Methane emission to the atmosphere and cycling in a shallow eutrophic lake
Nakamura, Takeshi; Nojiri, Yukihiro; Utsumi, Motoo; Nozawa, Takeshi; Otsuki, Akira
published: Mar 24, 1999
ArtNo. ESP141014404005, Price: 29.00 €
Methane (CH4) emission to the atmosphere and cycling were studied in Lake Kasumigaura, a shallow eutrophic lake without an anaerobic hypolimnion, to examine whether such lakes could be important sources of methane emission. Concentrations of dissolved CH4 in the water column ranged from 13 to 3,500 nM. A distinct seasonal pattern was observed, with higher CH4 concentrations in late summer and winter, and lower concentrations in late autumn and spring. Generally higher concentrations were found at the shallower sampling sites near the inputs of polluted rivers. Estimates of diffusive fluxes from the lake surface to the atmosphere varied from 0.54 to 28 mg CH4 m-2 d-1, peaking in summer when both dissolved CH4 concentrations and water temperatures were high. Concentrations of CH4 in the pore water in the upper 10 cm of bottom sediment fluctuated from 0.001 to 2.8 mM and were highest from summer to autumn. Bubble flux by ebullition ranged from 0 to 243 mg CH4 m-2 d-1 and was estimated to occur only from July to October when the pore water in the bottom sediment was more than about half saturated with CH4. CH4 production in the bottom sediment and bacterial oxidation of CH4 in the surface layer of the bottom sediment in 1993 were estimated from 17 to 300 mg CH4 m-2 d-1 and 15 to 120 m. CH4 m-2 d-1, respectively. The daily CH4 flux to the atmosphere from Lake Kasumigaura in 1993 averaged 31 mg CH4 m-2 d-1 The present study suggested that shallow eutrophic lakes without an anaerobic hypolimnion might not be important sources of atmospheric CH4 despite the high primary production by cyanobacterial blooms in summer that are caused by huge nutrient loading resulting from human activities.