[1] Everglades freshwater marshes were once carbon sinks, but human-driven hydrologic changes have led to uncertainty about the current state of their carbon dynamics. To investigate the effect of hydrology on CO 2 exchange, we used eddy covariance measurements for 2 years (2008)(2009) in marl (short-hydroperiod) and peat (long-hydroperiod) wetlands in Everglades National Park. The importance of site, season, and environmental drivers was evaluated using linear and nonlinear modeling, and a novel method was used to test for temporally lagged patterns in the data. Unexpectedly, the long-hydroperiod peat marsh was a small CO 2 source (19.9 g C m À2 from July to December 2008 and 80.0 g C m À2 in 2009), and at no time over the study period was it a strong sink. Contrary to previous research suggesting high productivity rates from a short-hydroperiod marsh, we estimated that the marl site was a small CO 2 sink in 2008 (net ecosystem exchange [NEE] = À78.8 g C m À2 ) and was near neutral for carbon balance in 2009. In addition, both sites had relatively low gross ecosystem exchange (GEE) over the 2 years of this study. The two sites showed similar responses for NEE versus air temperature, ecosystem respiration (R eco ) versus air temperature, and R eco versus water depth, although the magnitude of the responses differed. We saw small lags (30 min in most cases) between carbon fluxes and environmental drivers. This study is foundational for understanding the carbon balance of these ecosystems prior to implementation of the planned Everglades restoration of historical water flow that will likely alter the future trajectory of the carbon dynamics of the Everglades as a whole.
Although wetlands are among the world's most productive ecosystems, little is known of long-term CO 2 exchange in tropical and subtropical wetlands. The Everglades is a highly managed wetlands complex occupying >6000 km 2 in south Florida. This ecosystem is oligotrophic, but extremely high rates of productivity have been previously reported. To evaluate CO 2 exchange and its response to seasonality (dry vs. wet season) in the Everglades, an eddy covariance tower was established in a short-hydroperiod marl marsh. Rates of net ecosystem exchange and ecosystem respiration were small year-round and declined in the wet season relative to the dry season. Inundation reduced macrophyte CO 2 uptake, substantially limiting gross ecosystem production. While light and air temperature exerted the primary controls on net ecosystem exchange and ecosystem respiration in the dry season, inundation weakened these relationships. The ecosystem shifted from a CO 2 sink in the dry season to a CO 2 source in the wet season; however, the marsh was a small carbon sink on an annual basis. Net ecosystem production, ecosystem respiration, and gross ecosystem production were -49.9, 446.1 and 496.0 g C m -2 year -1 , respectively. Unexpectedly low CO 2 flux rates and annual production distinguish the Everglades from many other wetlands. Nonetheless, impending changes in water management are likely to alter the CO 2 balance of this wetland and may increase the source strength of these extensive short-hydroperiod wetlands.3
Global atmospheric concentrations of methane (CH4), a powerful greenhouse gas, are increasing, but because there are many natural and anthropogenic sources of CH4, it is difficult to assess which sources may be increasing in magnitude. Here we present a data set of δ2H‐CH4 measurements of individual sources and air in the Colorado Front Range, USA. We show that δ2H‐CH4, but not δ13C, signatures are consistent in air sampled downwind of landfills, cattle feedlots, and oil and gas wells in the region. Applying these source signatures to air in ground and aircraft samples indicates that at least 50% of CH4 emitted in the region is biogenic, perhaps because regulatory restrictions on leaking oil and natural gas wells are helping to reduce this source of CH4. Source apportionment tracers such as δ2H may help close the gap between CH4 observations and inventories, which may underestimate biogenic as well as thermogenic sources.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.