闽江口半咸水芦苇潮汐沼泽湿地甲烷动态

利用2008-2010年3年的测定数据研究了闽江口半咸水芦苇潮汐沼泽湿地的甲烷动态特征,其中2008-2009年连续2年采用静态箱—气相色谱法测定了芦苇潮汐沼泽湿地在涨潮前、涨落潮过程和落潮后3个阶段排向大气的甲烷通量;此外,还添加甲烷氧化抑制剂原位测定了芦苇沼泽湿地的甲烷产生与氧化,采用自行设计的悬管装置原位测定了芦苇植株介导的甲烷传输排放速率.芦苇沼泽湿地甲烷排放通量具有明显的季节变化,高温季节同时也是甲烷排放的高峰期;涨潮前、涨落潮过程和落潮后3个阶段甲烷排放通量分别是0.69～40.95、0.26～9.57和0.74～22.10 mg m-2 h-1,平均值分别为7.53,2.19和4.93 mg m-2 h-1;涨落潮过程排向大气的甲烷通量明显低于涨潮前和落潮后;夏季测定日甲烷产生和氧化均高于冬季测定日;冬夏两个测定日芦苇植株髓腔内甲烷浓度均表现出明显的夜高昼低及由底部向顶部迅速降低的特点;不同生长阶段的芦苇植株甲烷传输排放速率明显不同,快速生长阶段的芦苇植株甲烷传输排放速率最高,年尺度上单株芦苇植株介导的甲烷传输排放速率平均值为33.67 μg culm-1h-1,芦苇植株介导的甲烷传输排放量占芦苇沼泽湿地甲烷排放通量的2.3％～28.5％,植株距地面0～20 cm部位对整株传输排放甲烷的贡献率在不同季节均维持在较高水平,均值为43.4％.

Methane Dynamics of a Brackish-water Tidal Phragmites australis Marsh in the Minjiang River Estuary

In 2008 and 2009,methane emission to the atmosphere was measured seasonally using an enclosed static chamber technique in the Minjiang River estuary,southeast China,a brackish-water tidal marsh dominated by P.australis.Measurements were taken at three tidal stages.Potential rates of methane production and oxidation from the marsh sediments were also estimated in situ in summer and winter using acetylene as a methane oxidation inhibitor.We devised a ’hanging’ enclosed static chamber to measure methane transport and emission directly from single stems of P.australis on days of neap tide.Methane emission from the P.australis tidal marsh showed a seasonal variation in all the three tidal stages,and reached a maximum during the summer when soil temperature was relatively high.The ranges of methane flux were 0.69-40.95,0.26-9.57 and 0.74-22.10 mg m-2 h-1 before the flood,during the flood/ebb and after the ebb respectively and the average methane fluxes were 7.53,2.19 and 4.93 mg m-2 h-1,respectively.Methane production and oxidation potentials in summer were all higher than those in winter.Methane concentrations within the lacunal of the P.australis stems were the greatest at the base and decreased faster compared with stem height,which start at the stem base,and showed lower lacunal methane concentrations at daytime and higher lacunal methane concentrations at night-time.On an annual basis,the average methane transport and emission of a single P.australis culm was 33.67 μg.culm-1.h-1.These methane transport rates differed between growth stages,with the highest transport and emission detected within the stage of fastest plant growth.Nearly half(43.4%) of the whole plant transport and emission occurred from P.australis culms nearest the ground(0-20 cm above the ground).We estimated that plant-mediated methane transport contributed 2.3%-28.5% of the total methane emission within this P.australis-dominated marsh.