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Über dieses Buch

This book integrates the analyses of organic carbon and carbonate accumulation in soil and lake sediment in a typical arid region of China that has experienced significant climate and land-use changes.

It demonstrates that carbonate accumulation greatly exceeds organic carbon in both soil and sediment. It also shows that intensive cropping with sound land management in the arid land not only increases soil organic carbon stock, but also enhances accumulation of soil carbonate, particularly in subsoils. Carbon accumulation in the lake sediment increased between 1950 and 2000, after which it declined, and the authors explore how human activity and climate change may have caused the changes in carbon burial in the lake sediment.

This book is of interest to researchers in a number of fields such as soil science, limnology and global change, as well as to the policy-makers.



The Carbon Cycle in Yanqi Basin and Bosten Lake: Introduction

Without Abstract
Xiujun Wang, Jiaping Wang, Zhitong Yu, Juan Zhang

Introduction of the Yanqi Basin and Bosten Lake

The Yanqi Basin is formed on the basement of the Kuruktag fold belt and the southern Tianshan fold belt and located in the inland region of the Central Asia and in the transition zone between the Junggar Basin and the Tarim Basin. The Yanqi Basin is a typical arid region with extremely low precipitation (<100 mm/year) but strong evaporation (>2000 mm/year). The main soil types are brown desert soil and alluvial soil, which were developed from limestone parent materials. Land use types/coverages include cropland, shrubland, and desert land. The basin has access to water resources from the Kaidu River and underground waters, which are mainly from melting snows in the Tianshan Mountain. Bosten Lake is the largest freshwater lake in Xinjiang, which is the final converging place for the surface water and groundwater in the Yanqi Basin. Its main inflow water is from the Kaidu River on the west, and outflow is from the Kongque River on the southwest.
Changyan Tian, Lei Zhang, Shuai Zhao

Climate Change Over the Past 50 Years in the Yanqi Basin

There has been evidence of warming and significant change in precipitation in northwest China, implying climate change in the vast arid/semiarid regions. This study showed that there was an increasing trend in air temperature over the period of 1960–2014 in the Yanqi Basin, and the warming was most pronounced since the mid-1990s. The warming rate varied over space and between seasons, with a greater rate in autumn (0.30–0.40 °C/10a) and winter (0.29–0.45 °C/10a) than in spring (0.13–0.26 °C/10a) and summer (0.17–0.24 °C/10a). There was also large interannual to decadal variability in precipitation in the Yanqi Basin and runoff in the Kaidu River. Precipitation showed an overall small increasing trend over the period of 1960–2014. The lower reaches of the Kaidu River experienced a significant increase in runoff since the mid-1990s, which might be primarily a result of warming that enhanced melting of snow and glacier in the surrounding mountains.
Fengqing Jiang, Junyi Wang, Xiujun Wang

Characteristics of Soil Organic Matter and Carbon and Nitrogen Contents in Crops/Plants: Land Use Impacts

Change of land use is an important factor for the dynamics of soil organic matter and carbon and nitrogen cycles. Many parts of native land in the Yanqi Basin have been converted to cropland since 1950. To study the influence of land use change on carbon and nitrogen cycling, we collected plant and soil samples from 28 representative sites in crop and native land. Our results show a narrow range in carbon content (i.e., 44.2% in the native species and 41.7% in the crop species), but a large range in nitrogen content (0.3–3.9%). Plant C:N ratio may follow an order: native species (~31) < crops (~53), and aboveground tissues (~32) < belowground tissues (~52). Soil C:N ratio in native land (9.9) is closed to that in cropland. Both soil organic carbon and total nitrogen show a marked increase after long-term cultivation in Yanqi Basin, which may be associated with the increase of recalcitrant SOC.
Juan Zhang, Xiujun Wang, Jiaping Wang, Qingfeng Meng

Dynamics of Soil CO2 and CO2 Efflux in Arid Soil

Soil carbon dioxide (CO2) is an important component in the terrestrial ecosystem and regulates the atmosphere–land CO2 exchange. Studying the variation of CO2 in soil profile and surface CO2 efflux can improve our understanding of the carbon cycle in the terrestrial ecosystem. In this paper, we analyze the dynamics of soil CO2 and CO2 efflux in an arid region, Yanqi, northwest China. Both CO2 concentration and surface CO2 efflux showed a clear seasonal variation, with two peaks in summer and a gradual decrease in autumn. We found that surface CO2 efflux was exponentially related to soil temperature and linearly related to moisture when soil moisture was less than ~22%. We estimated surface CO2 efflux by linear regression of CO2 fluxes that were calculated by gradient method using Penman (1940), Marshall (1959), and Moldrup et al. (2013) models and found that the Marshall (1959) model did a better job than the other two models. However, there were considerable mismatches between the observation and model results. Our study indicates that the relationship is complex between the concentration of CO2 in soil profile and surface CO2 efflux in the arid region.
Junyi Wang, Xiujun Wang, Jiaping Wang, Tongping Lu

Land Use Impacts on Soil Organic and Inorganic Carbon and Their Isotopes in the Yanqi Basin

Assessments of both soil organic carbon (SOC) and inorganic carbon (SIC) under different land use types are lacking in arid regions. To advance the understanding of soil carbon dynamics and impacts of land use changes, a study was conducted in the central Xinjiang, the Yanqi Basin that had significant land use changes since the 1950s. Soil samples were collected at representative sites under various types of land use and vegetation, and SOC and SIC and their isotopes were measured over the 0–100 cm. This study revealed that both SOC and SIC stocks were the lowest in the desert land, but the highest in the agricultural land. Conversion of native land to cropland has caused a significant increase of SOC in the topsoil, and SIC in the subsoil. Total soil carbon stocks in the 0–100 cm are 11.6 ± 4.8, 44.7 ± 10.4, and 51.2 ± 5.6 kg C m−2 in the desert land, shrub land, and agricultural land, respectively. On average, soil inorganic carbon counts more than 80% of the total carbon stock in the soil profiles. δ13C of SOC shows no significant differences between land use types, but δ13C of SIC is much different among land use types, following an order: desert land (−0.6‰) > shrub land (−2.2‰) > agricultural land (−3.4‰). Our finding of SIC increase with depletion of 13C in the agricultural land indicates that there has been enhanced accumulation of pedogenic carbonate as a result of cropping.
Jiaping Wang, Xiujun Wang, Juan Zhang

Distribution of Pedogenic Carbonate and Relationship with Soil Organic Carbon in Yanqi Basin

Studying of pedogenic carbonate (PIC) has been lacking despite its importance in carbon sequestration. Using isotopic approach, vertical distribution of PIC over 0–100 cm is assessed for agricultural and native lands. In general, PIC stock is significantly higher in the agricultural land than in the native lands. There is a strong correlation (P < 0.001) between PIC stock and SOC stock, implying that an increase of 1 kg C m−2 in SOC stock may lead to an increase of 1.9 kg C m−2 in PIC formation. Conversion of native lands to agricultural land has led to an increase in both organic carbon and PIC in soil profiles of Yanqi Basin.
Xiujun Wang, Jiaping Wang, Junyi Wang

Spatial Distribution of Organic Carbon in Surface Sediment of Bosten Lake

Lake sediment is a vital carbon reservoir, which is affected by biogeochemical and hydrological processes in the watershed. To study the dynamics of organic carbon in surface sediment of the Bosten Lake, we analyzed total organic carbon (TOC) and its stable carbon isotopic composition (δ13Corg), total nitrogen (TN), and grain size in the surface (0–2 cm) sediment. Our data showed that there was a large spatial variability in both TOC (2.1–4.2%) and δ13Corg (−26.65 to −24.13‰) in surface sediment of the Bosten Lake. By using a three end member mixing model, we estimated that 54–90% of TOC was from autochthonous source. We found higher TOC concentration (>3.7%) near the mouth of the Kaidu River, in the central-north section and in the east section, which was attributable to autochthonous, autochthonous plus allochthonous, and allochthonous sources, respectively. The lowest TOC was seen in the mid-west section, which might mainly be due to the high kinetic energy levels. Our analyses suggested that the magnitude and spatial distribution of TOC in the surface sediment of Bosten Lake were influenced by complex processes and regulated by multiple factors.
Zhitong Yu, Xiujun Wang, Hang Fan

Temporal Variability of Carbon Burial and the Underlying Mechanisms in Bosten Lake Since 1950

The arid and semi-arid regions of northwest China have experienced significant climate changes and human activities since 1950, with implications for the carbon cycle. We collected two short sediment cores to investigate the anthropogenic and climate impacts on the carbon burial in Bosten Lake. Basic physical and chemical properties were measured, including total organic carbon (TOC) and total inorganic carbon (TIC), isotopic compositions of TOC (δ13Corg) and carbonate (δ13Ccarb and δ18Ocarb), grain size, and 137Cs and 210Pb. Our data showed carbon burials revealed a profound temporal variability with an overall increasing trend, and the TIC burial rate was proximately twice of the TOC since 1950. The remarked increasing trend in TOC burial rate since 1950 (TIC burial during 1950–2002) was a result of warming and/or increased human activities; the sharp decline in TIC during the recent decade (2002–2012) was associated with lower biological activity, reduced evaporation and a rapid decline in lake level. The role of carbon storage in lake sediments, especially in arid area, should deserve to be paid more attention to the terrestrial carbon cycle.
Zhitong Yu, Xiujun Wang

Carbon Sequestration in Arid Lands: A Mini Review

Without Abstract
Xiujun Wang, Jiaping Wang, Huijin Shi, Yang Guo
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