Huimin Yan

Land Surface Phenology

Land surface phenology (LSP) is a key indicator of ecosystem dynamics under a changing environment. Over the last few decades, numerous studies have used the time series data of vegetation indices derived from land surface reflectance acquired by satellite-based optical sensors to delineate land surface phenology. Recent progress and data accumulation from CO2 eddy flux towers offers a new perspective for delineating land surface phenology through either net ecosystem exchange of CO2 (NEE) or gross primary production (GPP). In this chapter, we discussed the potential convergence of satellite observation approach and CO2 eddy flux observation approach. We evaluated three vegetation indices (Normalized Difference Vegetation Index, Enhanced Vegetation Index, and Land Surface Water Index) in relation to NEE and GPP data from five CO2 eddy flux tower sites, representing five vegetation types (deciduous broadleaf forests, evergreen needleleaf forest, temperate grassland, cropland, and tropical moist evergreen broadleaf forest). This chapter highlights the need for the community to combine satellite observation approach and CO2 eddy flux observation approach, in order to develop better understanding of land surface phenology.

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.

Multiple cropping intensity in China derived from agro-meteorological observations and MODIS data

Double- and triple-cropping in a year have played a very important role in meeting the rising need for food in China. However, the intensified agricultural practices have significantly altered biogeochemical cycles and soil quality. Understanding and mapping cropping intensity in China’s agricultural systems are therefore necessary to better estimate carbon, nitrogen and water fluxes within agro-ecosystems on the national scale. In this study, we investigated the spatial pattern of crop calendar and multiple cropping rotations in China using phenological records from 394 agro-meteorological stations (AMSs) across China. The results from the analysis of in situ field observations were used to develop a new algorithm that identifies the spatial distribution of multiple cropping in China from moderate resolution imaging spectroradiometer (MODIS) time series data with a 500 m spatial resolution and an 8-day temporal resolution. According to the MODIS-derived multiple cropping distribution in 2002, the proportion of cropland cultivated with multiple crops reached 34% in China. Double-cropping accounted for approximately 94.6% and triple-cropping for 5.4%. The results demonstrat that MODIS EVI (Enhanced Vegetation Index) time series data have the capability and potential to delineate the dynamics of double- and triple-cropping practices. The resultant multiple cropping map could be used to evaluate the impacts of agricultural intensification on biogeochemical cycles.

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.

Remote sensing of suspended particulate matter in Himalayan lakes: a case study of Alpine lakes in the Mount Everest region.

Abstract This study presents satellite data and in situ measurements to estimate the concentration of suspended solids in high-altitude and remote lakes of the Himalayas. Suspended particulate matter (SPM) concentrations measured in 13 lakes to the south of Mount Everest (Nepal) in October 2008 and reflectance values of the Advanced Visible and Near Infrared Radiometer type 2 (AVNIR-2) onboard ALOS, acquired a few days after the fieldwork activities concluded, were combined to build a relationship (R2 u200a=u200a 0.921) for mapping SPM concentrations in lakes of the Mount Everest region. The satellite-derived SPM concentrations were compared with in situ data (R2 u200a=u200a 0.924) collected in the same period in 4 additional lakes, located to the north of Mount Everest (Tibet, China). The 13 water samples collected in lakes in Nepal were also used to investigate the absorption coefficients of particles ap(λ) and colored, dissolved organic matter aCDOM(λ), with the aim of parameterizing a bio-optical model. An accurate model (R2 u200a=u200a 0.965) to estimate SPM concentrations from ap(λ) was found and could be adopted in the future for retrieving suspended solids from satellite imagery independently of ground measurements. In such a remote area, remote sensing was demonstrated to be a suitable tool to characterize the state of lakes, whose loads of suspended solids might be assumed to be direct and quick-responding indicators of deglaciation processes and glacier–lake interactions. As a macrodescriptor of water quality, the assessment of SPM in glacial lakes of the Himalayas might also be of interest for resource use in the downstream region.

Impacts of ecological restoration projects on agricultural productivity in China

The changes in cropland quantity and quality due to land use are critical concerns to national food security, particularly for China. Despite the significant ecological effects, the ecological restoration program (ERP), started from 1999, has evidently altered the spatial patterns of China’s cropland and agricultural productivity. Based on cropland dynamic data from 2000 to 2008 primarily derived from satellite images with a 30-m resolution and satellite-based net primary productivity models, we identified the impacts on agricultural productivity caused by ERP, including “Grain for Green” Program (GFGP) and “Reclaimed Cropland to Lake” (RCTL) Program. Our results indicated that the agricultural productivity lost with a rate of 132.67×104 t/a due to ERP, which accounted for 44.01% of the total loss rate caused by land use changes during 2000–2005. During 2005–2008, the loss rate due to ERP decreased to 77.18×104 t/a, which was equivalent to 58.17% of that in the first five years and 30.22% of the total loss rate caused by land use changes. The agricultural productivity loss from 2000–2008 caused by ERP was more attributed to GFGP (about 70%) than RCTL. Although ERP had a certain influence on cropland productivity during 2000–2008, its effect was still much less than that of urbanization; moreover, ERP was already converted from the project implementation phase to the consolidation phase.

Narrowband Bio-Indicator Monitoring of Temperate Forest Carbon Fluxes in Northeastern China

Developments in hyperspectral remote sensing techniques during the last decade have enabled the use of narrowband indices to evaluate the role of forest ecosystem variables in estimating carbon (C) fluxes. In this study, narrowband bio-indicators derived from EO-1 Hyperion data were investigated to determine whether they could capture the temporal variation and estimate the spatial variability of forest C fluxes derived from eddy covariance tower data. Nineteen indices were divided into four categories of optical indices: broadband, chlorophyll, red edge, and light use efficiency. Correlation tests were performed between the selected vegetation indices, gross primary production (GPP), and ecosystem respiration (Re). Among the 19 indices, five narrowband indices (Chlorophyll Index RedEdge 710, scaled photochemical reflectance index (SPRI)*enhanced vegetation index (EVI), SPRI*normalized difference vegetation index (NDVI), MCARI/OSAVI[705, 750] and the Vogelmann Index), and one broad band index (EVI) had R-squared values with a good fit for GPP and Re. The SPRI*NDVI has the highest significant coefficients of determination with GPP and Re (R-2 = 0.86 and 0.89, p<0.0001, respectively). SPRI*NDVI was used in atmospheric inverse modeling at regional scales for the estimation of C fluxes. We compared the GPP spatial patterns inversed from our model with corresponding results from the Vegetation Photosynthesis Model (VPM), the Boreal Ecosystems Productivity Simulator model, and MODIS MOD17A2 products. The inversed GPP spatial patterns from our model of SPRI*NDVI had good agreement with the output from the VPM model. The normalized difference nitrogen index was well correlated with measured C net ecosystem exchange. Our findings indicated that narrowband bio-indicators based on EO-1 Hyperion images could be used to predict regional C flux variations for Northeastern Chinas temperate broad-leaved Korean pine forest ecosystems.

Salt Effect on the Aggregation Behaviors of an Anionic Carboxylate Gemini and a Cationic Surfactant

The synthesis method and conditions for the carboxylate Gemini surfactant O,O′‐bis(sodium 2‐lauricate)‐p‐benzenediol (C11pPHCNa) were explored. Surface tension data of the single and mixed systems of catanionic (cationic with anionic) surfactants with different salt concentrations were used to determine the CMC values and to obtain the information of self‐assembly behaviors of the surfactants. Aggregates morphologies were observed by transmission electron microscopy (TEM) and speculation was made according to the viscosity measurement results. The results show that large spherical aggregates formed in the mixed solution, which tend to transfer into branched and wormlike mixed micelles with the increases of the salt concentration. The viscosity of the mixed solution was found to increase gradually corresponding to the change of the catanionic surfactant mixtures morphology.

Potential promoted productivity and spatial patterns of medium- and low-yield cropland land in China

With a continuously increasing population and better food consumption levels, improving the efficiency of arable land use and increasing its productivity have become fundamental strategies to meet the growing food security needs in China. A spatial distribution map of medium- and low-yield cropland is necessary to implement plans for cropland improvement. In this study, we developed a new method to identify high-, medium-, and low-yield cropland from Moderate Resolution Imaging Spectroradiometer (MODIS) data at a spatial resolution of 500 m. The method could be used to reflect the regional heterogeneity of cropland productivity because the classification standard was based on the regionalization of cropping systems in China. The results showed that the proportion of high-, medium-, and low-yield cropland in China was 21%, 39%, and 40%, respectively. About 75% of the low-yield cropland was located in hilly and mountainous areas, and about 53% of the high-yield cropland was located in plain areas. The five provinces with the largest area of high-yield cropland were all located in the Huang-Huai-Hai region, and the area amounted to 42% of the national high-yield cropland area. Meanwhile, the proportion of high-yield cropland was lower than 15% in Heilongjiang, Sichuan, and Inner Mongolia, which had the largest area allocated to cropland in China. If all the medium-yield cropland could be improved to the productive level of high-yield cropland and the low-yield cropland could be improved to the level of medium-yield cropland, the total productivity of the land would increase 19% and 24%, respectively.

Status of land use intensity in China and its impacts on land carrying capacity

Land use intensity quantifies the impacts of human activities on natural ecosystems, which have become the major driver of global environmental change, and thus it serves as an essential measurement for assessing land use sustainability. To date, land-change studies have mainly focused on changes in land cover and their effects on ecological processes, whereas land use intensity has not yet received the attention it deserves and for which spatially-explicit representation studies have only just begun. In this paper, according to the degree and reversibility of surface disturbance by human activities, there are four main classes of land use intensity: artificial land, semi-artificial land, semi-natural land, and natural land. These were further divided into 22 subclasses based on key indicators, such as human population density and the cropping intensity. Land use intensity map of China at a 1-km spatial resolution was obtained based on satellite images and statistical data. The area proportions of artificial land, semi-artificial land, semi-natural land, and natural land were 0.71%, 19.36%, 58.93%, and 21%, respectively. Human and economic carrying capacity increased with the increase of land use intensity. Artificial land supports 24.58% and 35.62% of the total population and GDP, using only 0.71% of the total land, while semi-artificial land supported 58.24% and 49.61% of human population and GDP with 19.36% of China’s total land area.