The Yellow River Delta Wetland is one of the youngest wetlands, and also the most complete, extensive wetlands in China. The wetland in this delta is ecologically important due to their hydrologic attributes and their roles as ecotones between terrestrial and aquatic ecosystems. In the study, the spatial and temporal variation characteristics of CH4 and CO2 emission flux under five kinds of land use types in the wetland were investigated. The results indicated that the greenhouse gas emission flux, especially the CO2 and CH4, showed distinctly spatial and temporal variation under different land use types in the wetland. In the spring, the emission flux of CO2 was higher than that of CO2 in the autumn, and appeared negative in HW3 and HW4 in the autumn. CH4 emission flux of HW4 and HW5 was negative in the spring and autumn, which indicated that the CH4 emission process was net absorption. Among the five kinds of land use types, the CO2 emission flux of HW4 discharged the largest emission flux reaching 29.3 mg.m-2.h-1, but the CH4 emission flux of HW2 discharged the largest emission flux reaching 0.15 mg.m-2.h-1. From the estuary to the inland, the emission flux of CO2 was decreased at first and then appeared increasing trend, but the emission flux of CH4 was contrary to CO2.
Global warming has attracted wide attention and advanced research hotspot of global environmental problems, which is caused by increased greenhouse gas (GHG) emissions and the change of land use. Both CO2 and CH4 are considered as the most important greenhouse gases, accounting for 70% and 23% of the contribution to the temperature rising efficiency respectively [
Wetlands account for 6% of the world’s land surface [
The Yellow River Delta, one of the largest deltas in China, is situated in the northeast of Shandong Province on the southern bank of the Bohai Sea [
In this study, the spatial and temporal variation characteristics of CH4 and CO2 emission flux under different land use types in the Yellow River Delta Wetland were investigated, including: 1) The variation characteristics of CH4 and CO2 emission flux under different seasons; 2) The variation characteristics of CH4 and CO2 emission flux under different years; 3) The variation characteristics of CH4 and CO2 emission flux under different land use types. This study may have a large contribution to the protection of new-born frangibility, typical habitat and biodiversity in the wetland ecological system. It will also be beneficial for investigating the influence of the wetland carbon storage change on the terrestrial ecosystem carbon cycle and the global climate change.
The study was conducted at the Yellow River Delta Wetland (N36˚55' - N38°16', E117˚31' - E119˚18'), which is located in the southern bank of the Bohai bay and western bank of the Bohai Sea (
The monitoring sites and Lland use characteristics of the Yellow River Delta Wetland were shown in Figure2,
The emissions concentration and fluxes of CH4 and CO2 were measured by using the static opaque chamber-GC technique, an eddy covariance technique. Five sampling sites were selected to collect 0 - 20 cm of soil samples in every typical salt marsh plant community. The samples of soil, plants and water were stored at 4˚C and analyzed in 48 h after sampling. The other parameters, such as TN, TP, pH, and OM, were measured according to the Standard Methods of APHA [
The frequency of samples was taken every quarter of one year. The method of vegetation coverage degree is quadrat sampling method. The size of quadrat is 100 cm × 100 cm. In the quadrat, every vegetation coverage degree can be obtained.
Number | Sampling site | Longitude and latitude | Description of ecosystem situation |
---|---|---|---|
C1 | Woodland | E118˚55'32" N37˚45'96" | Woodland ecosystem, the vegetation types are mainly poplars. |
C2 | Cotton field | E118˚55'39" N37˚46'11" | Farmland ecosystem, the vegetation types are mainly cotton. |
C3 | Imperata cylindrica community | E118˚58'21" N37˚46'4" | The vegetation types are mainly Imperata cylindrical and Phragmites australis, with 0.5 - 1.2 m of plant height and about 80% of cover degree. |
C4 | Tamnrix chinesi community | E118˚58'21" N37˚46'9" | The vegetation types are mainly Tamnrix chinesi, with 0.5 - 2.5 m of plant height and about 60% of cover degree. |
C5 | Tamnrix chinesi community | E119˚1'1" N37˚45'51" | The vegetation type is Phragmites australis, with 0.5 - 1.5 m of plant height and about 40% of cover degree. |
C6 | Phragmites australi community | E119˚04'07" N37˚45'90" | The vegetation type is Phragmites australis, with 0.5 - 1.8 m of plant height and about 85% of cover degree. |
C7 | Mixed community of Phragmites australi and Suaeda salsa | E119˚9'20" N37˚44'48" | The vegetation types are mainly Phragmites australis and Suaeda salsa, with 0.5 - 1.2 m of plant height and about 65% of cover degree. |
C8 | Suaeda salsa community | E119˚11'22" N37˚44'68" | The vegetation types are mainly Suaeda salsa, with 0.5 - 1.0 m of plant height and about 45% of cover degree. |
C9 | Beaches bare land | E119˚13'44" N37˚43'04" | The vegetation types are mainly Suaeda salsa, with 0.2 - 0.6 m of plant height and about 15% of cover degree. |
C10 | Suaeda salsa community | E119˚12'76" N37˚43'46" | The vegetation types are mainly Suaeda, with 0.2 - 0.5 m of plant height and about 25% of cover degree. |
Number | Community type | Longitude and latitude | Description of ecosystem |
---|---|---|---|
HW1 | Beaches bare land | N37˚43'4" E119˚13'45" | The major land use is tidal flats, and scattered vegetation such as Phragmites australi and willow, height of 0.5 - 1 m. |
HW2 | Suaeda salsa | N37˚45'55" E119˚08'50" | The vegetation types are Suaeda salsa and Phragmites australi. |
HW3 | Phragmites australis | N37˚45'2" E119˚7'43" | The vegetation type is phragmites australis community, mainly including Phragmites australis, Suaeda salsa, Tamnrix chinesi and wild chrysanthemum, with 2 cm layer of litter at the surface. |
HW4 | Tamnrix chinesi | N37˚46'04.6" E119˚09'27.1" | The vegetation type is community of Tamnrix chinesi-Phragmites australi, and 80% of cover degree. There are oilfield pipelines and vehicles and other human activities around. |
HW5 | Farmland | N37˚46'2" E118˚55'38" | The vegetation type is cotton. |
The size of the static opaque chamber is 100 cm × 100 cm × 60 cm. The static opaque chamber method was used to measure CH4 and CO2 flux. The concentrations of CH4 and CO2 were determined with infrared carbon dioxide analyzer or G-C. The sampling time was 0, 20, 40, 60, 90, 120 min in 120 min sample period. At the same time, the temperature, air pressure and the concentration of CO2 were measured in the static opaque chamber. CH4 and CO2 flux was calculated by using the following formula [
where J represents the gas flux (mg∙m−2∙h−1); dc/dt is the straightslope for the gas concentration at the time change of sampling; M is molar mass of gas to be measured; P is the pressure in sampling site; T is the absolute temperature; V0, P0, T0 are molar volume of gas, air pressure and absolute temperature under the standard state condition; H is the height of sampling box above the water surface.
The load of annual emissions was calculated by using the following estimation formulas:
where L represents the load of annual emissions (t∙a−1); J is the mean gas flux (mg∙m−2∙h−1); S is the zone area (m2).
Five different plant communities were selected to monitor the carbon emissions on-site under different seasons. The emissions flux of CH4 and CO2 in different kinds of salt marsh plant communities was calculated. The results were shown in
The results of CH4 and CO2 emission flux presented distinct season diversity in the spring and autumn. In the spring, CO2 emission flux was higher than that in the autumn, and appeared negative in HW3 and HW4 in the autumn. CH4 emission flux of HW4 and HW5 was negative in the spring and autumn, which indicated that the CH4 emission process was net absorption.
The emissions flux of CH4 and CO2 in different kinds of salt marsh plant communities was calculated under different years. The results were shown in
From the
CO2 emission flux of HW3 and HW4 was opposite in the spring and autumn (
CH4 emission flux of HW4 and HW5 was all negative in the spring and autumn. While for other land use types, emission flux of CH4 was characterized by net carbon emissions.
From the
negative in 2012, the others were all positive.
Among the 5 kinds of land use types, the HW2 discharged the largest emission flux of CH4, reaching 0.15 mg∙m−2∙h−1. From the estuary to the inland, the emission flux of CH4 was increased at first and then showed decreasing trend. The order of CH4 emission flux: HW2 > HW1 > HW3 > HW4 > HW5. CH4 emission flux of HW4 and HW5 was negative, and showed the net carbon absorption.
The greenhouse gas emission flux, especially the CO2 and CH4, showed distinctly spatial and temporal variation under different land use types in the Yellow River Delta Wetland. In the spring, the emission flux of CO2 was higher than that of CO2 in the autumn, and appeared negative in HW3 and HW4 in the autumn. CH4 emission flux of HW4 and HW5 was negative in the spring and autumn, which indicated that the CH4 emission process was net absorption.
Among the 5 kinds of land use types, the HW4 discharged the largest emission flux of CO2, reaching 29.3 mg∙m−2∙h−1, but the HW2 discharged the largest emission flux of CH4, reaching 0.15 mg∙m−2∙h−1. From the estuary to the inland, the emission flux of CO2 was decreased at first and then showed decreasing trend, but the emission flux of CH4 was contrary to CO2. Among the 5 kinds of land use types, the order of CO2 emission flux: HW4 > HW5 > HW1 > HW2 > HW3. Except for CO2 emission flux of HW1 and HW3 was negative in 2012, the others were all positive. The order of CH4 emission flux: HW2 > HW1 > HW3 > HW4 > HW5. CH4 emission flux of HW4 and HW5 was negative and showed the net carbon absorption.
This study was jointly sponsored by National Natural Science Foundation of China (No. 41003033), and Major Science and Technology Program for Water Pollution Control and Treatment (2015ZX07203-005, 2015- ZX07203-007).
Qingfeng Chen,Junjian Ma,Changsheng Zhao,Rongbin Li, (2015) The Spatial and Temporal Variation Characteristics of CH4 and CO2 Emission Flux under Different Land Use Types in the Yellow River Delta Wetland. Journal of Geoscience and Environment Protection,03,26-32. doi: 10.4236/gep.2015.36005