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Widely distributed Mid-Neoproterozoic mafic rocks of the Qilian – Qaidam – East Kunlun region record the tectonic evolution of the northeastern Tibetan Plateau. This study presents whole-rock geochemistry, zircon U–Pb geochronology and Hf isotopes for the Xialanuoer gabbros of the central South Qilian Belt (SQB). Zircon laser ablation – inductively coupled plasma – mass spectrometry (LA-ICP-MS) U–Pb dating indicates that the gabbros were emplaced at ca. 738 Ma, indicating they are contemporaneous with mafic magmatism elsewhere in the northeastern Tibetan Plateau. The gabbros have low SiO2, Cr and Ni contents and Mg# values, are relatively enriched in light rare-earth elements (LREEs) and depleted in high-field-strength elements (HFSEs; e.g. Nb and Ta), have no positive Zr or Hf anomalies and have relatively high Nb/Ta but low Nb/La ratios. These data indicate that the Xialanuoer gabbros formed from calc-alkaline basaltic magmas that were originally generated by the partial melting of an enriched mantle of type-I (EMI-type) enriched region of the lithospheric mantle, underwent little to no crustal contamination prior to their emplacement, and have within-plate basalt geochemical affinities. Combining these data with the presence of widespread contemporaneous continental rift-related magmatism and sedimentation in the North Qilian, Central Qilian, South Qilian, Quanji, North Qaidam and East Kunlun regions suggests that the northeastern Tibetan Plateau underwent Mid-Neoproterozoic continental rifting, which also affected other Rodinian blocks (e.g. Tarim, South China, Australia, North America and Southern Africa). [ABSTRACT FROM AUTHOR]

Soils on the Qinghai-Tibetan Plateau (QTP) have distinct physical properties from agricultural soils due to weak weathering and strong erosion. These properties might affect permafrost dynamics. However, few studies have investigated both quantitatively. In this study, we selected a permafrost site on the central region of the QTP and excavated soil samples down to 200 cm. We measured soil porosity, thermal conductivity, saturated hydraulic conductivity, and matric potential in the laboratory. Finally, we ran a simulation model replacing default sand or loam parameters with different combinations of these measured parameters. Our results showed that the mass of coarse fragments in the soil samples (diameter > 2 mm) was ~ 55% on average, soil porosity was less than 0.3m³ m-3, saturated hydraulic conductivity ranged from 0.004 to 0.03mms-1, and saturated matric potential ranged from -14 to -604 mm. When default sand or loam parameters in the model were substituted with these measured values, the errors of soil temperature, soil liquid water content, active layer depth, and permafrost lower boundary depth were reduced (e.g., the root mean square errors of active layer depths simulated using measured parameters versus the default sand or loam parameters were about 0.28, 1.06, and 1.83 m). Among the measured parameters, porosity played a dominant role in reducing model errors and was typically much smaller than for soil textures used in land surface models. We also demonstrated that soil water dynamic processes should be considered, rather than using static properties under frozen and unfrozen soil states as in most permafrost models. We conclude that it is necessary to consider the distinct physical properties of coarse-fragment soils and water dynamics when simulating permafrost dynamics of the QTP. Thus it is important to develop methods for systematic measurement of physical properties of coarse-fragment soils and to develop a related spatial data set for porosity. [ABSTRACT FROM AUTHOR]

Small-scale patchiness intensified the spatial heterogeneous distribution of soil and vegetation organic carbon (C) and total nitrogen (N), thereby inducing large uncertainty in estimating ecosystem C and N stocks. However, patchiness at this scale was difficult to identify by satellite remote sensing and measure in situ. Aerial photographing can provide high-precision images and can potentially improve estimating accuracy in ecosystem C and N stocks. In this study, using combined methods of field sampling, aerial photographing and satellite images, we investigated the characteristics of patchiness, quantified ecosystem C and N stocks in different patches at plot scale (~ 1000 m 2 ) and eventually estimated the uncertainty in ecosystem C and N stocks caused by small-scale patchiness at basin scale. Results showed that: 1) mosaic of vegetation and bald patches coexisted for swamp meadow and alpine meadow, whereas vegetation presented as spot for steppe meadow and alpine steppe; 2) average ecosystem respiration, C and N stocks in intact grassland patches were 2.05 and 1.65, 1.66 and 1.65, 2.01 and 1.69 times higher than those of large and medium bare patches ( P < 0.05); and 3) neglecting the bare patches caused approximate 30%, 15% and 10% overestimation in estimations of ecosystem C emission, C and N stocks. We concluded that small-scale patchiness would result in ecosystem C loss due to decreasing in C input from vegetation and increasing in C output from soil erosion. Our study suggested that integration of field sampling, aerial photographing and satellite images could improve precision in estimation of ecosystem C emission, C and N stocks at basin scale. [ABSTRACT FROM AUTHOR]

Fractional vegetation cover (FVC) is an important parameter in studies of ecosystem balance, soil erosion, and climate change. Remote-sensing inversion is a common approach to estimating FVC. However, there is an important gap between ground-based surveys (quadrat level) and remote-sensing imagery (satellite image pixel scale) from satellites. In this study we evaluated that gap with unmanned aerial vehicle (UAV) aerial images of alpine grassland on the Qinghai–Tibetan Plateau (QTP). The results showed that: (1) the most accurate estimations of FVC came from UAV (FVCUAV) at the satellite image pixel scale, and when FVC was estimated using ground-based surveys (FVCground), the accuracy increased as the number of quadrats used increased and was inversely proportional to the heterogeneity of the underlying surface condition; (2) the UAV method was more efficient than conventional ground-based survey methods at the satellite image pixel scale; and (3) the coefficient of determination (R2) between FVCUAVand vegetation indices (VIs) was significantly greater than that between FVCgroundand VIs (p < 0.05,n = 5). Our results suggest that the use of UAV to estimate FVC at the satellite image pixel scale provides more accurate results and is more efficient than conventional ground-based survey methods. [ABSTRACT FROM PUBLISHER]

Actual evapotranspiration was observed by using eddy covariance (EC) technique, calculated by micrometeorological method the Bowen ratio energy balance (BREB) and measured by micro-lysimeter (ML) in the Suli alpine meadow which located in the northeastern edge of Qinghai-Tibet Plateau noted for its high elevation and cold environment during the growing season in 2011. Results showed that the energy balance ratio for half-hour data was 0.74. Without consideration of uncertainty, the evapotranspiration values estimated by BREB, ML, and EC were 270.6 mm, 238.9 mm, and 236.1 mm, respectively. Significant correlation existed between the evapotranspiration results by the three methods. Uncertainties of the evapotranspiration estimation by BREB, ML, and EC were 19.6 mm, 15.6 mm, and 15.1 mm, respectively. Deduced by facts on the natural and vegetation conditions, the value of evapotranspiration should be equal to that of precipitation, that is, about 252 mm. From this point, the evapotranspiration values estimated by the three methods were within a reliable range. The EC method has larger advantage and wider scope for the estimation of evapotranspiration in alpine meadow area. [ABSTRACT FROM AUTHOR]

As the largest high-altitude permafrost region in the world, the Qinghai–Tibetan Plateau (QTP) has experienced pronounced warming, which may exert a profound effect on ecosystem's CO 2 emissions due to the large amounts of organic carbon in the permafrost soil. In this study, response of ecosystem respiration to short-term experimental warming was investigated in the alpine meadow ecosystem of a permafrost site on the QTP during the 2012 growing season. The results showed that cumulative growing season ecosystem CO 2 emissions were 277.09 and 325.33 g C m − 2 for the control and warming plots, respectively. Thus, a 2.18 °C increase in ground surface temperature and a 0.62 °C increase in soil temperature prompted a 17.41% increase in the ecosystem's CO 2 emissions. The relationships between temporal variations in ecosystem respiration and soil temperature can be described through exponential equation. Soil temperature accounted for 50 and 64% of the variations in ecosystem respiration on a diurnal scale, and 71 and 84% of the variations in ecosystem respiration on a seasonal scale in the control and warming plots, respectively. Moreover, the temperature sensitivity (i.e. apparent Q 10 values) of the ecosystem respiration rates was significantly higher in the warming plots than in the control plots. Our results indicate that the effect of warming promoted CO 2 emissions of the alpine meadow ecosystem at a permafrost site on the QTP, and that soil temperature is the key factor controlling ecosystems' CO 2 emissions. In addition, while ecosystem respiration provides positive feedback on the rise in temperature through an increase in temperature sensitivity under warming conditions, at least in the short term, this feedback may be partially offset by an increase in above- and belowground biomass caused by warming. [ABSTRACT FROM AUTHOR]

Gravel is common in soil profiles of alpine grassland on the Qinghai-Tibetan plateau (QTP). However, little is known about the effect of gravel on soil and vegetation properties. In this study, we investigated the gravel content in the topsoil (0–40 cm) at three sites with different surface gravel mulch and analyzed the influence of gravel on soil organic carbon (SOC), soil total nitrogen (TN), fractional vegetation cover (FVC), and aboveground biomass (AGB). Results showed that (1) gravel content was the highest in sites with high surface gravel mulch, and the lowest in sites with light surface gravel mulch; (2) gravel was significantly negatively correlated with SOC, TN, FVC and AGB, and (3) gravel of 2–20 mm in size was the most important factor determining soil and vegetation properties. Our results suggested that the presence of gravel in the soil profile is not beneficial to soil nutrition sequestration and vegetation growth of alpine grassland on the QTP and should be considered in ecosystem modeling studies. [ABSTRACT FROM AUTHOR]