The change of gaseous carbon fluxes following the switch of dominant producers from macrophytes to algae in a shallow subtropical lake of China

Successions of lake ecosystems from clear-water, macrophyte-rich conditions into turbid states with abundant phytoplankton have taken place in many shallow lakes in China. However, little is know about the change of carbon fluxes in lakes during such processes. We conducted a case study in Lake Biandantang to investigate the change of carbon fluxes during such a regime shift. Dissolved aquatic carbon and gaseous carbon (methane (CH4) and carbon dioxide (CO2)) across air-water interface in three sites with different vegetation covers and compositions were studied and compared. CH4 emissions from three sites were 0.62 +/- 0.36, 0.70 +/- 0.36, and 1.31 +/- 0.57 mg m(-2) h(-1), respectively. Correlation analysis showed that macrophytes, rather than phytoplankton, directly positively affected CH4 emission. CO2 fluxes of three sites in Lake Biandantang were significantly different, and the average values were 77.8 +/- 20.4, 52.2 +/- 14.1 and 3.6 +/- 26.8 mg m(-2) h(-1), respectively. There were an evident trend that the larger macrophyte biomass, the lower CO2 emissions. Correlation analysis showed that in different sites, dominant plant controlled CO2 flux across air-water interface. In a year cycle, the percents of gaseous carbon release from lake accounting for net primary production were significantly different (from 39.3% to 2.8%), indicating that with the decline of macrophytes and regime shift, the lake will be a larger carbon source to the atmosphere. (c) 2006 Elsevier Ltd. All rights reserved.

Methane and carbon dioxide fluxes from a shallow hypereutrophic subtropical Lake in China

Up to now, there have been few studies in the annual fluxes of greenhouse gases in lakes of subtropical regions. The fluxes of methane (CH4) and carbon dioxide (CO2) across air-water interface were measured in a shallow, hypereutrophic, subtropical Lake Donghu (China) over a year cycle, using a static chamber technique. During the year, Lake Donghu emitted CH4 and CO2; the average flux of CH4 and CO2 was 23.3 +/- 18.6 and 332.3 +/- 160.1 mg m(-2) d(-1), respectively. The fluxes of CH4 and CO2 showed strong seasonal dynamics: CH4 emission rate was highest in summer, remaining low in other seasons, whereas CO2 was adsorbed from the atmosphere in spring and summer, but exhibited a large emission in winter. Annual carbon (C) budget across air-water interface in Lake Donghu was estimated to be 7.52 +/- 4.07 x 10(8) g. CH4 emission was correlated positively with net primary production (NPP) and temperature, whereas CO2 flux correlated negatively with NPP and temperature; however, there were no significant relationships between the fluxes of CH4 and CO2 and dissolved organic carbon, a significant difference from boreal lakes, indicating that phytoplankton rather than allochthonous matter regulated C dynamics across air-water interface of subtropical lake enriched nutrient content. (c) 2005 Elsevier Ltd. All rights reserved.

Diel variation of methane fluxes in summer in a eutrophic subtropical lake in China

The summer diel variation of methane (CH4) flux was investigated in a eutrophic, subtropical lake in China. The CH4 concentration was always supersaturated, and the emission rate ranged from 0.24 to 45.51 mg m(-2) h(-1). The diel variations of CH4 flux in June and August showed a single peak in early afternoon and a minimum in the morning, while the pattern varied irregularly in May. There was a moderate relationship between water and sediment temperature and CH4 emission rate in some months.

Microscopic three-body forces and kaon condensation in cold neutrino-trapped matter

We investigate the composition and the equation of state of the kaon condensed phase in neutrino-free and neutrino-trapped star matter within the framework of the Brueckner-Hartree-Fock approach with three-body forces. We find that neutrino trapping shifts the onset density of kaon condensation to a larger baryon density, and reduces considerably the kaon abundance. As a consequence, when kaons are allowed, the equation of state of neutrino-trapped star matter becomes stiffer than the one of neutrino free matter. The effects of different three-body forces are compared and discussed. Neutrino trapping turns out to weaken the role played by the symmetry energy in determining the composition of stellar matter, and thus reduces the difference between the results obtained by using different three-body forces.

Fluxes of CO2,CH4 and N2O from alpine grassland in the Tibetan Plateau

Using static chamber technique,fluxes of CO2,CH4 and N2O were measured in the alpine grassland area from July 2000 to July 2001,determinations of mean fluxes showed that CO2 and N2O were generally released from the soil,while the alpine grassland accounted for a weak CH4 sink.Fluxes of CO2,CH4 and N2O ranged widely.The highest CO2 emission occurred in August,whereas almost 90?of the whole year emission occurred in the growing season.But the variations of CH4 and N2O fluxes did not show any clear patterns over the one-year-experiment.During a daily variation,the maximum CO2 emission occurred at 16:00,and then decreased to the minimum emission in the early morning.Daily pattern analyses indicated that the variation in CO2 fluxes was positively related to air temperatures(R^2=0.73)and soil temperatures at a depth of 5 cm(R^2=0.86),whereas daily variations in CH4 and N2O fluxes were poorly explained by soil temperatures and climatic variables.CO2 emissions in this area were much lower than other grasslands in plain areas.

Short-term effect of increasing nitrogen deposition on CO2, CH4 and N2O fluxes in an alpine meadow on the Qinghai-Tibetan Plateau, China

National Key Research and Development Program [2010CB833500]; Natural Science Foundation of China [30590381]; Knowledge Innovation Project of Chinese Academy of Sciences [KZCX2-YW-432]