西南峡谷型水库的季节性分层与水质的突发性恶化

Thermal Stratification and Paroxysmal Deterioration of Water Quality in a Canyon-Reservoir,Southwestern China

选择西南云贵高原乌江流域的百花湖水库进行了气象、水温度和水化学(DO、FeⅡ和MnⅡ)的连续监测(13个月).结果表明,由于气候等原因,百花湖水库的水体在夏季形成分层,但是没有典型分层湖泊的温跃层变化,这种水体温度结构可以在4-10月保持稳定;这种"不显著的"温度分层结构,有效限制了上下水团的混合,形成显著的水体溶解氧分层,氧化/还原界面可达到水深8m左右.20世纪90年代初以来,贵州多座水库频繁出现的季节性水质恶化现象,与水库水体混合期(多为夏末初秋),水体分层结构失稳有关.上下层水体的垂直交替,使下层水体中的还原性物质带入上层湖水,造成表层水体缺氧和表观浑浊,鱼类窒息死亡.在百花湖水库的研究表明,西南地区深水水库,可以在夏季出现一定的水体温度分层结构,并导致显著的水体水化学(如溶解氧)分层,进而影响水库水环境质量.

In order to elucidate factors controlled the water column stratification in canyon-reservoirs, and describe the relative response of water quality, we present a 13-month survey and study of meteorological, physical and hydro chemical patterns during 2001 in a canyon-reservoir, southwestern China, especially including a intensive frequency study during the period from August to November of this year in which an event of water quality abruptly degeneration occurred. The study showed that: an obscure thermal stratification has been formed on vertical profile of water column during summer (about from April to October) in Baihua Lake reservoir, however, it could cause the very strong hydro chemical stratification (i. e. dissolved oxygen stratification) in same period in water column of the reservoir. During summer of 2001, the oxide-reduce interface could move up to 8 meter-depth from bottom of Baihua Lake reservoir. The survey results also confirmed that gravitationally unstable of the thermal stratification caused by surface cooling of water when the air temperature decreased abruptly in early fall, leaded to a vertical convection between the upper layer water and deep layer water. The reductants (e.g. Mn2+ , Fe2+ and H2 S ) formed in the anoxic hypolimnion companying with processes of organic maters degeneration would be brought to the epilimnion through the vertical eddy diffusion. These reductive matters would consume up the dissolved oxygen in the utter water rapidly as if such oxidization reactions were strong enough, and than a large number of aquatic organism dead due to oxygen deficient. This study showed that the seasonal thermal stratification, although not strong like typical alpine lakes, could play a key role in change of water quality in canyon-reservoirs.