干旱叠加海平面上升、氮负荷增加对河口潮汐沼泽生态系统净CO2交换的影响

河口潮汐沼泽湿地是全球重要的蓝碳生态系统之一。海平面上升和氮负荷增加是入海河流河口湿地面临的两个主要环境问题。近年来，干旱事件频发，干旱及其与海平面上升、氮负荷增加的叠加将如何影响河口潮汐沼泽湿地生态系统净CO₂交换，目前还未见报道。2020年夏秋，福建沿海经历了数月严重的气象干旱，这为揭示干旱对河口潮汐沼泽湿地生态系统净CO₂交换量(NEE)和生态系统呼吸(ER)的影响提供了一个契机。分别于2019年8—10月(正常天气)和2020年8—10月(干旱天气),在闽江河口微咸水短叶茳芏沼泽湿地运用光合作用测定仪+箱法测定不同处理(对照、模拟海平面上升、模拟氮负荷增加、模拟海平面上升+模拟氮负荷增加)短叶茳芏湿地生态系统NEE和ER,以期揭示气象干旱与海平面上升、氮负荷增加的叠加对河口沼泽湿地生态系统净CO₂交换的影响。与正常天气相比，干旱天气下各处理(包含对照)的NEE均显著降低(P<0.05);对照、海平面上升以及氮负荷增加处理样地的ER显著减少(P<0.05),海平面上升+氮负荷增加处理ER显著增加(P&l...

Effects of combination of drought and sea-level rise, nitrogen enrichment on net ecosystem exchange of CO2 in an estuarine tidal marsh

Estuarine tidal marsh is one of the coastal blue carbon ecosystems in the world. Sea level rise and nitrogen enrichment are two major global environmental issues facing by estuarine wetlands. In recent years, meteorological drought events often occurred. The influences of drought, and combination of drought and sea-level rise, and nitrogen enrichment on net ecosystem exchange (NEE) of CO₂ of estuarine tidal marshes remain poorly studied. A novel approach using the weirs for in-situ manipulating sea level rise (including the increase of depth and duration of flooding) at relatively larger spatial scale was developed in the journal of Methods in Ecology & Evolution, however at present, the method has not been actually used in-situ to study effects of sea level rise on carbon cycle in coastal tidal marsh ecosystem. In our study, we improved the weirs and used them to manipulate the sea level rise (SR) treatment in-situ, and meanwhile applied in-situ experimental manipulations of control, nitrogen enrichment (NE), and SR+NE in a tidal brackish marsh of Cyperus malaccensis in the Minjiang River estuary, southeastern China. In summer and autumn of 2020, the meteorological drought occurred in the coastal zone of Fujian Province, which provided an opportunity to determine the effects of drought, the combination of drought and simulated sea-level rise, nitrogen enrichment on the NEE and ecosystem respiration (ER). From August to October in 2019 and 2020, the NEE and ER were measured using transparent static chamber (or black cloth shading)+Licor-6800 method. Compared with 2019 (normal year), the NEE under each treatment (including control) was significantly reduced in 2020 (drought year), and the ER in the control, the SR, and the NE was also significantly decreased in 2020. NEE was significantly negatively correlated with the photosynthetically active radiation (PAR). The results indicate that drought event can reduce net CO₂ gain in estuarine tidal marshes, and this decrease still occurs under combination of drought and sea-level rise, nitrogen enrichment.