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1. chinaXiv:201907.00003 [pdf]

Silurian-Devonian sub-parallel ridge-trench interaction in Western Junggar and North-Central Tianshan in NW China: Alternative genesis of archipelagic architecture

Zhang, Ji'en; Chen, Yichao; Xiao, Wenjiao; Wakabayashi, John; Windley, Brian F.; Song, Shuaihua; Yin, Jiyuan
Subjects: Geosciences >> Geology

Western Junggar and North-Central Tianshan in NW China comprise a double magmatic belt, which evolved as a result of 446-380 Ma SSZ-type gabbro-basalt-andesite-diorite-granite-rhyolite magmatism that intruded a 504-446 Ma accretionary complex in SW Junggar and coeval magmatic arc in Central Tianshan. This orogenic framework is interpreted as a product of sub-parallel ridge-trench interaction, which generated the double magmatic belt together with adakitic intrusions in the older accretionary complex. In this model, a buoyant subducted ridge stalled and separated the double magmatic belts, resulting in the opening of a new 414-325 Ma intra-arc ocean, which is represented by Nb-depleted OIB- and MORB-type ophiolites. Mafic rocks generated by sea floor spreading in the modern Gulf of California record a similar evolution and chemistry. This new ocean split the northern accretionary complex along Mt. Xiemisitai-Barleik-Mayile line, leading to deposition of Devonian shallow marine-terrestrial sediments and cessation of magmatism at 380-349 Ma; this evolution also resembles that of the late Cenozoic passive margins of Baja California. Subsequent removal of the new ocean and its ridge-subduction gave rise to an archipelagic framework in the Late Paleozoic. A worldwide analysis of published examples of sub-parallel ridge-trench interaction indicates that a ridge jump can lead to multiple episodes of subduction, which could occur long before terminal ocean closure.

submitted time 2019-07-03 Hits2171Downloads119 Comment 0

2. chinaXiv:201906.00042 [pdf]

Effect of pruning intensity on soil moisture and water use efficiency in jujube (Ziziphus jujube Mill.) plantations in the hilly Loess Plateau Region, China

JIN Shanshan
Subjects: Geosciences >> Geography

Jujube (Ziziphus jujube Mill.) is a traditional economic forest crop and is widely cultivated in hilly areas of the Loess Plateau, China. However, soil desiccation was discovered in jujube plantations. Pruning is recognized as a water-saving method that can reduces soil water consumption. In this study, we monitored the jujube plots with control (CK), light (C1), medium (C2) and high (C3) pruning intensities during the jujube growing period of 2012–2015 to explore the effect of pruning intensity on soil moisture and water use efficiency (WUE) of jujube plantations in the hilly Loess Plateau Region. The results showed that pruning is an effective method for soil water conservation in jujube plantations. Soil moisture increased with increasing pruning intensity during the jujube growing period of 2012–2015. C1, C2 and C3 pruning intensities increased soil water storage by 6.1–18.3, 14.4–40.0 and 24.3–63.3 mm, respectively, compared to CK pruning intensity. Pruning promoted soil moisture infiltration to deeper soil layer. Soil moisture infiltrated to soil depths of 240, 280 and >300 cm under C3 pruning intensity, 220, 260 and 260 cm under C2 pruning intensity, 200, 240 and 220 cm under C1 pruning intensity, and 180, 200 and 160 cm under CK pruning intensity in 2013, 2014 and 2015, respectively. Soil water deficit was alleviated by higher pruning intensity. In 2013–2015, soil water change was positive under C2 (6.4 mm) and C3 (26.8 mm) pruning intensities but negative under C1 (–20.5 mm) and CK (–40.6 mm) pruning intensities. Moreover, pruning significantly improved fresh fruit yield and WUE of jujube plants. Fresh fruit yields were highest under C1 pruning intensity with the values of 6897.1–13,059.3 kg/hm2, which were 2758.4–4712.8, 385.7–1432.1 and 802.8–2331.5 kg/hm2 higher than those under CK, C2, and C3 pruning intensities during the jujube growing period of 2012–2015, respectively. However, C3 pruning intensity had the highest WUE values of 2.92–3.13 kg/m3, which were 1.6–2.0, 1.1–1.2 and 1.0–1.1 times greater than those under CK, C1 and C2 pruning intensities, respectively. Therefore, C3 pruning intensity is recommended to jujube plantations for its economic and ecological benefits. These results provide an alternative strategy to mitigate soil desiccation in jujube plantations in the hilly Loess Plateau Region, which is critical for sustainable cultivation of economic forest trees in this region.

submitted time 2019-06-20 From cooperative journals:《Journal of Arid Land》 Hits4143Downloads170 Comment 0

3. chinaXiv:201906.00045 [pdf]

A cultivated area forecasting approach in artificial oases under climate change and human activities

ZHANG Shaobo; CHEN Fulong
Subjects: Geosciences >> Geography

The cultivated area in artificial oases is deeply influenced by global climate change and human activities. Thus, forecasting cultivated area in artificial oases under climate change and human activities is of great significance. In this study, an approach named GD-HM-PSWROAM, consisting of general circulation model downscaling (GD), hydrological model (HM), and planting structure and water resource optimal allocation model (PSWROAM), was developed and applied in the irrigation district of the Manas River Basin in Xinjiang Uygur Autonomous Region of China to forecast the cultivated area tendency. Furthermore, the catchment export of the MIKE11 HD/NAM model was set to the Kensiwate hydrological station. The results show that the downscaling effects of temperature can be fairly satisfying, while those of precipitation may be not satisfying but acceptable. Simulation capacity of the MIKE11 HD/NAM model on the discharge in the Kensiwate hydrological station can meet the requirements of running the PSWROAM. The accuracy of the PSWROAM indicated that this model can perform well in predicting the change of cultivated area at the decadal scale. The cultivated area in the Manas River Basin under current human activities may be generally decreasing due to the climate change. But the adverse effects of climate change can be weakened or even eliminated through positive human activities. The cultivated area in the Manas River Basin may even be increasing under assumed human activities and future climate scenarios. The effects of human activities in the future can be generally predicted and quantified according to the cultivated area trends under current human activities and the situations in the study area. Overall, it is rational and acceptable to forecast the cultivated area tendency in artificial oases under future climate change and human activities through the GD-HM-PSWROAM approach.

submitted time 2019-06-20 From cooperative journals:《Journal of Arid Land》 Hits3958Downloads190 Comment 0

4. chinaXiv:201906.00047 [pdf]

Actual evapotranspiration of subalpine meadows in the Qilian Mountains, Northwest China

GAO Yunfei; ZHAO Chuanyan
Subjects: Geosciences >> Atmospheric Sciences

As a main component in water balance, evapotranspiration (ET) is of great importance for water saving, especially in arid and semi-arid areas. In this study, the FAO (Food and Agriculture Organization) Penman-Monteith model was used to estimate the magnitude and temporal dynamics of reference evapotranspiration (ET0) in 2014 in subalpine meadows of the Qilian Mountains, Northwest China. Meanwhile, actual ET (ETc) was also investigated by the eddy covariance (EC) system. Results indicated that ETc estimated by the EC System was 583 mm, lower than ET0 (923 mm) estimated by the FAO Penman-Monteith model in 2014. Moreover, ET0 began to increase in March and reached the peak value in August and then declined in September, however, ETc began to increase from April and reached the peak value in July, and then declined in August. Total ETc and ET0 values during the growing season (from May to September) were 441 and 666 mm, respectively, which accounted for 75.73% of annual cumulative ETc and 72.34% of annual cumulative ET0, respectively. A crop coefficient (kc) was also estimated for calculating the ETc, and average value of kc during the growing season was 0.81 (ranging from 0.45 to 1.16). Air temperature (Ta), wind speed (u), net radiation (Rn) and soil temperature (Ts) at the depth of 5 cm and aboveground biomass were critical factors for affecting kc, furthermore, a daily empirical kc equation including these main driving factors was developed. Our result demonstrated that the ETc value estimated by the data of kc and ET0 was validated and consistent with the growing season data in 2015 and 2016.

submitted time 2019-06-20 From cooperative journals:《Journal of Arid Land》 Hits3487Downloads911 Comment 0

5. chinaXiv:201906.00049 [pdf]

Morphological variation of star dune and implications for dune management: a case study at the Crescent Moon Spring scenic spot of Dunhuang, China

ZHANG Weimin; TAN Lihai
Subjects: Geosciences >> Geography

Aerial photographs and 3-D laser scans of a 90-m high star dune at the Crescent Moon Spring scenic spot in Dunhuang, China, are used to investigate the changes in dune morphology on timescales from months to decades. The result revealed that relative-equilibrium airflow strength in three wind directions of northeast, west and south was an important condition for the stability of star dunes with limited migration. Transverse and longitudinal airflows exerted a crucial impact on variation processes of star dune morphology. Controlled by transverse airflows, the easterly winds, the east side was dominated by wind erosion; and strong deposition occurred on the south-south-east arm with a maximum deposition rate of 0.44 m/a in the 46-a monitoring period, causing the east side becoming steep and high. Controlled by longitudinal airflows, the westerly winds, the west-north-west side was mainly eroded and the north arm migrated from west to east with a rate of 0.30 m/a, causing the dune slope becoming gentle and elongate. The local air circulation (southerly winds) exerted a significant impact on the development process of the star dune. Due to the influence of human activities, the south side present surface processes from a concave profile to a convex profile in 46 a, which is a potential threat to the Crescent Moon Spring. The results indicate that rehabilitating the airflow field at most is a crucial strategy to the protection of Crescent Moon Spring from burial. Opening up the passage of easterly, westerly and southerly winds through intermediately cutting the protection forest, demolishing the enclosed wall and changing the pavilion into a porous pattern have been suggested to protect the Crescent Moon Spring from burial.

submitted time 2019-06-20 From cooperative journals:《Journal of Arid Land》 Hits3352Downloads152 Comment 0

6. chinaXiv:201906.00048 [pdf]

Effects of land use and cover change on surface wind speed in China

LI Yupeng
Subjects: Geosciences >> Geography

The surface wind speed (SWS) is affected by both large-scale circulation and land use and cover change (LUCC). In China, most studies have considered the effect of large-scale circulation rather than LUCC on SWS. In this study, we evaluated the effects of LUCC on the SWS decrease during 1979–2015 over China using the observation minus reanalysis (OMR) method. There were two key findings: (1) Observed wind speed declined significantly at a rate of 0.0112 m/(s•a), whereas ERA-Interim, which can only capture the inter-annual variation of observed data, indicated a gentle downward trend. The effects of LUCC on SWS were distinct and caused a decrease of 0.0124 m/(s•a) in SWS; (2) Due to variations in the characteristics of land use types across different regions, the influence of LUCC on SWS also varied. The observed wind speed showed a rapid decline over cultivated land in Northwest China, as well as a decrease in China's northeastern and eastern plain regions due to the urbanization. However, in the Tibetan Plateau, the impact of LUCC on wind speed was only slight and can thus be ignored.

submitted time 2019-06-20 From cooperative journals:《Journal of Arid Land》 Hits3440Downloads406 Comment 0

7. chinaXiv:201906.00050 [pdf]

Hyper-spectral characteristics of rolled-leaf desert vegetation in the Hexi Corridor, China

WEI Huaidong; YANG Xuemei
Subjects: Geosciences >> Geography

Desert plants survive harsh environment using a variety of drought-resistant structural modifications and physio-ecological systems. Rolled-leaf plants roll up their leaves during periods of drought, making it difficult to distinguish between the external structures of various types of plants, it is therefore necessary to carry out spectral characteristics analysis for species identification of these rolled-leaf plants. Based on hyper-spectral data measured in the field, we analyzed the spectral characteristics of seven types of typical temperate zone rolled-leaf desert plants in the Hexi Corridor, China using a variety of mathematical transformation methods. The results show that: (1) during the vigorous growth period in July and August, the locations of the red valleys, green peaks, and three-edge parameters, namely, the red edge, the blue edge, and the yellow edge of well-developed rolled-leaf desert plants are essentially consistent with those of the majority of terrestrial vegetation types; (2) the absorption regions of liquid water, i.e., 1400–1500 and 1600–1700 nm, are the optimal bands for distinguishing various types of rolled-leaf desert plants; (3) in the leaf reflectance regions of 700–1250 nm, which is controlled by cellular structure, it is difficult to select the characteristic bands for differentiation rolled-leaf desert vegetation; and (4) after processing the spectral reflectance curves using a first-order differential, the envelope removal method, and the normalized differential ratio, we identify the other characteristic bands and parameters that can be used for identifying various types of temperate zone rolled-leaf desert plants, i.e., the 510–560, 650–700 and 1330–1380 nm regions, and the red edge amplitude. In general, the mathematical transformation methods in the study are effective tools to capture useful spectral information for species identification of rolled-leaf plants in the Hexi Corridor.

submitted time 2019-06-20 From cooperative journals:《Journal of Arid Land》 Hits3532Downloads137 Comment 0

8. chinaXiv:201906.00051 [pdf]

Assessment of desertification in Eritrea: land degradation based on Landsat images

Subjects: Geosciences >> Geography

Remote sensing is an effective way in monitoring desertification dynamics in arid and semi-arid regions. In this study, we used a decision tree method based on NDVI (normalized difference vegetation index), SAVI (soil adjusted vegetation index), and vegetation cover proportion to quantify and analyze the desertification in Eritrea using Landsat data of the 1970s, 1980s and 2014. The results demonstrate that the NDVI value and the annual mean precipitation declined while the temperature increased over the past 40 a. Strongly desertified land increased from 4.82×104 km2 (38.5%) in the 1970s to 8.38×104 km2 (66.9%) in 2014: approximately 85% of the land of the country was under serious desertification, which significantly occurred in arid and semi-arid lowlands of the country (eastern, northern, and western lowlands) with relatively scarce precipitation and high temperature. The non-desertified area, mostly located in the sub-humid eastern escarpment, also declined from approximately 2.1% to 0.5%. The study concludes that the desertification is a cause of serious land degradation in Eritrea and may link to climate changes, such as low and unpredictable precipitation, and prolonged drought.

submitted time 2019-06-20 From cooperative journals:《Journal of Arid Land》 Hits3540Downloads114 Comment 0

9. chinaXiv:201904.00091 [pdf]

Monitoring the Dynamics of Field-Saturated Soil Hydraulic Conductivity in a Wastewater Irrigated Cropland [V5].pdf

Siyi Zhang; Isaac Hopkins; Li Guo; Henry Lin
Subjects: Geosciences >> Geography

The maintenance of adequate hydraulic conductivity is a basic priority for the function and sustainability of long-term wastewater irrigated lands. An effective procedure to measure in situ hydraulic conductivity quickly, easily, and reliably is still elusive. This study aims to compare the performance of DualHead Infiltrometers, a novel instrument designed to measure field-saturated hydraulic conductivity (Kfs) quickly and in an automated fashion, with different parameters and old infiltrometer designs; and to investigate the dynamics of Kfs in a cropland that has been spray-irrigated with treated wastewater for fifty years. Our results showed that a modified procedure with a longer, single pressure cycle yielded results with lower coefficients of variation (CVs) for both pressures and infiltration rates, and performed better than the original procedure with two short pressure recycles. Kfs values measured by DualHead Infiltrometers were similar to those measured by double-ring infiltrometers in most conditions. Viscosity-corrected Kfs on irrigated croplands was 123.8±94.0 mm h-1, insignificantly higher than that on the non-irrigated croplands, 103.2±94.6 mm h-1. We observed seasonal variations in Kfs values between winter and summer conditions, but infiltration rates during all seasons remained much higher than the spray irrigation rate (4.25 mm h-1). Nevertheless, with CVs greater than 67%, caution must be exercised to ensure that hydraulic conductivity remains high enough to prevent runoff at all times, especially during winter frozen conditions.

submitted time 2019-04-15 Hits9916Downloads1089 Comment 0

10. chinaXiv:201904.00084 [pdf]

A simulation study of GNSS-R polarimetric scattering from the bare soil surface based on the AIEM model

Subjects: Geosciences >> Geochemistry

In the past two decades, Global Navigation Satellite System-Reflectometry (GNSS-R) has emerged as a new remote sensing technique for soil moisture monitoring. Some experiments showed that the antenna of V polarization is more favorable to receive the reflected signals, and the interference pattern technique (IPT) was used for soil moisture and other geophysical parameters retrieval. Meanwhile, the lower satellite elevation angles are most impacted by the multipath. However, electromagnetic theoretical properties are not clear for GNSS-R soil moisture retrieval. In this paper, the Advanced Integral Equation Model (AIEM) is employed using the wave synthesis technique to simulate different polarimetric scattering at the specular directions. Results show when the incidence angles are larger than 70º, scattering at RR polarization (The transmitted signal is Right Hand Circular Polarization (RHCP), while the received one is also RHCP) is larger than that one at LR polarization (The transmitted signal is RHCP, while the received one is Left Hand Circular Polarization (LHCP)), while scattering at LR polarization is larger than that at RR polarization for the other incident angles(1º~70º). There is an apparent dip for VV and VR scattering due to the Brewster angle, which will result in the notch in the final receiving power and this phenomenon can be used for soil moisture retrieval or vegetation corrections. The volumetric soil moisture (vms) effects on their scattering are also presented. The larger soil moisture will result in lower scattering at RR polarization, and this is very different from the scattering of the other polarizations. It is interesting to note that the surface correlation function only affects the amplitudes of the scattering coefficients at much less level, but it has no effects on the angular trends of RR and LR polarizations.

submitted time 2019-04-10 Hits5179Downloads301 Comment 0

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