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Anthropogenic‐driven global change, including changes in atmospheric nitrogen (N) deposition and precipitation patterns, is dramatically altering N cycling in soil. How long‐term N deposition, precipitation changes, and their interaction influence nitrous oxide (N2O) emissions remains unknown, especially in the alpine steppes of the Qinghai–Tibetan Plateau (QTP). To fill this knowledge gap, a platform of N addition (10 g m−2 year−1) and altered precipitation (±50% precipitation) experiments was established in an alpine steppe of the QTP in 2013. Long‐term N addition significantly increased N2O emissions. However, neither long‐term alterations in precipitation nor the co‐occurrence of N addition and altered precipitation significantly affected N2O emissions. These unexpected findings indicate that N2O emissions are particularly susceptible to N deposition in the alpine steppes. Our results further indicated that both biotic and abiotic properties had significant effects on N2O emissions. N2O emissions occurred mainly due to nitrification, which was dominated by ammonia‐oxidizing bacteria, rather than ammonia‐oxidizing archaea. Furthermore, the alterations in belowground biomass and soil temperature induced by N addition modulated N2O emissions. Overall, this study provides pivotal insights to aid the prediction of future responses of N2O emissions to long‐term N deposition and precipitation changes in alpine ecosystems. The underlying microbial pathway and key predictors of N2O emissions identified in this study may also be used for future global‐scale model studies., Our field experiments show that the alpine steppe was a net source of N2O. Our results also demonstrate that N addition intensified N2O emission, while altered precipitation and its interaction with N addition did not affect N2O emission.

To better understand the variation in mountainous discharge (MD) in the future, a basin case study was conducted in the upstream Taolai River Basin (UTRB) in arid northwestern China. The Blaney-Criddle (B-C) equation, Budyko framework, and water balance method were coupled for MD calculations. The outputs of 10 global climate models (GCMs) are synthesized to confirm the future changes in air temperature and precipitation under 3 selected Representative Concentration Pathway (RCP) scenarios. The climate elasticity (CE) method was used to determine the variation in MD, and the influence of climate factors on that was quantitatively analyzed. The results reveal that the coupling framework of the three methods is suitable for MD determination in the UTRB. The weight-based synthesis of the 10 GCM outputs shows overall increases in temperature (T) and precipitation (P) under the 3 scenarios during most of the time until 2099. The above climate change leads to an increase in MD. According to CE analysis, the positive effectiveness of precipitation is greater than the negative effectiveness of temperature on MD variation, and the increase in precipitation would induce more MD in the UTRB. Uncertainty analysis reveals that GCM outputs dominate in predicting precipitation, while the RCP scenarios influence temperature more. Overall, under the background of climate change, the risk of extreme floods during wet years might increase, and a water deficit will still occur during normal and dry years. The study provides a case example for better understanding MD responses to climate change in the upper reaches of inland river basins. Findings are helpful for reasonable water resource development and utilization in the middle and lower reaches of these basins in the future. As in the Taolai River Basin, considering the future water demand across the whole basin, the development of water-saving technologies and reasonable industrial structures is crucial for a sustainable future.

There are two important allocation hypotheses in plant biomass allocation: allometric and isometric. We tested these two hypotheses in an alpine steppe using plant biomass allocation under nitrogen (N) addition and precipitation (Precip) changes at a community level. An in situ field manipulation experiment was conducted to examine the two hypotheses and the responses of the biomass to N addition (10 g N m−2 y−1) and altered Precip (±50% precipitation) in an alpine steppe on the Qinghai–Tibetan Plateau from 2013 to 2016. We found that the plant community biomass differed in its response to N addition and reduced Precip such that N addition significantly increased aboveground biomass (AGB), while reduced Precip significantly decreased AGB from 2014 to 2016. Moreover, reduced Precip enhanced deep soil belowground biomass (BGB). In the natural alpine steppe, the allocation between AGB and BGB was consistent with the isometric hypotheses. In contrast, N addition or altered Precip enhanced biomass allocation to aboveground, thus leading to allometric growth. More importantly, reduced Precip enhanced biomass allocation into deep soil. Our study provides insight into the responses of alpine steppes to global climate change by linking AGB and BGB allocation., In summary, we demonstrated that altered precipitation and N addition led to changes in the relationship between aboveground and belowground biomass allocation. Moreover, we demonstrated that reduced precipitation had little impacts on aboveground and belowground biomass allocation, while it enhanced more biomass into deep soil. Therefore, our finding provides a novel insight into N and precipitation‐induced changes in the aboveground and belowground biomass allocation in the alpine steppe.

Alpine shrubland ecosystems in the Three Rivers Source Region (TRSR) store substantial soil organic carbon (SOC), but the storage, patterns and control of SOC in those ecosystems have rarely been investigated. In this study, using data from 66 soil profiles surveyed from 22 sites between 2011 and 2013, we estimated the storage and patterns of SOC, and their relationships with climatic factors, elevation, ground cover and slope. Our results showed that SOC storage in the top 100 cm across the TRSR shrubland was 0.68 ± 0.38 Pg C, with an average SOC density (soil carbon storage per area) of 26.21 ± 14.58 kg m−2. Spatially, SOC density increased with longitude and latitude. Vertically, SOC in the topsoil at 30 cm and 50 cm accounted for 56% and 75%, respectively, of the total at 100 cm. SOC density showed a decreasing trend with increasing elevation, but it was greater in regions of higher ground cover. The density had no relationship with either mean annual precipitation or slope. Increasing mean annual temperature had positive effects on SOC density, which is inconsistent with the global trend. With increasing soil depth, however, the effects of temperature on SOC density were not significant. Therefore, in a global warming scenario, increasing temperature gives shrubland considerable C sink potential on the topsoil, and the regions of C sequestration differ as a result of uneven increases in temperature. Hence, further monitoring of dynamic changes is necessary to provide a more accurate assessment of potential C sequestration in TRSR shrubland.

Global climate change and nitrogen deposition have been having broad impacts on microorganisms. On the Qinghai-Tibetan Plateau (QTP), the responses of soil microbial community assemblage and diversity to nitrogen deposition and changes in precipitation are poorly understood, especially in the alpine steppe. In this study, we conducted a field manipulative experiment of nitrogen deposition and precipitation amount in an alpine steppe on the northeastern QTP and investigated the responses of community composition, diversity, and community assemblage of soil fungi. Soil fungal community compositions were significantly altered under nitrogen addition, precipitation change, and their interaction, and positively related with soil moisture, soil pH, and plant species richness. However, they were negatively related to soil mineralizable N and soil available P content. Operational taxonomic units (OTU) richness and Chao 1 index decreased under nitrogen addition combined with precipitation reduction treatment, whereas the Shannon-Wiener index declined only under precipitation increment treatment. Convergent fungal community assembly processes were not acutely altered by both nitrogen addition and precipitation changes, indicating that environmental filtering was a dominant ecological process controlling fungal community assemblage. By elucidating the above questions, the study enhanced our ability to predict the responses of soil fungal communities to nitrogen deposition and precipitation changes at alpine steppes on the QTP in the future.

Accurate projection of future precipitation is a major challenge due to the uncertainties arising from the atmospheric predictors and the inherent biases that exist in the global circulation models. In this study, we employed multivariate recursive nesting bias correction (MRNBC) and multiscale wavelet entropy (MWE) to reduce the bias and improve the projection of future (i.e., 2006–2100) precipitation with artificial intelligence (AI)-based data-driven models. Application of the developed method and the subsequent analyses are performed based on representative concentration pathway (RCP) scenarios: RCP4.5 and RCP8.5 of eight Coupled Model Intercomparison Project Phase-5 (CMIP5) Earth system models for the upstream of the Heihe River. The results confirmed the MRNBC and MWE were important statistical approaches prudent in simulation performance improvement and projection uncertainty reduction. The AI-based methods were superior to linear regression method in precipitation projection. The selected CMIP5 outputs showed agreement in the projection of future precipitation under two scenarios. The future precipitation under RCP8.5 exhibited a significantly increasing trend in relative to RCP4.5. In the future, the precipitation will experience an increase by 15–19% from 2020 to 2050 and by 21–33% from 2060 to 2090.

Although large amounts of soil organic carbon (SOC) stored in the shrublands, information about SOC storage was little on the Tibetan Plateau. This study aims to evaluate the spatial patterns and storage of SOC in the shrublands and the relationships of climatic variables and soil pH on the Tibetan Plateau. We used 177 profiles of soil samples obtained from 59 shrubland sites on the northeast Tibetan Plateau from 2011 to 2013. Ordinary least squares regressions, curve estimation, and multiple linear regressions were used to evaluate controlling factors on SOC stock. Kriging interpolation was used to upscale sit-level measurements to the whole study area. We found that SOC storage in the northeast Tibetan shrublands was 1.36 Pg C in the top 1 m with an average SOC stock of 12.38 kg m−2. SOC stock decreased from east to west and south to north but generally increased significantly with the mean annual temperature (MAT) and the mean annual precipitation (MAP), and tended to decrease with soil pH. Although similar relationships were also observed in alpine shrublands, the trends among SOC stock, MAP, and MAT were not observed in desert shrublands. Our results indicate that a reduction in soil pH accelerates the C sequestration potential. Furthermore, global warming contributed to C sequestration in alpine shrublands, specifically, SOC stock increased 8.44 kg m−2 with an increased unit of MAT in alpine shrublands just considering temperature effects. Meanwhile, the C sequestration was different among different regions due to the uneven increases in precipitation. However, in desert shrublands, MAP and MAT did not significantly affect SOC stock. The results indicate that though a reduction in soil pH could contribute to C sequestration, MAT and MAP have different effects on SOC stock in different Tibetan Plateau shrublands. Increased MAT and MAP were 0.05 °C and 1.67 mm every year on the Tibetan Plateau, which will increase C sequestration in alpine shrublands, but might have limited impacts on desert shrublands, which help us comprehend soil C cycling in the global climate change scenario.

Climate variability and anthropogenic regulations are two interwoven factors in the ecohydrologic system across large basins. Understanding the roles that these two factors play under various hydrologic conditions is of great significance for basin hydrology and sustainable water utilization. In this study, we present an analytical approach based on coupling water balance method and Budyko hypothesis to derive effectiveness coefficients (ECs) of climate change, as a way to disentangle contributions of it and human activities to the variability of river discharges under different hydro-transitional situations. The climate dominated streamflow change ( Δ Q c ) by EC approach was compared with those deduced by the elasticity method and sensitivity index. The results suggest that the EC approach is valid and applicable for hydrologic study at large basin scale. Analyses of various scenarios revealed that contributions of climate change and human activities to river discharge variation differed among the regions of the study area. Over the past several decades, climate change dominated hydro-transitions from dry to wet, while human activities played key roles in the reduction of streamflow during wet to dry periods. Remarkable decline of discharge in upstream was mainly due to human interventions, although climate contributed more to runoff increasing during dry periods in the semi-arid downstream. Induced effectiveness on streamflow changes indicated a contribution ratio of 49% for climate and 51% for human activities at the basin scale from 1956 to 2015. The mathematic derivation based simple approach, together with the case example of temporal segmentation and spatial zoning, could help people understand variation of river discharge with more details at a large basin scale under the background of climate change and human regulations.

Though aboveground biomass (AGB) has an important contribution to the global carbon cycle, the information about storage and climatic effects of AGB is scare in Three-River Source Region (TRSR) shrub ecosystems. This study investigated AGB storage and its climatic controls in the TRSR alpine shrub ecosystems using data collected from 23 sites on the Tibetan Plateau from 2011 to 2013. We estimated the AGB storage (both shrub layer biomass and grass layer biomass) in the alpine shrubs as 37.49 Tg, with an average density of 1447.31 g m-2. Biomass was primarily accumulated in the shrub layer, which accounted for 92% of AGB, while the grass layer accounted for only 8%. AGB significantly increased with the mean annual temperature (P < 0.05). The effects of the mean annual precipitation on AGB were not significant. These results suggest that temperature, rather than precipitation, has significantly effects on of aboveground vegetation growth in the TRSR alpine shrub ecosystems. The actual and potential increase in AGB density was different due to global warming varies among different regions of the TRSR. We conclude that long-term monitoring of dynamic changes is necessary to improve the accuracy estimations of potential AGB carbon sequestration across the TRSR alpine shrub ecosystems.

Climate change and land use/cover change (LUCC) are two factors that produce major impacts on hydrological processes. Understanding and quantifying their respective influence is of great importance for water resources management and socioeconomic activities as well as policy and planning for sustainable development. In this study, the Soil and Water Assessment Tool (SWAT) was calibrated and validated in upper stream of the Heihe River in northwest China. The reliability of the SWAT model was corroborated in terms of the Nash–Sutcliffe efficiency (NSE), the correlation coefficient (R) and the relative bias error (BIAS). The findings proposed a new method employing statistical separation procedures using a physically based modeling system for identifying the individual impacts of climate change and LUCC on hydrology processes, in particular on the aspects of runoff and evapotranspiration. The results confirmed that SWAT was a powerful and accurate model for diagnosis of a key challenge facing the Heihe River basin. The model assessment metrics, NSE, R and BIAS in the data were, respectively, 0.91, 0.95 and 1.14% for the calibration period and 0.90, 0.96 and -0.15%, respectively, for the validation period. An assessment of climate change possibility showed that precipitation, runoff and air temperature exhibited upward trends with a rate of 15.7 mm, 6.1 mm and 0.38 °C per decade for the 1980 to 2010 period, respectively. Evaluation of LUCC showed that the changes in growth of vegetation, including forestland, grassland and the shrub area has increased gradually while the barren area has decreased. The integrated effects of LUCC and climate change increased runoff and ET values by 3.2% and 6.6% of the total runoff and ET, respectively. Climate change outweighed the impact of LUCC, thus showing respective increases in runoff and ET of about 107.3% and 81.2% of the total changes. The LUCC influence appeared to be modest by comparison, and showed about -7.3% and 18.8% changes relative to the totals, respectively. The increase in runoff caused by climate change factors are more than the offsetting decreases resulting from LUCC. The outcomes of this study show that the climate factors accounted for the notable effects more significantly than LUCC on hydrological processes in the upper stream of the Heihe River.

The ridge-furrow with full plastic film mulching system (PM) is one of the most popular and widely applied field management techniques in dryland areas of China. There is concern for soil carbon storage and crop productivity dynamics under the long-term application of this management, specifically given the background of global climate change. However, the long term effects of this management practice are still poorly understood. More evaluation is required. A process-based biogeochemical model revised through four years of field experiments and a model drive by RCP (Representative Concentration Pathway) projection was applied to explore how soil carbon storage and maize productivity would change under future climate change projections. The field experiment showed that biomass was significantly higher in the PM than cultivation without mulching (CK), and their four-year average biomass values were 4996 +/- 967 and 2850 +/- 817 kg C ha(-1), respectively. Meanwhile, the four-year average soil organic carbon (SOC) storage was 5.93 g C kg(-1) soil, 5.95 g C kg(-1) soil and 5.40 g C kg(-1) soil for (CK) and 5.83 g C kg(-1) soil, 5.78 g C kg(-1) soil and 558 g C kg(-1) soil for PM at depths of 0-10, 10-20 and 20-30 cm, respectively. SOC did not significantly differ between the two treatments within the four years of the experiment. The model simulation with various rainfall and temperature change scenarios indicated that SOC (0-30 cm) and biomass were more affected by climate change in CK compared to PM. During years 2016-2100, SOC and maize biomass constantly increased under PM and CK for the RCP 4.5 and RCP 85 scenarios, and biomass was higher for PM than CK. However, under the highest carbon dioxide emission scenario of RCP 8.5, the improved biomass and SOC in PM decreased when temperature increased by more than 2.85 degrees C after year 2060. The modeling results showed that the PM cultivation system maintained high productivity and increasing trends of SOC under the high and medium greenhouse gas emission scenarios, derived from climate change projections for before the year 2060. The PM is currently an effective way to increase productivity and is a possible measure for dryland agriculture to adapt to near future climate change. (C) 2016 Elsevier Ltd. All rights reserved.

Analysis of the impacts of climate variability on evapotranspiration (ET) is of great importance in understanding climate variability and its effect on hydrological aspects. In this study, temporal and spatial variations in reference evapotranspiration (ET0) and actual evapotranspiration (AET) were comprehensively detected in the Taohe River Basin from 1981 to 2010. The spatial distributions of annual sensitivity of ET0 and AET to climatic variables were investigated. The quantitative contributions, the possible causes and dominant controlling factors were analyzed. The results suggested the following. (1) Considerable changes in ET0 occurred due to climate variability in the Gannan Plateau area (GPA) and Loess Plateau area (LPA) by 3.54 mm/yr and 3.39 mm/yr from 1981 to 2010, respectively. (2) Net solar radiation was the most sensitive factor on ET0. The dominant factor was air temperature leading to increase in ET0 due to high sensitive coefficient to ET0 and also exhibited significant increasing magnitude. (3) Precipitation (PPT) was the most sensitive factor for AET. AET in the GPA is controlled by air temperature and in LPA is controlled by PPT. This study provides a beneficial reference to agriculture, water resource and eco-environment management strategies in this region for associated policymakers and stakeholders.

Based on direct measurements of half-hourly canopy evapotranspiration (ET; W m−2) using the eddy covariance (EC) system and daily soil evaporation (E; mm day−1) using microlysimeters over a crop ecosystem in arid northwestern China from 27 May to 14 September in 2013, a Bayesian method was used to simultaneously parameterize the soil surface and canopy resistances in the Shuttleworth–Wallace (S–W) model. Four of the six parameters showed relatively larger uncertainty reductions (> 50%), and their posterior distributions became approximately symmetric with distinctive modes. There was a moderately good agreement between measured and simulated values of half-hourly ET and daily E with a linear regression being y = 0.84 x + 0.18 (R2 = 0.83) and y = 1.01 x + 0.01 (R2 = 0.82), respectively. The causes of underestimations of ET by the S–W model was possibly attributed to the microscale advection, which can contribute an added energy in the form of downward sensible heat fluxes to the ET process. Therefore, the advection process should be taken into account in simulating ET in heterogeneous land surfaces. Also, underestimations were observed on or shortly after rainy days, which may be due to direct evaporation of liquid water intercepted in the canopy. Thus, the canopy interception model should be coupled to the S–W model in the long-term ET simulation.

The Recursive Digital Filter (RDF) and Isotopic Hydrogeochemical Method (IHM) were coupled to separate the monthly snow and ice melt (SIM) in the alpines of the northwest China. A multiple linear regression expression (MLRE) between the separated SIM and alpine air temperature and precipitation was used to analyze the alpine SIM characteristics to assess potential impacts of regional climate change on SIM. The results showed an overall increasing SIM rate of 0.48 mm/10 y in the study area from 1981 to 2010. The maximum increasing rate of 0.69 mm/10 y was found in the altitudinal zone between 3900 m and 4700 m, reflecting a distinct spatial pattern of the SIM under the alpine climate.

Summary A Bayesian method was used to fit the Shuttleworth–Wallace model to half-hourly measurements of evapotranspiration (ET) with the eddy covariance technique from an alpine grassland on the Qinghai-Tibetan plateau during the main growing season in 2008, and probabilistically estimated its parameters and predication uncertainties using both dataset-by-dataset and multi-data procedures. This enabled us to reveal the seasonal variations of some physiology-related parameters and the impacts of constant parameters on the performances of the model. Results indicated that the S–W model using the posterior mean parameter values obtained by different procedures all successfully reproduced the observed responses in ET. However, the seasonal variations in the canopy conductance parameter ( g max ) should be counted in long-term ET estimating. From simulated results, the daily mean partitioning [i.e. the ratio of the estimated daily soil evaporation ( E ) over total evapotranspiration (ET); E /ET] was relative low (0.02–0.07 with a mean of 0.04) for the alpine grassland when leaf area index (LAI) was more than 3 m 2 m −2 , and was closed related to LAI and vegetation condition. At the diurnal timescale, the canopy conductance was the main factor control the partitioning of ET.

Unprecedented levels of nitrogen (N) have entered terrestrial ecosystems over the past century, which substantially influences the carbon (C) exchange between the atmosphere and biosphere. Temperature and moisture are generally regarded as the major controllers over the N effects on ecosystem C uptake and release. N-phosphorous (P) stoichiometry regulates the growth and metabolisms of plants and soil organisms, thereby affecting many ecosystem C processes. However, it remains unclear how the N-induced shift in the plant N:P ratio affects ecosystem production and C fluxes and its relative importance. We conducted a field manipulative experiment with eight N addition levels in a Tibetan alpine steppe and assessed the influences of N on aboveground net primary production (ANPP), gross ecosystem productivity (GEP), ecosystem respiration (ER) and net ecosystem exchange (NEE); we used linear mixed-effects models to further determine the relative contributions of various factors to the N-induced changes in these parameters. Our results showed that the ANPP, GEP, ER and NEE all exhibited nonlinear responses to increasing N additions. Further analysis demonstrated that the plant N:P ratio played a dominate role in shaping these C exchange processes. There was a positive relationship between the N-induced changes in ANPP (ΔANPP) and the plant N:P ratio (ΔN:P), while the ΔGEP, ΔER and ΔNEE exhibited quadratic correlations with the ΔN:P. By contrast, soil temperature and moisture were only secondary predictors for the changes in ecosystem production and C fluxes along the N addition gradient. These findings highlight the importance of plant N:P ratio in regulating ecosystem C exchange, which is crucial for improving our understanding of C cycles under the scenarios of global N enrichment. This article is protected by copyright. All rights reserved.

Thus far, measurements and estimations of actual evapotranspiration (ET) from high-altitude grassland ecosystems in remote areas like the Qinghai-Tibetan plateau are still insufficient. To address these issues, a comparison between the results of the eddy covariance (EC) measurements and the estimates, considering the Katerji and Perrier (KP), the Todorovic (TD) and the Priestley-Taylor (PT) models, was carried out over an alpine grassland (38(o)03'1.7'' N, 100(o) 27' 26'' E; 3032 m a.s.l.) during the growing seasons in 2008 and 2009. The results indicated that the KP model after a particularly simple calibration gave the most effective ET values in different time scales, the PT model slightly underestimate ET at night and the TD model significantly overestimated ET at noon. In addition, the canopy resistance calculated by the TD model was completely different from that calculated using the inverted EC-measured data and the KP model, which may be due to some unrealistic assumptions made by the TD model. The KP parameters were a=0.17 and b=1.50 for the alpine grassland and appeared to be interannually stable. However, the PT parameter showed some interannual variations (= 0.83 and 0.74 for 2008 and 2009, respectively). Therefore, the KP model was preferred to estimate the actual ET at both hourly and daily time scales. The PT model, being the simplest approach and field condition dependent, was recommended when available weather data were rare. On the contrary, the TD model always overestimated the actual ET and should be avoided in case of the alpine grassland ecosystems. Copyright (c) 2012 John Wiley & Sons, Ltd.

This study simulated the watershed flow and sediment responses based on calibration of the SWAT model in the semi-arid Chinese Loess Plateau (LP) where soil erosion intensively occurs. After the model’s initiation and manual modification, a 7-year inconsecutively observed flow and sediment data from 1984 to 1990 was used to analyze the model’s application in the selected watershed called AJW in the Chinese LP region. The model procedure included sensitivity analysis, parameter calibration and model validation. The best parameter set was finally determined based on the combination of parameter localization and auto-calibration. Then the model was assessed for its accuracy based on the NSE estimation, resulting in 0.77 and 0.67 for calibration and 0.46 and 0.32 for validation on simulations for flow and sediment, respectively, which is a moderately satisfactory accuracy among the applications of the SWAT model. Annual watershed assessment on flow and sediment with the calibrated SWAT model resulted in a multiyear averaged annual runoff coefficient of about 2.7% and an erosion modulus of 797 t/(km2·a−1) in the AJW, indicating a beneficial consequence from the implementation of the historical soil and water conservations.

As one of the largest land cover types, grassland can potentially play an important role in the ecosystem services of natural resources in China. Nitrous oxide (N2O) is a major greenhouse gas emitted from grasslands. Current N2O inventory at a regional or national level in China relies on the emission factor method, which is based on limited measurements. To improve the accuracy of the inventory by capturing the spatial variability of N2O emissions under the diverse climate, soil and management conditions across China, we adopted an approach by utilizing a process-based biogeochemical model, DeNitrification-DeComposition (DNDC), to quantify N2O emissions from Chinese grasslands. In the present study, DNDC was tested against datasets of N2O fluxes measured at eight grassland sites in China with encouraging results. The validated DNDC was then linked to a GIS database holding spatially differentiated information of climate, soil, vegetation and management at county-level for all the grasslands in the country. Daily weather data for 2000–2007 from 670 meteorological stations across the entire domain were employed to serve the simulations. The modelled results on a national scale showed a clear geographic pattern of N2O emissions. A high-emission strip showed up stretching from northeast to central China, which is consistent with the eastern boundary between the temperate grassland region and the major agricultural regions of China. The grasslands in the western mountain regions, however, emitted much less N2O. The regionally averaged rates of N2O emissions were 0.26, 0.14 and 0.38 kg nitrogen (N) ha−1 y−1 for the temperate, montane and tropical/subtropical grasslands, respectively. The annual mean N2O emission from the total 337 million ha of grasslands in China was 76.5 ± 12.8 Gg N for the simulated years.

Land degradation due to erosion is one of the most serious environmental problems in China. To reduce land degradation, the government has taken a number of conservation and restoration measures, including the Sloping Land Conversion Program (SLCP), which was launched in 1999. A logical question is whether these measures have reduced soil erosion at the regional level. The objective of this article is to answer this question by assessing soil erosion dynamics in the Zuli River basin in the Loess Plateau of China from 1999 to 2006. The MMF (Morgan, Morgan and Finney) model was used to simulate changes in runoff and soil erosion over the period of time during which ecological restoration projects were implemented. Some model variables were derived from remotely sensed images to provide improved land surface representation. With an overall accuracy rate of 0.67, our simulations show that increased ground vegetation cover, especially in forestlands and grasslands, has reduced soil erosion by 38.8% on average from 1999 to 2006. During the same time period, however, the change in rainfall pattern has caused a 13.1% +/- 4.3% increase in soil erosion, resulting in a net 25.7% +/- 8.5% reduction in soil erosion. This suggests that China's various ecological restoration efforts have been effective in reducing soil loss.

Although the soils in the Tibetan Plateau shrublands store large amounts of total nitrogen (N), the estimated values remain uncertain because of spatial heterogeneity and a lack of field observations. In this study, we quantified the regional soil N storage, spatial and vertical density distributions, and related climatic controls using 183 soil profiles sampled from 61 sites across the Northeast Tibetan Plateau shrublands during the period of 2011–2013. Our analysis revealed a soil N storage value of 132.40 Tg at a depth of 100 cm, with an average density of 1.21 kg m−2. Soil N density was distributed at greater levels in alpine shrublands, compared with desert shrublands. Spatially, soil N densities decreased from south to north and from east to west, and, vertically, the soil N in the upper 30 and 50 cm accounted for 42% and 64% of the total soil N stocks in the Tibetan Plateau. However, compared with desert shrublands, the surface layers in alpine shrublands exhibited a larger distribution of soil N stocks. Overall, the soil N density in the top 30 cm increased significantly with the mean annual precipitation (MAP) and tended to decrease with the mean annual temperature (MAT), although the dominant climatic controls differed among shrubland types. Specifically, MAP in alpine shrublands, and MAT in desert shrubland, had a weak effect on N density. Soil pH can significant affect soil N density in the Tibetan Plateau shrublands. In conclusion, changes in soil N density should be monitored over the long term to provide accurate information about the effects of climatic factors.

Land degradation caused by serious soil erosion has made the Loess Plateau one of the poorest regions in China. To improve the environmental conditions, the government has taken a number of measures of ecological restoration, including the Sloping Land Conversion Program (SLCP) since 1999. A natural question is whether these measures have improved the regional environmental conditions. The objective of this paper is to answer this question, focusing on the soil erosion dynamics in the Zuli River basin. We adopt a soil erosion model to simulate the changes of runoff and soil erosion induced by implementing the ecological restoration efforts, with the assistance of remote sensing and GIS technologies for parameterization of the land surface attributes. Our results show that the improved ground vegetative cover, especially in forestland and grassland, has reduced soil erosion by 38.8% from 1998 to 2006. At the same time, however, the changed rainfall pattern has resulted in a 13.1% increase in soil erosion. Thus the net reduction in soil erosion was 25.7%. This suggests that China's various ecological restoration efforts have been effective in reducing soil loss on a regional scale.

Lanzhou Univ, Minst Educ, Key Lab Western Chinas Environm Syst, Lanzhou 730000, Peoples R China

Traditional static methods have disadvantages of being lack of considering the spatiality of the data and new developments in spatial techniques (e.g., GIS) can help us in dealing with the spatiality problems. In this research, a semi-lumped conflux model (i.e., C. O. Clark method) is modified to be a semi-distributed conflux model by GIS- assisted partitions of spatial variables influencing the net precipitation into a spatially homogeneous watershed. Specifically, the spatial attributes of the dynamic processes were depicted through GIS-assisted DEM delineation of watershed geomorphology and spatiality of the factors modulating the hydrographs are considered by the adjustment factor K. Our results show that the GIS-assisted and spatially-improved Clark model generated more realistic results than the lumped original model, implying that the spatiality of the hydrogeomorphic factors that modulate the net precipitation plays a significant role in surface runoff generation in the entire watershed and thus in conflux processes in the outlet even within a small watershed.

In this research, GIS technology was used to deal with the data preparation of the land use and soil type in the whole watershed. The spatial difference of the time-step based on typical precipitation was calculated by the interpolated method of the Inverse Distance Weight (IDW) provided in the GIS software Arc/info 9.0. The vegetation interception capacity was calculated based on the LAI (leaf area index), which was gained through remote sensing ways. The classical Horton theory of infiltration was used to calculate the infiltrated rainfall in view of the excess overland flow generation mechanism in semi-arid regions. After the calculation of the above, the water quantity balance function was used to calculate the overland flow generation. All of the variables involved in the hydrological portions calculation were ensured according to the results of the experiments in outside fields. Because of the small scale of the watershed, a high resolution of the DEM was selected. The result shows that the simulation methods above can be used to simulate overland flow generation in a basin-scale in the semi-arid Chinese loess plateau. In this research, remote sensing method was used to calculate the LAI and solve the problem of vegetation interception better.

The 30-year normalized-difference vegetation index (NDVI) time series from AVHRR/MODIS satellite sensors was used in this study to assess the regional vegetation dynamic changes in the Tao River Basin, which cuts across the Eastern Tibetan Plateau (ETP) and the Southwestern Loess Plateau (SLP). First, principal component and correlation analyses were carried out to determine the key climatic variables driving ecological change in the region. Then, regression models were tested to correlate NDVI with the selected climatic variables to determine their predictive power. Finally, Sen's slope method was used to determine how terrestrial vegetation has responded to regional climate change in the region. The results indicated an average winter season NDVI value of 0.14 in the ETP but only 0.04 in the SLP. Primarily driven by increasing temperature, vegetation growth has generally been enhanced since 1981; spring NDVI increased by 0.03 every 10 years in the ETP and 0.02 in the SLP. Further, results from trend analyses suggest vegetation growth in the ETP shifted to earlier-start and earlier-end dates, however in the SLP, the growing season has been extended with an earlier-start and later-end date. The precipitation threshold for vegetation germination, measured by the cumulative spring rainfall, was found to be 44 mm for both the ETP and SLP.