Studies On Emission Of CO₂ And CH₄ From Mangrove Wetlands In Southeastern China And Their Controlling Factors

Mangrove wetlands are important sources for atmosphericandbecause of their anaerobic environment which is under the influence of periodic tidal flooding.However,the magnitude ofefflux from mangrove wetlands and the relative contribution to climate warming remain controversial.Moreover,the mechanisms and controlling factors ofandproduction in mangrove wetland soils are poorly understood under various scenarios of climate warming and land use change.In this study,bothandeffluxes from mangrove wetlands were measured during low or no tide periods at three tidal zones of two mangrove ecosystems in southeastern China using a static chamber technique.Combining both in-situ measurements and existing literature data for mangrove wetlands worldwide,this study aimed to evaluate the magnitude and relative contribution ofefflux from mangrove wetlands to climate warming in comparison withefflux.In addition,the effect of temperature change onandproduction rates was investigated experimentally for different types of wetlands,including mangrove wetlands,constructed wetlands,and freshwater wetlands.The main results and conclusions are listed as follows:?1?The magnitude and relative contribution ofefflux from undisturbed mangrove soils to climate warming were often very low and marginal in comparison withefflux,butefflux could be increased by nutrient input and freshwater discharge.In southeastern China,efflux was small and almost negligible in most sampling sites,ranging from 1.52 to 4.91?mol m^-2 h^-1 in the Zhangjiang Estuary Mangrove Wetlands and 0.65 to 14.18?mol m^-2 h^-1 in the Qinglan Harbour Mangrove Wetlands.The highestefflux(123.59?mol m^-2 h^-1)was observed at the landward zone in the Zhangjiang Estuary Mangrove Wetlands during the wet season,which received nutrient input and freshwater discharge from nearby aquacultural activities.In addition,theefflux data from literature for the mangrove wetlands worldwide also showed that theefflux from undisturbed mangrove wetlands was quite low,but could be stimulated by the input of aquacultural wastewater and excessive freshwater.?2?All types of wetlands showed higher soilproduction rates in aerobic or anaerobic environments at elevated temperature,but the level of response varied with vegetation types in the order of mangrove wetlands?Avicennia marina,Kandelia obovata?>constructed wetlands?shrimp ponds,fish ponds?>freshwater wetlands?Nymphaea lotus,Phragmites australis?,which could be explained by the differences in carbon substrate distribution and nutrient concentrations among different vegetation types.Elevated temperature could enhance theproduction rates in an anaerobic environment,especially in the soils from the A.marina forest.The higher response to elevated temperature in A.marina forest is mainly due to higher ammonium and phosphorus availability in the soils,enhancing higher mineralization of soil organic matter.It can be concluded from the above results thatefflux from mangrove wetlands is strongly influenced by anthropogenic activities.Future inventories and evaluation ofefflux from mangrove wetlands at regional or global scales should consider the impact of anthropogenic activities.It was also demonstrated that temperature exerts significant effects onproduction rates in both aerobic and anaerobic soils as well asproduction rates in anaerobic soils of mangrove wetlands.More research work is needed to concentrate on the response and adaptation of soil carbon pools to climate warming.The findings from this study enhance our basic understanding of carbon cycles in mangrove wetlands and controlling mechanisms,which can provide scientific guidance for mangrove wetland management and ecological engineering projects.