Factors influencing CO2 and CH4 emissions from coastal wetlands in the Liaohe Delta, Northeast China

Other literature type, Article English OPEN
Olsson, L. ; Ye, S. ; Yu, X. ; Wei, M. ; Krauss, K. W. ; Brix, H. (2015)
  • Publisher: Copernicus Publications
  • Journal: (issn: 1726-4189, eissn: 1726-4189)
  • Related identifiers: doi: 10.5194/bg-12-4965-2015
  • Subject: Ecology | QH540-549.5 | QE1-996.5 | QH501-531 | Geology | Life

Many factors are known to influence greenhouse gas emissions from coastal wetlands, but it is still unclear which factors are most important under field conditions when they are all acting simultaneously. The objective of this study was to assess the effects of water table, salinity, soil temperature and vegetation on CH<sub>4</sub> emissions and ecosystem respiration (<i>R</i><sub>eco</sub>) from five coastal wetlands in the Liaohe Delta, Northeast China: two <i>Phragmites australis</i> (common reed) wetlands, two <i>Suaeda salsa</i> (sea blite) marshes and a rice (<i>Oryza sativa</i>) paddy. Throughout the growing season, the <i>Suaeda</i> wetlands were net CH<sub>4</sub> sinks whereas the <i>Phragmites</i> wetlands and the rice paddy were net CH<sub>4</sub> sources emitting 1.2–6.1 g CH<sub>4</sub> m<sup>−2</sup> yr<sup>−1</sup>. The <i>Phragmites</i> wetlands emitted the most CH<sub>4</sub> per unit area and the most CH<sub>4</sub> relative to CO<sub>2</sub>. The main controlling factors for the CH<sub>4</sub> emissions were water table, temperature, soil organic carbon and salinity. The CH<sub>4</sub> emission was accelerated at high and constant (or managed) water tables and decreased at water tables below the soil surface. High temperatures enhanced CH<sub>4</sub> emissions, and emission rates were consistently low (< 1 mg CH<sub>4</sub> m<sup>−2</sup> h<sup>&minus;1</sup>) at soil temperatures < 18 °C. At salinity levels > 18 ppt, the CH<sub>4</sub> emission rates were always low (< 1 mg CH<sub>4</sub> m<sup>−2</sup> h<sup>&minus;1</sup>) probably because methanogens were out-competed by sulphate-reducing bacteria. Saline <i>Phragmites</i> wetlands can, however, emit significant amounts of CH<sub>4</sub> as CH<sub>4</sub> produced in deep soil layers are transported through the air-space tissue of the plants to the atmosphere. The CH<sub>4</sub> emission from coastal wetlands can be reduced by creating fluctuating water tables, including water tables below the soil surface, as well as by occasional flooding by high-salinity water. The effects of water management schemes on the biological communities in the wetlands must, however, be carefully studied prior to the management in order to avoid undesirable effects on the wetland communities.
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