N<sub>2</sub>O fluxes from the littoral zone of a Chinese reservoir

Abstract

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.

Carbon Dioxide Emissions from the Littoral Zone of a Chinese Reservoir

“…There may be other sources of error, for example the linear models (Table 3) used in evaluating the balance were themselves rather weak, especially the N 2 O model. However, the N 2 O emission (6.8 µg m −2 h −1 on average, see [17]) was small compared to that of CO 2 and CH 4 (1.3 mg m −2 h −1 on average, see [18]), and so we would not expect any big influence on the overall balance from the lack-of-fit of the N 2 O model. Finally, for the flooded areas, the flux observed after removal of shoots might include respiration of the phytoplankton.…”

“…Elsewhere, we have reported the emissions of CH 4 and N 2 O from the Miyun Reservoir, and we demonstrated that this littoral zone can be regarded as a hot spot for emissions [17,18]. In the present paper, we evaluate (i) the spatiotemporal variation of CO 2 emissions from the littoral zone; and (ii) the influence of environmental factors, especially flooding.…”

“…The study area and the experimental design of the present research was exactly the same as in the previous CH 4 and N 2 O study [17,18]. [17,18].…”

“…CO2 flux was observed using the dark chamber and gas chromatography techniques (for details see [17,18]). The gas samples were repeatedly taken six times in the year to cover the different seasons (November 2011, May, July, August, September and October 2012) and covering the transition in and out of the flooding season.…”

“…Weekly precipitation, daily air temperature and daily water level were accessed online. Wind speed, soil water content and dissolved oxygen in water were recorded in situ, for detailed methods, see Yang et al [17].…”