| Peatlands play an important role in the global carbon cycle. However, it was still no adequate information to assess the effects of human activities on the carbon flux and storage in peatland. Therefore, the Zoige Plateau peatland of Sichuan province, South-western China, as the biggest alpine wetland in the world, was selected as the study site. To study the influences of human activities on the carbon fluxes and storage in the Zoige Plateau peatland(including the natural, drained, and grazing peatland). Carbon dioxide(CO2) and methane(CH4) were measured by fast greenhouse gas analyzer(FGGA) in situ, and the air and soil temperature and water table was measured. Additionally, the plant and soil samples were collected, the carbon concentration of all samples were analyzed in laboratory, the objective of the study was to investigate the influence rules of human activities on the carbon fluxes and storage in the Zoige Plateau peatland, the work will help to accurately compile inventory of greenhouse gas from wetlands in China, and to provide basic information for the wetland protection and restoration. Results showed that:(1) Apparent seasonal variations of CH4 emission in the original peatlands were observed and CH4 emission peak occured in summer or autumn. With the increasing time of drained peatland, the seasonal variations of CH4 emission was not obvious. CH4 emision was significantly correlated with temperature, but the relationships were restricted by water table. CH4 emission was significantly(P<0.05) and positively correlated with soil temperature when water table was near or above the surface of peat, wihle CH4 emission was weak correlated with temperature when water table was below the surface of peat. Obvious annual variations of CH4 emission in peatlands were observed, this result may be attributed to the change of water table, rather than the air and soil temperature and plant biomass. Apparent spatial variations of CH4 emission from peatland in Zoige Plateau were observed. The natural peatland was a strong source of atmospheric CH4 while the drained peatland was a weak source of atmoshperic CH4, or even to a sink of atmospheric CH4(-0.01±0.01 mg/(m2·h)). Mean CH4 emission(±standard error) during the two growing seasons(in 2013 and 2014 year) from the permanently flooded microrelief hollows and permanently flooded hummocks, humid lawns, seasonally flooded microrelief hollows and dried hummocks were 45.46±6.25 mg/(m2·h), 37.48±3.96 mg/(m2·h), 3.61±0.78 mg/(m2·h), 5.94±1.58 mg/(m2·h), and 3.74±1.06 mg/(m2·h), respectively. After drainage of the peatland, CH4 emission from the drained site 1(Ds1, drained in 1970s) and the drained site 2(Ds2, drained in 1990s) during the two growing seasons(in 2013 and 2014 year) was 0.06±0.02 mg/(m2·h) and 0.84 ± 0.16 mg/(m2·h), respectively. The spatial variations of CH4 emission in the Zoige Plateau peatland were due to the change of the water table and explain 79.5% of CH4 emission variations in all sites. The mean CH4 emissions(0.45 mg/(m2·h) in the two drained peatlands were 97.3% lower than that in natural peatland.(2) Apparent seasonal variations of CO2 emission in the natural and drained peatlands were observed and CO2 emission peak occured in summer. Seasonal variations of CO2 emission in Zoige Plateau peatland were significantly and positively correlated with soil temperature(from 5 cm to 30 cm depth of soil), the seasonal variations of CO2 emission in peatland were significantly(P<0.05) correlated with the water table when the water table was greatly fluctuated, while the CO2 emission in peatland was weak(P>0.05) correlated with the water table when the water table was small fluctuated. Apparent annual variations of CO2 emission in Zoige Plateau peatland were no observed, there were no significant difference(P>0.05) in air temperature, water table and plant biomass within sites, except permanently flooded site. Apparent spatial variations of CO2 emission in Zoige Plateau peatland were ovserved, CO2 emission in the natural peatland was low generally, while the drained peatland was relatively high, the CO2 emission was slightly decreased when the ground surface is dry, which was caused by the water table drawdown. CO2 emissions(±standard error) during the two growing seasons(in 2013 and 2014 year) from the permanently flooded microrelief hollows and permanently flooded hummocks, humid lawns, seasonally flooded microrelief hollows and dried hummocks were 143.74±16.49 mg/(m2·h), 443.55±82.01 mg/(m2·h), 522.86±68.72 mg/(m2·h), 522.60±84.77 mg/(m2·h), and 946.95±136.95 mg/(m2·h), respectively; After peatland was drained, CO2 emission in the drained site Ds1 and Ds2 during the two growing seasons(in 2013 and 2014 year) was 1010.90±79.51 mg/(m2·h) and 605.56±100.84 mg/(m2·h), respectively. Apparent spatial variatons of CO2 emission among sites, which may be attrituted to the water table variations and account for explained 67.7% of CO2 emission variations among all sampling sites. CO2 emission(808.23 mg/(m2·h) in the two drained peatlands was 52.7% lower than that in natural peatland.(3) The ecosystems carbon storage in three natural peatland refered as(soil and plants) ranged from 761.56 to 1045.81 t/hm2, with a mean value of 872.37 t/hm2. The ecosystems carbon storage in the drained peatland Ds1 and Ds2 sites were 592.49 t/hm2 and 737.01 t/hm2, respectively. The ecosystems carbon storage in the two drained peatlands decreased 23.5%, which was related the decrease of soil organic carbon storage, in addition, the plant carbon storage showed no significant difference(P>0.05) between the natural peatlands and drained peatland. The soil organic carbon storage in three natural peatlands ranged from 748.12 to 1030.88 t/hm2, while the soil organic carbon storage in two drained peatlands Ds1 and Ds2 sites were 574.01 and 720.55 t/hm2, respectively. Soil organic carbon storage in two drained peatlands decreased 24.5%(or 209.99 t/hm2) compared with three natural peatlands. Water table was low after drainage, which could accelerate the decomposition of soil organic matter and then subsequently, increase CO2 emission.(4) The emission of CH4 and CO2 fluxes during the growing season showed no significant difference(P>0.05) between the grazing and fencing sites. However, during the main grazing period(from late July to September), CH4 emission in the grazing site was 54.3% higher than that in the fencing site(P<0.05). In addition, the CH4 emission of the two clipping sites was also increased by 308.0% and 335.9% compared with non-clipping site(P<0.05), which was due to shortening the transfer distance from soil to athmosphere by grazing or clipping. While CO2 emission of the two clipping sites significantly increased by 47.7% and 39.7% compared with the non-clipping site, the results were probably due to the increasing respiration of root.(5) While long-term grazing lead to the degradation in peatland, CH4 emissions during the growing season in 2014 year in the moderately degraded meadow wetland(0.27±0.27 mg(m2·h)) was 97.5% lower than that in the control site(11.31±7.51 mg(m2·h))(P<0.05), while the severe drought degradation peatland as a sink of atmospheric CH4(-0.05±0.03 mg(m2·h)). CO2 emissions during the growing season in the moderately degraded meadow wetlands(732.58±240.75 mg(m2·h)) was 86.9% higher than that in the control site(391.93±156.84 mg(m2·h))(P<0.05), and the severe drought degradation peatland(1197.52±351.99 mg(m2·h)) was obviously 205.5% higher than that in the control site(P<0.05). Therefore, the ecosystem carbon storage of the moderately degraded meadow wetlands(393.07±95.96 t/hm2) were 64.4% lower than that in the control site(P<0.05), and the ecosystem carbon storage of the severe drought degradation peatland was 52.3% lower than that in the control site(P<0.05). About 98.0% of total carbon pools was within the deep soil organic horizons, there was no significantly difference on the plant carbon storage between degraded and the cotrol peatland. After peatland degradation was caused by graziing, the soil organic carbon storage(384.73±95.57 t/hm2 for moderately degraded wetlands and 518.39±33.07 t/hm2 for severely degraded peatland) were decreased by between 64.5% and 52.4% than that the control site(P<0.05). Both the decrease of the water table and the increase of the soil temperature enhanced the CO2 emission. |
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