Short-term effects of macrophyte removal on emission of CO2 and CH4 in shallow lakes

Mass development of macrophytes in freshwater ecosystems is today considered a worldwide problem and substantial resources are spent on macrophyte removal each year. By removing the dominant primary producer, however, this management practice radically changes the ecosystem overnight. Here, we studied short-term effects of the removal of a mass development of free-floating (Pontederia crassipes), submerged (Elodea nuttal-lii) and emergent (mix of Ludwigia grandi?ora and L. peploides) macrophytes on fluxes of CH4 and CO2 in three lakes. In our field experiment, we assigned an impact site where macrophytes were removed, and a control site where vegetation remained. Before and after removal, diffusive fluxes of CO2 and CH4 were determined in lakes dominated by P. crassipes and E. nuttallii, whereas total emission of CH4 was determined in all three case study lakes. Additionally, plant biomass, and physical and chemical parameters were measured before and after removal. While removal of emergent Ludwigia spp. showed no clear effect on total CH4 emission, removal of submerged E. nuttallii reduced both CO2 fixation and total CH4 emission. Removal of free-floating P. crassipes, on the other hand, increased CH4 fluxes and stimulated phytoplankton blooms. The lack of a universal response across our case study lakes suggests that both macrophyte life forms and environmental parameters can be important factors determining effects of removal. Additionally, indirect effects of macrophyte removal on tem-perature and dissolved oxygen can help to explain carbon emissions. Long-term effects should be studied to allow development of sustainable management practices.

Automated summary

Mass development of macrophytes in freshwater ecosystems is a global problem that requires substantial resources for removal. This study examines the short-term effects of removing different types of macrophytes on CH4 and CO2 fluxes in three lakes. The findings suggest that removing submerged macrophytes reduces CO2 fixation and CH4 emissions, while removing free-floating macrophytes increases CH4 fluxes and stimulates phytoplankton blooms. The lack of a universal response indicates that macrophyte life forms and environmental parameters play important roles in the effects of removal.