Effects of tidal fluctuations on CO2 and CH4 fluxes in the littoral zone of a brackish-water lake.

Abstract  We examined the effects of tidal fluctuations on CO2 and CH4 fluxes from sediment or soil to the atmosphere in the littoral zone of a brackish-water lake during the growing seasons in 2004 and 2005. The dominant plants at the study site formed three sub-zones (Phragmites zone, Juncus zone and Miscanthus zone) across a topographic gradient on the shoreline. In the Phragmites and Juncus zones, we observed a positive correlation between hourly changes in CO2 and CH4 fluxes and changes in the water table. In particular, the magnitude and pattern of daily variation in CO2 and CH4 fluxes were different on days during spring tide and neap tide in the Phragmites and Juncus zones. Variations in CO2 and CH4 fluxes in the Phragmites and Juncus zones over the course of a day during spring tide were correlated with water-table level. We found that the rate of change of the water table, as distinguished from just differences in the water table, was a major environmental factor controlling the CO2 and CH4 fluxes. In the Miscanthus zone during spring tide, soil temperature was the main factor affecting daily variation in CO2 and CH4 fluxes. [ABSTRACT FROM AUTHOR]