pleistocene loessic Paleolithic sites in the Qinling Mountains, central China

Abstract Hinterland intermountain basins and northern and southern piedmonts of the Qinling Mountains accumulated a large amount of loess during the Pleistocene. The loess strata not only record local paleogeographic and paleoenvironmental changes, but also contain rich hominin fossils and Paleolithic remains. In the northern piedmont of the Qinling Mountains and the lower valley of the South Luohe River, the loess strata have multi loess-paleosol sequences with aeolian loess continuously accumulating during glacial and interglacial cycles. In contrast to the northern piedmont, loess stratigraphy in the hinterland intermountain basins of the Qinling Mountains is relatively thin and contains finer loess particles. In this “mini” type of loess stratum, the density of Paleolithic remain generally is higher than the Loess Plateau in the north of the Qinling Mountains. Based on stratigraphic, chronological, and lithic artifacts analysis in recent years, it appears that the regional lithic assemblage belongs to the Oldowan (Mode I) lithic industry, and it is dominated by choppers, cores, flakes, and simple retouched flake tools from 1.15 to 0.6 Ma. Paleolithic open-air sites such as Gongwangling and Chenjiawo in the Lantian area, Shangbaichuan and Liuwan in the Luonan Basin, Qiaojiayao in the Lushi Basin, Longgangsi and Yaochangwan in the Hanzhong Basin, Guanmiao in the Ankang Basin, and the Yunxian Man Site in the Yunxian Basin are representative sites in the region; from 400 to 250 ka, the Longyadong cave site in the Luonan Basin inherited the characteristics of the local Mode I lithic industry, the stone assemblage is made up of cores, flakes, and small retouched flake tools, such as scrapers, points, and burins; during the period from 250 to 50 ka, bi-facially retouched Acheulean tools (Model II), such as hand-axes, picks, and cleavers, were commonly found in the Qinling Mountains region. The emergence of a large number of Model II artifacts indicates that local lithic industries went through a major transition process. Zhanghuokou, Guoyuan, and Huaishuping sites in the Luonan Basin, Diaozhai, Ganyu, Laochihe, and Xiehu sites in the Lantian area, Hejialiang site in the Hanzhong Basin are representative sites in this period; to the turn of the Late Pleistocene and Early Holocene, it may also exist a small flake-retouched tools lithic industry in the piedmonts of the northern and southern sides of the Qinling Mountains. The lithic assemblages in different stages of the Qinling Mountains region reflect the hominin behavioral changes and the development of lithic technology during the Pleistocene.