长江中下游滨岸带水体温室气体释放的时空分布特征

内陆河流生态系统作为大气中温室气体通量交换的热点区域,对全球的碳循环有重要影响。分别于平水期(2017年5月)和丰水期(2018年7月)对长江中下游滨岸带水体两种温室气体(CH_4和CO_2)释放通量进行了调查研究。结果表明:平水期时,CH_4和CO_2的释放通量分别为0.39～9 668.83 nmol·m~(-2)·h~(-1)和0.25～3 229.41μmol·m~(-2)·h~(-1),平均值为298.24±1 308.65 nmol·m~(-2)·h~(-1)和290.75±645.99μmol·m~(-2)·h~(-1);丰水期时,二者的释放通量为-22.80～329.76 nmol·m~(-2)·h~(-1)和-110.21～16.39μmol·m~(-2)·h~(-1),平均值为21.51±49.56 nmol·m~(-2)·h~(-1)和-3.63±13.25μmol·m~(-2)·h~(-1)。水体温度、pH、溶解性总磷浓度、溶解性有机碳和溶解性有机氮比值是影响CH_4和CO_2通量的重要因素。CH_4和CO_2释放通量还受到通江湖泊的缓冲和入江河流输入的影响,表现为河口水系高,湖口水系低的特点。由于外源污染和滨岸带土地利用的差异,城市岸带的CH_4和CO_2排放量最高,其次为自然岸带,湿地岸带和河口较低,通量最低的为化工园岸带。估算表明,长江全年碳排放以CO_2为主,年释放量约为1.93×10~7 t(C),CH_4年释放量约为2.28×10~(4 )t(C),低于世界上一些其他大型河流。

Seasonal and Spatial Variations in Greenhouse Gases(CH4 and CO2)Emission Along the Riparian Zone of Middle and Lower Reaches of Yangtze River

Inland rivers are hotpots for the exchange of greenhouse gases(GHGs) with the atmosphere and have a significant influence on global carbon cycle. GHGs(CH4 and CO2) emission from waters of the riparian zone of middle and lower reaches of Yangtze River was measured during the normal season of 2017 and flood season of 2018. Results showed that the fluxes of CH4 and CO2 across the water-air interface ranged from 0.39 to 9668.83 nmol·m-2·h-1 and 0.25 to 3 229.41 μmol·m-2·h-1 in normal season, respectively, while -22.80 to 329.76 nmol·m-2·h-1 and -110.21 to 16.39 μmol·m-2·h-1 in wet season, respectively, for CH4 and CO2. Water temperature, pH, total dissolved phosphorus, and C/N ratio were important influencing factors on CH4 and CO2 fluxes. In addition, the fluxes of CH4 and CO2 at river-connected areas were significantly higher than at lake-connected areas. Due to differences in the external pollutions and land use characteristics, urban zones showed the highest CH4 and CO2 fluxes, followed by natural, wetland and estuarine zones. Industrial areas showed the lowest CH4 and CO2 fluxes. An annual carbon emission of middle and low reaches of Yangtze River was dominated by CO2, with an estimation of 1.93×107 t(C)/a, while only 2.28×104 t(C)/a for CH4. Compared to other large rivers, the estimation value of annual carbon emission of Yangtze River was relatively lower.