Coupling Solid-Aqueous-Gas Phases of Carbon and Nitrogen

Across Topographic Gradients and Extreme Weather Events

Sandra Petrakis1, Rodrigo Vargas1, Angelia Seyfferth1, Shreeram Inamdar1

Introduction Results: Rewetting of soils Results: Changes over time

1Department of Plant and Soil Sciences, University of Delaware

“This project was supported by Agriculture and Food Research Initiative Competitive Grants

Program award no. 2013-02758 from the USDA National Institute of Food and Agriculture.”

Figure 5 – Percent Carbon (a) , percent Nitrogen (b), and C:N ratio (c), for all soil locations

before and after the re-wetting experiment.

Table 1 – Changes in magnitude of GHG Fluxes during the experiment. Arrows are

arranged by phase and soil location. Color indicates GHG, (CO2: black, N2O: purple, CH4:

green) Arrow size represents the intensity of fluxes, (Large arrows; largest fluxes, medium

arrows; moderate-high fluxes, small arrows; low gas flux, smallest arrows; very low gas flux).

Eh and pH values are in parentheses, respectively.

Table 2 – CO2 equivalencies (CO2 eq) of GHG fluxes in g m-2 day -1, and the percent CO2

equivalent each soil location contributed. IPCC 2013 report values for 100 year GWP

accounting for situations with and without Carbon Climate Feedback.

Figure 3 – Comparisons of CO2 (a, b, c,

d), CH4 (e, f, g, h) and N2O (i, j, k, l) to

soil moisture, for each of the 5 phases,

by soil location.

Figure 4 – Comparisons of CO2 to CH4 (a,

b, c, d), N2O to CH4 (e, f, g, h) and CO2 to

N2O (i, j, k, l) for each of the 5 phases, by soil

location.

Conclusions

Water pulses suppressed CO2 fluxes but enhanced CH4 in Creek and

Wetland soils, while N2O increased in Upland and Lowland soils.

There is not necessarily a trend with θ and GHG fluxes grouped by

phase.

Redox conditions could provide the information of conditions which

drive greenhouse gas production following extreme pulse events.

With GWP accounting for carbon-climate feedback, Upland and

Lowland soil types contributed the greatest percentage of GHGs in

terms of CO2 equivalent.

Extreme water pulses can drive responses of gas fluxes not captured

by a linear empirical model.

(GWP values taken from Table 8.7 of Myhre, G., D. Shindell, F.-M. Bréon, W. Collins, J. Fuglestvedt, J. Huang, D. Koch, J.-F. Lamarque, D. Lee, B. Mendoza, T. Nakajima, A. Robock, G.

Stephens, T. Takemura and H. Zhang, 2013: Anthropogenic and Natural Radiative Forcing. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the

Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M.

Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA).

Figure 2 – Time series of GHGs (CO2 CH4, and N2O) and Soil Moisture for Wetland (a, b, c, d) Creek (e,

f, g, h), Upland (i, j, k, l) and Lowland (m, n, o, p) soils. Vertical lines represents the application of a water

pulse. Roman numerals I-V denote time periods (phases) of the experiment.

Extreme weather events influence the full range of greenhouse gas

(GHG) fluxes from soils, impacting the global warming potential

(GWP) of terrestrial ecosystems.

Soils exposed to extreme precipitation events may experience shifts in

GHG fluxes.

We seek to understand the influence of these extreme pulses of

water, because water is known to be important to biogeochemistry

and GHG fluxes from soils.

We used extreme pulses of water for a rewetting experiment to

explore GHG flux responses of four different soils representative of

a watershed.

Soil samples were collected by removing the upper 10 cm of soil

by inserting 20 cm diameter PVC rings across a hillslope transect

in a forested watershed within the Maryland Piedmont region.

Upland forested soils in this region are described as Glenelg

series. Soils were collected from Wetland, Creek, Upland and

Lowland locations within the watershed.

Soils were placed in the lab, allowing us to manipulate soil

moisture via six pulses of water which were applied over the

duration of the experiment, while maintaining temperature (21 to

23° C).

Continuous measurements of GHGs were taken using an

LI8100-A multiplexed system with automated chambers, and a

Picarro G2508 measured CO2, CH4, and N2O in primary soil

collars.

Figure 1 – Output screen of the Picarro G2508.

Study site and methods