The inclusion of trees and the introduction of non-native earthworms may increase greenhouse gas emissions from riparian buffer strips.

     Forested riparian buffer strips (FRBS) are common in temperate agroecosystems due to their ability to sequester nutrients from agricultural runoff and to sequester carbon. The full environmental benefits of FRBS can only be evaluated, however, by accounting for a wide range of criteria that go beyond stream water quality. For example, it is important to determine the net greenhouse gas (GHG) balance of FRBS relative to adjacent agricultural fields. It is also important to identify the factors controlling these GHG emissions in order to propose optimal FRBS designs that maximize their environmental benefits. One such factor is the spread of non-native earthworms, whose burrowing activities may modify soil emission rates of CO₂, N₂O and CH₄. To test the effects of earthworms on GHG emissions, microcosm studies were conducted using a replicated factorial design comprising of three soil origins (deciduous FRBS, coniferous FRBS, agricultural field) × two soil textures (field conditions, high clay) × three EW life habits (anecic, endogeic, no earthworms). At different intervals over the course of a 10-week trial, we measured net CO₂ emissions under aerobic conditions, as well as potential N₂O emissions in microcosms amended with acetylene gas.  In a separate trial using the same experimental design, we measured gross production and consumption rates of CH₄, in both aerobic and anaerobic conditions, using an ¹³CH₄ isotope dilution technique. Anecic earthworms had a positive effect on soil CO₂ and denitrification, which decreased after a few weeks. Increasing soil clay content had a negative effect on the emission of these two GHGs. Additionally, soils from FRBS emitted more CO₂, N₂O and CH₄ than soils from agricultural fields. Gross CH₄ consumption rates were greater under aerobic than aerobic conditions, especially under deciduous trees.  Results suggest that the inclusion of trees in riparian buffer strips combined with the introduction of non-native earthworm species could substantially increase GHG emissions of agroecosystems and mitigate the environmental benefits of FRBS.

(Note: The first and second authors contributed equally to this presentation).