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Browsing by Author "Vidon, P."
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Item Hydro-geomorphic controls of greenhouse gas fluxes in riparian buffers of the White River watershed, IN (USA)(Elsevier, 2017-09) Jacinthe, Pierre-André; Vidon, P.; Earth Science, School of ScienceRiparian ecosystems are defined by the nature and regularity of the interactions between a given river system and its floodplains, and past studies have often presented vegetation cover as the exclusive expression of these interactions. There has been to our knowledge, no systematic attempt at linking greenhouse gases (GHG) fluxes and types of riparian buffers. The present study was conducted to investigate the intensity and seasonality of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) fluxes in riparian buffers in three common hydro-geomorphic settings (HGM) across the White River watershed (Indiana, USA). These classes included riparian sites located: (i) in till plain depressions near 1st order streams (HGM-1), (ii) in incised narrow valleys with thin alluvium layers above glacial till (HGM-2), and (iii) along 3rd–4th order streams in broad floodplains with thick alluvial and glacial outwash deposits (HGM-3). For each class, 3 sites were selected and GHG fluxes were measured during the wet (May) and dry seasons (August). Strong relationships were found between GHG fluxes, soil properties and environmental factors, but these relationships varied with season and gas species, making it challenging to rely on these relationships for GHG fluxes upscaling. Analysis of variance and discriminant analysis showed that the HGM-defined riparian buffers were distinct in terms of GHG flux intensity. Regardless of season, the HGM-1 sites emitted CO2 at rates 1.6 times higher than at the other sites, likely due to difference in soil C quality. During the wet season, N2O emission was significantly higher at the HGM-3 than at the other sites (0.88 vs 0.27 mg N m− 2 d− 1), and was negatively related with the gradient of the adjacent channel (r2: 0.69). The riparian buffers acted as CH4 sinks, with the HGM-2 sites exhibiting CH4 uptake rates significantly greater than the other riparian types (− 0.80 vs − 0.34 mg CH4-C m− 2 d− 1). The consistency of these results underscores the potential of an HGM-based monitoring approach to derive watershed-scale GHG budgets for riparian buffers.Item Soil methane and carbon dioxide fluxes from cropland and riparian buffers in different hydrogeomorphic settings(ACSESS, 2015) Jacinthe, Pierre-André; Vidon, P.; Fisher, K.; Liu, X.; Baker, M. E.; Department of Earth Sciences, School of ScienceRiparian buffers contribute to the mitigation of nutrient pollution in agricultural landscapes, but there is concern regarding their potential to be hot spots of greenhouse gas production. This study compared soil CO2 and CH4 fluxes in adjacent crop fields and riparian buffers (a flood-prone forest and a flood-protected grassland along an incised channel) and examined the impact of water table depth (WTD) and flood events on the variability of gas fluxes in riparian zones. Results showed significantly (P < 0.001) higher CO2 emission in riparian areas than in adjoining croplands (6.8 ± 0.6 vs. 3.6 ± 0.5 Mg CO2–C ha−1 yr−1; mean ± SE). Daily flux of CO2 and soil temperature were significantly related (P < 0.002), with Q10 values ranging between 1.75 and 2.53. Significant relationships (P < 0.05) were found between CH4 daily flux and WTD. Flood events resulted in enhanced CH4 emission (up to +44.5 mg CH4–C m−2 d−1 in a swale) under warm soil conditions (>22°C), but the effect of flooding was less pronounced in early spring (emission <1.06 mg CH4–C m−2 d−1), probably due to low soil temperature. Although CH4 flux direction alternated at all sites, overall the croplands and the flood-affected riparian forest were CH4 sources, with annual emission averaging +0.04 ± 0.17 and +0.92 ± 1.6 kg CH4–C ha−1, respectively. In the riparian forest, a topographic depression (<8% of the total area) accounted for 78% of the annual CH4 emission, underscoring the significance of landscape heterogeneity on CH4 dynamics in riparian buffers. The nonflooded riparian grassland, however, was a net CH4 sink (−1.08 ± 0.22 kg CH4–C ha−1 yr−1), probably due to the presence of subsurface tile drains and a dredged/incised channel at that study site. Although these hydrological alterations may have contributed to improvement in the CH4 sink strength of the riparian grassland, this must be weighed against the water quality maintenance functions and other ecological services provided by riparian buffers.