闽江河口潮汐湿地二氧化碳和甲烷排放化学计量比

为了阐明河口潮汐湿地碳源温室气体排放的化学计量比特征,对闽江河口潮汐湿地二氧化碳和甲烷排放进行了测定与分析。结果表明:芦苇湿地和短叶茳芏湿地二氧化碳与甲烷排放均呈现正相关;涨潮前、涨落潮过程和落潮后芦苇湿地和短叶茳芏湿地CO2∶CH4月平均值分别为55.4和185.0,96.3和305.5,68.7和648.6,3个过程芦苇湿地和短叶茳芏湿地CO2∶CH4差异均不显著(P>0.05),2种植物湿地CO2∶CH4对潮汐的响应并不一致,但均在涨潮前表现为最低;涨潮前、涨落潮过程和落潮后均表现为芦苇湿地CO2∶CH4低于短叶茳芏湿地(P<0.05);河口潮汐湿地CO2∶CH4为空间变异性>时间变异性,潮汐、植物和温度均对CO2∶CH4的变化具有一定的调节作用。

Stoichiometry of carbon dioxide and methane emissions in Minjiang River estuarine tidal wetland

Gas exchange between soils and the atmosphere is an important contributory factor to global climate change due to increasing release of greenhouse gases(N2O,CO2,CH4,etc.).CO2 and CH4 are the principal gases.Wetland is one of the important ecosystems for carbon cycle,especially for the CO2 and CH4 exchange.Wetland ecosystem emits CO2 and CH4 through aerobic and anaerobic respiration and fixes carbon(CO2) through photosynthesis.So the ratio of CO2 to CH4 is important to reveal the greenhouse gas emissions of carbon sources and to mediate their emissions. An amount of approximately 18,000 km of coastline in China is covered by an estimated 12,000 km2 of tidal estuary wetlands.These tidal wetlands are generally rich in animal and plant diversity and appear to have important biogeochemical roles within the entire estuary ecosystem.One of these important tidal wetland ecosystems is found within the Minjiang River estuary in southeast China,which is located at the transition of mid-and southern subtropical climate zones in China. Vegetation and tide are two important factors influencing the biochemistry process of estuarine wetland and thereby controlling CO2 and CH4 emissions.Most of the previous studies have been showed that plants act as a key control on the spatial variability of CO2 and CH4 emissions due to their influence on the formation and transportation.Tidal systems are likely to be affected by tidal processes including time of inundation and salinity.Flooding is known to reduce CO2 and CH4 emissions,probably by blocking the pathway of CO2 and CH4 release.However,the effects of vegetation and tide on CO2 ∶ CH4 values are not clear. This study was conducted in the Shanyutan wetland(119°34′12″—119°40′40″E,26°00′36″ —26°03′426″N),which is the largest tidal wetland(nearly 3120 hm2) in the Minjiang River estuary.The climate is warm and wet,with a mean annual temperature of 19.6℃ and a mean annual precipitation of 1346 mm.The Shanyutan wetland is belt-shaped.The sediment surface at the study site is submerged for 3—3.5 hours during each tidal inundation.The vegetation mainly occupies two zones: a 150—200 m wide Scirpus lacustris zone close to the sea,and a 150 m wide Phragmites australis and Cyperus malaccensis var.brevifolius zone which extends from the intertidal zone to near the bank. Here we examined the stoichiometry characteristics of carbon-source greenhouse gas emissions in Minjiang River estuarine tidal wetland.The results showed that the emission fluxes of CO2 in both Phragmites australis wetland and Cyperus malaccensis var.brevifolius wetland were positively correlated with the emission fluxes of CH4.The monthly average CO2 ∶ CH4 values in P.australis wetland and C.malaccensis wetland were 55.4 and 185.0,96.3 and 305.5,and 68.7 and 648.6 in the stages of before high tide,during tidal fluctuation,and after ebb,respectively.But the monthly average CO2 ∶ CH4 values were not significantly different in the three different stages for both P.australis wetland and C.malaccensis wetland(P>0.05).The lowest CO2 ∶ CH4 values were found before high tide in both wetlands but with different responses to tide.The monthly average CO2 ∶ CH4 values in the three stages for P.australis wetland were lower than those for C.malaccensis wetland(P<0.05).Our results indicated that the spatial variation of CO2 ∶ CH4 values was greater than the temporal one in estuarine tidal wetland,and tide,vegetation type and temperature were the key factors controlling the variation of CO2 ∶ CH4.