• Evaluation of the permafrost stability degradation from 1980 to 2010 in China
• YouHua Ran, Xin Li
• DOI: 10.3724/SP.J.1226.2016.00359
• 2016, Vol.8 (5): 359–366 Abstract ( 446) HTML PDF (4418 KB) ( 320 )
• The degradation of permafrost stability in China over the past 30 years is evaluated using a new, high-resolution near-surface air temperature reanalysis dataset. Results show that the permafrost extent clearly decreased by 22% from 1980 to 2010, that is, a loss of 12.68⁴;104 km². The degradation occurred not only in the transition regions between permafrost and seasonally frozen ground, but also and more importantly, in the interior of the permafrost regions. The degradation in the interior of permafrost regions accounted for 87% of the total degraded areas. The degradation occurred mainly during the 1980s to 1990s in the northeast permafrost area and the Qilian Mountains, and during the 1990s to 2000s in most areas of the Qinghai-Tibet Plateau (QTP). This degradation will have systemic impacts on engineered infrastructures in permafrost regions, the water balance, and the global carbon budget. A more robust physical model should be used to evaluate the permafrost thermal stability at finer resolution in the future.

• Atmospheric insight to climatic signals of δ¹⁸O in a Laohugou ice core in the northeastern Tibetan Plateau during 1960-2006
• WenTao Du, ShiChang Kang, Xiang Qin, XiaoQing Cui, WeiJun Sun
• DOI: 10.3724/SP.J.1226.2016.00367
• 2016, Vol.8 (5): 367–377 Abstract ( 422) HTML PDF (6039 KB) ( 1189 )
• Ice documentation and response to prominent warming, especially after the 1990s, is further investigated because it is concerned whether ice records have absence. A δ¹⁸O series of a Laohugou (LHG) shallow ice core (20.12 m) in the northeastern Tibetan Plateau was reconstructed covering the period of 1960-2006. The ice core δ¹⁸O record had significant positive correlations with the warm season (May-September) air temperatures at adjacent meteorological stations and the 500 hPa temperatures in boreal China, indicating that the δ¹⁸O record could be considered a credible proxy of regional temperature. A clear, cold temperature event in 1967 and rapid warming after the 1990s were captured in the LHG δ¹⁸O series, revealing that it could record extreme air-temperature events on both regional and global scales. The LHG δ¹⁸O variations had evident positive correlations with both the summer surface outgoing longwave radiation (OLR) in the Mongolia region and the summer meridional wind at 500 hPa in the LHG region during 1960-2006, suggesting that the increased OLR in the Mongolia region might have intensified the Mongolia Low and expanded the pressure gradient to the LHG region (the Shulehe High), which would have pushed the westerlies further north and suppressed southward incursions of cold air into the LHG region, and thus augmented the temperature rise. The regional atmospheric circulation difference (1985-2006 minus 1960-1984) suggested that the anticyclone in the Mongolia region might have developed the easterly wind, which transported warmer air from the east toward the LHG region and weakened the cold penetration of the westerlies, resulting in the temperature rise since the middle 1980s.

• Effect of sub-cloud evaporation on the δ¹⁸O of precipitation in Qilian Mountains and Hexi Corridor, China
• ZongXing Li, Qi Feng, YaMin Wang, JianGuo Li, XiaoYan Guo, YongGe Li
• DOI: 10.3724/SP.J.1226.2016.00378
• 2016, Vol.8 (5): 378–387 Abstract ( 615) HTML PDF (4243 KB) ( 422 )
• The sub-cloud evaporation effect refers to the evaporation process for raindrops that fall from the cloud base to the ground, which is usually accompanied by depleted light isotopes and enriched heavy isotopes in the precipitation. Based on 461 event-based precipitation samples collected from 12 weather stations in the Qilian Mountains and the Hexi Corridor from May to August of 2013, our results indicated that sub-cloud evaporation has a great influence on the δ¹⁸O of precipitation, especially in small-amount precipitation events. In May, June, July, and August the δ¹⁸O composition was enriched by 35%, 26%, 39%, and 41%, respectively, from the cloud base to the ground. This influence clearly strengthened with temperature rise, from the Qilian Mountains to the Hexi Corridor. When falling raindrops are evaporated by 1.0% in the Qilian Mountains and the Hexi Corridor, the composition of δ¹⁸O would be enriched by 1.2% and 2.6%, respectively. Temperature dominated the sub-cloud evaporation in the Qilian Mountains, whereas relative humidity controlled it in the Hexi Corridor. These results provide new proofs of the evolutional process of stable isotopes in precipitation in arid regions.

• A late Holocene winter monsoon record inferred from the palaeo-aeolian sand dune in the southeastern Mu Us Desert, northern China
• Bing Liu, HeLing Jin, Fan Yang
• DOI: 10.3724/SP.J.1226.2016.00388
• 2016, Vol.8 (5): 388–399 Abstract ( 337) HTML PDF (11104 KB) ( 174 )
• The variation of the Asian winter monsoonal strength has seriously affected the climate and environmental conditions in the Asian monsoonal region, and even in marginal islands and the ocean in the East Asian region. However, relevant understanding remains unclear due to the lack of suitable geological materials and effective proxies in the key study areas. Here, we present a grain-size record derived from the palaeo-aeolian sand dune in the southeastern Mu Us Desert, together with other proxies and OSL dating, which reflect a relatively detailed history of the winter monsoon and abrupt environmental events during the past 4.2 ka. Our grain-size standard deviation model indicated that >224 μm content can be considered as an indicator of the intensity of Asian winter monsoon, and it shows declined around 4.2-2.1 ka, enhanced but unstable in 2.1-0.9 ka, and obviously stronger since then. In addition, several typical climate events were also documented, forced by the periodic variation of winter monsoonal intensity. These include the cold intervals of 4.2, 2.8, 1.4 ka, and the Little Ice Age (LIA), and relatively warm sub-phases around 3.0, 2.1, 1.8 ka, and the Medieval Warm Period (MWP), which were roughly accordant with the records of the aeolian materials, peat, stalagmites, ice cores, and sea sediments in various latitudes of the Northern Hemisphere. Combined with the previous progresses of the Asian summer monsoon, we preliminarily confirmed a millennial-scale anti-correlation of Asian winter and summer monsoons in the Late Holocene epoch. This study suggests that the evolution of the palaeo-aeolian sand dune has the potential for comprehending the history of Asian monsoon across the desert regions of the modern Asian monsoonal margin in northern China.

• Cutting of Phragmites australis as a lake restoration technique: Productivity calculation and nutrient removal in Wuliangsuhai Lake, northern China
• Jan Felix Köbbing, Niels Thevs, Stefan Zerbe
• DOI: 10.3724/SP.J.1226.2016.00400
• 2016, Vol.8 (5): 400–410 Abstract ( 430) HTML PDF (2545 KB) ( 761 )
• Reed is one of the most frequent and dominant species in wetlands all over the world, with common reed (Phragmites australis (Cav.) Trin. ex Steud.) as the most widely distributed species. In many wetlands, P. australis plays a highly ambivalent role. On the one hand, in many wetlands it purifies wastewater, provides habitat for numerous species, and is a potentially valuable raw material, while on the other hand it is an invasive species which expands aggressively, prevents fishing, blocks ditches and waterways, and builds monospecies stands. This paper uses the eutrophic reed-swamp of Wuliangsuhai Lake in Inner Mongolia, northern China, as a case to present the multiple benefits of regular reed cutting. The reed area and aboveground biomass production are calculated based on field data. Combined with data about water and reed nutrient content, the impact of reed cutting on the lake nutrient budget (N and P) is investigated. Currently, at this lake around 100,000 tons of reed are harvested in winter annually, removing 16% and 8% of the total nitrogen and phosphorus influx, respectively. Harvesting all available winter reed could increase the nutrient removal rates to 48% and 24%, respectively. We also consider the effects of summer harvesting, in which reed biomass removal could overcompensate for the nutrient influx but could potentially reduce reed regrowth.

• Vertical distribution of Artemisia halodendron root system in relation to soil properties in Horqin Sandy Land, NE China
• YongQing Luo, XueYong Zhao, JiePing Ding, Tao Wang
• DOI: 10.3724/SP.J.1226.2016.00411
• 2016, Vol.8 (5): 411–418 Abstract ( 287) HTML PDF (2274 KB) ( 537 )
• Root distribution plays an important role in both vegetation establishment and restoration of degraded land through influencing soil property and vegetation growth. Root distribution at 0~60 cm depth of A. halodendron was investigated in Horqin Sandy Land. Soil organic carbon (SOC) and nitrogen (SN) concentration as well as carbon and nitrogen in root biomass and necromass were measured. Root length density (RLD) was estimated. Total root biomass, necromass and the RLD at 0~60 cm depth was 172 g/m², 245 g/m², and 368 m/m², respectively. Both biomass and necromass of A. halodendron roots decreased with soil depth, live roots were mainly at 0~20 cm (76% of biomass and 63% of root length), while 73% of the necromass was within 0~30 cm depth. N concentration of roots (biomass and necromass) was about 1.0% and 1.5%, respectively. There were significant differences in SOC concentration between soil layers, but insignificant for SN. Soil C/N ratio decreased with depth (P<0.05). C and N storage for belowground system at 0~60 cm decreased markedly with depth; 41.4% of C and 31.7% of N were allocated to the 0~10 cm layer. Root bio- and necromass together contained similar amount of C to that of the soil itself in the top layer. N stock was dominated by soil nitrogen at all depths, but more so in deeper layers. It is clear that differentiating between soil layers will aid in interpreting A. halodendron efficiency in soil restoration in sandy land.

• Measuring and modeling two-dimensional irrigation infiltration under film-mulched furrows
• YongYong Zhang, PuTe Wu, XiNing Zhao, WenZhi Zhao
• DOI: 10.3724/SP.J.1226.2016.00419
• 2016, Vol.8 (5): 419–431 Abstract ( 402) HTML PDF (8982 KB) ( 293 )
• Furrow irrigation with film-mulched agricultural beds is being promoted in the arid region of northwest China because it im-proves water utilization. Two-dimensional infiltration patterns under film-mulched furrows can provide guidelines and criteria for irrigation design and operation. Our objective was to investigate soil water dynamics during ponding irrigation infiltration of mulched furrows in a cross-sectional ridge-furrow configuration, using laboratory experiments and mathematical simulations. Six experimental treatments, with two soil types (silt loam and sandy loam), were investigated to monitor the wetting patterns and soil water distribution in a cuboid soil chamber. Irrigation of mulched furrows clearly increased water lateral infiltration on ridge shoulders and ridges, due to enhancement of capillary driving force. Increases to both initial soil water content (SWC) and irrigation water level resulted in increased wetted soil volume. Empirical regression equations accurately estimated the wetted lateral distance (R_l) and downward distance (R_d) with elapsed time in a variably wetted soil medium. Optimization of model parameters followed by the Inverse approach resulted in satisfactory agreement between observed and predicted cumulative infiltration and SWC. On the basis of model calibration, HYDRUS-2D model can accurately simulate two-dimensional soil water dynamics under irrigation of mulched furrows. There were significant differences in wetting patterns between unmulched and mulched furrow irrigation using HYDRUS-2D simulation. The R_d under the mulched furrows was 32.14% less than the unmulched furrows. Therefore, film-mulched furrows are recommended in a furrow irrigation system.

• Land use and land cover change and its driving forces in Maqu County, China in the past 25 years
• JunFeng Lu, ZhiBao Dong, GuangYin Hu, WenJin Li, WanYin Luo, MingLiang Tan
• DOI: 10.3724/SP.J.1226.2016.00432
• 2016, Vol.8 (5): 432–440 Abstract ( 417) HTML PDF (4771 KB) ( 583 )
• Maqu County is located in the northeast Qinghai-Tibetan Plateau, and it is the main watershed for the Yellow River. The ecosystem there is extremely vulnerable and sensitive to climate change and human activities, which have caused significant deterioration of the eco-environment in this region. In order to restore the ecological environment, a government project to restore the grazing areas to grassland was implemented in Maqu County in early 2004. This study evaluates the effects of that restoration project on land use and land cover change (LUCC), and explores the driving forces of LUCC in Maqu County. In the study we used Landsat images obtained in 1989, 2004, 2009, and 2014 to establish databases of land use and land cover. Then we derived LUCC information by overlaying these layers using GIS software. Finally, we analyzed the main forces responsible for LUCC. The results showed that forests, high-coverage grasslands, and marshes experienced the most significant decreases during 1989-2004, by 882.8 ha, 35,250.4 ha, and 2,753.4 ha, respectively. However, moderate- and low-coverage grasslands and sand lands showed the opposite trend, increasing by 12,529.7 ha, 25,491.0 ha, and 577.5 ha, respectively. LUCC in 2004-2009 showed that ecological degradation slowed compared with 1989-2004. During 2009-2014, high- and moderate-coverage grasslands increased obviously, but low-coverage grasslands, marshes, unused lands, sand lands, and water areas showed the opposite trend. These results suggested that the degradation of the eco-environment was obvious before 2009, showing a decrease in the forests, grasslands, and water areas, and an increase in unused lands. The ecological degradation was reversed after 2009, as was mainly evidenced by increases in high- and moderate-coverage grasslands, and the shrinkage rate of marshes decreased obviously. These results showed that the project of restoring grazing lands to grassland had a positive effect on the LUCC. Other major factors that influence the LUCC include increasing temperature, variation in the seasonal frozen soil environment, seasonal overgrazing, and pest and rodent damage.

• The efficacy of Kriging spatial interpolation for filling temporal gaps in daily air temperature data: A case study in northeast China
• YanLin Zhang, XiaoLi Chang, Ji Liang, DongLiang Luo, RuiXia He
• DOI: 10.3724/SP.J.1226.2016.00441
• 2016, Vol.8 (5): 441–449 Abstract ( 358) HTML PDF (2342 KB) ( 338 )
• Quality-controlled and serially complete daily air temperature data are essential to evaluating and modelling the influences of climate change on the permafrost in cold regions. Due to malfunctions and location changes of observing stations, temporal gaps (i.e., missing data) are common in collected datasets. The objective of this study was to assess the efficacy of Kriging spatial interpolation for estimating missing data to fill the temporal gaps in daily air temperature data in northeast China. A cross-validation experiment was conducted. Daily air temperature series from 1960 to 2012 at each station were estimated by using the universal Kriging (UK) and Kriging with an external drift (KED), as appropriate, as if all the observations at a given station were completely missing. The temporal and spatial variation patterns of estimation uncertainties were also checked. Results showed that Kriging spatial interpolation was generally desirable for estimating missing data in daily air temperature, and in this study KED performed slightly better than UK. At most stations the correlation coefficients (R²) between the observed and estimated daily series were >0.98, and root mean square errors (RMSEs) of the estimated daily mean (T_mean), maximum (T_max), and minimum (T_min) of air temperature were <3℃. However, the estimation quality was strongly affected by seasonality and had spatial variation. In general, estimation uncertainties were small in summer and large in winter. On average, the RMSE in winter was approximately 1℃ higher than that in summer. In addition, estimation uncertainties in mountainous areas with complex terrain were significantly larger than those in plain areas.