Flooding-related increases in CO2 and N2O emissions from
a temperate coastal grassland ecosystem
Amanuel W. Gebremichael1,2, Bruce Osborne1,2, and Patrick Orr11UCD School of Earth Sciences, University College Dublin, Belfield, Dublin 4, Ireland 2UCD School of Biology and Environmental Sciences, University College Dublin, Belfield, Dublin 4, Ireland
Received: 30 Nov 2016 – Accepted for review: 19 Dec 2016 – Discussion started: 03 Jan 2017
Abstract. Given their increasing trend in Europe, an understanding of the role that flooding events play in carbon and nitrogen cycling and greenhouse gas (GHG) emissions will be important for improved assessments of local and regional GHG budgets. This study presents the results of an analysis of the CO2 and N2O fluxes from a coastal grassland ecosystem affected by episodic flooding that was of either a relatively short or long duration (SFS and LFS sites, respectively). Compared to the SFS, the annual CO2 and N2O emissions were 1.4 and 1.3 times higher at the LFS, respectively. Mean CO2 emissions during the period of standing water were 144 ± 18.18 and 111 ± 9.51 mg CO2-C m−2 h−1, respectively, for the LFS and SFS sites. During the growing season, when there was no standing water, the CO2 emissions were significantly larger from the LFS (244 ± 24.88 mg CO2-C m−2 h−1) than the SFS (183 ± 14.90 mg CO2-C m−2 h−1). Fluxes of N2O ranged from −0.37 to 0.65 mg N2O-N m−2 h−1 at the LFS and from −0.50 to 0.55 mg N2O-N m−2 h−1 at the SFS, with the larger emissions associated with the presence of standing water at the LFS and during the growing season at the SFS. Overall, soil temperature and moisture content were identified as the main drivers of the seasonal changes in CO2 fluxes, but neither adequately explained the variations in N2O fluxes. Analysis of total Carbon (C), Nitrogen (N), microbial biomass and Q10 values, indicated that the higher CO2 emissions from the LFS were linked to the flooding-associated influx of nutrients and alterations in soil microbial populations. These results demonstrate that annual CO2 and N2O emissions can be higher in longer-term flooded sites that receive significant amounts of nutrients and where diffusional limitations due to the presence of standing water is limited to periods of the year when the temperatures are lowest.
Gebremichael, A. W., Osborne, B., and Orr, P.: Flooding-related increases in CO2 and N2O emissions from
a temperate coastal grassland ecosystem, Biogeosciences Discuss., doi:10.5194/bg-2016-522, in review, 2017.