Browsing by Subject "riparian buffers"

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    EFFECT OF SOIL TYPE AND HYDROLOGY ON THE COMPOSITION OF NITROGEN GASES EMITTED FROM RIPARIAN BUFFERS
    (Office of the Vice Chancellor for Research, 2012-04-13) Bebinger, Lori; Jacinthe, Pierre-Andre
    The US Corn Belt States are the leading contributors to nitrate (NO3-) enrichment and the so-called dead-zone in the Gulf of Mexico. Located at the interface between agricultural fields and surface water bodies, riparian buffers have shown great capacity to remove NO3- from agricultural runoff, and thus reduce fertilizer N export to streams. Under the right conditions (organic carbon, moist to wet soils), riparian soil microbes can convert NO3- into nitrous oxide (N2O) and dinitrogen (N2).However, from an air quality standpoint, a low N2O production relative to N2 (mole fraction of N2O) would be preferred because N2O contributes to the greenhouse effect and depletion of the ozone layer, With the hypothesis that frequent water saturation is favorable to the reduction of N2O into N2 (thus a low N2O mole fraction), a study was conducted to identify controlling factors of N2O mole fraction across various riparian buffers, including well-drained (WR), artificially-drained (LWD), and poorly-drained (SF) sites. The relative production of N2O and N2 was measured in the laboratory using the acetylene (C2H2) block technique. In the absence of C2H2, there was no difference in N2O production rate among the sites. However, in the presence of C2H2, N2O production at SF (30 μg N2O kg-1 soil h-1) was much higher than at the other sites (3.31 at LWD and 8.42 at WR). Conversely, the N2O mole fraction at SF (0.11) was lower than at WR (0.28). These results are consistent with the greater soil moisture, and higher total soil organic C at SF compared to the other sites. The low N2O production at LWD is probably due to the presence of tile drains and infrequent soil saturation. Future studies will examine the impact of tile-drain on the composition of N gases from these types of buffers.
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    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 Science
    Riparian 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.