| 其他摘要 | Increase in concentration of green house gases (GHG) in the atmosphere will affect the climate，environment and the human’s activity, so much attentions are paid to the sources and sinks of the GHG. Damming the river, as an important impact of human’s activities on the concentration of the GHG in the atmosphere, has been concerned by more and more researchers. The distributions of the main GHG (CO2﹑CH4﹑N2O) in the two reservoirs s(Hongfeng Lake and Baihua Lake) located near Guiyang, a capital city of Guizhou Province, southwest China during different months have been analyzed and the factors that may affect the variability of them are discussed in combination with the special hydrological environment in the two reservoirs, in order to illustrate the mechanisms of the CO2, CH4, N2O in the water column of the two reservoirs. Conclusions are as following:
1. Due to the similarity of geography and climate, the variations of the pCO2 in the two reservoirs are similar: the pCO2 in the two reservoirs are higher than the partial pressure of CO2 in the atmosphere during June and August, but lower in the other sampling periods. On the annual scale, the pCO2 in the surface water of the Hongfeng Lake is 874.2±774.4µatm, and that of Baihua Lake is 1131.7±1164.0µatm, both can be sources of the atmospheric CO2. The negative relationship between Chla and pCO2 suggests that the photosynthesis and the respiration are the main factors that affect the seasonal variability of the pCO2 in the two reservoirs.
2. The degradation of organic matter produced by the photosynthesis in summer season cause the sharp increase of CO2 in the metalimnion. And the degradation of the organic matter in the sediments had important effect on the accumulation of CO2 in the hypolimnion, which were weaker during autumn and winter, and might have be related to the water temperature. In addtion, the CO2 accumulated in the hypolimnion during summer was returned to the water column by the mixing of the water during autumn and the pCO2 in the surface water increased.
3. In comparison with the other researches reported previously, we found that: (1) the CO2 in the surface waters of the Hongfeng and Baihua Lakes is smaller than the boreal temperate lakes, and contribution to the sources of the CO2 in the atmosphere are smaller due to their situation in the karstic moutain region and the limited input of the terrestrial organic matter; (2) the two reservoirs became the source of the CO2 in the atmosphere during summer because of the eutrophication of the lake, and the CO2 in the surface waters were lower than the boreal temperate lakes. It is suggested that return of the CO2 fixed by the photosynthesis are less.
4. The CH4 concentrations in the surface water of the two reservoirs during the low flow period are more than those during the high flow period, but the two reservoirs are always the source of atmospheric CH4 during all of the sampling periods. On the annual scale, the CH4 concentration of the surface water in the HF-N and HF-S were0.19±0.09µmol/L and 0.48±0.53µmol/L, respectively; the CH4 concentrations of the surface water in the BH-1 and BH-2 were 0.32±0.29µmol/L, 0.29±0.20µmol/L, respectively. The variability of the CH4 concentrations in surface water of the two reservoirs may due to (1) the longer retention time of the water in the reservoir that promoted the accumulation of CH4 during the low flow period; (2) the increase of the DO by the photosynthesis that caused the oxidation of CH4 in the surface water during the high flow period.; (3) the increase of the inflow and precipitation during the high flow period that may result in the dilution of CH4 in the surface water of the two reservoirs.
5. The CH4 concentrations in the bottom water of the two reservoirs are more during the high flow period than the low flow period. On the annual scale, the CH4 concentration of the bottom water in the HF-N and HF-S were 16.49±26.16µmol/L and 8.80±15.30µmol/L; respectively, while those in BH-1 and BH-2 were 6.03±7.07µmol/L and 4.41±7.00µmol/L, respectively. The temperature and oxic-anoxic environment in the bottom and the organic matter produced by the photosynthesis by photoplankton during summer were the mail factors that affect the production of CH4 in the bottom of the two reservoirs. In addition, SO42- may restrain the production of CH4 in the bottom of the reservoirs.
6. The primary production in the epilimnion and the degradation in the sediments had effects on the CH4 in the water column during summer. And thermal stratification and anoxic environment promote the accumulation of CH4 in the hypolimnion, which were oxidized during autumn when the water were mixed and oxygen in the water column increased.
7. The N2O concentrations in the surface water during summer were significantly lower than those in the other seasons, but the N2O in the surface water of the two reservoirs during all the sampling periods were sources of the N2O for the atmosphere. On the annual scale, the N2O concentrations in the surface water at two sampling sites of the Hongfeng Lake were 46.31±29.65nmol/L, 36.93±18.41nmol/L, respectively; those at two sampling sites in the Baidu Lake were 102.13±79.53nmol/L，99.51±75.77nmol/L, respectively. Nitrification affected by water temperature, DO and NO3- was the main mechanism that resulted in the production of N2O in the surface water of the two reservoirs.
8. By comparing the distribution of N2O with NO3-, NH4+ in the water column, we found that nitrification prevailed in the water column in the Hongfeng Lake during spring and in the epilimnion of the two reservoirs during summer, and denitrification prevailed in the bottom of the two reservoirs during summer. Although there happened nitrification or denitrification in some sampling site, the mixing of the water was the main mechanism that affects N2O in the two reservoirs during winter. |
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