Abstract
Abstract. Given their increasing trend in Europe, an understanding of the role that flooding events play in carbon (C) and nitrogen (N) 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 (SFS) or long (LFS) duration. 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 but during the growing season at the SFS. Overall, soil temperature and moisture 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 C, 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, although this may depend on the restriction of diffusional limitations due to the presence of standing water to periods of the year when the potential for gaseous emissions are low.
Highlights
The frequency of flooding events has increased in Europe in the last 3 decades and is likely to increase further in a warmer climate as a consequence of climate change (Beniston et al, 2007; Christensen and Christensen, 2007)
It is recognised that flooding could have significant implications for greenhouse gas (GHG) emissions, for example, due to water acting as a barrier to gaseous diffusion, as well as via alterations to soil biological and physio-chemical processes (Hansen et al, 2014; Peralta et al, 2013)
The annual emissions of CO2 found in this study are in line with those previously reported for floodplain wetlands (10.91 ± 0.54 Mg CO2–C ha−1 yr−1) (Batson et al, 2015), coastal plain wetlands (11.29 Mg CO2–C ha−1 yr−1) (Morse et al, 2012) and occasionally (9.7 Mg CO2–C ha−1 yr−1) or frequently flooded (13 Mg CO2–C ha−1 yr−1) riparian forests (Jacinthe, 2015)
Summary
The frequency of flooding events has increased in Europe in the last 3 decades and is likely to increase further in a warmer climate as a consequence of climate change (Beniston et al, 2007; Christensen and Christensen, 2007). Recent studies on the impact of longer-term flooding (LFS) have attributed differences in GHG emissions to a range of factors, including nutrient availability (Juutinen et al, 2001; Samaritani et al, 2011), soil microbial activity (Unger et al, 2009; Peralta et al, 2013), oxygen concentration (McNicol and Silver, 2014) and vegetation characteristics (Lewis et al, 2014). The impact of flooding will depend on the timing, extent and duration of the period of inundation, as well as on site-related variations in topography and hydrology. The extent of freshwater flooding will depend on the frequency and magnitude of rainfall events
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