Centre for Coastal Biogeochemistry, School of Environment, Science and Engineering, Southern Cross University, PO Box 157, Lismore, NSW, 2480, Australia.
Glob Chang Biol. 2015 Sep;21(9):3219-45. doi: 10.1111/gcb.12923. Epub 2015 May 12.
Nitrous oxide is a powerful, long-lived greenhouse gas, but we know little about the role of estuarine areas in the global N2 O budget. This review summarizes 56 studies of N2 O fluxes and associated biogeochemical controlling factors in estuarine open waters, salt marshes, mangroves, and intertidal sediments. The majority of in situ N2 O production occurs as a result of sediment denitrification, although the water column contributes N2 O through nitrification in suspended particles. The most important factors controlling N2 O fluxes seem to be dissolved inorganic nitrogen (DIN) and oxygen availability, which in turn are affected by tidal cycles, groundwater inputs, and macrophyte density. The heterogeneity of coastal environments leads to a high variability in observations, but on average estuarine open water, intertidal and vegetated environments are sites of a small positive N2 O flux to the atmosphere (range 0.15-0.91; median 0.31; Tg N2 O-N yr(-1) ). Global changes in macrophyte distribution and anthropogenic nitrogen loading are expected to increase N2 O emissions from estuaries. We estimate that a doubling of current median NO3 (-) concentrations would increase the global estuary water-air N2 O flux by about 0.45 Tg N2 O-N yr(-1) or about 190%. A loss of 50% of mangrove habitat, being converted to unvegetated intertidal area, would result in a net decrease in N2 O emissions of 0.002 Tg N2 O-N yr(-1) . In contrast, conversion of 50% of salt marsh to unvegetated area would result in a net increase of 0.001 Tg N2 O-N yr(-1) . Decreased oxygen concentrations may inhibit production of N2 O by nitrification; however, sediment denitrification and the associated ratio of N2 O:N2 is expected to increase.
一氧化二氮是一种强大且寿命长的温室气体，但我们对河口地区在全球 N2 O 预算中的作用知之甚少。本综述总结了 56 项关于河口开阔水域、盐沼、红树林和潮间带沉积物中 N2 O 通量及其相关生物地球化学控制因素的研究。大多数原位 N2 O 产生是由于沉积物反硝化作用，尽管水相中悬浮颗粒的硝化作用也会向大气中输送 N2 O。控制 N2 O 通量的最重要因素似乎是溶解无机氮 (DIN) 和氧气的供应，而这又受到潮汐周期、地下水输入和大型植物密度的影响。沿海环境的异质性导致观测结果的高度变异性，但平均而言，河口开阔水域、潮间带和植被环境是向大气输送少量正 N2 O 通量的地点（范围为 0.15-0.91；中位数 0.31；Tg N2 O-N yr(-1)）。大型植物分布和人为氮负荷的全球变化预计将增加河口的 N2 O 排放。我们估计，目前硝酸盐（-）浓度增加一倍，将使全球河口水-气 N2 O 通量增加约 0.45 Tg N2 O-N yr(-1)，约增加 190%。如果 50%的红树林生境丧失，变成无植被的潮间带，将导致 N2 O 排放量净减少 0.002 Tg N2 O-N yr(-1)。相比之下，如果 50%的盐沼转变为无植被区域，将导致 N2 O 排放量净增加 0.001 Tg N2 O-N yr(-1)。氧气浓度的降低可能会抑制硝化作用产生 N2 O；然而，沉积物反硝化作用以及与之相关的 N2 O:N2 比值预计会增加。
