The role of management on methane emissions from subtropical wetlands embedded in agricultural ecosystems

Authors: DELUCIA, NICHOLAS - University Of Illinois; GOMEZ-CASANOVAS, NURIA - University Of Illinois; BOUGHTON, ELIZABETH - Archbold Biological Station; Bernacchi, Carl

Submitted to: Journal of Geophysical Research-Biogeosciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/23/2019
Publication Date: 8/23/2019
Citation: DeLucia, N.J., Gomez-Casanovas, N., Boughton, E.H., Bernacchi, C.J. 2019. The role of management on methane emissions from subtropical wetlands embedded in agricultural ecosystems. Journal of Geophysical Research-Biogeosciences. 124(9):2694-2708.

Interpretive Summary: Wetlands are greenhouse gas sources but little is known regarding how surrounding agricultural practices impact their methane emissions. Nested within the larger grazed pasture agricultural landscape in Central Florida, a dominant cow-calf region for beef production, are wetlands that are important for many ecosystem services. These embedded wetlands are located within intensely managed pastures where the land is optimized for beef production and semi-native pastures where biodiversity is higher and beef production is lower. This research investigates how surrounding land management impacts the greenhouse gas emissions from these wetlands. The wetlands in the intensively managed pastures have higher methane emissions than wetlands surrounded by semi-native landscapes. Whether a wetland was grazed or ungrazed had no impact on the amount of methane released from the wetland. This research demonstrates a link between agricultural management practices and wetland greenhouse gas emissions that can help lead to improved management practices and help constrain ecosystem and global models that currently neglect the management impact on wetlands.

Technical Abstract: Wetlands are an important source of CH4 globally. However, there is large uncertainty surrounding the impact of anthropogenic activities on CH4 emissions from wetlands. This study investigated how landscape context, here defined as grazing of wetlands and/or management intensity of the landscape in which wetlands are embedded, influences net CH4 emissions from isolated, seasonal subtropical wetlands. This research further determined key mechanisms by which management decisions at the landscape scale modulates CH4 emissions from the embedded wetlands. Net CH4 exchange was measured using a closed chamber system over two complete wet/dry seasonal cycles in 16 wetlands embedded either in heavily fertilized and grazed managed pastures (improved wetlands) or less intensively grazed unfertilized pastures (semi-native wetlands) as well as in grazed and ungrazed wetlands in each treatment. Emissions of CH4 were higher from improved wetlands (2.82 µmol m-2 s-1) than semi-native wetlands (0.75 µmol m-2 s-1), particularly during the wet season. Enhanced CH4 emissions in improved wetlands relative to semi-native wetlands were caused by increased soil wetness as well as by higher biomass in improved than semi-native wetlands. Unlike subtropical flooded pastures, our results showed that grazers do not alter CH4 emissions from subtropical wetlands. Current and future changes in management intensity of pastures may cause shifts in net soil CH4 emissions from embedded subtropical wetlands which could further enhance this emission source.