Qingbai Wu

Responses of Permafrost on the Qinghai-Tibet Plateau, China, to Climate Change and Engineering Construction

ABSTRACT Monitoring of permafrost along the Qinghai-Tibet (Xizang) Highway shows that there is a large difference in the response of permafrost to climate change and to engineering construction. The change in cold (<−1.5°C) permafrost is greater than that in warm (≥−1.5°C) permafrost under the effect of climate change, while the cold permafrost is less sensitive to the disturbances from engineering activities. However, warm permafrost is very sensitive to both climate warming and the impacts from engineering construction. This is because engineering construction has more immediate and direct impacts on the thermal and moisture regimes of underlying permafrost, and consequently greater influence than climate change during the first few years after engineering construction. Assuming constant annual rates of warming, the surface of cold permafrost would approach the warming due to engineering construction in 50 yr, while it would take about 20 yr in areas with warm permafrost. At a depth of 6 m, the temperature rise under engineered surfaces would be reached within 20 and 5–8 yr in cold and warm permafrost, respectively. Therefore, the warming immediately following disturbances of engineering construction would occur naturally in a few years under warm permafrost, but it would take decades for cold permafrost to have the similar thermal effects. Therefore, climate change will have more direct and immediate impacts on the thermal regime of warm permafrost and on the stability and reliability of engineering infrastructures above warm permafrost.

Pyrosequencing investigation into the bacterial community in permafrost soils along the China-Russia Crude Oil Pipeline (CRCOP).

The China-Russia Crude Oil Pipeline (CRCOP) goes through 441 km permafrost soils in northeastern China. The bioremediation in case of oil spills is a major concern. So far, little is known about the indigenous bacteria inhabiting in the permafrost soils along the pipeline. A pilot 454 pyrosequencing analysis on the communities from four selected sites which possess high environment risk along the CRCOP is herein presented. The results reveal an immense bacterial diversity than previously anticipated. A total of 14448 OTUs with 84834 reads are identified, which could be assigned into 39 different phyla, and 223 families or 386 genera. Only five phyla sustain a mean OTU abundance more than 5% in all the samples, but they altogether account for 85.08% of total reads. Proteobacteria accounts for 41.65% of the total OTUs or 45% of the reads across all samples, and its proportion generally increases with soil depth, but OTUs numerically decline. Among Proteobacteria, the abundance of Beta-, Alpha-, Delta- and Gamma- subdivisions average to 38.7% (2331 OTUs), 37.5% (2257 OTUs), 10.35% (616 OTUs), and 6.21% (374 OTUs), respectively. Acidobacteria (esp. Acidobacteriaceae), Actinobacteria (esp. Intrasporangiaceae), Bacteroidetes (esp. Sphingobacteria and Flavobacteria) and Chloroflexi (esp. Anaerolineaceae) are also very common, accounting for 8.56% (1237 OTUs), 7.86% (1136 OTUs); 7.35% (1063 OTUs) and 8.27% (1195 OTUs) of total libraries, respectively. The ordination analysis indicates that bacteria communities in the upper active layer cluster together (similar), while bacterial consortia from the lower active layer and permafrost table scatter (less similar). The abundance of Rhodococcus (12 OTUs), Pseudomonas (71 OTUs) and Sphingomonas (87 OTUs) is even less (<0.01%). This effort to profile the background diversity may set the first stage for better evaluating the bacterial dynamics in response to accidental oil spills.

Technical approaches on permafrost thermal stability for Qinghai–Tibet Railway

Widespread warm permafrost with a high ice content is a key problem for the roadbed stability of the Qinghai–Tibet Railway. A new approach is proposed to alleviate the effect of global warming and engineering construction on permafrost by cooling the roadbed and positively protecting the permafrost. Measures for cooling the roadbed by adjusting solar radiation, conduction, and convection are studied and applied to prevent ground ice from thawing and to ensure roadbed stability in permafrost regions. The results of monitoring permafrost embankments at Beiluhe and along the Qinghai–Tibet Railway show that the measures adopted for cooling the roadbed are very effective in raising permafrost table and reducing the soil temperature.

Carbon and Nitrogen Properties of Permafrost over the Eboling Mountain in the Upper Reach of Heihe River Basin, Northwestern China

Abstract The sensitivity of soil carbon and nitrogen to warming is a major uncertainty in projections of climate. However, previous studies about soil organic carbon (SOC) stocks and potential emission predominantly concentrated on the shallow soil layer in high latitude ecosystems. In this study, we analyzed the SOC, total nitrogen (TN) and soil inorganic carbon (SIC) stocks, C/N ratios, and stable carbon isotope (&dgr;13C) in the active layer and permafrost layer on the Eboling Mountain in the upper reach of Heihe River basin, northwestern China. Our results showed that the average stocks of SOC, TN, and SIC in permafrost layer above soil parent materials (71.7 kg m-2, 8.0 kg m-2, 34.7 kg m-2) were much higher than those in the active layer (44.3 kg m-2, 5.3 kg m-2, 12.2 kg m-2). The &dgr;13C pattern in the soil profiles indicated that historical drainage conditions and pedogenesis were important factors in determining soil organic matter (SOM) stocks in this permafrost region. The &dgr;13C and C/N ratios of the transient layer and some layers of permafrost implied that the degradation of SOM was different. These results highlight that carbon and nitrogen in permafrost regions with Alpine Kobresia meadow could make significant contribution to Chinas terrestrial carbon cycle.

Carbon loss and chemical changes from permafrost collapse in the northern Tibetan Plateau

Permafrost collapse, known as thermokarst, can alter soil properties and carbon emissions. However, little is known regarding the effects of permafrost collapse in upland landscapes on the biogeochemical processes that affect carbon balance. In this study, we measured soil carbon and physiochemical properties at a large thermokarst feature on a hillslope in the northeastern Tibetan Plateau. We categorized surfaces into three different microrelief patches based on type and extent of collapse (control, drape, and exposed areas). Permafrost collapse resulted in substantial decreases of surface soil carbon and nitrogen stocks, with losses of 29.64.2% and 28.93.1% for carbon and nitrogen, respectively, in the 0-10cm soil layer. Laboratory incubation experiments indicated that control soil had significantly higher CO2 production rates than that of drapes. The results from Fourier transform infrared spectroscopy analysis showed that exposed soils accumulated some organic matter due to their low position within the feature, which was accompanied by substantial changes in the chemical structure and characteristics of the soil carbon. Exposed soils had higher hydrocarbon and lignin/phenol backbone content than in control and drape soils in the 0-10cm layer. This study demonstrates that permafrost collapse can cause abundant carbon and nitrogen loss, potentially from mineralization, leaching, photodegradation, and lateral displacement. These results demonstrate that permafrost collapse redistributes the soil organic matter, changes its chemical characteristics, and leads to losses of organic carbon due to the greenhouse gas emission.

Changes of Soil Thermal Regimes in the Heihe River Basin Over Western China

Abstract Investigation of the changes in soil thermal regimes is essential to the understanding of ecohydrological processes, resource development, and climate change. We use soil temperatures from 12 meteorological stations of the China Meteorological Administration in the Heihe River Basin to estimate soil seasonal freeze depth, the onset and end dates of soil freeze, and the duration of soil freeze. Based on the characteristics of the soil temperature in the seasonal freezing layer, the freeze/thaw processes of this layer were divided into four stages: the winter freezing stage, spring thawing stage, summer warming stage, and autumn cooling stage. Spring, summer, autumn, and winter ground surface temperatures in the basin exhibit significant increasing trends in 1972–2006, of 0.65 °C decade-1, 0.73 °C decade-1, 0.48 °C decade-1, and 0.44 °C decade-1, respectively. Mean annual soil temperature at 0.0–0.20 m depths reveals an increasing trend of 0.58–0.63 °C decade-1 in 1972–2006. The onset date of soil freeze, the end date of soil freeze, and the duration of soil freeze in 1972–2006 exhibit a statistically significant trend of +2 days decade-1, -4 days decade-1, and -6 days decade-1, respectively. The maximum thickness of the seasonally frozen ground for 1960–2007 reveals a statistically significant trend of -4.0 cm decade-1 and a net change of -19.2 cm for the 48-year period. These are all related to the increase in spring, summer, autumn, and winter air temperature and the mean annual air temperature in the basin, a possible result of global warming.

Modeling Chinese cryospheric change by using GIS technology

Abstract The Chinese Cryospheric Information System (CCIS) is an integrated geographic information system (GIS) for storing, managing and analyzing the cryospheric data within China. Three regions were selected as the case study areas of CCIS. They are the Qinghai–Tibet Plateau, the regions along the Qinghai–Tibet Highway and the Urumqi River Basin of Tianshan Mountain. A draft geo-classification system that can express the logical hierarchy of cryospheric data was established. Based on this, CCIS stored large volumes of data, including maps of glacier, frozen ground and other environmental elements, digital elevation data, observation data of meteorological stations, hydrological gauges and permafrost boreholes and remote sensing data. CCIS is managed by ARC/INFO and can export data to other GIS environments easily, since data exchange interfaces were paid particular attention in the system. Based on CCIS, several GIS-based models about cryospheric processes and cryospheric response to global change have been developed. The models introduced are the following: a response model of high-altitude permafrost to global change, an evaluation model of engineering properties in permafrost regions along the Qinghai–Tibet Highway and a model of glacier mass balance estimation. The modeling results showed that the permafrost and glaciers in Chinese cryosphere will have significant changes under climatic warming.

Thermal–moisture dynamics of embankments with asphalt pavement in permafrost regions of central Tibetan Plateau

Subsurface moisture content is one of the critical factors that control the thermal dynamics of embankments. However, information on the subsurface moisture movement and distribution in embankments is still limited. To better understand the coupled water and heat transport within embankments, subsurface temperature and moisture of an asphalt pavement highway were extensively measured from 2009 to 2011. Collected data indicate that pure heat conduction is the overall main mechanism of heat transport in the embankment and heat convection plays a relatively unimportant role in heat transport. The results also indicate that subsurface moisture and temperature dynamics in the asphalt layer is strongly related to the rainfall events, while the subsurface moisture content below the road base course maintains relatively constant. Rainfall in summer leads to rapid cooling of the subsurface soil. Our results suggest that frequent and small rainfall events favour the thermal stability of the embankment due to the loss of latent heat of water evaporation. Moisture migration during freezing still occurred in the gravel fill and the water infiltrated into the active layer during thawing period. Freezing-induced water migration may result in the increase in water content of the embankment and the decrease in compactness of gravel fill.

Relative Roles of Deterministic and Stochastic Processes in Driving the Vertical Distribution of Bacterial Communities in a Permafrost Core from the Qinghai-Tibet Plateau, China

Understanding the processes that influence the structure of biotic communities is one of the major ecological topics, and both stochastic and deterministic processes are expected to be at work simultaneously in most communities. Here, we investigated the vertical distribution patterns of bacterial communities in a 10-m-long soil core taken within permafrost of the Qinghai-Tibet Plateau. To get a better understanding of the forces that govern these patterns, we examined the diversity and structure of bacterial communities, and the change in community composition along the vertical distance (spatial turnover) from both taxonomic and phylogenetic perspectives. Measures of taxonomic and phylogenetic beta diversity revealed that bacterial community composition changed continuously along the soil core, and showed a vertical distance-decay relationship. Multiple stepwise regression analysis suggested that bacterial alpha diversity and phylogenetic structure were strongly correlated with soil conductivity and pH but weakly correlated with depth. There was evidence that deterministic and stochastic processes collectively drived bacterial vertically-structured pattern. Bacterial communities in five soil horizons (two originated from the active layer and three from permafrost) of the permafrost core were phylogenetically random, indicator of stochastic processes. However, we found a stronger effect of deterministic processes related to soil pH, conductivity, and organic carbon content that were structuring the bacterial communities. We therefore conclude that the vertical distribution of bacterial communities was governed primarily by deterministic ecological selection, although stochastic processes were also at work. Furthermore, the strong impact of environmental conditions (for example, soil physicochemical parameters and seasonal freeze-thaw cycles) on these communities underlines the sensitivity of permafrost microorganisms to climate change and potentially subsequent permafrost thaw.

Diversity and community structure of fungi through a permafrost core profile from the Qinghai-Tibet Plateau of China

While a vast number of studies have addressed the prokaryotic diversity in permafrost, characterized by subzero temperatures, low water activity, and extremely low rates of nutrient and metabolite transfer, fungal patterns have received surprisingly limited attention. Here, the fungal diversity and community structure were investigated by culture‐dependent technique combined with cloning‐restriction fragment length polymorphism (RFLP) analysis of sediments in a 10‐m‐long permafrost core from the Qinghai‐Tibet Plateau of China. A total of 62 fungal phylotypes related to 10 distinct classes representing three phyla were recovered from 5031 clones generated in 13 environmental gene libraries. A large proportion of the phylotypes (25/62) that were distantly related to described fungal species appeared to be novel diversity. Ascomycota was the predominant group of fungi, with respect to both clone and phylotype number. Our results suggested there was the existence of cosmopolitan psychrophilic or psychrotolerant fungi in permafrost sediments, the community composition of fungi varied with increasing depth, while these communities largely distributed according to core layers.