Zoige Peatland Research Articles

Effects of soil warming, rainfall reduction and water table level on CH4 emissions from the Zoige peatland in China

The Zoige Plateau features approximately 4605 km2 of peatlands, making it the largest peatland area in China. This area stored 2.9 Pg peat during the Holocene, yet little is known about methane (CH4) emissions from this region. In this study, we designed a mesocosm experiment to measure CH4 emissions during the growing seasons of 2009–2010 under different scenarios involving soil warming, 20% reduction in rainfall and changes in the water table level. Our results showed that CH4 emissions were higher in 2009 than in 2010 under all experimental conditions. Average soil temperature was approximately 11.4 °C under control conditions, 13.3 °C under soil warming conditions, 12.7 °C with 20% rainfall reduction, and 13.4 °C under combined conditions of soil warming and 20% reduced rainfall. For the single factor effect, soil warming treatment increased average CH4 emissions by 28%, while rainfall reduction increased it by 30%; however, neither increase was statistically significant. In contrast, the combined effect of soil warming and rainfall reduction significantly decreased CH4 emissions by an average of 58%. Extending this result across the entire peatland area in the Zoige Plateau translates into approximately 5.3 Gg of CH4 uptake per year. These results suggest that a drier and warmer Zoige Plateau will become a CH4 sink. Our study also found a positive relationship between water table level and CH4 emissions. Average CH4 emissions decreased by approximately 82% as water drawdown varied from 0 (0.94 mg CH4 m−2 h−1) to −50 cm (0.17 mg CH4 m−2 h−1). When we simultaneously examined the effect of all three factors of water table level, soil warming and rainfall reduction on CH4 emissions, we found soil warming and rainfall effect on CH4 emissions varied with water table levels. However, none of the three factors significantly affected CH4 emissions at a water table depth of 30 cm below peat depth.

Remotely sensing the ecological influences of ditches in Zoige Peatland, eastern Tibetan Plateau

Zoige Peatland in the eastern Tibetan Plateau, the largest alpine peatland in China, was widely ditched in 1970s for pasture expansion. The ditching is believed to have caused peatland degradation, but there is still no widespread agreement on this due to the absence of essential regional and temporal information about ditch drainage. Therefore, this study used both remote-sensing observations and field surveys to examine the ecological influences of ditching for this alpine peatland. In the study, ditch distribution was interpreted with remote-sensing imagery and the ecological responses were investigated with temporal observation by Moderate Resolution Imaging Spectroradiometer (MODIS) and field surveys. The results showed that there were ~1200 km ditches interpreted, mainly in three spatial patterns depending on hydro-geomorphologies. The MODIS enhanced vegetation index (EVI) was more sensitive to peatland surface water depth (R2 = 0.678, P < 0.001) than the normalized difference water index (NDWI) (R2 = 0.583, P < 0.001), because the latter would become saturated at a certain surface water depth (~50 cm in Zoige). The temporal MODIS imagery reflected the ecological responses of ditched peatland to drainage in terms of vegetation density and water conditions. This study indicated that ditching depressed the surface water depth of the Zoige Peatland in summer, but not to the extent of completely transforming peatland into steppe due to the recharging of local beneficial hydro-geomorphologies. The MODIS indices investigated in the study could be used to monitor the annual regional status of vegetation cover and surface water for Zoige peatland.

The carbon stock of alpine peatlands on the Qinghai–Tibetan Plateau during the Holocene and their future fate

Most studies about carbon dynamics of peatlands have been focused on boreal, subarctic and tropical peatlands. However, there is limited data about carbon dynamics of alpine peatlands, like Zoige peatlands on the Qinghai–Tibetan Plateau (QTP), which are sensitive to climate change and human disturbance. We studied the role of these peat deposits on the Zoige as a C reserve and sink by measuring peat depth, radiocarbon age and peat and C accumulation rates at 7 sites. The peat depths of the sample sites ranged from 0.20 to 6.0 m; the basal age on the plateau varied from 1635 to 14095 cal yr BP; the peat accumulation rates ranged from 0.12 to 0.85 mm yr−1, and the C accumulation rates from 5 to 48 g m−2 yr−1. Based on data of field studies and remote sensing, we regarded that with 3179 km2 of intact peatlands, about 1426 km2 of degraded peatlands, and the total area of Zoige peatlands was 4605 km2. The current peat C stock of Zoige peatlands was0.477 Pg (ranging from 0.206 to 0.672 Pg). We also estimated that peatlands covered an area of about 5091 km2on the QTP and sequestered 0.543 Pg C, 88% in Zoige and the rest in other parts of the plateau. Human activities, together with the ubiquitous warming on the plateau (temperature increased by 0.2 °C per decade over the past 50 years) not only shrank the area of intact peatlands, but also caused substantial carbon releasing from peatlands.

Degradation and structure change of humic acids corresponding to water decline in Zoige peatland, Qinghai-Tibet Plateau

As the largest plateau-type wetland in the world and the largest peat storage in China, Zoige wetland faces severe water decline, and consequently accelerated peat degradation and carbon emission. Here, a variety of characterization approaches, including elemental analysis, UV–vis spectra, FT-IR spectra, and solid state 13C NMR spectra were used to investigate the degradation and the structural shift of humic acids (HAs) in correspondence with serious water loss in Zoige peatland. Water loss derived from both natural slope and artificial drainage caused a substantial degradation of organic matter and HAs. Compared with the blocks immersed by free surface water, HAs extracted from the drier blocks had more pronounced signals of carboxyl and carbonyl groups, but carried lower content of methoxyl, carbohydrate, alcohol and ether groups. The total aliphatic carbon in HAs from natural-slope drier site decreased almost one half, but in the artificial-drained site, only slightly decreased. Correspondingly, the HA aromaticity substantially increased in the site undergoing the longer time of aerobic oxidation, whereas varied little in the site impacted by extensive water leaching.

Relationship between archaeal community structure and vegetation type in a fen on the Qinghai–Tibetan Plateau

The contribution of different methanogenic precursors probably depends on vegetation in the cold Zoige peatlands. This study was carried out to elucidate the relationship between archaeal community dynamics and vegetation type over growing season. Soil samples were collected monthly during the growing season from two vegetation types (communities dominated by Carex muliensis vs. Eleocharis valleculosa) on an open fen at the Wetland National Nature Reserve of the Zoige peatlands on the Qinghai–Tibetan Plateau. Archaeal community structure was determined with terminal restriction fragment length polymorphism analysis of the 16S rRNA gene fragment. Methanosarcinales, Methanosaeta, Methanomicrobiales, Methanobacteriales, uncultured RC-II, and uncultured Crenarchaeota were detected in both vegetation types. The results suggested that seasonal change affects the activity rather than the structure of the archaeal community over the growing season. Ordination analyses indicated that archaeal community composition was related to vegetation type and plant height.

Recent Peat Accumulation Rates in Zoige Peatlands, Eastern Tibet, Inferred by 210Pb and 137Cs Radiometric Techniques

210Pb and 137Cs dating techniques are used to characterize recent peat accumulation rates of alpine peatlands located in Zoige, Tibetan plateau. Several cores were collected in different parts of the peatlands. Cores were 210Pb- and 137Cs-dated, and these data were used to calculate sediment accumulation rates. Ranges of dry mass accumulation rates were 0.021∼0.048g cm-2 yr−1 (the mean value is 0.033g cm-2 yr−1). The mean sediment fluxes of SOC, LC and TN in the marsh soil were 113g m-2 yr−1, 12g m-2 yr−1 and 5g m-2 yr−1 seperatly during 1952∼2004 using 137Cs and 210Pb techenique. The changes of SOC, TN and LC accumulation flux were similar with that of the temperature of May.

Methane emissions from wetlands on the Qinghai-Tibet Plateau

The areal extent of cold freshwater wetlands on the Qinghai-Tibet Plateau (QTP) is estimated at 0.133 × 106 km2, suggesting a significant methane potential. Methane fluxes from wet alpine meadows, peatlands,Hippuris vulgaris mires and secondary marshes were 43.18, 12.96, −0.28 and 45.90 mg · m−2 · d−1, respectively based on the transect flux studies at the Huashixia Permafrost Station (HPS) from July to August 1996. Average CH4 fluxes in the thaw season were extrapolated at 5.68 g · m−2 according to the areal percentage of wetland areas in the Huashixia region. The CH4 fluxes at four fixed sites, representative of similar ecosystems, ranged from −19.384–347.15 mg · m−2 · d−1, and the average CH4 fluxes varied from 6.54 to 71.97 mg · m−2 · d−1 at each site during the observation period from April to September 1997. The CH4 emissions at each site during the entire thaw season was estimated from 1.21 to 10.65 g · m−2, displaying strong spatial variations. Seasonal variations of CH4 fluxes also were observed at four sites: CH4 outbursts occurred upon the spring thaw in May and June, CH4 fluxes increased afterwards with rising soil temperatures. Episodic fluxes were observed in summer, which influenced the average CH4 fluxes considerably. Annual CH4 emissions from cold wetlands on the QTP were estimated at about 0.7–0.9 Tg based on the distribution of wetlands, representative CH4 fluxes, and number of thaw days. The centers of CH4 releasing were located in the sources of the Yangtze and Yellow rivers, and Zoige Peatlands.