水库热分层期藻类水华与温跃层厌氧成因分析

Algal Bloom and Mechanism of Hypoxia in the Metalimnion of the Lijiahe Reservoir During Thermal Stratification

以西安市李家河水库为研究对象,通过对水体理化因子和浮游植物的连续监测,对热分层期藻类垂向分布与温跃层厌氧成因进行了初步分析.结果表明:①6～9月,李家河水库水体稳定指数为2～10 m^(-1),处于稳定热分层状态,水体溶解氧呈明显的垂向以及季节差异,p H、电导率均与溶解氧呈现相同的分层结构;②李家河水体的富营养状态诱导夏季藻类水华暴发;藻细胞密度垂向差异大,集中悬停于水深0～5 m区域内,最高为2. 95×10~8cells·L^(-1),叶绿素a含量最大为46. 42mg·m^(-3);高密度藻类在温跃层内堆积分解,水深5～24 m内出现较大面积的厌氧区,pH下降、电导率和高锰酸盐指数升高;③高密度藻类分解耗氧是夏季分层期温跃层厌氧形成的主要原因.

The present study was completed at the Lijiahe Reservoir in Xi’an,northwest China.Based on persistent monitoring of the physical and chemical indexes,in addition to phytoplankton activity,the correlation between phytoplankton distribution and dissolved oxygen depletion in metalimnion were analyzed during the thermal stratification periods.The results showed that:①During the summer stratification(from June to September),an obviously steady structure of dissolved oxygen,p H,as well as conductivity,was formed in a water column with RWCS/H indexes between 2 and 10 m-1.②The algal bloom was induced by the intense stratification with maximum biomass concentration of 2.95×108 cells·L-1 and chl.a of 46.42 mg·m-3.With a sharp density gradient due to thermal stratification,the decayed algae cells accumulated above the metalimnion and largely consumed the dissolved oxygen,which affected the p H,conductance,as well as the permanganate index.③Decomposition of high-density algae was,therefore,the main cause of metalimnion hypoxia during the summer stratification periods.