天目湖溶解氧变化特征及对内源氮释放的影响

Variation of Dissolved Oxygen and Its Influence on Release of Endogenous Nitrogen in Tianmuhu Reservoir in Liyang,China

为弄清水库水体溶解氧(DO)含量的变化规律及其对水质的影响,于2006、2007年对天目湖水体DO和其他水质参数进行调查。结果表明,对于表层水体,在非夏季月份,温度增加会导致DO浓度和饱和度降低;而在夏季月份,由于浮游生物的活动,导致表层DO浓度较高,并可能出现过饱和的现象。对于中、底层水体,温度分层是影响DO浓度的关键因素。温跃层存在期间底层出现缺氧现象,温度分层消失时底层又出现复氧现象,致使在1a之中底层DO存在缺氧-复氧-缺氧交替循环的现象。水库DO浓度对内源氮的释放有明显的影响,尤其是大坝取水口附近,由于夏季底层水体缺氧,导致沉积物中氨氮向底层水体释放,并导致同期表层水体氨氮浓度也有所升高。对于疏浚前后水体氨氮的调查分析表明,底泥疏浚可以有效地减少夏季内源氮的释放,从而降低了DO浓度变化对氮释放的影响强度。

Dissolved oxygen（DO） is one of the key factors affecting aquatic ecosystem and changes with water temperature.A study of spatial-temporal distribution of dissolved oxygen in Tianmuhu,a reservoir 12 km2 in water surface and 14 meters in depth（maximum）,was conducted during 2006 and 2007.It was found that in non-summer seasons the increase in water temperature caused reduction of the concentration and saturation of DO in the surface water layer,but in summer it led to increase in DO concentration and likely to over-saturation of DO due to the activities of plankton.In the middle and bottom water layers,temperature stratification is the key factor affecting DO concentration.When there was a thermocline in the water body,the bottom water was in hypoxia,and when thermocline disappeared,DO restored in the bottom water.As a result,the bottom water followed the alternation of hypoxia-DO restoration-hypoxia in a year.The hypoxia of the bottom water layer in summer caused release of ammonia nitrogen from sediments into water,thus leading to rise of the ammonia concentration in the surface water.The investigation and analysis of ammonia nitrogen concentration in the water body before and after dredging demonstrate that dredging of bottom sediments could effectively reduce the release of endogenous nitrogen in summer,thus mitigating the impact of the variation of DO concentration in the water on the release of nitrogen from sediments.