The impact of water management practices on subtropical pasture methane emissions and ecosystem service payments

Abstract

Pastures are an extensive land cover type; however, patterns in pasture greenhouse gas (GHG) exchange vary widely depending on climate and land management. Understanding this variation is important, as pastures may be a net GHG source or sink depending on these factors. We quantified carbon dioxide (CO ) and methane (CH ) fluxes from subtropical pastures in south Florida for three wet-dry seasonal cycles using eddy covariance, and estimated two annual budgets of CO , CH , and GHG equivalent emissions. We also estimated the impact of water retention practices on pasture GHG emissions and assessed the impact of these emissions on stakeholder payments for water retention services in a carbon market framework. The pastures were net CO sinks sequestering up to 163 ± 54 g CO -C·m ·yr (mean ± 95% CI), but were also strong CH sources emitting up to 23.5 ± 2.1 g CH -C·m ·yr . Accounting for the increased global warming potential of CH , the pastures were strong net GHG sources emitting up to 584 ± 78 g CO -C eq.·m ·yr , and all CO uptake was offset by wet season CH emissions from the flooded landscape. Our analysis suggests that CH emissions due to increased flooding from water management practices is a small component of the pasture GHG budget, and water retention likely contributes 2-11% of net pasture GHG emissions. These emissions could reduce water retention payments by up to ~12% if stakeholders were required to pay for current GHG emissions in a carbon market. It would require at least 93.7 kg CH -C emissions per acre-foot water storage (1 acre-foot = 1233.48 m ) for carbon market costs to exceed water retention payments, and this scenario is highly unlikely as we estimate current practices are responsible for 11.3 ± 7.2 kg CH -C emissions per acre-foot of water storage. Our results demonstrate that water retention practices aimed at reducing nutrient loading to the Everglades are likely only responsible for a minor increase in pasture GHG emissions and would have a small economic consequence in a carbon market.

Seasonal Controls of CO2 and CH4 Dynamics in a Temporarily Flooded Subtropical Wetland

“…Average annual precipitation (1980 to 2015) was 1,310 mm, with two thirds of total annual precipitation falling during the wet season (DayMet database; Thornton et al, ). By quantifying the biophysical controls of CO 2 and CH 4 fluxes from a subtropical wetland and the direct and indirect influence of these controls on C fluxes by combining high‐resolution greenhouse gas (GHG) data with structural equation modeling, this study complements previous work from MAERC that investigated the effect of grazing on C fluxes of subtropical pastures (Gomez‐Casanovas, DeLucia, Bernacchi, et al, ; Gomez‐Casanovas, DeLucia, Bernacchi, et al, ) and the effect of water management (Chamberlain et al, , ) on CH 4 emissions from a subtropical pasture monoculture. Other studies in the area include Chamberlain et al () that investigated the contribution of CH 4 emissions from ruminant fermentation to CH 4 fluxes in a wetland‐pasture landscape mosaic and DeLucia et al () that evaluated the impact of surrounding land use on CH 4 emissions from subtropical wetlands.…”

“…Fluxes of CH 4 from the subtropical wetland were well within the range of values found in tropical mangroves and swamp forests (Table ; Bartlett et al, ; Harriss et al, ; Sjögersten et al, ). However, they were higher than emissions from grazed subtropical and tropical pastures (Chamberlain et al, , ; Gomez‐Casanovas, DeLucia, Bernacchi, et al, ; Gomez‐Casanovas, DeLucia, Hudiburg, et al, ) indicating that although these systems cover an ~3% of global land area, they can contribute significantly to regional CH 4 emissions (Melton et al, ).…”

“…Gaps in half‐hour CH 4 and H 2 O and sensible heat fluxes were filled using a linear interpolation when gaps were short (<2.5 hr) and using the mean diurnal variation method over four adjacent days for longer gaps (Chamberlain et al, ; Dengel et al, ; Gomez‐Casanovas, DeLucia, Bernacchi, et al, ; Gomez‐Casanovas, DeLucia, Hudiburg, et al, ). Total uncertainty was derived by adding random flux uncertainty to gap‐filling uncertainty (Richardson & Hollinger, ).…”

A Biogeochemical Compromise: The High Methane Cost of Sequestering Carbon in Restored Wetlands

“…Interpolations based on seasonal measurements, where necessary, are detailed in Petrescu et al (2015). More information can be found in the supporting information and existing literature (Chamberlain, Groffman, et al, 2017;Chu et al, 2015;Desai et al, 2015;Flanagan & Syed, 2011;Friborg et al, 2000Friborg et al, , 2003Herbst et al, 2013;Holm et al, 2016;Jammet et al, 2017;Krauss et al, 2016;Lee et al, 2016;Long et al, 2010;Mastepanov et al, 2008;Olson et al, 2013;Parmentier et al, 2011;Pugh et al, 2017;Rinne et al, 2007;Runkle et al, 2013;Sachs et al, 2010Sachs et al, , 2008Shurpali et al, 1993Shurpali et al, , 1995Tiemeyer, 2013;Y. Zhang et al, 2012;Zona et al, 2009).…”

Trade‐offs and synergies in a payment‐for‐ecosystem services program on ranchlands in the Everglades headwaters

“…However, wet soils and flooding events on subtropical pastures are an important source of methane (Chamberlain et al. , ) and methane emissions may, in part, offset greenhouse sink strength (Allard et al. , Soussana et al.…”