Jiyuan Liu

Assessment of effects of climate change and grazing activity on grassland yield in the Three Rivers Headwaters Region of Qinghai–Tibet Plateau, China

Inter-annual dynamics of grassland yield of the Three Rivers Headwaters Region of Qinghai–Tibet Plateau of China in 1988–2005 was analyzed using the GLO-PEM model, and the herbage supply function was evaluated. The results indicate that while grassland yield in the region showed marked inter-annual fluctuation there was a trend of increased yield over the 18xa0years of the study. This increase was especially marked for Alpine Desert and Alpine Steppe and in the west of the region. The inter-annual coefficient of variation of productivity increased from the east to the west of the region and from Marsh, Alpine Meadow, Alpine Steppe, Temperate Steppe to Alpine Desert grasslands. Climate change, particularly increased temperatures in the region during the study period, is suggested to be the main cause of increased grassland yield. However, reduced grazing pressure and changes to the seasonal pattern of grazing could also have influenced the grassland yield trend. These findings indicate the importance of understanding the function of the grassland ecosystems in the region and the effect of climate change on them especially in regard to their use to supply forage for animal production. Reduction of grazing pressure, especially during winter, is indicated to be critical for the restoration and sustainable use of grassland ecosystems in the region.

Simulation and analysis of urban growth scenarios for the Greater Shanghai Area, China

This research investigates the potential of an integrated Markov chain analysis and cellular automata model to better understand the dynamics of Shanghais urban growth. The model utilizes detailed land cover categories to simulate and assess landscape changes under three different scenarios, i.e., baseline, Service Oriented Center, and Manufacturing Dominant Center scenarios. In the study, multi-temporal land use datasets, derived from remotely-sensed images from 1995, 2000, and 2005, were used for simulation and validation. Urban growth patterns and processes were then analyzed and compared with the aid of landscape metrics. This research represents the first scenario-based simulations of the future growth of Shanghai, and is one of the few studies to use landscape metrics to analyze urban scenario-based simulation results with detailed land use categories. The results indicate that the future expansion of both high-density and low-density residential/commercial zones is always located around existing built-up urban areas or along existing transportation lines. In contrast to the baseline and Service Oriented Center scenarios, industrial land under the Manufacturing Dominant Center scenario in 2015 and 2025 will form industrial parks or industrial belts along the transportation channels from Shanghai to Nanjing and Hangzhou. The studys approach, which combines scenario-based urban simulation modeling and landscape metrics, is shown to be effective in representing, understanding, and predicting the spatial-temporal dynamics and patterns of urban evolution, including urban expansion trends

What are hot and what are not in an urban landscape: quantifying and explaining the land surface temperature pattern in Beijing, China

ContextUnderstanding how landscape components affect the urban heat islands is crucial for urban ecological planning and sustainable development.ObjectiveThe purpose of this study was to quantify the spatial pattern of land surface temperatures (LSTs) and associated heat fluxes in relation to land-cover types in Beijing, China, using portable infrared thermometers, thermal infrared imagers, and the moderate resolution imaging spectroradiometer.MethodsThe spatial differences and the relationships between LSTs and the hierarchical landscape structure were analyzed with in situ observations of surface radiation and heat fluxes.ResultsLarge LST differences were found among various land-use/land-cover types, urban structures, and building materials. Within the urban area, the mean LST of urban impervious surfaces was about 6–12xa0°C higher than that of the urban green space. LSTs of built-up areas were on average 3–6xa0°C higher than LSTs of rural areas. The observations for surface radiation and heat fluxes indicated that the differences were caused by different fractions of sensible heat or latent heat flux in net radiation. LSTs decreased with increasing elevation and normalized difference vegetation index.ConclusionsVariations in building materials and urban structure significantly influenced the spatial pattern of LSTs in urban areas. By contrast, elevation and vegetation cover are the major determinants of the LST pattern in rural areas. To alleviate urban heat island intensity, urban planners and policy makers should pay special attention to the selection of appropriate building materials, the reasonable arrangement of urban structures, and the rational design of landscape components.

Spatio-temporal pattern and rationality of land reclamation and cropland abandonment in mid-eastern Inner Mongolia of China in 1990-2005

The Mid-eastern Inner Mongolia of China, a typical agro-pastoral transitional zone, has undergone rapid agricultural land use changes including land reclamation and cropland abandonment in past decades due to growing population and food demand, climatic variability, and land use policy such as the “Grain for Green” Project (GFG Project). It is significant to the regional ecology and sustainability to examine the pattern and its rationality of land use change. The processes of land reclamation and cropland abandonment were accessed by using land use change dataset for four periods of 1990, 1995, 2000, and 2005, derived from the interpretation of Landsat TM images. And then the rationality of land reclamation and cropland abandonment was analyzed based on the habitat suitability for cultivation. The results indicated that: (1) land reclamation was the dominant form of agricultural land use change from 1990 to 2005, the total cropland area increased from 64,954.64xa0km2 in 1990 to 76,258.51xa0km2 in 2005; However, the speed of land reclamation decreased while cropland abandonment increased around 2000. The Land Reclamation Degree decreased from 1995–2000 to 2000–2005, meanwhile, Cropland Abandonment Degree increased. (2) As for the habitat suitability levels, moderately and marginally suitable levels had largest areas where cropland was widespread. Pattern of agricultural land use trended to become more rational due to the decrease of land reclamation area in low suitable levels and the increase of cropland abandonment in unsuitable area after 2000. (3) The habitat suitability-based rationality analysis of agricultural land use implicated that the GFG Project should take cultivation habitat suitability assessment into account.

Has climate change driven spatio-temporal changes of cropland in northern China since the 1970s?

Improving the understanding of cropland change and its driving factors is a current focus for policy decision-makers in China. The datasets of cropland and cropland changes from the 1970s to the 2000s were used to explore whether climate change has produced spatio-temporal changes to cropland in northern China since the 1970s. Two representative indicators of heat and water resources, which are important determinants of crop growth and productivity, were considered to track climate change, including active accumulated temperatures ≥10xa0°C (AAT10) and the standardized precipitation evapotranspiration index (SPEI). Our results showed that rapid cropland change has occurred in northern China since the 1970s, and the area of cropland reclamation (10.23 million ha) was much greater than that of abandoned cropland (2.94 million ha). In the 2000s, the area of cropland with AAT10 higher than 3,000xa0°C·d increased, while the area of cropland with an SPEI greater than 0.25 decreased compared to the 1970s, 1980s and 1990s. It appears that climate warming has provided thermal conditions that have aided rapid cropland reclamation in northern China since the 1970s, and drier climatic conditions did not become a limiting factor for cropland reclamation, especially from the 1990s to the 2000s. Approximately 70xa0% of cropland reclamation areas were located in warmer but drier regions from the 1990s to the 2000s, and approximately 40xa0% of cropland abandonment occurred in warmer and wetter conditions that were suitable for agriculture during the periods from the 1970s to the 1980s and the 1990s to the 2000s. Our results suggest that climate change can be considered a driving factor of cropland change in the past several decades in northern China, in addition to socioeconomic factors.

Variation characteristics of soil respiration fluxes in four types of grassland communities under different precipitation intensity

A two consecutive years’ field experiment was carried out on four types of semiarid grassland along precipitation gradient in Xilin River Basin of Inner Mongolia during 2001–2003 using a static enclosed black chamber technique. The variation characteristics of soil respiration fluxes from four different types of grassland along precipitation gradient were compared. The possible effect of water-heat factors on characteristics of grassland soil respiration was statistically analyzed and the numerical relational model between soil respiration and water-heat factors was established. Meanwhile the soil CO2 annual emissions of different types of grassland were estimated based on the consecutive and complete set of field observation data. The results indicate that soil respiration has apparent seasonal variation laws, seasonal variation patterns of soil respiration from different types of grassland along precipitation gradient are basically the same, soil respiration fluxes of various grassland communities are relatively high in late spring and summer but relatively low in autumn and winter, negative fluxes of soil respiration were observed from different types of grassland in winter and the further study of their mechanism is favorable for the accurate estimation of soil respiration amount; soil annual (or growth season) respiration amount of four types of grassland along precipitation gradient decreases progressively along the gradient in the order ofStipa baicalensis meadow steppe >Aneurolepidium chinense steppe >Stipa grandis steppe >Stipa krylovii steppe; soil respiration of different types of grassland during growth season is positively correlated with soil water content at depths of 0–10 and 10–20 cm to different degrees but the correlativity with air temperature and top depth soil temperature is relatively weak, variations of surface soil water content of four types of grassland during growth season can normally explain 70.2%–94.7% of the variations of soil respiration fluxes, whereas during non-growth season of the plants, soil respiration are more likely restricted by air temperature and top depth soil temperature, and variations of temperature conditions can explain over 70% of the variations of soil respiration fluxes.

Spatial-temporal changes of cropland and climate potential productivity in northern China during 1990–2010

Large areas of cropland expansion have been reported in northern China. The sustainable use of cropland may be greatly affected by climate and is vulnerable to climatic changes, particularly in northern China. Here, we investigated climate change during 1961–2010 and the spatial and temporal characteristics of climate resources in newly converted cropland during 1990–2010 across northern China. Significant climate warming occurred in the last 50xa0years concurrently with relative stable precipitation rates, which provided a favorable climatic background for expanding the extent of cropland. During 1990–2010, the major cropland expansion had shifted from the humid northeast of China with good natural conditions to the arid northwest with fragile environmental conditions. In the newly converted cropland areas, temperatures increased significantly with small fluctuations; the average precipitation decreased considerably from 422.40 to 257.97xa0mm, with high and increasing inter-annual and seasonal variability. Water shortages became the most important climatic factor, limiting sustainable use of newly converted cropland. The average climate potential productivity of newly converted cropland decreased considerably from 672.41 to 440.40xa0t/km2, indicating a substantial decline in the quality of newly converted cropland. Understanding the spatial and temporal changes in climatic resources is critical to coordinating cropland expansion and sustainable land use.

Development of a surface modeling method for mapping soil properties

High accuracy surface modeling (HASM) is a method which can be applied to soil property interpolation. In this paper, we present a method of HASM combined geographic information for soil property interpolation (HASM-SP) to improve the accuracy. Based on soil types, land use types and parent rocks, HASM-SP was applied to interpolate soil available P, Li, pH, alkali-hydrolyzable N, total K and Cr in a typical red soil hilly region. To evaluate the performance of HASM-SP, we compared its performance with that of ordinary kriging (OK), ordinary kriging combined geographic information (OK-Geo) and stratified kriging (SK). The results showed that the methods combined with geographic information including HASM-SP and OK-Geo obtained a lower estimation bias. HASM-SP also showed less MAEs and RMSEs when it was compared with the other three methods (OK-Geo, OK and SK). Much more details were presented in the HASM-SP maps for soil properties due to the combination of different types of geographic information which gave abrupt boundary for the spatial variation of soil properties. Therefore, HASM-SP can not only reduce prediction errors but also can be accordant with the distribution of geographic information, which make the spatial simulation of soil property more reasonable. HASM-SP has not only enriched the theory of high accuracy surface modeling of soil property, but also provided a scientific method for the application in resource management and environment planning.

Comparison of arsenic and heavy metals contamination between existing wetlands and wetlands created by river diversion in the Yellow River estuary, China

Samples were collected at 71 sites in the Yellow River Delta Natural Reserve in December 2010 to represent soil conditions before and after the Yellow River (YR) diversion. The As, Cd, Cu, Pb, Zn, and Ni concentrations were measured to determine metal contamination levels. Results suggest that Cd concentrations were significantly higher after the YR diversion than before. The As, Cd, Cr, Cu, Ni, Pb, and Zn soil contamination indices did not exceed contamination levels, although the heavy metal content increased after the YR diversion. The mean concentrations of these heavy metals were lower than the Class I criteria. Correlation analysis shows significant correlations between As and Cr, Cu, Ni, Pb, and Zn concentrations both before and after the YR diversion. However, no significant correlations were observed between heavy metal concentration and pH before the diversion, and no heavy metal concentration was correlated with salinity. The principal component analysis indicates that these trace elements, including As, were closely correlated with each other and therefore likely originated from shared pollution sources before the diversion. These results are useful for assessing the heavy metal contamination and proposing feasible suggestions to improve soil quality.

The characteristics of land cover and macroscopical ecology changes in the Source Region of Three Rivers in Qinghai-Tibet plateau during last 30 years

We obtained four phases of land cover spatial data sets by interpreting MSS images of middle and late 1970s and three phases of TM images of late 1980s, 2004 and 2008 based on field investigation in Three Rivers Source Region. We analyzed the temporal and spatial characteristics of land cover and macro ecological changes in Three Rivers Source Region in Qinghai-Tibet plateau since middle and late 1970s. Indicated by land cover condition index change rate and land cover change index, land cover and macroscopical ecological condition degenerated (7090 period Zc −0.63, LCCI −0.58)-obviously degenerated (9004 period, Zc −0.94, LCCI −1.76)-slightly meliorated (0408 period, Zc 0.06, LCCI 0.33). This course was jointly driven by climate change, grassland stocking pressure and implement of ecological construction project.