三峡水库不同运行状态下支流澎溪河水-气界面温室气体通量特征初探

水电是具有显著减排效益的清洁能源形式,但水库潜在的温室气体效应近年来备受关切,在一定程度上影响了人们对水库清洁能源属性的认识.本研究分别于2010年8月水库低水位运行期及12月高水位运行期,对三峡库区典型支流——澎溪河上游温泉至下游双江6个沿程断面进行水样的采集及温室气体通量的监测研究.结果表明,在河流纵向上,表层水体水温、pH逐渐沿程增加,而CO2分压(pCO2)和碱度(TA)则有相反趋势.在低水位的8月,开县以下断面CO2通量为负,且浮游植物可能是控制水体CO2通量及营养盐的关键因素之一.澎溪河回水区CO2通量相对天然河道背景断面(温泉)平均降低了3.26 mmol.(m2.h)-1,而CH4通量却大幅度增加了.在高水位运行的12月,澎溪河各断面均为CO2释放通量,CH4通量相比低水位则明显降低.相比较天然河道的温泉断面,澎溪河回水区在高水位运行状态下CO2与CH4通量分别增加了4.16mmol.(m2.h)-1和0.007 mmol.(m2.h)-1.初步的净通量分析发现,该水域较加拿大实验水库的净通量特征低.

Air-Water Surface Greenhouse Gas Flux in Pengxi River at Different Operational Stages of the Three Gorges Reservoir

Impoundment of the Three Gorges Reservoir has not only changed the ecosystem structure and biogeochemical processes of the major elements, but also affected the GHG flux intensity in air-water interface of Pengxi River. In this study, six water samples were collected and GHG fluxes were monitored from upstream of Wenquan spot to downstream of Shuangjiang spot in low water level period in August and high water level period in December, respectively. The results show the surface water temperature, pH and DO gradually increase along the river, but was opposite for pCO₂ and TA. Downstream of Kaixian spot, the water was a sink of CO₂.Regression analysis showed that for the surface water, phytoplankton growth and metabolism were key factors in controlling CO₂ flux. Preliminary analysis of net flux shows that in August the average of CO₂flux reduced 3.26 mmol·(m²·h)^-1 in backwater area, however, CH₄ flux significantly increased. In high water level operational modes, only surface water temperature and pH gradually increased along the river, pCO₂, TA and DO were opposite. The entire river as a source of CO₂ and CH₄ fluxes was significantly lower compared to the low water level. Characteristics of net flux shows that during high water level period in December, CO₂and CH₄flux increased 4.16 mmol·(m²·h)^-1 and 0.007 mmol·(m²·h)^-1, respectively.