The effects of short-term rainfall variability on leaf isotopic traits of desert plants in sand-binding ecosystems

Author's manuscript made available in accordance with the publisher's policy.Sand-binding vegetation is effective in stabilizing sand dunes and reducing soil erosion, thus helps minimize the detrimental effects of desertification. The aim of this study is to better understand the relationships between water and nutrient usage of sand-binding species, and the effects of succession and rainfall variability on plants’ water–nutrient interactions. We examined the effects of long-term succession (50 years), inter-annual rainfall variability (from 65% of the mean annual precipitation in 2004 to 42% in 2005) and seasonality on water–nutrient interactions of three major sand-binding species (Artemisia ordosica, Hedysarum scoparium and Caragana korshinskii) by measuring foliar δ13C, δ15N and [N]. Long-term succession in general did not significantly alter δ13C, δ15N and [N] of the three species. Short-term rainfall variability, however, significantly increased foliar δ13C levels of all three species by 1.0–1.8‰ during the severely dry year. No significant seasonal patterns were found in foliar δ13C and δ15N values of the three species, whereas foliar [N] varied by season. For the two leguminous shrubs, the correlations between δ13C and δ15N were positive in both sampling years, and the positive correlation between [N] and δ13C was only found in the severely dry year. The results indicate that these sand-binding plants have developed into a relatively stable stage and they are able to regulate their nitrogen and water use in responding to environmental conditions, which reinforces the effectiveness of plantation of native shrubs without irrigation in degraded areas. However, the results also indicate that short-term climate variability could have severe impact on the vegetation functions

Dendroclimatological Investigations Of Sea Buckthorn (Hippophae Rhamnoides) And Reconstruction Of The Equilibrium Line Altitude Of The July First Glacier In The Western Qilian Mountains, Northwestern China

Radial growth characteristics of a high-elevation shrub species, sea buckthorn (Hippophae rhamnoides), were investigated at four sites in a river valley at altitudes ranging from 3,333 to 3,820 m a.s.l. close to the terminus of the July First Glacier in the western Qilian Mountains of northwestern China. Radial growth of the sea buckthorn was significantly and positively correlated with the mean monthly temperature in June of the current growing season. Based on the fact that fluctuations in the shrub’s radial growth and the glacier’s equilibrium-line altitude (ELA) are affected by climatic variables, a tree-ring width chronology of the four sites was used to reconstruct the ELA from 1950 to 2003. The resulting ELA model explained more than 55.3% of the variance in the ELA of the July First Glacier series. On a decadal time scale, the cumulative-departure curve of the reconstructed ELA series showed an increasing trend from the 1950s to the mid-1960s, followed by a descending trend from the mid-1960s to the mid-1970s. The ELA appears to have remained stable from the mid-1970s to the mid-1990s, but has displayed dramatic variations during the past decade.This item is part of the Tree-Ring Research (formerly Tree-Ring Bulletin) archive. For more information about this peer-reviewed scholarly journal, please email the Editor of Tree-Ring Research at [email protected]

Human activity impacts on the stem radial growth of Populus euphratica riparian forests in China's Ejina Oasis, using tree-ring analysis

Over the last several decades, riparian forests in Northwest China have been extremely vulnerable to the increasing pressures from human activity and climate change. However, it is unclear how forests correlate with these influences over time and on a wide scale. In the present study, we developed 28 tree-ring chronologies of Populus euphratica in the Ejina Oasis, in the lower reaches of Northwestern China's Heihe River, to evaluate the oasisscale riparian forest growth variation and its correlation with the runoff regulation. We identified three hydrologic periods using regime-shift analysis: a natural runoff period from 1954 to 1989, when the oasis was sustained by natural river flows; a degradation period from 1990 to 2002, when excessive upstream withdrawals of runoff decreased flows to the oasis; and a recovery period, from 2003 to 2010, when water allocation projects restored flows. In general, stem radial growth of poplar trees in the oasis showed decreasing and increasing trends in the degradation period and recovery period, respectively, with high spatial heterogeneity in each period. Our analysis of the relationship between the chronologies and corresponding hydrologic and climatic data revealed that the runoff-recharged hyporheic groundwater depth was the major factor that limited tree stem radial growth. Thus, it is important to allocate water between the middle and lower reaches, and inside the lower reaches, to mitigate or prevent the adverse effects of low runoff. Our study also demonstrates that researchers must carefully consider the high spatial heterogeneity during dendrochronological research in an arid riparian forest

Progress on socio-hydrology

In order to promote the development of socio-hydrology research and its application in basin water resources management, it is necessary to carry on a stage review of the researches and studies on socio-hydrology in recent years and recommend future research directions. The paper firstly introduces the establishment of socio-hydrology from the development of hydrology and explains its concept and connotation, then analyses the differences and similarities in content, method and theory between social-hydrology and traditional hydrology, eco-hydrology and hydro-economics; after that summaries the research progress of social-hydrology. The institution, policy and culture have been strengthened in the hydrological researches and some preliminary and exploratory researches have been carried out in case basins, however most of these studies were still based on either traditional hydrology, co-evolution or water resources management, the theory and method of socio-hydrology has not been fully developed. The following research actions are recommended for the future development of social-hydrology: strengthening quantitative research of its societal part, developing the process, historical and comparative socio-hydrology by historical analysis and hydrological reconstruction, and existing case studies; investigating the driving forces of the societal and hydrological systems to explore their dynamic mechanism; introducing the nonlinear dynamic theory to depict the complex feedback mechanism of the coupling human-water system, improving the generalized mathematical expression of the socio-hydrology; and promoting the application of the “big data” and knowledge mining technology in socio-hydrology research

Co-evolutionary dynamics of the human-environment system in the Heihe River basin in the past 2000years

There is limited quantitative understanding of interactions between human and environmental systems over the millennial scale. We aim to reveal the co-evolutionary dynamics of the human-environment system in a river basin by simulating the water use and net primary production (NPP) allocation for human and environmental systems over the last 2000years in Heihe River basin (HRB) in northwest China. We partition the catchment total evapotranspiration (ET) into ET for human and environmental systems with a social-hydrological framework and estimate the NPP for human and environmental systems using the Box-Lieth model, then classify the co-evolutionary processes of the human-environment system into distinct phases using the rate of changes of NPP over time, and discover the trade-offs or synergies relationships between them based on the elasticity of change of the NPP for humans to the change of NPP for environment. The co-evolutionary dynamics of human-environment system in the HRB can be divided into four periods, including: Phase I (Han Dynasty-Yuan Dynasty): predevelopment characterized by nearly no trade-offs between human and environment; Phase II (Yuan Dynasty-RC): slow agricultural development: characterized by a small human win due to small trade-offs between human and environment; Phase III (RC-2000): rapid agricultural development: characterized by a large human win due to large trade-offs between human and environment, and Phase IV (2000-2010): a rebalance characterized by large human wins with a small-environment win due to synergies, although these occurred very occasionally. This study provides a quantitative approach to describe the co-evolution of the human-environment system from the perspective of trade-offs and synergies in the millennial scale for the first time. The relationships between humans and environment changed from trade-off to synergy with the implementation of the water reallocation scheme in 2000. These findings improve the understanding of how humans influence environmental systems and responses to environmental stresses

Hydrological processes in the different landscape zones of alpine cold regions in the wet season, combining isotopic and hydrochemical tracers

C1 - Journal Articles Referee