Varying effects of stream restoration on riparian soil carbon persistence and methane emissions in the southern Rocky Mountains, United States

Introduction Channel incision can disconnect streams from their floodplains, potentially depleting carbon (C) in riparian soils by stimulating microbial decomposition. Stream restoration may offer an opportunity to replenish soil C pools by saturating riparian soils with water and slowing microbial activity. Objectives Assess how stream restoration affects soil C persistence and greenhouse gas emissions in riparian soils. Methods We measured soil C pools and methane (CH 4 , a strong greenhouse gas) emissions adjacent to stream reaches restored with plug‐and‐ponds or beaver dam analogs (BDAs) in northern New Mexico. We also measured mineral‐associated organic carbon (a persistent C pool) and particulate organic matter (particulate organic C [POC], a more labile C pool) as indicators of soil C persistence and their isotopic composition to inform formation pathways. Results Plug‐and‐ponds increased POC from 22.3 ± 2.34 g C/kg to 62.5 ± 9.71 g C/kg within 3 years, with increases in soil moisture and decreases in δ 13 C together suggesting suppression of microbial decomposition. While plug‐and‐ponds also increased CH 4 emissions (from 0.14 ± 0.055 μg C m −2 s −1 to 1.73 ± 0.93 μg C m −2 s −1 ), preliminary calculations suggest that this did not offset the climate benefit of increased POC. BDAs did not consistently increase soil C or soil moisture; steeper slopes at the BDA sites may have prevented water saturation that is necessary to slow microbial decomposition. Conclusions Stream restoration efforts can increase soil C accumulation enough to offset increased CH 4 emissions, but success depends on initial site characteristics, like slope.