人们普遍认为,富营养化的湖泊对一氧化二氮(N2O)的排放有很大的贡献。然而,这些排放如何受到地层的影响,失踪,这些湖泊中藻华的机制尚未得到系统研究。本研究考察并确定了超富营养化太湖时空N2O产生途径的相对贡献。同步,在野外和微观世界中,使用氧(δ18O)和整体氮(δ15N)与N2O和分子内15N位点偏好(SP)的同位素比,测量了藻类对N2O产生和释放潜力的多重影响。结果表明,太湖中N2O的产生源于微生物作用(硝化和不完全反硝化)和水空气交换。N2O的生产也受到N2O还原过程的影响。爆发前水柱中溶解的N2O平均浓度,爆发,和藻类积累的衰变阶段几乎相同(0.05μmol·L-1),比湖泊地区高2-10倍的藻类没有积累。然而,除了中央湖区,由于水柱中溶解的N2O过饱和,所有调查区域(有和没有积累的藻类)都显示出强释放潜力并充当排放源。爆发前的平均N2O释放通量,爆发,藻类聚集区的衰变阶段分别为17.95、26.36和79.32μmol·m-2·d-1,比非藻类聚集区的值高2.0-7.5倍。此外,藻类的腐烂和分解释放出大量的营养物质,改变了水柱的理化性质。此外,藻类生物量的增加促进了N2O的释放,并将反硝化过程产生的N2O比例提高到9.8-20.4%。当同位素数据证明反硝化过程中的N2O消耗时,该比例变得更高。然而,当藻类生物量在富营养化状态下过量时,藻类的分解也消耗了大量的氧气,因此,由于完全反硝化以及在缺氧或缺氧条件下通过硝化的硝酸盐底物供应有限,限制了N2O的产生。Further,藻类在水面上的过度积累通过阻碍溶解的N2O向大气中的迁移来降低N2O的释放通量。这些发现为准确评估富营养化湖泊中藻类过程驱动的N2O释放通量提供了新的视角和理解。
It is generally accepted that eutrophic lakes significantly contribute to nitrous oxide (N2O) emissions. However, how these emissions are affected by the formation, disappearance, and mechanisms of algal blooms in these lakes has not been systematically investigated. This study examined and determined the relative contribution of spatiotemporal N2O production pathways in hypereutrophic Lake Taihu. Synchronously, the multi-impacts of algae on N2O production and release potential were measured in the field and in microcosms using isotope ratios of oxygen (δ18O) and bulk nitrogen (δ15N) to N2O and to intramolecular 15N site preference (SP). Results showed that N2O production in Lake Taihu was derived from microbial effects (nitrification and incomplete denitrification) and water air exchanges. N2O production was also affected by the N2O reduction process. The mean dissolved N2O concentrations in the water column during the pre-outbreak, outbreak, and decay stages of algae accumulation were almost the same (0.05 μmol·L-1), which was 2-10 times higher than in lake areas algae was not accumulating. However, except for the central lake area, all surveyed areas (with and without accumulated algae) displayed strong release potential and acted as the emission source because of dissolved N2O supersaturation in the water column. The mean N2O release fluxes during the pre-outbreak, outbreak, and decay stages of algae accumulation areas were 17.95, 26.36, and 79.32 μmol·m-2·d-1, respectively, which were 2.0-7.5 times higher than the values in the non-algae accumulation areas. In addition, the decay and decomposition of algae released large amounts of nutrients and changed the physiochemical properties of the water column. Additionally, the increased algae biomass promoted N2O release and improved the proportion of N2O produced via denitrification process to being 9.8-20.4% microbial-derived N2O. This proportion became higher when the N2O consumption during denitrification was considered as evidenced by isotopic data. However, when the algae biomass was excessive in hypereutrophic state, the algae decomposition also consumed a large amount of oxygen, thus limiting the N2O production due to complete denitrification as well as due to the limited substrate supply of nitrate by nitrification in hypoxic or anoxic conditions. Further, the excessive algae accumulation on the water surface reduced N2O release fluxes via hindering the migration of the dissolved N2O into the atmosphere. These findings provide a new perspective and understanding for accurately evaluating N2O release fluxes driven by algae processes in eutrophic lakes.