西安黑河金盆水库季节性热分层的水质响应特征

Response characteristics of water quality to the seasonal thermal stratification in Jin-pen reservoir along the Heihe river,Xi'an city in China

以西安市金盆水库为对象,通过对水温、水化学及水生生物因子的连续监测,初步探明其动态水体分层过程与季节性水质迁移分布的内在相关性。研究表明:水库于每年3—12月间形成并保持热分层状态,水温梯度的稳定存在有效限制了垂向水层间氧的传质交换,加速库底向厌氧状态过渡,滞水层溶解氧(DO)平均浓度随时间呈明显线性衰减趋势,水层呼吸速率高达0.0356～0.0372mg/(L·d)(O_2);缺氧/厌氧环境下,沉积物中N、P、Fe等大量释放并向上覆水扩散,底层水质污染加剧。同温混合期后(1—2月),分层结构破坏,全库处于好氧(DO大于8mg/L)、微碱性(pH为7.1～7.3)状态,垂向水质分层异质特征消失。监测期间,水库湖泊区稳态叶绿素a含量(基于Lois Elle稳态假设前提)随混合深度增大而降低,两者存在显著指数负相关。热分层效应的稳定存在是加速金盆水库富营养化进程的重要因素;而其周期性结构失稳所带来的水质突发性污染风险将伴随水库运行时间的延长而上升。

By taking Jin-pen reservoir of Xi＇ an City in China as the main research object, vertical wa- ter-quality monitoring was carried out monthly in order to investigate the correlation between thermal stratification and seasonal water-quality variance. The results show that during thermally stratified period from March to December, the steady temperature gradient could effectively restrict oxygen transfer and exchange among the vertical water layers, which accelerates water at the bottom to anaerobic state. The average concentration of dissolved oxygen （DO） in the hypolimnion shows a linear decline with time,and the average oxygen consumption rate of water here is as high as 0.0356-0.0372mg/（L.d）（O2）, which has caused accel- erating release of pollutants such as nitrogen, phosphorus and iron from sediments to overlying water and deterioration of water pollution. During the isothermally mixed period, the understable failure of stratification structure occurs. The whole reservoir is in aerobic （DO〉8mg/L） and slight alkaline （pH：7.1-7.3） state, moreover, the water quality becomes homogeneous under the influence of convective mixing among vertical water layers. During the whole monitoring period, the steady chlorophyll-a content （based on Lois Elle＇s steady state assumption） has negative exponential correlation with mixing depth and varies in unimodal form. The existence of thermal stratification in Jin-pen reservoir is considered a promotion factor for increasing water eutrophication. In addition, with the running time extension of reservoir, the risk of sudden water pollution caused by understable failure of stratification would increase.