Abstract
Abstract. Riparian zones play a fundamental role in regulating the amount of carbon (C) and nitrogen (N) that is exported from catchments. However, C and N removal via soil gaseous pathways can influence local budgets of greenhouse gas (GHG) emissions and contribute to climate change. Over a year, we quantified soil effluxes of carbon dioxide (CO2) and nitrous oxide (N2O) from a Mediterranean riparian forest in order to understand the role of these ecosystems on catchment GHG emissions. In addition, we evaluated the main soil microbial processes that produce GHG (mineralization, nitrification, and denitrification) and how changes in soil properties can modify the GHG production over time and space. Riparian soils emitted larger amounts of CO2 (1.2–10 g C m−2 d−1) than N2O (0.001–0.2 mg N m−2 d−1) to the atmosphere attributed to high respiration and low denitrification rates. Both CO2 and N2O emissions showed a marked (but antagonistic) spatial gradient as a result of variations in soil water content across the riparian zone. Deep groundwater tables fueled large soil CO2 effluxes near the hillslope, while N2O emissions were higher in the wet zones adjacent to the stream channel. However, both CO2 and N2O emissions peaked after spring rewetting events, when optimal conditions of soil water content, temperature, and N availability favor microbial respiration, nitrification, and denitrification. Overall, our results highlight the role of water availability on riparian soil biogeochemistry and GHG emissions and suggest that climate change alterations in hydrologic regimes can affect the microbial processes that produce GHG as well as the contribution of these systems to regional and global biogeochemical cycles.
Highlights
Riparian zones are hotspots of nitrogen (N) transformations across the landscape, providing a natural filter for nitrate (NO−3 ) transported from surrounding lands via runoff and subsurface flow paths (Hill, 1996; Vidon et al, 2010)
We identified the importance of each X variable by using variable importance on the projection (VIP) scores, calculated as the sum of square of the partial least squares regression (PLS) weights across all components
There were no significant differences in mean annual net N mineralization and net nitrification rates among riparian zones
Summary
Riparian zones are hotspots of nitrogen (N) transformations across the landscape, providing a natural filter for nitrate (NO−3 ) transported from surrounding lands via runoff and subsurface flow paths (Hill, 1996; Vidon et al, 2010). Riparian zones can account by 70 % of global (natural processes and human activities) terrestrial emissions of nitrous oxide (N2O) to the atmosphere, a powerful greenhouse gas (GHG) with 298 times the global warming potential of carbon dioxide (CO2) (Audet et al, 2014; Groffman et al, 2000; Hefting et al, 2003). Riparian soils can significantly contribute to global CO2 emissions because they can hold high rates of heterotrophic and autotrophic respiration (Chang et al, 2014). Riparian zones can support large methane (CH4) fluxes that account for the 15–40 % of global emissions (Audet et al, 2014; Segers, 1998).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
