N₂O fluxes from the littoral zone of a Chinese reservoir

Abstract. There have been few studies of greenhouse gas emissions from reservoirs, despite the remarkable growth in the number of reservoirs in developing countries. We report a case study that focuses on the littoral zone of a major Chinese reservoir, where we established measurements of N₂O fluxes using the static chamber technique at five different water levels (deep water, shallow water, seasonally flooded, control for seasonally flooded, and non-flooded). The "control for seasonal flooded" had similar vegetation to the "seasonally flooded" but was not actually flooded as it was on a higher piece of land. Seasonal, diurnal and spatial variations of N₂O flux and environmental factors were monitored throughout the growing season which included a flood event during summer rains. The N₂O flux ranged from −136.6 to 381.8 μg m⁻² h⁻¹ averaging 6.8 μg m⁻² h⁻¹. Seasonal and spatial variation was significant but diurnal variation was not. Non-flooded dry land emitted more N₂O than flooded land, no matter whether it was permanently or seasonally flooded. Piecewise correlation was found between N₂O flux, air temperature and soil nitrate concentration. Positive correlation was shown between N₂O flux and dissolved oxygen in water. There were significantly higher emissions from farmland. We compared these results with our recently published study of CH₄ emissions, carried out simultaneously at the same site as those in the present study. Completely different patterns between the two gases are demonstrated. We conclude that the littoral zone is a hotspot for N₂O emissions in the summer, especially when the shores of the lake are used for the farming of maize. But in terms of the overall greenhouse gas budget, the fluxes of N₂O are not as important as those of CH₄.