Effects of spring flood and water level draw‐down on methane dynamics in the littoral zone of boreal lakes

Abstract

1. The annual dynamics of methane (CH4) in a temporarily flooded meadow, mire bank, lacustrine sedge fen, temporarily and continuously inundated sedge (Carex sp.) and reed (Phragmites australis) marshes were studied from June to November in the humic mesoeutrophic Lake Mekrijärvi and in eutrophicated parts of the mesotrophic Lake Heposelkä in the southern part of East Finland. The effects of water level and temperature on littoral CH4 fluxes were determined. Vegetation zonation along the moisture gradient, and associated CH4 fluxes, were evaluated. 2. The CH4 flux increased along the moisture gradient from –0.2 to 14.2 mg CH4 m–2 h–1, and was highest in the permanently inundated marshes. The duration of anoxia in the sediment caused differences in the CH4 flux. Estimated emissions for the period 1 June – 30 September in continuously inundated sparse reed and sedge marshes, drying sedge marsh, and lacustrine sedge fen were 13, 11 and 6 g CH4 m–2, respectively. 3. In continuously inundated vegetation, the fluxes were highest in late July/early August. The seasonal CH4 flux pattern suggested that the fluxes were regulated by the supply of organic matter during the course of the summer and the water level. In the temporarily flooded zone, the seasonal CH4 flux dynamics was greatly affected by changes in the lake water level, the fluxes being highest during the spring flood in early June.

High methane emissions from a littoral zone on the Qinghai-Tibetan Plateau

“…In the present study we also found that CH 4 efflux from the littoral zone of Huahu Lake on the Qinghai-Tibetan Plateau was relatively high among those of boreal and temperate lakes (Juutinen et al, 2001, Kankaala et al, 2003, Wang et al, 2006; summarized in Table 4) and higher than those from alpine wetlands in the same region (Hirota et al, 2004;Chen et al, 2008). This may be partly attributed to high dissolved organic carbon (DOC) input from nearby peatlands, whose soil is rich in organic carbon on the Qinghai-Tibetan Plateau (Wang et al, 2002).…”

“…The littoral zone of lakes has been regarded as hotspots of CH 4 fluxes through several studies (Juutinen et al, 2001;Kankaala et al, 2003;Wang et al, 2006;Hirota et al, 2007). In the present study we also found that CH 4 efflux from the littoral zone of Huahu Lake on the Qinghai-Tibetan Plateau was relatively high among those of boreal and temperate lakes (Juutinen et al, 2001, Kankaala et al, 2003, Wang et al, 2006; summarized in Table 4) and higher than those from alpine wetlands in the same region (Hirota et al, 2004;Chen et al, 2008).…”

“…Among them wetlands are considered the most important source. However, recent studies on CH 4 effluxes from littoral wetlands, mainly of boreal lakes (Juutinen et al, 2001;Kankaala et al, 2004;Duan et al, 2005;Wang et al, 2006;Bergstrom et al, 2007) suggest that the importance of the littoral zones of the lakes as one of the major natural sources of atmospheric CH 4 may have been underestimated. Therefore, we need more researches on the littoral zones of lakes to get more accurate estimate of CH 4 effluxes.…”

“…However, in sparse stands and non-vegetated areas, bubbling and diffusion are more important mechanisms of CH 4 transport (Chanton and Dacey, 1991;Van Der Nat and Middelburg, 1998;Kankaala et al, 2004). Due to the above-mentioned complicated biogeochemical processes in the littoral zone, CH 4 fluxes from the lake littoral zones may differ considerably with even a short (1-50 m) distance (Juutinen et al, 2001;Kaki et al, 2001).…”

Summer fluxes of methane and carbon dioxide from a pond and floating mat in a continental Canadian peatland

“…Ebullition appears to be of particular importance for CH 4 release to the atmosphere (Walter et al, 2006;Wik et al, 2013) and varies on scales of several tens to hundreds of meters (Bastviken et al, 2004;Wik et al, 2013). Emissions of CH 4 are generally lower in the pelagic than in the littoral zone, where plant habitats further influence fluxes (Juutinen et al, 2001;Larmola et al, 2004). On the other hand, Trudeau et al (2013) found 2.5 to 5 times lower CH 4 fluxes at the border of fen pools than in the center of the pools with areas of 60 and 200 m 2 .…”