Mountain-basin System Research Articles

Inheritance recharge of subsurface brine constrains on formation of K-bearing sand-gravel brine in the alluvial fan zone of mountain-basin system on the Qinghai-Tibetan Plateau

The deep brines enriched in potassium (K), lithium (Li), boron (B) resource elements in sedimentary basins are valuable potential mineral resources. There is a widely accepted consensus that evaporite and brine resources were formed in terminal salt lakes, however, newly discovered sand-gravel brine (SGB) occurred in the piedmont alluvial fan zone on the northern Qinghai-Tibetan Plateau (QTP). Currently, there is a key scientific issue on where does the solute of SGB in the alluvial fan zone come from? The existing understanding is that the solute of high Na+, Cl− originates from halite dissolution by meteoric water, but lack of isotope geochemical linkage between brine and evaporite. The Mahai Basin (MHB) on the northern QTP is a natural experimental site for the study on the above unsolved problems, due to harboring similar brine reservoir, small geographical area, thin evaporite layers and various waters in this basin. This study presents detailed analysis of H-O-Cl-Li isotopic compositions and hydrogeochemical parameters for intercrystalline brine, SGB and halite from drilling cores in the MHB. The results reveal several key findings: (1) the SGB in the piedmont alluvial fan zone of Altyn Tagh and Saishiteng Mountains presents similar geochemical characteristics of low TDS, high Na+, Cl− and relatively high K+ contents (1.12–3.65 g/L in MHB), which established new occurrence model of brine resource in the ‘Fan-Lake’ system. (2) The δD (−56.90 ‰∼−17.60 ‰) and δ18O (−5.70 ‰∼6.00 ‰) values of SGB in the MHB are higher, the isotopic disparity exists in these two mountain-fan-lake systems, but they are meteoric origin and accord with their respective hydrologic circulation process. (3) The CNa/CCl molar ratio (∼0.80), δ37Cl (−0.26 ‰∼+0.25 ‰) and δ7Li values (+33.84 ‰∼+43.82 ‰) of SGB are comparable with those of intercrystalline brine in the MHB, indicating that inheritance recharge of salt lake brine for the formation of SGB in this basin. (4) The metallogenic model of SGB in the MHB is multi-condition constraints (northward migration of depocenter, hydrological lateral recharge of river water along the alluvial fault zone and strata subsidence along with the mountain uplift), which develops the topographic difference between brine aquifers of salt lake and alluvial fan zone resulting into subsurface brines recharge for the alluvial-pluvial fan reservoir.

Altitude effect of precipitation isotopes in an arid mountain-basin system: Observation and modelling around the world’s second-largest shifting desert

The stable water isotopes of precipitation provide important information about the hydrological circulation. In the arid mountain-basin system in central Asia, the altitude effect of precipitation isotopes has been a controversial topic in recent years, but the sample availability in extreme environments constrains the accurate understanding of the relationship between altitude and stable isotopes in precipitation. Based on the observation of precipitation isotopes around the Tarim Basin covered by the world’s second-largest shifting desert, we examined the relationship between altitude and isotope composition. There is an altitude effect of precipitation isotopes between the basin and the surrounding mountains, with the modelled gradient for annual mean δ18O being approximately 1.96 ‰ per 1000 m, which is weaker than the observed gradient focusing on the oases (2.75 ‰ per 1000 m). The largest modelled difference in δ18O between 1000–2000 m and 2000–3000 m above sea level occurs in August and September. The periods with a larger gradient of altitude effect usually have higher temperature and more precipitation. Across the westerlies-dominated central Asia, the below-cloud evaporation enhances the altitude gradient of precipitation isotopes for most areas. The findings are useful to understand the local and remote drivers of precipitation isotopes and the paleoaltimetry of stable isotopes in climate proxies.

Increased late Holocene dust activity revealed by loess accumulation rates in Central Asia

Dust from the vast arid and semi-arid regions of arid Central Asia (ACA) makes a large contribution to global-scale dust cycles. However, systematic and regional-scale reconstructions of dust activity in ACA are lacking, thus hindering the exploration of its relationship with climate change. Aeolian loess deposits provide valuable records of past dust activity and its linkages to climate. We constructed a stacked, normalized dust mass accumulation rate (MAR) record from 17 loess sections with high-resolution dating, together with a probability density record based on 189 absolute ages from 39 Holocene loess sections. These records were used to reconstruct the temporal pattern of Holocene dust activity in ACA, which shows a pronounced increase during the late Holocene. After evaluating the temporal variation of moisture conditions at different altitudes in ACA, we conclude that while dust activity during the early and middle Holocene was driven predominantly by climate change, this was not the case in the late Holocene. Taking the mountain-basin system of the Yili Basin in Xinjiang as an example, we propose that dust activity on a large spatial scale was not completely controlled by changes in moisture conditions, and that regional factors, such as fluvial geomorphic processes, played an important role in increasing the materials supply to the areas of dust accumulation. We speculate that dust activity may intensify in ACA under future global warming scenarios.

Moisture changes in a mountain–basin system since the last deglaciation revealed by the pollen record of Genggahai Lake, northeastern Qinghai-Tibetan Plateau

Asia’s mountainous arid and semiarid regions feature forests in wet high-mountain areas and grasslands/deserts in dry basins. Assessing changes in millennial-scale effective moisture in mountain–basin systems can provide a valuable reference for understanding how climate change and human activities affect terrestrial water resources and drylands. Here, a continuous pollen record from Genggahai Lake on the northeastern Qinghai-Tibetan Plateau exhibited detailed changes in regional vegetation and effective moisture since ∼ 15.3 ka. The pollen sequence suggests that steppe vegetation developed in the basin and that sparse forest vegetation developed in the surrounding mountain areas during 15.3–11.7 ka and 6.3–0 ka, and that desert steppe vegetation developed in the basin and denser forest vegetation developed in the surrounding mountain areas during 11.7–6.3 ka. Based on comparison of regional palaeoclimatic records, the pollen assemblage results suggest antiphase moisture changes between mountains and the basin and imply that the low Artemisia/Chenopodiaceae (A/C) ratio during 11.7–6.3 ka in the basin likely indicates that the low effective moisture conditions likely resulted from the high permeability of loose and porous sediments and the high evaporation in the basin induced by high summer solar insolation. In contrast, the high A/C ratio during 15.3–11.7 ka and 6.3–0 ka indicates a high level of effective moisture during these periods, possibly in response to less evapotranspiration loss in the basin caused by the strong water-binding capacity of palaeosols, ameliorated vegetation conditions, and low summer solar insolation. Our results also suggest that both climatic conditions and anthropogenic activities may have altered the natural vegetation in the late Holocene and that change in the percentage of tree pollen from Genggahai Lake were synchronous with changes in the intensity of the Indian summer monsoon.

Land Use Transition of the Mountain-Basin System under the Background of Rural Revitalization: Based on Four Typical Mountain-Basin Systems

Land Use Transition of the Mountain-Basin System under the Background of Rural Revitalization: Based on Four Typical Mountain-Basin Systems

Study on the influence of meteorological elements on growing season vegetation coverage in Xinjiang, China

<abstract><p>Xinjiang is a typical arid and semi-arid Mountain basin system, which make the regional ecosystem extremely fragile. Studying the influence of climate on vegetation is conducive to qualitatively analyze the change trend of vegetation coverage in this region. Therefore, utilizing vegetation coverage and main meteorological elements (temperature, precipitation, relative humidity, sunshine hours) data in Xinjiang province, this paper carried out the influence of multiple meteorological elements on vegetation coverage changes, and constructed a model of the impact of multiple meteorological elements on the growing season vegetation coverage based on random forest. The model can better simulate the vegetation coverage in 2017 and 2018, with an average error of 0.027, in consequence it can well forecast whether the vegetation is high-density or low-density in this area. Correlation analysis and variable importance show that the critical meteorological factors affecting vegetation cover change are relative humidity and sunshine hours, accounting for 73% of the vegetation coverage area. The results are helpful to understand how meteorological factors affect the vegetation coverage, and then provide a theoretical reference for the construction of ecological security in Xinjiang.</p></abstract>

An inverse relationship between moisture and grazing intensity in an arid mountain-basin system

Precipitation has been suggested as a crucial influencing factor in the primary productivity in arid and semi-arid regions, yet how moisture fluctuation in an arid mountain-basin system of the north Qinghai–Tibetan Plateau has affected human activities is poorly understood. Here, we reconstruct the variations of grazing intensity in high elevations and regional humidity based on independent and high-resolution records of Sporormiella-type coprophilous fungal spores and pollen grains in the same well-dated sediment core from Lake Tian’E in the western Qilian Mountains over the past 3500 years. We find that stronger grazing activity was associated with low regional effective moisture, and propose that the drier regional climate pushed people and their livestock into the mountainous areas. A notable exception was a reduction of human and grazing activities in arid region with high mountains during 380–580 CE caused by centennial-length dry and cold conditions. In addition, it is also noteworthy that intensified grazing activity occurred during 580–720 CE and after ∼1920 CE, corresponding to a warmer and wetter climate and diverse subsistence strategies with social developments in the lowlands of the Hexi Corridor. Our findings potentially provide a historical reference for understanding how ancient people adapted to the climate change in arid region with high mountains.

Impact of climate change on plant species richness across drylands in China: From past to present and into the future

It is commonly believed that climate plays an important role in shaping the patterns of plant species richness. However, it remains unclear how climate may affect plant richness across large spatial scales and also over long-terms, for example across massive arid regions during the Quaternary and into the future. To fill this knowledge gap, we examined the long-term trends in plant species richness across vast drylands in China based on our newly developed climate-species richness models. We first generated optimal random forest models based on the relationships between the current (CUR, 1970–2000) annual, perennial, woody and total species richness and climatic variables. We subsequently hindcasted and forecasted plant species richness in five other periods: last interglacial (LIG, 120,000–140,000 years BP), last glacial maximum (LGM, about 22,000 years BP), mid-Holocene (MH, about 6000 years BP), 2041–2060 (2050), and 2061–2080 (2070). Our results showed that total and herbaceous species richness exhibited similar patterns that were driven by temperature and precipitation. Both groups of species formed a transition zone between arid and semi-arid regions in all periods except LIG. In contrast, woody species richness did not form any transition zone because it was regulated mainly by temperature. Furthermore, the mean richness of herbaceous, woody and all species exhibited gradually increasing trends from LIG to 2070 across drylands in China. On the one hand, herbaceous species were much more sensitive to climate change than woody species. On the other hand, plant species richness in mountain-basin systems and Taklamakan Desert regions were more sensitive to climate change than in meadows and steppes. These results shed new insights into the past and future changes in plant species richness over vast drylands and provide valuable information for future conservation efforts under global warming.

Glacier-Induced Alluvial Fan Development on the Northeast Tibetan Plateau Since the Late Pleistocene

The origin of alluvial fans at the drainage basin or the margins of the arid sedimentary basin on the northeastern Tibetan Plateau (NETP) has been a focus of debate among scientific communities. Extensive alluvial fans had developed in the mountain-basin systems of this region during the late Pleistocene. Based on geomorphic/stratigraphic studies and the optically stimulated luminescence (OSL) chronology, we investigated numerous alluvial sequences in the drainage basin of the coupled mountain-basin system on the NETP. Sedimentologic analyses showed that these alluvial sediments mainly comprise crudely meter and decimeter beds of fanglomerate and sandy lenticles, which occasionally contain boulders in the thinner layers. OSL dating results showed that the alluvial sediments were mainly developed during the late MIS 5, MIS 3, and Last Glaciation and Deglaciation (maximum aggradations), while little had occurred during the early Holocene. Comparing our ages and their probability density curves with those of glacial advances from the northeastern/eastern TP, the consistency of both records during different stages since the late Pleistocene suggested that the development of alluvial fans was driven by glacier activities, which yielded abundant outwash, feeding alluvial aggradations. Based on this finding, together with results of previous studies, we argued that the dynamics of alluvial geomorphic processes had a paleoclimatic origin rather than surface uplifts. Further studies indicated that the precipitation of glaciations originated from the ISM northward intrusion during the late MIS 5, MIS 3, and Holocene; however, it was mainly influenced by the westerlies during the Last Glaciation and Deglaciation. Therefore, the development of alluvial fans on the NETP represents coupling signals of the ISM and the westerlies on the interglacial–glacial cycle timescales. The coupling evolution of glacier activities and alluvial aggradations in the drainage basins of mountain-basin systems on the NETP provides a model for assessing the linkages between regional geomorphic processes and atmospheric circulations on hemispheric scales.

Precipitation in surrounding mountains instead of lowlands facilitated the prosperity of ancient civilizations in the eastern Qaidam Basin of the Tibetan Plateau

Precipitation fluctuation has been suggested as a crucial influencing factor in the evolution of ancient civilizations across the world. Nuomuhong culture (~3400–2450 BP) and Tuyuhun (313–663 CE) were unique ancient civilizations that developed in the eastern Qaidam Basin of the north Tibetan Plateau. However, how precipitation variation in the mountain–basin system has affected the rise and fall of these two ancient civilizations is not well understood. Based on analyses of grain size, magnetic susceptibility, Rb/Sr ratio, loss on ignition, and optically stimulated luminescence dates from an aeolian deposit sequence, lowland climate change in the Qaidam Basin during the late Holocene is reconstructed. The Rb/Sr ratio varies from 0.31 to 0.33 during ~2500–2300 BP, it increases from 0.33 to 0.44 during ~2300–1600 BP, and decreases from 0.44 to 0.29 during ~1600–1400 BP, suggesting the climate was relatively dry during ~2500–2300 BP and ~1600–1400 BP and relatively wet during ~2300–1600 BP in the lowlands of the eastern Qaidam Basin, which corresponded well to the gap between the Nuomuhong and Tuyuhun periods. However, the prosperous periods of the Nuomuhong and Tuyuhun were synchronous with high precipitation in the surrounding mountains. Therefore, high precipitation in the surrounding mountains nourished the expansion of oases and then facilitated the development of Nuomuhong and Tuyuhun, which was inconsistent with precipitation variation in the lowlands of eastern Qaidam Basin. The spatiotemporal pattern of precipitation in the mountain–basin system of the Qaidam Basin during the late Holocene was likely affected by solar activity through uplifting–subsiding air flow mechanism, with more precipitation in the mountain and less precipitation in the basin under higher solar activity. A cognitive model is provided to illustrate how solar activity affected the spatiotemporal patterns of precipitation in the mountain–basin structure of the eastern Qaidam, and then human settlement and civilization evolution during the late Holocene.

Optimizing Cropping Systems of Cultivated Pastures in the Mountain–Basin Systems in Northwest China

Cultivated pastures are effective supporting systems of natural grassland preservation and sustainable agriculture in arid regions of northwest China. The adaptive combination of forage species enhances the yields and ecological functions of cultivated pastures. Legume–grass intercropping is a valuable sowing regime because of the niche differentiation and resource acquisition. Understanding the effects of species interactions in legume–grass intercropping systems can provide scientific and practical guidance on cultivated pasture management. In this study, we conducted a field experiment to determine the advantages and effects of alfalfa (Medicago sativa L.) annual grass intercropping on cultivated pastures. We analyzed the data on population traits, community characteristics and dry matter in the growing period to evaluate the effects of variety and sowing patterns with the following treatments: three alfalfa varieties (Algonquin, Leafy king, WL354HQ) sown in monocultures and mixed with oat (Avena sativa L.) or sudangrass (Sorghum sudanense (Piper) Stapf.) with two seeding ratios. Our results suggest that in mixtures, the plant traits of alfalfa were determined by their own characters at the earlier stage but were affected more by companion grass at the later stage. The annual forage grass companion impaired the growth of alfalfa during the growth period. In mixtures, sudangrass displayed a stronger inhibiting effect on alfalfa than oat. Alfalfa–grass intercropping was proved to be a feasible cropping practice in terms of yield, production stability and weed control, due to their complementary use of resources in comparison with alfalfa monocropping. Alfalfa–annual grass intercropping is a beneficial alternative strategy to obtain effective cultivated pastures in arid regions.

Response of grassland productivity to climate change and anthropogenic activities in arid regions of Central Asia.

BackgroundQuantitative evaluations of the relative impacts of climate change and anthropogenic activity on grasslands are significant for understanding grassland degradation mechanisms and controlling degraded grasslands. However, our knowledge about the effects of anthropogenic activities and climate change on the grassland in a mountain basin system in arid regions of Central Asia is still subject to great uncertainties.MethodsIn this research, we have chosen the net primary productivity (NPP) as an index for revealing grassland dynamics processes. Moreover, the human appropriation of net primary production (NPPH), which was calculated as the potential NPP (NPPP) minus the actual NPP (NPPA), was applied to distinguish the relative influences of climate change and human activities on the grassland NPP variations in a mountain basin system of Central Asia from 2001–2015.ResultsThe results indicated that the grassland NPPA showed an increasing trend (35.88%) that was smaller than the decreasing trend (64.12%). The respective contributions of human activity, climate change and the two together to the increase in the NPPA were 6.19%, 81.30% and 12.51%, respectively. Human activity was largely responsible for the decrease in the grassland NPPA, with the area experiencing human-induced decreases accounting for 98.21% of the total decreased area, which mainly occurred during spring/autumn pasture and winter pasture. Furthermore, the average grazing pressure index (GPI) values of summer pastures, spring/autumn pasture and winter pastures were 1.04, 3.03 and 1.83, respectively, from 2001–2015. In addition, negative correlations between the NPP and GPI occupied most of the research area (92.41%).DiscussionOur results indicate that: (i) anthropogenic activities were the primary cause of the reduction in the grassland NPP, especially grazing activities. (ii) For areas where the grassland NPP has increased, precipitation was the dominant climatic factor over temperature in controlling the grassland NPP changes in the study area. (iii) The findings of the current research indicate that some measures should be taken to reduce livestock pressure, and artificial grasslands can be built along the Irtysh River and the Ulungur River to relieve grazing pressure on spring/autumn pastures and winter pastures. Our results could provide reliable information for grassland management and the prevention of grassland degradation in arid regions of Central Asia.

Exploring Connections among Ecosystem Services Supply, Demand and Human Well-Being in a Mountain-Basin System, China.

Stakeholder perception and supply–demand relations are the main challenges and future directions for research on ecosystem services (ES). Based on spatial data and statistical data, we mapped eight key ES supply between 2005–2015 in the Huailai mountain-basin area. Using data from 507 survey questionnaires, we identified the ES demand and the public perceptions of the changes in ES. In addition, we also reveal the characteristics of the spatial distribution of ES demand, analyze the spatial supply–demand matching of ES, and explore the relationships between ES supply–demand and human well-being. From 2005 to 2015, a general upward trend was observed in the supply of four types of product provisioning services, which is different from the trend perceived by the stakeholders. An increasing trend was observed for carbon sequestration and forest recreation, which was in line with the perceptions of change. A spatial mismatch existed between the ES demand and supply, whereby the supply of carbon sequestration, soil conservation, habitat quality, and forest recreation services exceeded the demand in townships in the mountainous and hilly regions. On the other hand, townships located in the valley plains experienced a high imbalance between the demand and the supply. For the four types of product provisioning services, most towns and villages showed a balance in demand and supply. Linking ES supply–demand and human well-being showed that a threshold may exist in the supply–demand imbalance of regulating and supporting services before it begins to impact human well-being. Our study would enrich the theory and methodology research on relationships between ecosystem services and human well-being, and support knowledge to land allocation and management.

Sustainability of sown systems of cultivated grassland at the edge of the Junggar Desert Basin: An integrated evaluation of emergy and economics

An environmentally sustainable cultivated grassland at the edge of the Junggar Desert Basin in China is vital for the ecological conservation of the mountain-basin system (MBS) in the arid region of Central Asia and the stable settlement of herdsmen in the northern China. To evaluate the sustainability of sown systems, this study applied emergy and economic analysis to three traditional sown systems, silage corn (SC), oil sunflower (OS), and seed melon (SM), and three innovative sown systems, leafy king monocropped (LM), leafy king-sudangrass intercropped (LSI) and algonquin-sudangrass intercropped (ASI), in a cultivated grassland at the edge of the Junggar Desert Basin. The emergy results revealed that all systems required 85.65%–90.32% of emergy investments from outside systems, and 74.17%–84.46% of the investments were nonrenewable emergy inputs. The emergy sustainability ratio revealed that ASI, LSI and LM had superior ecological benefits with lower environmental burdens than SC, OS and SM. The economic analysis illustrated that OS and ASI had high economic profits, while ASI, LSI and LM had high income-to-cost ratios. LSI and ASI could achieve both ecological and economic benefits. The chemical fertilizer and irrigation water simulations indicated that the sustainability of all these systems could be enhanced by applying drip irrigation and reducing chemical fertilizer by 20%. Therefore, water-saving irrigation and renewable resource utilization need to be implemented. Appropriate adjustments to the plantation structure and long-term financial and policy support for cultivated grassland construction are recommended. Advanced cultivated technology should be investigated and promoted. Additionally, the rationally allocated and scientifically managed cultivated grassland at the edge of desert basin can be an optimized strategy for sustainable development of ecological and economic in similar MBSs of the arid regions of Central Asia.

Response of Vegetation and Soil Characteristics to Grazing Disturbance in Mountain Meadows and Temperate Typical Steppe in the Arid Regions of Central Asian, Xinjiang.

Grazing is one of the most common causes of grassland degradation, therefore, an assessment of soil physicochemical properties and plant nutrients under grazing is important for understanding its influences on ecosystem nutrient cycling and for formulating appropriate management strategies. However, the effects of grazing on grassland soil physicochemical properties and plant nutrients in mountain meadow and temperate typical steppe in the arid regions are still unclear. Therefore, we investigated the vegetation nutrient concentrations of nitrogen, phosphorus and potassium (N, P, and K) as well as soil physicochemical properties in the topmost 40 cm depth soil, to evaluate how these factors respond to grazing disturbance in a mountain meadow and temperate typical steppe within a mountain basin system in arid regions. Our results revealed that the soil bulk density values at depth of 0–40 cm increased after grazing in the mountain meadow and temperate typical steppe, whereas the soil water content decreased in the mountain meadow and increased in the temperate typical steppe after grazing. In the mountain meadow, soil total N and available P in addition to vegetation N and P concentrations increased in response to high-intensity grazing, while soil available N, available K and vegetation K decreased after grazing; in addition, soil pH, soil total P and K showed no significant changes. In the temperate typical steppe, the soil total P, soil available N, P, and K, and vegetation N, P, and K increased under relatively low-intensity grazing, whereas soil pH and soil total K showed no significant changes except for the deceasing soil total N. Our findings showed the different responses of different grassland ecosystems to grazing. Moreover, we propose that further related studies are necessary to better understand the effects of grazing on grassland ecosystems, and thereby provide a theoretical basis for the sustainable use of animal husbandry and ecological restoration of grasslands.

Elevation and Climate Effects on Vegetation Greenness in an Arid Mountain-Basin System of Central Asia

Mountain-basin systems (MBS) in Central Asia are unique and complex ecosystems, wherein their elevation gradients lead to high spatial heterogeneity in vegetation and its response to climate change. Exploring elevation-dependent vegetation greenness variation and the effects of climate factors on vegetation has important theoretical and practical significance for regulating the ecological processes of this system. Based on the MODIS NDVI (remotely sensed normalized difference vegetation index), and observed precipitation and temperature data sets, we analyzed vegetation greenness and climate patterns and dynamics with respect to elevation (300–3600 m) in a typical MBS, in Altay Prefecture, China, during 2000–2017. Results showed that vegetation exhibited a greening (NDVI) trend for the whole region, as well as the mountain, oasis and desert zones, but only the desert zone reached significant level. Vegetation in all elevation bins showed greening, with significant trends at 400–700 m and 2600–3500 m. In summer, lower elevation bins (below 1500 m) had a nonsignificant wetting and warming trend and higher elevation bins had a nonsignificant drying and warming trend. Temperature trend increased with increasing elevation, indicating that warming was stronger at higher elevations. In addition, precipitation had a significantly positive coefficient and temperature a nonsignificant coefficient with NDVI at both regional scale and subregional scale. Our analysis suggests that the regional average could mask or obscure the relationship between climate and vegetation at elevational scale. Vegetation greenness had a positive response to precipitation change in all elevation bins, and had a negative response to temperature change at lower elevations (below 2600 m), and a positive response to temperature change at higher elevations. We observed that vegetation greenness was more sensitive to precipitation than to temperature at lower elevations (below 2700 m), and was more sensitive to temperature at higher elevations.

Impacts of climate change and anthropogenic activities on grasslands in a mountain-basin system in Xinjiang, Central Asia's arid regions

Impacts of climate change and anthropogenic activities on grasslands in a mountain-basin system in Xinjiang, Central Asia's arid regions

Does Climate Change or Human Activity Lead to the Degradation in the Grassland Ecosystem in a Mountain-Basin System in an Arid Region of China?

In mountain-basin systems in the arid region, grasslands are sensitive to the impacts of climate change and human activities. In this study, we aimed to resolve two key scientific issues: (1) distinguish and explain the laws of grassland ecosystem deterioration in a mountain-basin system and identify the key factors related; and (2) evaluate whether damaged grasslands ecosystem have the potential for natural revegetation. Hence, by combining spatial analysis with statistical methods, we studied the trends of the deterioration of the grassland ecosystem and its spatial characteristics in Kulusitai, a mountain-basin system in the arid region of Northwest China. According to our results, vegetation coverage and productivity exhibited significant decreasing trends, while the temperature vegetation drought index (TVDI) exhibited a significant increasing trend. Drainage of groundwater, because of increase in irrigation for the expanded irrigated area around Kulusitai, and climate warming were the critical triggers that leaded to the soil drought. Soil drought and overgrazing, resulting from the impact of human activities, were the main factors responsible for the deterioration of the grassland ecosystems. However, limiting the number of livestock to a reasonable scale and reducing the irrigated area may help to increase the soil moisture, thus promoting the germination of soil seed banks and facilitating the normal growth of grassland vegetation. Furthermore, based on analysis of the phenology of the grassland vegetation, the reasonable period for harvesting and storage is from July 29 to August 5. The results of this study provide a scientific basis and practical guide for restoring mountain-basin grassland systems in arid regions.

Drainage geomorphic evolution in response to paleoclimatic changes since 12.8 ka in the eastern Kunlun Mountains, NE Qinghai-Tibetan Plateau

Investigation of the geomorphologic evolution of drainage basins can provide insight into the response of mountain-basin systems to paleoclimate fluctuations. This study investigates the evolution of geomorphic units and their connectivity, from upstream piedmont to downstream salt lake, since the late Quaternary in the Golmud River catchment of the eastern Kunlun Mountains (KLM). The study aims to elucidate the debate over linkages between: (1) landform evolution and paleoclimatic change and (2) dynamic geomorphic processes and lake evolution in the lower basin. Based on geomorphic and sedimentological observations and an optically stimulated luminescence (OSL) chronology, we show three main phases of geomorphic processes: (1) upstream piedmont alluvial fans and an alluvial delta fan at the salt lake margin have surface sediment OSL ages of 12.8–11.4 ka, suggesting a valley aggradation stage in which mass periglacial detritus were eroded and redeposited in the drainage basin; (2) incision terraces in alluvial valley fills provide ages between 11.4 and 8.8, 8.1–6.2, and 4.9–3.9 ka. Incision is ascribed to the reduction in supply of detritus owing to glacial recession and enhanced precipitation in the early to middle Holocene; and (3) widely distributed swamp sediments in the distal delta fan date to 3.2–1.8 ka, suggesting a wetter stage within the late Holocene climatic deterioration. Loess, indicative of aridity, was deposited intermittently during the middle to late Holocene. We reconstructed a wetness index, based on wetness scores of drainage geomorphic units, which is consistent with published moisture proxies. This association implies that (1) landform processes in KLM responded well to precipitation fluctuations in Indian summer monsoon (ISM) dominant regions, indicating their climatic forcing and (2) precipitation variations in the eastern KLM have been mainly controlled by ISM intensity since 12.8 ka. Linking the geomorphologic evolution of mountain-basin systems to downstream arid basin evolution shows that the periods of fluvial terrace incision (early to middle Holocene) were probably important sources of lake salt mineral enrichment. The landscape evolution patterns of mountain-basin systems in the eastern KLM offer a model for assessing the linkages between geomorphic processes, paleoclimatic changes, and lake evolution in other arid regions.

Characteristics of soil organic carbon and total nitrogen under various grassland types along a transect in a mountain-basin system in Xinjiang, China

Soil organic carbon (SOC) and soil total nitrogen (STN) in arid regions are important components of global C and the N cycles, and their response to climate change will have important implications for both ecosystem processes and global climate feedbacks. Grassland ecosystems of Funyun County in the southern foot of the Altay Mountains are characterized by complex topography, suggesting large variability in the spatial distribution of SOC and STN. However, there has been little investigation of SOC and STN on grasslands in arid regions with a mountain-basin structure. Therefore, we investigated the characteristics of SOC and STN in different grassland types in a mountain-basin system at the southern foot of the Altai Mountains, north of the Junggar Basin in China, and explored their potential influencing factors and relationships with meteorological factors and soil properties. We found that the concentrations and storages of SOC and STN varied significantly with grassland type, and showed a decreasing trend along a decreasing elevation gradient in alpine meadow, mountain meadow, temperate typical steppe, temperate steppe desert, and temperate steppe desert. In addition, the SOC and STN concentrations decreased with depth, except in the temperate desert steppe. According to Pearson's correlation values and redundancy analysis, the mean annual precipitation, soil moisture content and soil available N concentration were significantly positively correlated with the SOC and STN concentrations. In contrast, the mean annual temperature, pH, and soil bulk density were significantly and negatively correlated with the SOC and STN concentrations. The mean annual precipitation and mean annual temperature were the primary factors related to the SOC and STN concentrations. The distributions of the SOC and STN concentrations were highly regulated by the elevation-induced differences in meteorological factors. Mean annual precipitation and mean annual temperature together explained 97.85% and 98.38% of the overall variations in the SOC and STN concentrations, respectively, at soil depth of 0–40 cm, with precipitation making the greatest contribution. Our results provide a basis for estimating and predicting SOC and STN concentrations in grasslands in arid regions with a mountain-basin structure.