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研究报告

Spatial and temporal variations and influencing factors of nitrous oxide emissions from surface water in Min River Estuary

摘要：以闽江口水体为研究对象，研究了闽江河口上段（城市河口段）、河口中段和河口下段（口外海滨段）不同季节水体N₂O的溶存浓度、水-气界面通量及其环境影响因子.结果表明，闽江口水体N₂O溶存浓度为0.99~55.92 nmol·L^-1，N₂O饱和度为8.0%~396%，水-气界面N₂O释放通量为-5.21~7.91 μg·m^-2·h^-1.从季节差异看，7月（夏季）、9月（秋季）和12月（冬季）水体中N₂O过饱和，表现为N₂O的排放“源”；4月（春季）水体中N₂O不饱和，表现为N₂O“汇”.水-气界面N₂O释放通量呈夏、秋和冬季高，春季低的季节变化规律.在空间变化上，水-气界面N₂O释放通量从河口上段到下段降低，与氮含量变化趋势一致.N₂O间接性释放因子为0.004%~0.128%，低于IPCC推荐值（0.25%）.温度、盐度、pH、NO₃^-、DO、悬浮颗粒物浓度是影响N₂O溶存浓度与释放通量的主要影响因素.因此，季节性变化和人类活动导致河口N₂O释放存在较大的时空差异性，从而增加了河口N₂O排放评估的不确定性.

Abstract：In this study， seasonal variability of N₂O concentrations and fluxes and associated environmental factors were investigated in the upper section （urban estuary）， the middle section and the lower section （coastal section outside the estuary） of Min River Estuary. The results indicated that N₂O concentrations， N₂O saturations and N₂O fluxes were in a range of 0.99~55.92 nmol·L^-1， 8.0%~396%， and -5.21~7.91 μg·m^-2·h^-1. Water N₂O was supersaturated in July （summer）， September （autumn） and December （winter）， representing the "source" of N₂O emission. However， N₂O emissions exhibited the "sink" in April （spring）. N₂O fluxes were significantly higher in summer， autumn and winter than in spring， and decreased from the upper to lower estuary. Indirect N₂O emission factors ranged from 0.004% to 0.128%， which was significantly lower than the IPCC default value （0.25%）. Temperature， salinity， pH， NO₃^-， DO and suspended particulate matter were the crucial factors affecting dissolved N₂O concentrations and fluxes. Therefore， seasonal changes and human activities can trigger the large variability of N₂O emissions， leading to the increasing uncertainty of N₂O projections.