Temperature and water-level effects on greenhouse gas fluxes from black ash (Fraxinus nigra) wetlands in the Upper Great Lakes region, USA

Authors: TOCZYDLOWSKI, ALAN - University Of Minnesota; SLESAK, ROBERT - University Of Minnesota; KOLKA, RANDALL - Forest Service (FS); Venterea, Rodney - Rod

Submitted to: Applied Soil Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/20/2020
Publication Date: 3/18/2020
Citation: Toczydlowski, A., Slesak, R., Kolka, R., Venterea, R.T. 2020. Temperature and water-level effects on greenhouse gas fluxes from black ash (Fraxinus nigra) wetlands in the Upper Great Lakes region, USA. Applied Soil Ecology. 153:103565. https://doi.org/10.1016/j.apsoil.2020.103565.
DOI: https://doi.org/10.1016/j.apsoil.2020.103565

Interpretive Summary: Forested black ash (Fraxinus nigra) wetlands are an important economic, cultural, and ecological resource in the northern Great Lake States, USA, and are threatened by the invasive insect, emerald ash borer (Agrilus planipennis Fairmmaire [EAB]). EAB-induced ash mortality can modify wetland hydrology by elevating the water table and increasing air temperature following canopy dieback, both of which may alter gaseous fluxes of carbon and nitrogen. We sampled and incubated intact soil cores containing either mineral or peat soils from two black ash wetlands, monitored soil oxidation-reduction potential (Eh), and measured the efflux of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) at two water-level treatments nested in three temperature treatments, 10°C, 15°C, or 20°C. The water-level treatments were either saturated or drawdown, in which the water-level was incrementally lowered in a repeated cycle. Mean CO2 fluxes increased with increasing temperature but did not vary significantly by soil type or water-level. Peat soil had significantly greater CH4 flux in the saturated treatment and had minimal N2O loss across all treatments, while mineral soils had eight to 43 times significantly greater N2O flux in the saturated treatment, and minimal CH4 loss across all treatments. Gas fluxes generally increased and became more variable with increasing temperature. The drawdown treatment resulted in significantly higher Eh during unsaturated periods in both soil types, but the response was more variable in the peat soil. These results suggest that elevated water tables in mineral soil black ash wetlands would result in greater N2O fluxes and export of nitrogen from the ecosystem. In peat soils, elevated water tables in black ash wetlands would result in greater CH4 fluxes and carbon release into the atmosphere. Increased soil temperature will lead to greater gaseous fluxes in both wetland ecosystems. Our findings demonstrate potential indirect effects of EAB in black ash wetlands, with implications for ecosystem functions associated with C and N cycling. These results will be useful to land managers interested in mitigating and managing the effects of EAB on forest ecosystem health and broader environmental impacts.

Technical Abstract: Forested black ash (Fraxinus nigra) wetlands are an important economic, cultural, and ecological resource in the northern Great Lake States, USA, and are threatened by the invasive insect, emerald ash borer (Agrilus planipennis Fairmmaire [EAB]). EAB-induced ash mortality can modify wetland hydrology by elevating the water table and increasing air temperature following canopy dieback, both of which may alter gaseous fluxes of carbon and nitrogen. We sampled and incubated intact soil cores containing either mineral or peat soils from two black ash wetlands, monitored soil oxidation-reduction potential (Eh), and measured the efflux of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) at two water-level treatments nested in three temperature treatments, 10°C, 15°C, or 20°C. The water-level treatments were either saturated or drawdown, in which the water-level was incrementally lowered in a repeated cycle. Mean CO2 fluxes increased with increasing temperature but did not vary significantly by soil type or water-level. Peat soil had significantly greater CH4 flux in the saturated treatment and had minimal N2O loss across all treatments, while mineral soils had eight to 43 times significantly greater N2O flux in the saturated treatment, and minimal CH4 loss across all treatments. Gas fluxes generally increased and became more variable with increasing temperature. The drawdown treatment resulted in significantly higher Eh during unsaturated periods in both soil types, but the response was more variable in the peat soil. These results suggest that elevated water tables in mineral soil black ash wetlands would result in greater N2O fluxes and export of nitrogen from the ecosystem. In peat soils, elevated water tables in black ash wetlands would result in greater CH4 fluxes and carbon release into the atmosphere. Increased soil temperature will lead to greater gaseous fluxes in both wetland ecosystems. Our findings demonstrate potential indirect effects of EAB in black ash wetlands, with implications for ecosystem functions associated with C and N cycling.