Long-term Water Balance of an Inland River Basin in an Arid Area, North-Western China

China, like many other countries in the region suffers from the water scarcity and problems of desertification and land degradation. One of the most useful approaches to deal with such a problem in the region is water balance study and analysis of different components involved to get an overview of the water supply and demand of the region so that engineers and policy makers can use that in their decision. Different hydrologic models have been developed for different conditions e.g. catchment size and data availability. Hydrologic Modeling System (HEC-HMS) among them is capable to simulate different catchment sizes with well detailed information as well as limited data availability. Geographic Information System (GIS) is also used as a useful tool to delineate sub-basins and extract terrain and physical characteristics of the region and associate them to the hydrologic model. Long term water balance for years between 1963 and 2001 was studied at Shiyang River basin, an inland catchment in Gansu province in western part of China. Calibration for the model could not be applied because of immense data limitation, though the model computes a fairly good estimation of water volume of the region which was applied in water balance equation. The hydrologic components e.g. water supply and demand of the region was determined and the trend of changes of the components were also presented for the study period. The study shows a good cooperation between GIS and HEC-HMS to apply for water balance study and gives a good estimation of component values despite limited data

Does intercropping have a future in China? : insights from a case study in Gansu Province

Intercropping is the simultaneous cultivation of two or more crop species in the same field. It has been practiced in China for thousands of years. In recent decades, researchers in several disciplines have shown increasing interest in intercropping systems, due to their potential to generate higher yields and counteract resource degradation. Much research on intercropping has been carried out from an eco-physiological perspective in China in recent decades. However, a socio-economic analysis is critically needed to obtain more insight into why farmers adopt intercropping or not and why they shift from one production system to another. This study tries to fill this gap in the existing literature. Its main aim is to obtain a better understanding of farmers’ decisions on intercropping in China. The analysis conducted in two distinct perspectives. The first empirical study aims to present an overview of the current prevalence of intercropping, and its recent trends in China, using national survey dataset. The other empirical studies focus on (relay) intercropping in small-scale farming, using a case study on household decision-making in Gaotai County, Gansu Province, northwest China. Results from the first study show that intercropping was practiced on approximately three percent of the arable land in the surveyed villages, while agroforestry was practiced on approximately one percent of the arable land and one percent of the area of plantation plus forest land. The use of both these systems did not significantly change between 2009 and 2014. An explorative village-level analysis of factors associated with mixed species cultivation practices (intercropping and agroforestry) reveals a significant positive association with labour availability, and a smaller, but mostly significant, negative association with agricultural machinery power. In the case study, results reveal that technical efficiency scores are positively affected by the share of land assigned to intercropping. Other findings are that natural assets (land and irrigation water) are important determinants of the use of intercropping, while human assets (including labor-land ratios) and financial assets do not have a significant effect. Water and labor scarcity and declining maize prices all affect negatively the potential use of intercropping in the future; among the aforementioned three factors, (rural) labor scarcity has the most negative impact on intercropping. To conclude, intercropping is practiced on a small but non-negligible proportion of China’s arable land, and has not declined in recent years. Policies aimed at dealing with resources scarcity and liberalizing maize market should take the impact on use of intercropping into account, and appropriate machinery for intercropping should be developed. Given its relatively high land use efficiency, and its relatively high profit in the case study region in northwest China, intercropping may continue to provide pathways for the intensification of agricultural food production and to contribute to the growth of farmers’ income in China.</p

Integrated Ecosystem Assessment of Western China

Western Development is an important strategy of China Government. The ecological environment in the western region of China is very fragile, and any improper human activity or resource utilization will lead to irrecoverable ecological degradation. Therefore, the integrated ecosystem assessment in the western region of China is of great significance to the Western Development Strategy. This project, Integrated Ecosystem Assessment of Western China (MAWEC), will provide very important scientific foundations for both the central and local governments to make decisions on ecological construction, thus assuring the successful implementation of the Western Development Strategy. Meanwhile, MAWEC as one of the MA sub-global assessments is contributing to strengthen capability in boosting the development of the ecological science, interaction between different subjects, and combination between scientific research and practice, and pushing forward international cooperation in the relevant fields

Chinese cropping systems are a net source of greenhouse gases despite soil carbon sequestration

This work was funded by National Basic Research Program of China (2014CB953800), Young Talents Projects of the Institute of Urban Environment, Chinese Academy of Sciences (IUEMS201402), National Natural Science Foundation of China (41471190, 41301237, 71704171), China Postdoctoral Science Foundation (2014T70144) and Discovery Early Career Researcher Award of the Australian Research Council (DE170100423). The work contributes to the UK-China Virtual Joint Centres on Nitrogen “N-Circle” and “CINAg” funded by the Newton Fund via UK BBSRC/NERC (grants BB/N013484/1 and BB/N013468/1, respectively).Peer reviewedPostprintPostprin

Ecohydrology in water-limited environment using quantitative remote sensing - the Heihe River basin (China) case

Water-limited environments exist on all continents of the globe and they cover more than 30% of the Earth’s land surface. The eco-environments of these regions tend to be fragile and they are changing in a dramatic way through processes like land desertification, shrinking of oases, groundwater depletion, and soil erosion. These are either human induced or results of a changing climate. Implications of these changes for both the regional hydrologic cycle and the vegetation have been documented. Since these changes occur over a wide range of scales in space and time, remote sensing methods are needed to monitor the land surface characteristics, to observe changes in vegetation and hydrological states, and to compare these with predictions from hydrological models. It is widely accepted that remote sensing methods offer the ability to acquire spatially continuous measurements over large areas. Remote sensing can also help to visualize complex processes because the spatial data can be captured regularly over time. China is one of several countries with large arid and semi-arid areas. The Heihe River basin, situated in the arid inland of northwestern China, is one of the areas severely affected by ecoenvironmental degradation and recovery. The problem of the degraded environment is due to overexploitation of surface and ground water leading to shrinking of oases, including the decline and death of natural vegetation, and the lowering of the groundwater table. Exhaustive (over-)use of water resources is the main cause of land degradation in the lower reaches of the basin, called the Ejina oasis. The whole Heihe River basin is therefore selected as study area in this thesis to analyze the long-term eco-environmental changes. What happens in this river basin is likely to have a growing influence on regional hydrological cycles, even affecting human life. Effective management of eco-environmental problems in this critical zone of water-limited conditions will provide scientific evidence for protecting and improving the eco-environment in these Chinese northwestern arid regions, eventually resulting in land improvement. Studies on quantifying the relationship between the vegetation and the water resources are a critical step in developing an ecohydrological approach to resources management in order to minimize environmental degradation. Remote sensing measurements can help us to better understand the effects of changes in water management on hydrological processes and their subsequent feedback to the eco-environment at the regional scale. Remote sensing methods can also provide information to quantify heterogeneity and change at a large scale. Therefore, the main objective of this thesis is to develop a methodology for the quantitative assessment of eco-environmental changes at a large scale in arid regions by integrating remote sensing methods in ecohydrological approaches. Chapter 1 outlines the significance of quantitative assessment of eco-environmental changes using remote sensing methods and applying them for ecohydrology in northwestern China, resulting in the specific research objectives of this thesis. Chapter 2 quantifies both the vertical and horizontal distribution of vegetation in the Qilian Mountains area, representing the upper reaches of the Heihe River basin, based on MODIS NDVI images from the year 2000 - 2006. Our analysis reveals that elevation and aspect are two important impact factors for the vertical distribution of vegetation in a mountainous area. The NDVI increases with the elevation and reaches a maximum value at a certain elevation threshold, and then decreases as the elevation increases beyond this threshold. The optimal vegetation growth is on the shady side of the mountains because of less evapotranspiration. The best combination of temperature and precipitation is assessed providing good conditions for vegetation growth. Chapter 3 presents an efficient method to estimate the regional annual evapotranspiration (ET) based on the SEBS algorithm (Surface Energy Balance System) in the Zhangye basin, representing the middle reaches of the Heihe River basin. The method proposed is a combination of the daily SEBS results and data collected by meteorological stations. The result shows that the annual ET increased gradually during the period 1990-2004 and the main impact factor on the long-term increase of annual ET was the vegetation change. The accuracy of the ET result is validated using a water balance for the whole watershed and the validation reveals that the SEBS algorithm can be used to effectively estimate annual ET in the Zhangye basin. Chapter 4 establishes the quantitative relationship between the runoff of the Heihe River and the long-term vegetation change of the Ejina oasis, located in the lower reaches of the Heihe River. In this part, two time periods are distinguished corresponding to before and after the implementation of a new water allocation scheme in the Heihe River basin. The GIMMS NDVI and MODIS NDVI data sets are used to quantify the long-term change of the oasis vegetation in the first period 1989-2002 and the second period 2000-2006, respectively. The vegetation change shows a decreasing trend from 1989 to 2002 and an increasing trend between 2000 and 2006. Good relation between the runoff of the river and the vegetation growth are found at both stages and the time lag of the observed hysteresis effect of the runoff of the river on the oasis vegetation is one year. In addition, the yearly smallest water amount which sustains the demand of the eco-environment of the Ejina area is estimated to be 4×108 m3 based on MODIS images. Chapter 5 explores a method to quantify the effect of the groundwater depth on the vegetation growth in the year 2000 in the oasis area by combining MODIS NDVI with groundwater observation data. The result demonstrates that the groundwater depth suitable for vegetation growth in this region ranges from 2.8 to 5 m, depending on species composition. Hardly any vegetation growth occurs when the groundwater depth is below 5 m because the rooting depth of the occurring species is limited and cannot maintain adequate water supplies to their canopies when the water depth is below 5 m. The situation changes after implementation of the new water allocation scheme since 2000. The mean NDVI increased and the annual conversion of bare land into vegetated land is about 38 km2 per year during the period 2000 – 2008. It reflects a potential recovery of the eco-environment of the Ejina area. Chapter 6 comprises the main conclusions and the outlook for possible improvements in future research. The main contribution of this study is the successful integration of remote sensing with ecohydrology in quantifying the relationship between water resources and vegetation occurrence at large scale. It provides a methodology to evaluate the long-term vegetation change and the water resources impact using remote sensing data in water-limited areas. The approach of vegetation dynamics, runoff and groundwater impacts presented in this thesis serves as a sound foundation for predicting the effects of future environmental changes. <br/

Bioarchaeology of Adaptation to Climate Change in Ancient Northwest China

The 4000 BP climate event was a time of dramatic change, including a cooling and drying climate and the emergence of pastoral practices and a distinct cultural identity across northern Eurasia. However, the link between the climatic changes and the cultural changes has not yet been thoroughly explored. This dissertation therefore assesses human biological measures such as frailty, physiological stress, and nutritional status to ask whether late Holocene climate change precipitated a crisis and collapse of subsistence practices, as has been claimed. The dissertation employs the theoretical framework of the “adaptive cycle,” an understanding of complex systems that incorporates both change and continuity. The dissertation asks whether the Bronze Age transition, in which humans adapted to the arid climate of the second and first millennia BCE, constituted a “collapse” or “transformational adaptation,” in which the human-environment system changed categorically; or an “incremental adaptation,” in which defining system elements persisted with only peripheral changes. Skeletal samples from six populations (spanning 2600-221 BCE) were examined for bioarchaeological markers of oral health, nonspecific infectious lesions, trauma, stature, and fertility. There was broad continuity and some improvement in population health measures in the Bronze Age study populations, with a decline in health in the Iron Age groups. Bronze Age subsistence systems therefore seem to have been resilient enough to adapt to the new climate, while the sociopolitical conditions of the Iron Age led to poorer health outcomes. The Bronze Age transition has often been described in terms of “collapse,” and by critically engaging with this narrative, the current project demonstrates that the transition in fact entailed an incremental adaptation, rather than a collapse. These findings also point to how sociocultural factors can serve as a buffer against environmental stressors in some groups, while themselves serving as stressors in others.Doctor of Philosoph

Ancient Great Wall Building Materials Reveal Environmental Changes Associated with Oases in Northwestern China

Plant materials used in the construction of segments and beacon towers of the ancient Great Wall in northwestern China contain untapped potential for revealing local paleoclimatic and environmental conditions. For the first time, we characterize the molecular preservation and stable carbon and nitrogen isotope compositions of AMS-dated common reeds (Phragmites) collected from ancient Great Wall fascines in today’s Gansu and Xinjiang using a combination of chromatographic techniques and isotope analyses. Our molecular data, along with Scanning Electron Microscopy, demonstrate excellent preservation of these ancient reeds, which were harvested from nearby habitats during periods of significant expansion of Imperial China when climate conditions sustained sizeable oases in the region. Stable isotope data capture differential rates of environmental change along the eastern margin of the Tarim Basin since the Han Dynasty (170 BC), implying that significant surface-water hydrological changes occurred only after the Song Dynasty (1160 AD) due to regional climate change. This study reveals the wealth of environmental and climate information obtainable from these site-specific organic building materials and establishes the foundation for further applications of advanced molecular, biochemical, and isotopic technologies to study these common and widely-distributed organic archaeological materials

Dew formation characteristics in the gravel desert ecosystem and its ecological roles on Reaumuria soongorica

As an additional source of water to plants besides rainfall, dew may have a positive impact on vegetation in the arid ecosystems. Knowledge regarding dew formation characteristics and its ecological effects on vegetation water status and photosynthetic performance in the gravel desert ecosystem is still lacking. In this study, the dew variability and formation frequency on a gravel desert were measured by microlysimeters. We quantified dew formation characteristics, investigated vegetation water response to dew events in the gravel desert ecosystem at the edge of a desert oasis, Northwestern China. The results showed water adsorption was a primary pathway of dew formation in such system, and the average daily amount of dew is 0.06 mm. Dew occurred on 36% of growing season days, the number of days with dew amounts >0.03 mm accounted for 82% of the total dew events, and the cumulative amount of dew for those days was 3.41 mm. Relative humidity, air temperature, wind speed, the difference between air temperature and soil surface temperature had significant effects on dew formation. A threshold of RH ≥30% is taken to mark possible condensation in the gravel desert ecosystem. A significant positive correlation between dew amounts and the relative moisture in the near-surface air was found when RH ≥30%. The moderate wind velocity (1–1.8 m/s) was favorable to dew formation, and when wind speed >5.47 m/s, there was no dew formation. Because of the water-absorbing scales on the leaves of Reaumuria soongorica, dew events significantly improved their relative water content, water potential, and photosynthetic performance in the early morning and ameliorating the adverse effects of plants exposed to prolonged drought. The study highlights dew is an important supplementary source of water in the gravel desert ecosystem. Although the absolute dew amounts were found not high, it can be a frequent and stable water resource. Furthermore, this study provides a comprehensive understanding of the effects of dew on plant water status in the gravel desert ecosystem

Sustainability in China: Bridging Global Knowledge with Local Action

China’s road to sustainability has attracted global attention. Since the “Reform & Opening Up” policy, China’s rapid pace of both urbanization and industrialization has made its being the second largest economy but meantime a heavy environmental price has been paid over the past few decades for addressing the economic developmental target. Today, as the biggest developing country, China needs to take more responsibilities for constructing its local ecological-civilization society as well as for addressing the global challenges such as climate change, resources scary and human beings well-fare; therefore, we need to have deeper understandings into China’s way to sustainability at very different levels, both spatially and structurally, concerns ranging from generating sustainable household livelihoods to global climate change, from developing technological applications to generate institutional changes. In this spirit, this publication, “Sustainability in China: Bridging Global Knowledge with Local Action” aims to investigate the intended and spontaneous issues concerning China’s road to sustainability in a combined top-down and bottom-up manner, linking international knowledge to local-based studies

On yield gains and yield gaps in wheat-maize intercropping : opportunities for sustainable increases in grain production

Intercropping is the cultivation of two or more crop species simultaneously in the same field, while relay intercropping means that the growing periods of the crop species are only partially overlapping. Intercropping has advantages with respect to productivity, resource capture, build-up of soil organic matter, and pest and disease suppression. This thesis aims to quantify and explain the yield advantages in wheat-maize relay intercropping and to assess the importance of intercropping for food production and land use efficiency. Wheat-maize intercropping had land equivalent ratios around or above one in two experiments in the Netherlands. Wheat in border rows showed major yield increases, and this yield increase was due to increases in the number of tillers per plant and the number of kernels per ear. The yield advantage of intercropped wheat was associated with a high radiation interception and radiation use efficiency (RUE). Under Dutch growing conditions, maize performance in the intercrop was constrained. Intercropping had a negative effect on the yield per plant and radiation use efficiency of maize. A strip intercrop model was developed, parameterized and tested with data on wheat-maize intercropping in the Netherlands. The model simulates radiation interception and growth in relay-strip intercrops with two species in different planting configurations. The model also allows simulating the consequences of border row effects for total system productivity. Bayesian analysis was applied to calibrate radiation use efficiency of wheat and maize in sole crops and intercrop. Intercropped wheat had higher a RUE than sole wheat, while intercropped maize had a lower RUE than sole maize. Intercropped maize had less favourable leaf traits (e.g. nitrogen content) during the flowering stage than sole maize in 2014, but the leaves in the intercrop had a higher photosynthetic rate than those in the sole crop. Possible explanations for this finding include differences between sole and mixed crops in water acquisition from soil, light distribution in the canopy, nitrogen distribution within the leaf and the contribution of the ear leaf to the growth of the cob. The low radiation use efficiency in intercropped maize may relate to nitrogen deficiency during grain filling. New concepts for potential yield, yield gain and yield gap in intercropping were developed in this thesis. Using crop model simulations and farm survey data, those concepts were operationalized in the context of wheat and maize production in an oasis area (Zhangye city) in northwest China. Wheat-maize intercropping resulted in substantial yield gains under potential and actual growing conditions. A comparison of potential and actual yields indicated a yield gap of 33% for sole wheat, 49% for sole maize, 15% for intercropped wheat, and 51% for intercropped maize. The land use analysis showed that discontinuing the use of intercropping in this region will decrease grain production substantially. Overall, this thesis studied the growth and productivity of wheat-maize intercropping at organ, plant and cropping system level, and also assessed its contribution to grain production at a regional level. The findings suggest that intercropping of food crops provides opportunities to meet increasing food demands. New technologies are needed to make strip intercropping efficient in terms of labour use and breeding should pay attention to cultivars that are suitable for intercropping.</p