Studies On Carbon Cycling And Budget In Lake Donghu

Carbon cycling and budget in the shallow, eutrophic Lake Donghu were studied from April 2003 to March 2004. This thesis mainly included:1) the fluxes of carbon dioxide and methane across water-air interface, 2) seasonal changes in DOC ( dissolved organic carbon ), TOC( total organic carbon ) and DIC( dissolved inorganic carbon ) in the water column, and 3) carbon budget of the whole lake. The main results and conclusions are as follows:Methane concentration in the lake water was always supersaturated and the methane emission rate at Stations I , II and III was 0.97, 1.071 and 1.136 mg m-2 h"1, respectively. Most of the methane emission took place in the summer. There was no significant relationship between methane flux across water-air interface and trophic level, but the maximum emission was associated with high trophic level. Temperature significantly promoted methane emission. There was great variation in carbon dioxide flux across water-air interface, and the average emission rates of carbon dioxide at Stations I , II and HI were 9.87, 13.33, 26.06 mg m-2 h-1, respectively. There was a negative relationship between carbon dioxide fluxes across water-air interface and trophic levels, but there was no significant relationship between carbon dioxide fluxes across water-air interface and temperature.The average concentrations of DOC, TOC and DIG in the water column were 7.31, 8.78 and 11.89 mg/L, respectively. The concentrations of both DOC and TOC were the highest in autumn, whereas the DIG concentration was higher in spring andsummer than in autumn and winter. Based on cluster and principal composition analyses, the carbon concentrations in the water column were divided into three groups: 1) highest concentrations of DOC and TOC due to higher temperature and trophic level, 2) medium concentrations of DOC and TOC, and 3) lowest DOC and POC values due to strong rainfall.Using inventory method, the carbon budget of Lake Donghu during April 2003 and March 2004 were estimated from water-air, water-land and water-sediment interfaces. Lake Donghu was a sink of carbon (8018.9t in total). The gaseous carbon released from the water-air interface was 880.2t, accounting for 22.6% of the total outflow. Compared with other lakes (e.g., Lake Ontario), this proportion was small. Compared with wetlands in San Jiang Plain, the water-air interface of Lake Donghu is a smaller source of carbon.