Temporal and Spatial Variation in Methane Emissions from a Flooded Transgression Shore of a Boreal Lake

• Published in: Biogeochemistry Vol. 68; no. 3; pp. 297 - 311
• Main Authors: Kankaala, Paula, Ojala, Anne, Käki, Tiina
• Format: Journal Article
• Language: English
• Published: Heidelberg Kluwer Academic Publishers 01.04.2004; Springer; Springer Nature B.V
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Anthropogenic factors; Aquatic plants; Biological and medical sciences; Biomass; Boiling; Earth sciences; Earth, ocean, space; Emissions; Eutrophication; Exact sciences and technology; Floating plants; Fresh water ecosystems; Freshwater; Fundamental and applied biological sciences. Psychology; Growing season; Hydrology; Hydrology. Hydrogeology; Lakes; Lakeshores; Methane; Peatlands; Phragmites australis; Plants; Pollutant emissions; Seasonal variations; Sediments; Shorelines; Synecology; Vegetation; Water depth; Scandinavia; Finland; Methane emission; biomass; shorelines; Transgression shore; time variations; atmospheric emission; fresh-water environment; Phragmites australis; eutrophication; Europe; vegetation; human activity; lacustrine environment; carbon; peat bogs; methane; temperature; vegetation effects; spatial variations; lakes; Typha latifolia; seasonal variations; Boreal lake
• ISSN: 0168-2563; 1573-515X
• DOI: 10.1023/b:biog.0000031030.77498.1f

Variation of CH4 emissions over a three-year period was studied in a reed-dominated (Phragmites australis) littoral transect of a boreal lake undergoing shoreline displacement due to postglacial rebound. The seasonal variation in plant-mediated CH4 emissions during open-water periods was significantly correlated with sediment temperature. The highest plant-mediated emission rates (up to 2050 mg CH4 m-2 d-1) were found in the outermost reed zone, where culms of the previous growing seasons had accumulated and free-floating plants grew on the decomposing culms. In reed zones closer to the shoreline as well as in mixed stands of reed and cattail, the maximum daily rates were usually > 500 mg CH4 m-2 d-1. The total plant-mediated CH4 emission during the open-water period was significantly correlated with the seasonal maximum of green shoot biomass. This relationship was strongest in the continuously flooded (water depth > 25 cm) outermost zones. In this area, emissions through ebullition were of greatest importance and could exceed plant-mediated emissions. In general, total emissions of the open-water periods varied from ca. 20 to 50 g CH4 m-2 a-1, but in the outermost reed zone, the plant-mediated emissions could be as high as 123 g CH4 m-2 a-1; ebullition emissions from this zone reached > 100 g CH4 m-2 a-1. The proportion of CH4 released in winter was usually < 10% of annual emissions. Emissions of CH4 were higher in this flooded transgression shore the than those measured in boreal peatlands, but the role of ancient carbon stores as a substrate supply compared with recent anthropogenic eutrophication is unknown.