[Emission of Nitrous Oxide (N 2 O) from Lake Taihu and the Corresponding Potential Driving Factors].

Nitrous oxide (NO) is one of the six greenhouse gases stipulated in the Kyoto Protocol. Its greenhouse potential over the past century was 298 times that of CO, and the concentration of atmospheric NO has been continuously and rapidly increasing during the past hundred years. Shallow lakes are an important source of atmospheric NO. In order to explore the temporal and spatial changes and potential driving factors of NO emissions from eutrophic water, we conducted field observations in February (winter) and August (summer) in Lake Taihu. We used the coefficient of diffusion-headspace bottle method to trace the variability in the NO concentration[(NO)] and efflux[(NO)] from surface water bodies and explored the potential driving factors of NO emissions. The optical measurements of dissolved organic matter (DOM) are an effective approach for tracing the source and composition of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON). The migration and transformation processes of DOM also release a large amount of inorganic nitrogen, which changes the redox potential of the water column and thereby affects NO emissions. Our results showed that the variability in (NO) and (NO) in the surface waters of Lake Taihu were strongly affected by water temperature and nutrient levels. The average (NO) of the surface waters was (19.7±2.7) nmol·L, corresponding to a mean (NO) of (41.1±1.8) μmol·(m·d), and the means of both (NO) and (NO) were higher in summer than those in winter (-test, <0.01). The input and accumulation of DOM could increase the production and emission potential of NO in water bodies, as supported by both (NO) and (NO) significantly increasing with increasing level of terrestrial humic-like C1. The integration ratio of peak C to peak T : of DOM and the spectral slope results indicated that there were high inputs of terrestrial DOM in the northwestern inflowing river mouths, concurring with the high production and emission of NO found there. This suggested that the accumulation and degradation of terrestrial DOM potentially fueled the emission of NO. Our results showed that water temperature, DOM composition, and nutrient level were all important factors affecting NO emission from Lake Taihu. Long-term continuous observation can be applied to better evaluate the impact of various environmental factors on the production and emission of NO in water bodies and to help with providing scientific emission reduction plans.