闽江河口养殖塘水体溶存氧化亚氮浓度及扩散通量研究

水产养殖生态系统由于其高氮负荷而成为氧化亚氮(N_2O)的潜在释放源.本文以福建闽江河口养虾塘为研究对象,采用静态顶空-气相色谱法测定分析了表层水体溶存N_2O浓度和饱和度,基于薄边界层模型计算了水-气界面N_2O扩散通量,在此基础上结合气象要素与水环境因子分析其主要影响因素.结果表明,养殖塘水体溶存N_2O浓度和饱和度的均值分别为17.96 nmol·L~(-1)和198.03%,时间变化上表现为养殖中期显著高于养殖末期和初期,且具有一定的日变化特征.相关分析表明,N_2O浓度及饱和度与温度、水体NH~+_4-N和叶绿素a浓度呈显著正相关(p0.05),与气压、风速和水体pH值呈显著负相关(p0.05).LM86、W92和RC01模型估算的养殖塘水-气界面N_2O扩散通量的均值分别为20.80、183.75和298.52 nmol·m~(-2)·h~(-1),3种扩散通量均呈现出随着养殖时间推移显著增加的特征,风速和水体溶存N_2O是影响河口养殖塘N_2O扩散通量的重要因子.N_2O扩散通量与扩散系数的取值密切相关,但不同模型方程计算得出的扩散系数存在显著差异,比较发现,RC01模型更适合河口区养殖塘水-气界面N_2O扩散通量估算.本研究结果可为完善水产养殖生态系统的N_2O排放清单编制和近海水环境保护提供一定的科学依据.

Dissolved nitrous oxide concentration and diffusive nitrous oxide fluxes in the aquaculture ponds in the Min River estuary

Aquaculture ponds which is rich in nutrients due to a large amount of organic matter supply from daily input of feeds, is an important sources of atmospheric nitrous oxide (N₂O). In this study, dissolved N₂O concentration and saturation in surface water were determined using static headspace-gas chromatography method in the shrimp ponds in the Min River estuary of Fujian Province. N₂O diffusive fluxes across the water\air interface in shrimp ponds were also estimated by the two-layer model of diffusive gas exchange. Meanwhile, the meteorological parameters and water environmental indicators were measured. The average concentration and saturation of dissolved N₂O among different culture stages were 17.96 nmol·L^-1 and 198.03%, respectively. Significant differences in mean N₂O concentration were recorded among the three shrimp culture stages and the highest values was detected in the middle period of culture. The N₂O concentration and saturation in the shrimp ponds were positively correlated with temperature, NH₄⁺-N and chlorophyll a (p<0.05), while being negatively correlated to air pressure, wind speed and water pH (p<0.05). The averaged N₂O diffusive fluxes calculated by LM86, W92 and RC01 models from aquaculture ponds were 20.80, 183.75 and 298.52 nmol·m^-2·h^-1, respectively. N₂O diffusive fluxes across the the water\air interface in the shrimp ponds greatly varied among different culture stages, which showing a remarkable increasing tendency over time. The wind speed and dissolved N₂O are important factors controlling the changed in N₂O diffusive fluxes. Furthermore, the N₂O diffusive fluxes were closely related to the gas transfer velocity. There are differences in N₂O transfer velocity across water\air interface in the shrimp ponds among the three models. Our results suggest that RC01 model is the more suitable method to estimate the N₂O transfer velocity and diffusive fluxes in shrimp ponds in the Min River estuary than the LM86 and W92 model. These results provided scientific reference for the inventory compilation of N₂O emission from coastal aquaculture ponds and the protection of coastal water environment.