A little sedge goes a long way : emergent vegetation as a key driver of littoral methane flux

Abstract

In northern (>50°N) freshwater ecosystems, aquatic vegetation is expanding, potentially enhancing methane (CH₄) emissions through plant-mediated transport and organic matter input. Despite this, most studies do not directly measure CH₄ flux from shoreline emergent vegetation. To understand influences of emergent water sedges (Carex aquatilis) on CH₄ emissions, we measured diffusive, ebullitive, and plant-mediated flux along a vegetated edge of a large, post-glacial lake in Kaska Dene ancestral territory (now called Northern British Columbia). Chamber-based CH₄ fluxes from vegetated zones (86.2 ± 57.3 mg C m⁻² d⁻¹; mean ± std; diffusion + plant mediated) were 3.8 times greater than diffusive fluxes from adjacent open areas (22.7 ± 19.5 mg C m⁻² d⁻¹). Ebullitive fluxes were similar across vegetated and open water areas, emitting 18.1 ± 28.7 and 22.0 + 28.0 mg C m⁻² d⁻¹, respectively. Using temperature incubations at 20 and 30°C we found that treatments with benthic vegetation had the higher cumulative potential CH₄ production rates (52.2 and 252 nmol CH₄ per grams dry weight (g DW)) and temperature sensitivity (Q₁₀ = 9.8) compared to sediment (37.6 and 35.7 nmol CH₄ g DW⁻¹; Q₁₀ = 4.7) and sediment + benthic vegetation (39.2 and 109 nmol CH₄ g DW⁻¹; Q₁₀ = 7.4) treatments. Our results suggest that as aquatic vegetation expands in northern lakes, we are likely to see increased CH₄ emissions facilitated by plant transport and inputs of more labile organic matter, increasing the temperature sensitivity of CH₄ production