Abstract
Climate change has altered global precipitation patterns and has led to greater variation in hydrological conditions. Wetlands are important globally for their soil carbon storage. Given that wetland carbon processes are primarily driven by hydrology, a comprehensive understanding of the effect of inundation is needed. In this study, we evaluated the effect of water level (WL) and inundation duration (ID) on carbon dioxide (CO2 ) fluxes by analysing a 10-year (2008-2017) eddy covariance dataset from a seasonally inundated freshwater marl prairie in the Everglades National Park. Both gross primary production (GPP) and ecosystem respiration (ER) rates showed declines under inundation. While GPP rates decreased almost linearly as WL and ID increased, ER rates were less responsive to WL increase beyond 30cm and extended inundation periods. The unequal responses between GPP and ER caused a weaker net ecosystem CO2 sink strength as inundation intensity increased. Eventually, the ecosystem tended to become a net CO2 source on a daily basis when either WL exceeded 46cm or inundation lasted longer than 7months. Particularly, with an extended period of high-WLs in 2016 (i.e., WL remained >40cm for >9months), the ecosystem became a CO2 source, as opposed to being a sink or neutral for CO2 in other years. Furthermore, the extreme inundation in 2016 was followed by a 4-month postinundation period with lower net ecosystem CO2 uptake compared to other years. Given that inundation plays a key role in controlling ecosystem CO2 balance, we suggest that a future with more intensive inundation caused by climate change or water management activities can weaken the CO2 sink strength of the Everglades freshwater marl prairies and similar wetlands globally, creating a positive feedback to climate change.
Highlights
Climate change has altered global precipitation patterns, resulting in significant changes in regional hydrology and increasing the frequency and intensity of both seasonal and episodic drought or flooding (IPCC, 2013)
This study has shown links between inundation and ecosystem CO2 exchange rates in a freshwater wetland
Our results indicate that an increase in water level (WL) caused a decline in maximum ecosystem CO2 uptake rate (Pmax) (Figure 3b; Table 2)
Summary
Climate change has altered global precipitation patterns, resulting in significant changes in regional hydrology and increasing the frequency and intensity of both seasonal and episodic drought or flooding (IPCC, 2013). Sustained inundation can limit the decomposition activities of soil microbes and reduce CO2 emission from heterotrophic respiration (Anderson & Smith, 2002; Conner & Day, 1991; Fenner & Freeman, 2011; Happelll & Chanton, 1993; but see Zona et al, 2012) These changes between CO2 uptake and emission are usually unequal, which can lead to significant shifts in the ecosystem CO2 balance. We used eddy covariance (EC) data and the normalized difference vegetation index (NDVI; 2008–2017) from a site in the Everglades short‐hydroperiod freshwater wetland to answer the following questions: (a) How do changes in water depth and ID affect the components of ecosystem CO2 flux (i.e., NEE, GPP and ER)? | 3321 processes needed for accurate representation of wetlands in ecosystem and Earth‐system models
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