Soil water deficit and vegetation restoration in the refuse dumps of the Heidaigou open-pit coal mine,Inner Mongolia,China

The sustainability of ecosystem restoration of refuse dumps in open-pit coal mines depends on plant species selection, their configuration, and the optimal usage of water resources. This study is based on field experiments in the northern refuse dump of the Heidaigou open-pit coal mine in Inner Mongolia of China established in 1995. Eight plant configurations, including trees, shrubs, grasses, and their combinations, as well as the adjacent community of natural vegetation, were selected. The succession of the revegetated plants, soil water storage, the spatiotemporal distribution of plant water deficits degree and its compensation degree were also studied. Results indicated that the vegetation cover （shrubs and herbaceous cover）, richness, abundance, soil nutrients （soil organic matter, N and P）, and biological soil crust coverage on the soil surface are significantly influenced by the vegetation configurations. The average soil water storage values in the shrub ＋ grass and grass communities throughout the growing season are 208.69 mm and 206.55 mm, which are the closest to that of in the natural vegetation community （215.87 mm）. Plant water deficits degree in the grass and shrub ＋ grass communities were the lowest, but the degrees of water deficit compensation in these configuration were larger than those of the other vegetation configurations. Differences in plant water deficit degree and water compensation among the different config- urations were significant （P 〈0.05）. Plant water deficit degrees were predominantly minimal on the surface, increased with increasing soil depth, and remained stable at 80 cm soil depth. The soil moisture compensation in the natural vegetation, shrub ＋ grass, and grass communities changed at 10%, while that in other vegetation communities changed between 20% and 40%. Overall, we conclude that the shrub ＋ grass and grass configuration modes are the optimal vegetation restoration models in terms of ecohydrology for future ecological engineering projects.

Stability of water yield in watersheds

The hydrological system of a watershed is intricately influenced by both underlying characteristics and climate conditions.Understanding the variability in water yield is essential for effective water resources management and water security in the context of changing environments.In this study,we adopted the Budyko framework and leveraged simulations from the CMIP6 model to investigate the compensation effects of climate and underlying characteristics on watershed water yield.Based on Taylor expansion and Budyko framework,we estimated the sensitivity of watershed water yield to climate and underlying characteristics(the first-and second-order partial derivatives).By combining external watershed characteristics(e.g.,water yield ratios and underlying characteristics)with internal sensitivity coefficients,this study further used vine copula and principal component analysis to quantify the stability of watershed water yield.Our findings show:(1)Water-yield changes related to underlying characteristics could be offset by climate-related water-yield changes across all climate zones,maintaining the water yield ratio steady(i.e.,the compensation effects).(2)However,global watersheds will turn more sensitive to underlying characteristics and less sensitive to climate variation in the future.Both climate-and underlying-related sensitivities increase in watersheds with arid climates.(3)The stability of watershed water yield will gradually diminish in the future.From 1901–1950to 2051–2100,the global stability of 280 watersheds drops from 0.054 to 0.021(i.e.,stability index identified by the joint probability).Particularly,the largest change in stability of water yield reaches-0.347±0.18 in arid regions.In semi-arid,semihumid,and humid regions,the changes are-0.039±0.010,-0.028±0.005,and-0.005±0.002,respectively.The findings provide a reference for the future sustainable water resources development under climate change,highlighting the vulnerability of the water resources in arid and semi-arid watersheds.

The driving effects of urbanization on economic growth and water use change in China： A provincial-level analysis in 1997-2011

As one of the key issues in China＇s sustainable development, rapid urbanization and continuous economic growth are accompanied by a steady increase of water consump- tion and a severe urban water crisis. A better understanding of the relationship among ur- banization, economic growth and water use change is necessary for Chinese decision mak- ers at various levels to address the positive and negative effects of urbanization. Thus, we established a complete decomposition model to quantify the driving effects of urbanization on economic growth and water use change for China and its 31 provincial administrative regions during the period of 1997-2011. The results show that, （1） China＇s urbanization only contrib- uted about 30% of the economic growth. Therefore, such idea as urbanization is the major driving force of economic growth may be weakened. （2） China＇s urbanization increased 2352×10^8 m3 of water use by increasing the economic aggregate. However, it decreased 4530×10^8 m3 of water use by optimizing the industrial structure and improving the water use efficiency. Therefore, such idea as urbanization is the major driving force of water demand growth may be reacquainted. （3） Urbanization usually made greater contribution to economic and water use growth in the provincial administrative regions in east and central China, which had larger population and economic aggregate and stepped into the accelerating period of urbanization. However, it also made greater contribution to industrial structure optimization and water use efficiency improvement, and then largely decreased total water use. In total, urbanization had negative effects on water use growth in most provincial administrative re- gions in China, and the spatiotemporal differences among them were lessened on the whole. （4） Though urbanization helps to decrease water use for China and most provincial adminis- trative regions, it may cause water crisis in urban built-up areas or urban agglomerations. Therefore, China should construct the water transfer and compensation mechanisms be- tween urban and rural areas, or low and high density urban areas as soon as possible.

Growth and Physiological Response of Organs of Phragmites australis to Different Water Compensation in Degraded Wetlands

To study the effect of different water compensation on growth and physiology of reed in degraded wetlands,three water treatments in the field were conducted to test the height and photosynthesis of reed,the ions and soluble sugar contents of different organs.In the controls(without extra water compensation for 10 years),the height of reed was only 50 cm,the net photosynthetic rate,stomatal conductance,the intercellular CO2 concentration and transpiration rate were very low.The contents of Na + and Clin rhizome were higher than those in other organs.Discontinuous water compensation(continuous for 8 years,then stopped for 2 years)increased the height(2.1-fold),the net photosynthetic rate(41.8%),stomatal conductance(1.8-fold),transpiration rate(1.3-fold)of reed(Phragmites australis),and decreased the content of Na + (62.3%)and Cl- (71.1%)of rhizome significantly.Continuous water compensation(continuous for 10 years)increased the height(3.2-fold),the net photosynthetic rate(104%),stomatal conductance(2.4-fold),transpiration rate(1.5-fold)of reed,and decreased Na + (82.5%)and Cl - (64.7%)contents in rhizome, then accumulated the K+ ,H2PO4-,SO42- and soluble sugar contents significantly in rhizome.Interrupting water compensation led to the decrease of height(25.3%),the net photosynthetic rate(30.7%),stomatal conductance(17.3%) and increase of Na + (1.16-fold)in rhizome when comparing to the continuous water compensation.These results showed that recovering the degraded reed wetlands needed continuous water compensation yearly to promote reed growth.The organs of reed had corresponding physiological response characteristic to the different water compensation condition.Under long-time dry and waterlogging condition,the rhizomes both helped reed to adapt located environment,by enriching the ions such as Na+ ,Cl- ,and K+ ,H2PO4-,SO42- ,respectively.