Summertime fluxes of N2O, CH4and CO2from the littoral zone of Lake Daming, East Antarctica: effects of environmental conditions

Nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2) fluxes were investigated from the algal-rich littoral zone of Lake Daming, East Antarctica during the summers of 2008/09 and 2009/10, using a static chamber technique. High N2O emissions occurred in the littoral zone with the mean flux range of 0.19–7.11 μmol N2O m-2h-1. The mean CH4fluxes ranged from 2.51–5.32 μmol CH4m-2h-1, and they were significantly affected by the lake thermal regime. There were significant differences (P< 0.05) in CH4and N2O fluxes under the light and dark conditions, and sunlight greatly increased N2O emissions by stimulating the algal photosynthesis, but decreased CH4emissions. Overall the littoral zone represented a weak CO2sink with the mean flux range of -0.37–0.13 mmol CO2m-2h-1. The mean ecosystem respiration and photosynthesis rates varied from 0.47–2.90 mmol CO2m-2h-1and from -0.33 to -2.63 mmol CO2m-2h-1. The combined global warming potential (GWP) of N2O and CH4fluxes completely counteracted and surpassed CO2uptake by the algal photosynthesis, and high GWP-positive of N2O and CH4emissions might convert an algal-rich lake site with a net CO2uptake into a net radiative forcing source during the ice-free period.

Release of ²²²Rn from some soils

Measurements have been made of 222Rn release from diverse soils in the region surrounding Málaga, Spain. These flux measurements were carried out by two methods. A direct method using a static chamber technique and another indirect method obtained from concentration profile measurements of 222Rn in the soil air. The effects of meteorological variables and other parameters on 222Rn flux were studied. The factors that most affected the instantaneous value of 222Rn release were humidity and soil thermal gradient. The directly measured 222Rn fluxes at investigated sites are higher than 222Rn fluxes derived by the indirect method.

SHORT COMMUNICATION: Methane emission from a usually well-drained prairie soil after snowmelt and precipitation

Usually well-drained soils, when they are flooded periodically, are a sporadic source for greenhouse gases such as methane. Using a static chamber technique in the field, we found methane emission, which ranged from 7.8 (cultivated site) to 10.5 mg m−2 d−1 (grassland site), from the lower slope positions after snowmelt in the spring. Smaller methane emission was also observed after rainfall in the summer: 0.02–0.64 mg m−2 d−1 after 23–79 mm of precipitation. Key words: Methane emission, spring snowmelt, short-term flooding

Microtopography and methane flux in boreal peatlands, northern Ontario, Canada

Fluxes of methane were measured by a static chamber technique at hummock, hollow, and lawn microtopographic locations in 12 peatland sites near Cochrane, northern Ontario, from May to October 1991. Average fluxes (mg∙m−2∙d−1) were 2.3 (SD = 1.9) at hummocks, 44.4 (SD = 49.0) at hollows, and 15.6 (SD = 12.9) at lawns. Methane flux was negatively correlated with average water table position based on the 36 locations (r2 = 0.649, p < 0.001), with hummocks having a smaller flux than hollows or lawns, where the water table depth was < 25 cm. Peat samples from a bog hummock and hollow failed to produce methane during anaerobic incubations in the laboratory; samples from a poor fen hollow produced < 1.4 μg∙g−1∙d−1. The production decreased with depth but was greater than the rates observed during the incubation of samples from an adjacent hummock. Rates of methane consumption during aerobic incubations ranged from 1 to 55 μg∙g−1∙d−1 and were greatest in the surface layers and decreased with depth. Differences in methane emissions between hummocks and hollows appear to be controlled primarily by greater methane production rates in hollows compared with hummocks. Of secondary importance are the capacity of the peat profiles to consume methane during its transport to the peat surface and warmer temperatures at the water table beneath hollows compared with hummocks. Key words: peatlands, methane, bog, fen, decomposition.