Intra-annual stem diameter growth of Tamarix ramosissima and association with hydroclimatic factors in the lower reaches of China's Heihe River

High-resolution observations of cambial phenology and intra-annual growth dynamics are useful approaches for understanding the response of tree growth to climate and environmental change. During the past two decades, rapid socioeconomic development has increased the demand for water resources in the oases of the middle reaches of the Heihe River in northwestern China, and the lower reaches of the Heihe River have changed from a perennial river to an ephemeral stream with a decreased and degraded riparian zone. Tamarisk（Tamarix ramosissima） is the dominant shrub species of the desert riparian forest. In this study, the daily and seasonal patterns of tamarisk stem diameter growth, including the main period of tree ring formation, were examined. Observations concerning the driving forces of growth changes, along with implications for the ecology of the dendrohydrological area and management of desert riparian forests in similar arid regions, are also presented. The diurnal-seasonal activity of stem diameter and the dynamics of growth ring formation were studied using a point dendrometer and micro-coring methods during the 2012 growing season in shrub tamarisk in a desert riparian forest stand in the lower reaches of the Heihe River in Ejin Banner, Inner Mongolia of northwestern China. Generally, the variation in diurnal diameter of tamarisk was characterized by an unstable multi-peak pattern, with the cumulative stem diameter growth over the growing season following an S-shaped curve. The period from late May to early August was the main period of stem diameter growth and growth-ring formation. Among all of the hydroclimatic factors considered in this study, only groundwater depth was significantly correlated with stem diameter increment during this period. Therefore, for the dendrochronological study, the annual rings of the tamarisk can be used to reconstruct processes that determine the regional water regime, such as river runoff and fluctuations in groundwater depth. For the management of desert riparian forests, suitable groundwater depths must be maintained in the spring and summer to sustain tree health and a suitable stand structure.

Simulation of hydrological processes of mountainous watersheds in inland river basins: taking the Heihe Mainstream River as an example

The hydrological processes of mountainous watersheds in inland river basins are complicated.It is absolutely significant to quantify mountainous runoff for social,economic and ecological purposes.This paper takes the mountainous watershed of the Heihe Mainstream River as a study area to simulate the hydrological processes of mountainous watersheds in inland river basins by using the soil and water assessment tool(SWAT)model.SWAT simulation results show that both the Nash–Sutcliffe efficiency and the determination coefficient values of the calibration period(January 1995 to December 2002)and validation period(January 2002 to December 2009)are higher than 0.90,and the percent bias is controlled within±5%,indicating that the simulation results are satisfactory.According to the SWAT performance,we discussed the yearly and monthly variation trends of the mountainous runoff and the runoff components.The results show that from 1996 to 2009,an indistinctive rising trend was observed for the yearly mountainous runoff,which is mainly recharged by lateral flow,and followed by shallow groundwater runoff and surface runoff.The monthly variation demonstrates that the mountainous runoff decreases slightly from May to July,contrary to other months.The mountainous runoff is mainly recharged by shallow groundwater runoff in January,February,and from October to December,by surface runoff in March and April,and by lateral flow from May to September.

Study of temperature and precipitation change in upstream mountain area of the Hexi inland river basin since 1960s

All rivers in the Hexi inland region of Gansu Province, China, originate from the northern slope of the Qilian Mountains. They are located in the southern portion of the region and respectively belong to the three large river systems from east to west, the Shiyang, Heihe and Shule river basins. These rivers are supplied by precipitation, snowmelt and ice-melt runoff from the Qilian Mountain area. Therefore, changes of precipitation and temperature in the upstream watersheds of these rivers have an important effect on changes of mountainous runoff and reasonable utilization of water resources in this region. For this reason, the Qilian Mountain area, upstream watersheds and runoff forming areas of these rivers are chosen as the study area. The change characteristics and variation trend of temperature and precipitation in this area under the backdrop of global warming axe analyzed based on observa- tional data of relational weather and hydrologic stations in the area. Results show that temperatures in the upriver mountain areas of these three large river basins have been increasing, although the increasing degree is differentially affected by global warming. The rising extent of annual and seasonal temperatures in the upstream mountain area of the Shule river basin located in the west- em Qilian Mountains, were all largest over the past 50 years. Precipitation in the upstream mountain areas of Hexi region＇ three river basins located respectively in the western, middle and eastern Qilian Mountains have been presenting an increasing trend to varying degrees as a whole for more than 50 years. This means that climate in the upstream mountain areas of Hexi region＇ three river basins are becoming increasingly warmer and moister over the past 50 years, which will be very good for the ecological en- vironment and agricultural production in the region.

Effects of salt and alkali stress on Reaumuria soongorica germination

Seed germination and early seedling growth are crucial stages for plant establishment. Two neutral(Na Cl and Na2SO4) and two alkali(Na HCO3 and Na2CO3) salts were selected to investigate their effects on germination and recovery responses in Reaumuria soongorica. Results show that both salt types significantly reduced germination and radicle elongation. The rate of germination and emergence of R. soongorica seeds continuously decreased as salinity increased, and the time to achieve maximum germination rate was delayed. The speed of seed germination dropped rapidly as salt concentration increased.Alkaline salts restricted the germination rate of R. soongorica seeds, and stresses resulting from alkaline salts and high concentrations of neutral salts resulted in many deformed seedlings. The length of the radicle and germ decreased with increasing salt concentration, but certain concentrations of salt and increased p H promoted germ growth. The results of regression analysis show that salt concentration was the dominant factor inhibiting R. soongorica seed germination rate. Salinity, buffering capacity, and p H all affected embryo growth, but salinity had the most pronounced effect. Seed viability under highly saline conditions appears to be a better indicator of adaptation to saline environments than seed germination under saline conditions.

Microcoring and dendrometer-detected intra-annual wood formation of Populus euphratica in the Ejina Oasis,northwestern China

Seasonal stem radial growth and wood formation of trees have become research hotspots because of their significance for dendroclimatological and dendroecological studies. However, until recently, these studies concentrated on coniferous tree species in high-altitude and high-latitude regions,while detailed information on arid-zone riparian forests is scarce. The main focus of this study is to monitor the intra-annual dynamics of radial growth and tree ring formation in a deciduous species, Populus euphratica. In 2013, we combined the dendrometer and microcoring methods to study this species in the riparian forest of the Ejina Oasis, in arid northwestern China. Vessel enlargement began in early May, and the maximum rate of cell production occurred in early June. The cell division then ceased from early to mid-July. The dendrometer method failed to reliably detect the date of growth initiation and cessation, but succeeded to detect the time of maximum growth rate just like the microcoring method did. We found that weekly stem radial increment data described xylem growth more accurately than daily datasets. Based on correlation analysis among climatic and hydrologic variables, and weekly stem radial increment, weekly ring width increase dataset, the depth to groundwater was the main factor that limited tree ring growth. From a practical perspective, such studies of intra-annual wood formation can provide empirical guidance for seasonal water allocations within a river basin.

Evaluation of groundwater sustainability based on groundwater age simulation in the Zhangye Basin of Heihe River watershed, northwestern China

Water resources, as the primary limiting factor, constrain the economic and social development in arid inland areas. The Zhangye Basin is a representative area of inland river basins, which is located in the middle parts of the Heihe River watershed, northwestern China. Facing with the huge water shortage, people exploited ground- water at a large scale in recent years. The reducing recharge from surface water and over-exploitation of ground- water led to the decline of groundwater levels and threatened the sustainability of water resources. This study con- structed a conceptual and numerical groundwater flow model and calibrated the model based on the observed wells A solute transport model was built using MT3DMS to calculate the groundwater age distribution in the Zhangye Basin. The simulated result shows that the youngest groundwater is distributed near the most upstream areas in the model domain, which is less than 1,000 a, older groundwater is distributed in deeper parts of the aquifer and near the discharge outlets, ranging from 6,000 a to over 20,000 a. Spatial variation of groundwater ages in the middle area indicates the recharge diversity between unconfined and confined aquifer. Groundwater age can serve as an indicator to evaluate groundwater＇s renewal capacity and sustainability. The formation of groundwater resources in the lower stream area would spend 10,000 a or even more than 20,000 a, so exploitation of groundwater in these areas should be restrained.

An analysis on ecological civilization construction in Gansu based on a quantified SWOT framework

Ecological civilization （EC） construction has become one of the key elements of China＇s reform and development process, since it was put forward at the 17th National People＇s Congress （NPC） in 2007 and improved at the 18th NPC in 2012, and stressed at the third plenary session of the 18th NPC. The provincial areas are the most important pilot units of EC strategy. Therefore, research on EC at the provincial level can meet the practical demand for EC in China. Based on the existing provincial circumstances in Gansu and its significant position as an ecological barrier in northwestern China, and aiming at the core issue of why and how to build EC in Gansu, this paper employs SWOT （strengths, weaknesses, opportunities, threats） analysis, the Delphi method, and a combined quantitative analysis and coordinate method, and then calculates the relevant strategic orientation angle （0 = 1.4605） and strength coefficient （p = 0.53）. The results show that Gansu should take an opportunities-dominated strategy, and choose opportunity-strength measures, so the province can increase its in- ternal strengths and decrease its weaknesses with external promote an EC construction strategy. opportunities. Specific measures are recommended to actively

Water use measurement by non-irrigated Tamarix ramosissima in arid regions of Northwest China

Tamarix ramosissima Ledeb. is a typical hardy desert plant growing in arid regions of Northwest China. Sap flow in stems of Z ramosissima plants were measured continuously to determine the diurnal and seasonal variations of sap flow and to understand the water requirements of this species and the response of sap flow to meteorological factors. This article compared the sap flow rate measured by the heat balance method with the transpiration rate measured by rapid weighing, and validated that heat balance sap flow gauges were reliable for monitoring transpiration. The influence of meteorological factors on stem sap flow during the growing season was： solar radiation 〉 vapor pressure deficit 〉 air temperature 〉 rela- tive humidity 〉 wind speed. Bidirectional sap flows occurred at night, and negative sap flow generally corresponded to high atmospheric humidity. The average error in predicted sap flow rate ranged from -0.78% to 14.00% from June to September and for transpiration the average error was 8.19%. Therefore, based on the functional equations between sap flow and meteorological factors as well as sapwood area, transpiration of an individual plant, and even the stand-level transpiration, can be estimated accurately through extrapolation.

Dynamic evaluation of groundwater resources in Zhangye Basin

Groundwater resource is vital to the sustainable development of socio-economics in arid and semi-arid regions of Northwest China. An estimation of the groundwater resources variation in Zhangye Basin was made during 1985-2013 based on long-term groundwater observation data and geostatistical method. The results show that from 1985 to 2013, groundwater storage exhibited tremendous dissimilarity on temporal and spatial scale for the whole Zhangye Basin, especially before and after implementation of the water diversion policy. Trend of groundwater storage varied from quick to slow decline or increase. The accumulative groundwater storage decreased nearly 47.52~ 108 m3, and annual average depletion rate reached 1.64x 108 m3/a. Among which, the accumulative groundwater storage of the river and well water mixed irrigation district decreased by 37.48x 108 m3, accounting for about 78.87% of the total groundwater depletion of the Zhangye Basin. Accumulative depletion of groundwater storage varied in respective irrigation districts. Though groundwater resources depletion rate slowed down from 2005, the overall storage in the whole basin and re- spective districts during 1985-2013 was still in a severe deficit such that, the groundwater resource was in a rather negative balance, which could threaten the local aquifer. This is the joint effect of climate change and human activities, however human activities, such as water diversion policy and groundwater exploitation, became increasingly intense. Our research results could provide a reasonable estimation for the groundwater balance in Zhangye Basin, providing a scientific basis for water resources unified planning and, this method can provide a relatively reliable way of estimation for large scale groundwater resources.

Research advances in eco-hydrological process and function

Present studies on the coupling relationship and hydrology mechanism between basin ecosystem and hydrological process has become an international research frontier in hydrology. This paper investigates this coupling relationship, and also summarizes research and presents a method of combining isotopic technology with hydro-chemical methods, for the study of eco-hydrological process and function in different landscape zones. We then examine research trends for future direction and development of this field.

Water sources of plants and groundwater in typical ecosystems in the lower reaches of the Heihe River Basin

Stable oxygen and hydrogen isotopic compositions （δ18O and δD） of soil water and shallow groundwater of a riparian forest, an artificial shrub forest, and Gobi of the lower reaches of the Heihe River Basin are used to study the recharge water sources of those ecosystems. IsoSource software is used to determine the δ180 values for root water of Populous euphratica and Tamarix ramosissima in the riparian forest ecosystem, Haloxylon ammodendron in the artificial shrub forest, and Reaumuria soongorica in the Gobi, as well as for local soil water and groundwater, and precipitation in the upper reaches of the Heihe River Basin. Our results showed that soil water and shallow groundwater of the riparian forest and the artificial shrub forest were recharged by river water which originated from precipitation in the upper reaches, and strong evaporation occurred in the artificial shrub forest. Soil water of the Gobi was not affected by Heihe River water due to this area being far away from the river channel. The main water sources of Populous euphratica were from 40-60-cm soil water and groundwater, and of Tamarix ramosissima were from 40-80-cm soil water in the riparian forest ecosystem. In the artificial forest, Haloxylon ammodendron used 200-cm saturated-layer soil water and shallow groundwater. The Reaumuria soongorica mainly used soil water from the 175-200-cm depth in the Gobi. Therefore, soil water and groundwater are the main water sources which maintain survival and growth of the plants in the extremely arid regions of the lower reaches of the Heihe River Basin.

Englacial hydrological characteristics of a typical continental-type glacier in China as detected by ground-penetrating radar

The englacial structures and ice thickness of the Laohugou No. 12 （L12） Glacier in the Qilian Mountains, China, were retrieved from ground-penetrating radar （GPR） profile dzta acquired in August of 2007. Here the interpretation of a typical GPR image is validated using two-dimensional, Finite-Difference Time-Domain （FDTD） numerical modeling. Data analyses revealed many en- glacial characteristics, such as temperate ice, crevasses, and cavities at the position of convergence between the eastern and west- ern glacial branches of L12, and at an altitude between 4,600 and 4,750 m a.s.1, on the east branch. Combining ice thickness, en- glacial structures, subglacial topography, and surface flow velocities of this glacier, we analyzed the reasons for the distribution of temperate ice. The results show that greater englacial water content is associated with englacial crevassing and surface moulins, which allow water to be channeled to the temperate ice aquifer beneath the surface cold ice layer. Analysis of air temperature data shows that as more meltwater imports into the ice body, this has a great effect on water conservation and dynamics conditions. With climate warming, and under the influence of crevasses, subglacial structures, and ice thickness, ice thickness reduction on the L12 east branch is more rapid than that on the west branch.