周村水库主库区热分层初期氮素降低的驱动因子分析

为了探究周村水库热分层前期氮素的变化趋势及其驱动因子,于2016年2~4月定期对周村水库主库区进行水质指标监测,并在采样点采集新鲜水样和表层沉积物,实验室模拟水库氮素变化过程中,水体和沉积物的反硝化作用量.结果表明周村水库在热分层初期,库区总氮浓度由(2.28±0.09)mg·L~(-1)降至(1.08±0.09)mg·L~(-1),硝氮浓度由(1.66±0.09)mg·L~(-1)降至(0.25±0.06)mg·L~(-1),氨氮浓度总体变化不大,亚硝氮的浓度几乎不变.与此同时,叶绿素没有明显增加,藻类的影响不大;氮素降低主要由于好氧反硝化菌的反硝化作用造成.热分层初期水库的温度逐渐增加、DO、pH的变化以及以小分子量为主的有机物组成均利用好氧反硝化菌的生长繁殖,菌数从1.06×105cfu·L~(-1)增加到8.33×106cfu·L~(-1),使得水库的反硝化作用增强,水库氮素下降;与此同时的模拟实验中,仅有水体好氧反硝化菌作用时,培养瓶的总氮去除量为0.7 mg,水体和表层沉积物共同作用时,总氮去除量为3.3 mg,水体与表层沉积物的反硝化去除氮量之比大体为1∶4,表层沉积物的反硝化作用是水库氮素去除的重要因素.

Analysis of Driving Factors on the Nitrogen Decrease in the Early Stage of the Thermal Stratification in Main Area of Zhoucun Reservoir

In order to explore the trend and driving factors of nitrogen in the early stage of the thermal stratification in Zhoucun reservoir, the water quality indicators in main reservoir area of Zhoucun reservoir were monitored regularly form February to April (2016). Meanwhile, the fresh water and surface sediments in the sampling point were collected to study the effect of water and sediment denitrification by simulation in laboratory. The results showed that: the concentration of TN decreased from (2.28±0.09) mg·L^-1 to (1.08±0.09) mg·L^-1, the concentration of nitrate nitrogen decreased from (1.66±0.09) mg·L^-1 to (0.25±0.06) mg·L^-1, whereas the concentration of ammonia nitrogen and nitrite showed little change in the early thermal stratification of Zhoucun reservoir. At the same time, chlorophyll was not significantly increased, so the algae had little effect on nitrogen; the decreasing nitrogen was mainly due to the aerobic denitrification. Gradually increased temperature,the changes of DO and pH and the composition of organic matter (low molecular weight) were beneficial to the growth of aerobic denitrifying bacteria. Furthermore, the number of bacteria increased from 1.06×10⁵ cfu·L^-1 to 8.33×10⁶ cfu·L^-1, which enhanced the denitrification of the reservoir; Meanwhile, in the simulation experiments, the TN removal rates of water and water-sediment systems reached 0.7 mg and 3.3 mg, respectively. Water and sediment denitrification ratio was generally 1:4, and the aerobic denitrification of surface sediment was an important factor in the removal of nitrogen in reservoir.