Research about Liaohe Delta

USGS2016

Inter-annual variability of area-scaled gaseous carbon emissions from wetland soils in the Liaohe Delta, China

Global management of wetlands to suppress greenhouse gas (GHG) emissions, facilitate carbon (C) sequestration, and reduce atmospheric CO 2 concentrations while simultaneously promoting agricultural gains is paramount. However, studies that relate variability in CO 2 and CH 4 emissions at large spatial scales are limited. We investigated three-year emissions of soil CO 2 and CH 4 from the primary wetland types of the Liaohe Delta, China, by focusing on a total wetland area of 3287 km 2 . One percent is Suaeda salsa , 24% is Phragmites australis , and 75% is rice. While S . salsa wetlands are under somewhat natural tidal influence, P . australis and rice are managed hydrologically for paper and food, respectively. Total C emissions from CO 2 and CH 4 from these wetland soils were 2.9 Tg C/year, ranging from 2.5 to 3.3 Tg C/year depending on the year assessed. Primary emissions were from CO 2 (~98%). Photosynthetic uptake of CO 2 would mitigate most of the soil CO 2 emissions, but CH 4 emissions would persist. Overall, CH 4 fluxes were high when soil temperatures were >18°C and pore water salinity <18 PSU. CH 4 emissions from rice habitat alone in the Liaohe Delta represent 0.2% of CH 4 carbon emissions globally from rice. With such a large area and interannual sensitivity in soil GHG fluxes, management practices in the Delta and similar wetlands around the world have the potential not only to influence local C budgeting, but also to influence global biogeochemical cycling.

Liaohe Delta↗

USGS2015

Factors influencing CO 2 and CH 4 emissions from coastal wetlands in the Liaohe Delta, northeast China

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 4 emissions and ecosystem respiration ( R eco ) from five coastal wetlands in the Liaohe Delta, northeast China: two Phragmites australis (common reed) wetlands, two Suaeda salsa (sea blite) marshes and a rice ( Oryza sativa ) paddy. Throughout the growing season, the Suaeda wetlands were net CH 4 sinks whereas the Phragmites wetlands and the rice paddy were net CH 4 sources emitting 1.2–6.1 g CH 4 m −2 y −1 . The Phragmites wetlands emitted the most CH 4 per unit area and the most CH 4 relative to CO 2 . The main controlling factors for the CH 4 emissions were water table, temperature and salinity. The CH 4 emission was accelerated at high and constant (or managed) water tables and decreased at water tables below the soil surface. High temperatures enhanced CH 4 emissions, and emission rates were consistently low (< 1 mg CH 4 m −2 h) at soil temperatures <18 °C. At salinity levels > 18 ppt, the CH 4 emission rates were always low (< 1 mg CH 4 m −2 h −1 ) probably because methanogens were outcompeted by sulphate reducing bacteria. Saline Phragmites wetlands can, however, emit significant amounts of CH 4 as CH 4 produced in deep soil layers are transported through the air-space tissue of the plants to the atmosphere. The CH 4 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.

Liaoning Province↗