Methanotrophic activity in relation to methane efflux and total heterotrophic bacterial production in a stratified, humic, boreal lake

Abstract

We studied methanotrophic activity in the water column in relation to heterotrophic bacterial production and efflux of methane (CH 4 ) from the lake surface in a small, stratified, humic, boreal lake (Valkea-Kotinen, southern Finland). During summer and winter stratification, the highest methanotrophic activities were in the metalimnion, where oxygen concentration was Ͻ6 mmol m Ϫ3 . During an incomplete spring turnover and summer stratification period, 3-5 times more CH 4 was consumed by methanotrophs in the water column than was released to the atmosphere. The highest CH 4 effluxes (1.2-5.1 mmol m Ϫ2 d Ϫ1 ) to the atmosphere occurred during the autumnal turnover despite observed methanotrophic activity in the whole water column. In winter, the amount of CH 4 consumed by methanotrophs (0.20 mol CH 4 m Ϫ2 during 6.5 months) was of the same order of magnitude as that during the ice-free period (0.22 mol CH 4 m Ϫ2 during 5.5 months). Annually ϳ80% of CH 4 diffused from the sediment was consumed by methanotrophs in the water column, and only 20% (0.11 mol CH 4 m Ϫ2 yr Ϫ1) was released to the atmosphere. During the ice-free period, bacterial production measured as [14 C]leucine uptake showed a bell-shaped relation to CH 4 concentration. The highest production was found in the metalimnion at CH 4 concentrations ranging from 5 to 10 mmol m Ϫ3. During summer stratification, net production of methanotrophs corresponded to 23-47% of total bacterial production, but during the autumn turnover, this proportion was higher (27-81%), indicating that methanotrophs offer a potentially significant source of carbon to zooplankton in stratified humic lakes.

Fossil chironomid δ13C as a proxy for past methanogenic contribution to benthic food webs in lakes?

“…Amongst such remains are cladoceran ephippia, head capsules of non-chironomid midge larvae such as Ceratopogonidae, Simuliidae, or Thaumaleidae and mites. Indeed, methane-derived carbon has been detected in Daphnia biomass in modern lake ecosystems with d 13 C values reported as low as -50.3% (Jones et al 1999;Kankaala et al 2006;Taipale et al 2007). Fossil ephippia of the cladoceran Daphnia from the Slotseng sediments show d 13 C values between -28.0 and -26.5% (Table 2).…”

Developmental Changes in the Historical and Present-Day Trophic Status of Brown Water Lakes. Are Humic Water Bodies a Uniform Aquatic Ecosystem?

“…Existence of both the humic lake and the wetland is mutually related and shaped by a complex of biogeochemical processes (Fenner and Freeman 2013). Optimum conditions for forming of these lakes occur in northern regions of the world, with a cool, humid climate (Salonen et al 1983;Kankaala et al 2006). Among humic lakes those from Northern America and Europe are the most extensively studied featuring in numerous scientific monographs (Hessen and Tranvik 1998;Findlay and Sinsabaugh 2003;Steinberg 2003).…”

Connecting silvan and lacustrine ecosystems: transport of carbon from forests to adjacent water bodies

“…In Valkea-Kotinen, 80% of the CH 4 produced in sediments was oxidised in the water column and the annual CH 4 flux was 1.3 g C m -2 yr -1 (Kankaala et al 2006). Even though the CH 4 emissions from lakes can be important in terms of climate change, as the global warming potential of CH 4 is 25 times greater than that of CO 2 (Forster et al 2007), the contribution of CH 4 to carbon fluxes and carbon cycling in general is minor (Bastviken et al 2004, Huotari 2011.…”

“…The CO 2 exchange between lake and atmosphere resulted in a flux of 3200 kg C yr -1 to the atmosphere. In addition, the CH 4 flux of 54 kg C yr -1 (Kankaala et al 2006) contributed to the export to the atmosphere. The other outputs from the lake were sedimentation (115 kg C yr as DIC) (Fig.…”