深水水库磷的生物地球化学循环

BIOGEOCHEMICAL CYCLING OF PHOSPHORUS IN DEEP-WATER RESERVOIRS

我国水能资源居世界第一。密集的水电开发形成数量庞大的梯级水库群,成为我国淡水资源最重要的存储形式之一。在这些水库中,磷的来源、生物地球化学循环过程与生态环境效应独具自身特点,但相关研究较为薄弱。本文以西南地区典型水库为例,系统地阐明了水库水体和沉积物中磷的赋存形态、时空变化特征、迁移转化规律及生物可利用性。随着国家水环境保护工作的有力推进,我国水库水体总磷(TP)浓度(0.02~0.21 mg/L)呈持续降低趋势。统计结果表明,水库水体叶绿素a(Chl.a)与TP浓度呈显著正相关,表明水库藻类生长仍主要受TP浓度的影响。相较于中国东部浅水湖泊,西南地区水库沉积物中TP含量通常更高(均值>1300 mg/kg),且活性磷组分(氧化还原敏感态磷:BD-P;Fe/Al结合态磷:NaOH-P;弱吸附态磷:NH4Cl-P)占比超过50%。高分辨率观测发现,西南水库在夏季分层期显示出更高的内源磷释放速率(0.15~0.29 mg/(m^(2)·d)),远高于东部浅水湖泊(0.09~0.15 mg/(m^(2)·d))。季节性缺氧诱导的Fe/Mn结合态磷的还原溶解是水库沉积物内源磷释放的关键机制。此外,还论述了加强水库磷生物地球化学循环研究的重要意义,并提出了未来重点研究方向。

China's hydropower resources rank first in the world.The large number of cascade reservoirs formed by the intensive hydropower development is one of the most important storage forms of freshwater resources in China.In these reservoirs,the sources,biogeochemical cycles and its eco-environmental effects of phosphorus(P)have their own characteristics,but the related research is scare.In this study,taking typical reservoirs(Hongfeng(26°26'~26°35'N,106°19'~106°28'E),Baihua(26°35'~26°41'N,106°27'~106°32'E)and Aha(26°30'~26°34'N,106°37'~106°40'E)reservoirs with areas of 57.2 km^(2),14.5 km^(2)and 3.4 km^(2),and average depths of 10.5 m,10.8 m and 13.0 m in Southwest China)as examples,the P fraction in the sediment,the P concentration of the water,and the water quality parameters were determined respectively by chemical sequential P extraction method,spectrophotometric method and a multi-parameter water quality monitor(YSI 6600-V2,YSI Inc.,Yellow Springs,USA).The occurrence forms,temporal and spatial variation characteristics,migration and transformation rules and bioavailability of P in reservoir water and sediment were systematically clarified.The results indicated that:(1)With the development of national water environment protection,the concentration of total phosphorus(TP)in reservoir water(0.02~0.21 mg/L)presents a continuous decreasing trend;(2)In the reservoir water,Chl.a was significantly positively correlated with TP concentration,indicating that algae growth in the reservoirs was still mainly controlled by TP;(3)Compared with the eastern shallow reservoirs,the TP content in reservoir sediments in Southwest China is usually higher(mean>1300 mg/kg),in which the proportion of active P components(redox sensitive P:BD-P,Fe/Al bound P:NaOH-P,loosely adsorbed P:NH4Cl-P)accounts for more than 50%;(4)High resolution observation showed that the reservoirs have higher internal P release rates(0.15~0.29 mg/(m^(2)·d))in summer stratification period,which was much higher than that of shallow lakes in Eastern China(0.09~0.15 mg/(m^(2)·d));(5)Seasonal anoxia induced reductive dissolution of Fe/Mn bound P is the key mechanism of internal P release from sediments.In addition,the significance of the study on the biogeochemical cycle of P in reservoirs was emphasized,and the future research direction was proposed.