Yongheng Gao

Methane emissions from newly created marshes in the drawdown area of the Three Gorges Reservoir

The study aimed to understand the methane (CH4) emission and its controlling factors in the Three Gorges Reservoir Region and to explore its implication for large dams. We measured CH4 emissions from four vegetation stands in newly created marshes in the drawdown area of the Three Gorges Reservoir, China, in the summer of 2008. The results showed highly spatial variations of methane emissions among the four stands, with the smallest emission (0.25 +/- 0.65 mg CH4 m(-2) h(-1)) in the Juncus amuricus stand, and the greatest (14.9 +/- 10.9 mg CH4 m(-2) h(-1)) in the Scirpus triqueter stand. We found that the spatial variations of CH4 emissions are caused by difference in standing water depth and dissolved organic carbon (DOC). Results also showed a special seasonal variation of CH4 emissions in this area, i.e., maximal emissions in early July followed by a low and steady value before the winter flooding. The seasonality of CH4 emissions was found closely related to temperature and standing water depth. Because of the large area of the drawdown zones for global dam reservoirs and a large CH4 emission rate, such newly created marshes should not be neglected when estimating CH4 emissions from reservoirs.

Determinants influencing seasonal variations of methane emissions from alpine wetlands in Zoige Plateau and their implications

To understand the seasonality of methane flux from alpine wetlands in Zoige Plateau, 30 plots were set to measure the methane emissions in the growing and nongrowing seasons in three environmental types: dry hummock (DH), Carex muliensis (CM), and Eleocharis valleculosa (EV) sites. There were clearly seasonal patterns of methane flux in different environmental types in the growing and nongrowing seasons. Mean methane emission rate was 14.45 mg CH4 m(-2) h(-1) (0.17 to 86.78 mg CH4 m(-2) h(-1)) in the growing season, and 0.556 mg CH4 m(-2) h(-1) (0.002 to 6.722 mg CH4 m(-2) h(-1)) in the nongrowing season. In the growing season, the main maximum values of methane flux were found in July and August, except for a peak value in September in CM sites. In the nongrowing season, the similar seasonal variation pattern was shared among all the three sites, in which the methane emissions increased from February to April. In the growing season, the determining factors were surface temperatures (r(2) = 0.55, P < 0.05), standing water depths (r(2) = 0.32, P < 0.01) and plant community heights (r(2) = 0.61, P < 0.01), while in the nongrowing season, ice thickness (r(2) = 0.27, P < 0.05; in CM and EV sites) was found most related to flux. In our understanding, the seasonality of methane emissions in our study areas was temperature- and-plant-growth-dependent, and the water table position was also very important to shape the temperature- and-plant-growth-dependent seasonal variation of flux with its vigorous variations in alpine wetland ecosystems. Different environmental types within the wetland also influenced the seasonal pattern of methane flux. For an accurate estimate of the global methane source strength of alpine wetlands, the pronounced seasonal or even temporal variability in methane emission from alpine wetlands should be taken into consideration.

Spatial variations on methane emissions from Zoige alpine wetlands of Southwest China.

This study was aimed to understand the spatial variation of CH(4) emissions from alpine wetlands in Southwest China on a field-scale in two phenological seasons, namely the peak growing season and the spring thaw. Methane emission rates were measured at 30 plots, which included three kinds of environmental types: dry hummock, Carex muliensis and Eleocharis valleculosa sites. There were highly spatial variations of methane emissions among and within different environmental types in both phenological seasons. Mean methane emission rates ranged from 1.1 to 37.0 mg CH(4) m(-2) h(-1) in the peak growing season and from 0.004 to 0.691 mg CH(4) m(-)(2) h(-1) in the spring thaw. In the peak growing season, coefficients of variation (CV) averaged 38% among environmental types and 64% within environmental types; while in the spring thaw, CV were on the average 61% among environmental types and 96% within environmental types. The key influencing factors were the standing water table and the plant community height in the peak growing season, while in the spring thaw, no significant correlations between factors and methane emissions were found.

Inter-Annual Variations of Methane Emission from an Open Fen on the Qinghai-Tibetan Plateau: A Three-Year Study

The study aimed to understand the inter-annual variations of methane (CH4) emissions from an open fen on the Qinghai-Tibetan Plateau (QTP) from 2005 to 2007. The weighted mean CH4 emission rate was 8.37±11.32 mg CH4 m−2 h−1 during the summers from 2005 to 2007, falling in the range of CH4 fluxes reported by other studies, with significant inter-annual and spatial variations. The CH4 emissions of the year of 2006 (2.11±3.48 mg CH4 m−2 h−1) were 82% lower than the mean value of the years 2005 and 2007 (13.91±17.80 mg CH4 m−2 h−1 and 9.44±14.32 mg CH4 m−2 h−1, respectively), responding to the inter-annual changes of standing water depths during the growing season of the three years. Significant drawdown of standing water depth is believed to cause such significant reduction in CH4 emissions from wetlands in the year 2006, probably through changing the methanogen composition and decreasing its community size as well as activating methanotrophs to enhance CH4 oxidation. Our results are helpful to understand the inter-annual variations of CH4 emission and provide a more reasonable regional budget of CH4 emission from wetlands on the QTP and even for world-wide natural wetlands under climate change.

Differences in pedotransfer functions of bulk density lead to high uncertainty in soil organic carbon estimation at regional scales: Evidence from Chinese terrestrial ecosystems

Accurate estimation of soil organic carbon (SOC) storage is important for evaluating carbon sequestration of terrestrial ecosystems at regional scale. How the selected pedotransfer functions (PTFs) of bulk density (BD) influence the estimates of SOC storage is still unclear at large scales, although BD is an important parameter in all equations. Here we used data from the second national soil survey in China (8210 soil profiles) to evaluate the influence of eight selected PTFs on the estimation of SOC storage. The results showed that different PTFs may result in a higher uncertainty of SOC storage estimation and the coefficient of variation (CV, %) for the eight PTFs varied from 10.61% to 70.46% (mean = 12.75%). The observed CV values were higher in the 0-20 cm layer (12.48%) than in the 20-100 cm layer (10.05%). CV values were relatively stable (10-15%) when SOC content ranged from 0.13% to 3.45%. The findings indicate that PTFs may be used cautiously in soils with higher or lower SOC content. Estimates of SOC storage in the 0-100 cm soil layer varied from 67.19 to 95.97 Pg C in the eight PTFs in China, with an average of 87.36 +/- 8.93 Pg C (CV = 10.23%). Our findings provide the insight that differences in PTFs are important sources of uncertainty in SOC estimates. The development of better PFTs, or the integration of various PFTs, is essential to accurately estimate SOC storage at regional scales.

Effects of nitrogen and sulfur deposition on CH4 and N2O fluxes in high-altitude peatland soil under different water tables in the Tibetan Plateau

Abstract The effects of nitrogen (N) and sulfur (S) deposition on methane (CH4) and nitrous oxide (N2O) emissions under low (10 cm below soil surface) and high (at soil surface) water tables were investigated in the laboratory. Undisturbed soil columns from the alpine peatland of the Tibetan Plateau were analyzed. CH4 emission was higher and N2O emission was lower at the high water table than those at the low water table regardless of nutrient application. Addition of N (NH4NO3 (ammonium nitrate), 5 g N m−2) decreased CH4 emission up to 57% and 50% at low and high water tables, respectively, but correspondingly increased N2O emission by 2.5 and 10.4 times. Addition of S (Na2SO4 (sodium sulfate), 2.5 g S m−2) decreased CH4 and N2O emission by 64% and 79% at the low water table, respectively, but had a slightly positive effect at the high water table. These results indicated that the responses of CH4 and N2O emissions to the S deposition depend on the water table condition in the high-altitude peatland.

Effectiveness of Exclosures on Restoration of Degraded Alpine Meadow in the Eastern Tibetan Plateau

Restoration of degraded alpine meadow caused by overgrazing is directly related to land sustainable and economical development in the Tibetan Plateau. The objective of this study was to evaluate changes in vegetation and soil characteristics in areas under overgrazing and exclosed for 5 to 10 years for grazing in a degraded alpine meadow on the eastern Tibetan Plateau. Results showed that excluding livestock grazing resulted in significant increases in vegetation coverage and plant biomass by enhancing development of perennial grasses and sedges. Soil organic carbon and total nitrogen in the 0–10 cm soil layer increased significantly with increasing exclosure time. Soil clay and water contents were higher in the exclosed sites than in the grazed site. The results suggested that the degraded alpine meadow due to overgrazing in this region can be reversed and significant increases in soil fertility, vegetation diversity, cover, and biomass can be achieved by implementing adequate protecting practices.

Nitrification and denitrification in an alpine meadow soil of the eastern Tibetan Plateau

Nitrification and denitrification represent two of the main biological processes involved in the N cycle, which contribute to the regulation of NO3 availability to plants reduction to N2 (Vitousek et al., 1982; Conen et al., 2000). Moreover, they represent the main source of the greenhouse gas N2O in terrestrial ecosystems (Williams et al., 1992). Both processes are directly limited by substrate availability (NH4 , NO3 , organic C) and low temperatures, and indirectly by water content and soil capacity to retain water (Granli & Bøkman, 1994). In an alpine meadow ecosystem on the Tibetan Plateau, being characterized by an extreme climate with low temperatures and a short vegetation season, inorganic (available) N is usually present in low concentrations, although alpine meadow soils are noted for their large quantities of total N; most of this resides in organic (unavailable) form (Cao & Zhang, 2001). Therefore, knowledge of N transformation in highly N limited and fragile alpine ecosystems is necessary for managing both the N supply to the pasture grass crop and the potential N losses to the environment. However, there are no available data on soil nitrification and denitrification activities in the region. In this study we measured the seasonal dynamics of nitrification and denitrification in an alpine meadow soil on the eastern Tibetan Plateau.

Restoration of high-altitude peatlands on the Ruoergai Plateau (Northeastern Tibetan Plateau, China)

Introduction All over the world, high-altitude peatlands are the product of co-evolution between nature and pastoral communities. Over thousands of years, people, looking for subsistence and resources, have changed the character of fragile mountain landscapes and their peatlands through deforestation and livestock grazing (Trimble and Mendel 1995). Increasing population pressure, the quest for mineral resources and perverse policies have in recent times intensified these changes. The character of high-altitude peatlands can be paraphrased as ‘cold and steep and wet and sheep’. The high altitude induces colder and more humid conditions and – upwind of the mountain – more precipitation. Excessive exposure to ultraviolet radiation at high altitudes requires special adaptation of the biota, whereas the climatic island character explains the disjunct distribution of species and the high degree of endemism (Korner 2003, 2008; Spehn et al. 2010). The colder climate also discourages arable agriculture so that pastoralism – with a wide variety of livestock – is the principal form of subsistence. High rainfall and relatively steep slopes generate surface runoff, exposing the landscape and the sensitive peatlands to strong erosive forces (Evans and Warburton 2007). The worlds largest concentration of high-altitude peatlands is found in the northeastern part of the Qinghai–Tibetan Plateau (China). There, in the provinces of Sichuan and Gansu right in the heart of China (Figure 13.1), the Ruoergai (or Zoige) Plateau is located at an altitude of about 3500 m a.s.l. In contrast to the drier western and central parts of Tibet, the Ruoergai Plateau, a plain glacial landscape with low mountain ranges of some hundred metres in height, has a humid climate with long winters and short summers (Lehmkuhl and Liu 1994) which have facilitated the development of 474 000 ha of peatlands (Schumann, Thevs and Joosten 2008). In this chapter, we explore the history and drivers of peatland degradation on the Ruoergai Plateau, the loss of important ecosystem services and the impact of such loss on livelihoods. We discuss how integrated projects may facilitate the restoration of ecosystem services and biodiversity while contributing to poverty alleviation. Case studies present the various approaches and illustrate how participatory community involvement is integral to the successful implementation of peatland conservation and restoration programmes.