南四湖表层沉积物中N的形态及其分布特征

Distribution characteristics of different forms of nitrogen in the surface sediments of Nansi Lake

采用分级浸取分离法分别对南四湖的7个表层沉积物样品中的离子交换态氮(IEF-N)、弱酸可浸取态氮(WAEF-N)、强碱可浸取态氮(SAEF-N)及强氧化剂可浸取态氮(SOEF-N)进行提取,并将沉积物的N划分为可转化态氮(TTN)和非转化态氮(NTN),对南四湖表层沉积物中各形态N含量及其分布特征和相关环境因素进行了分析。分析结果表明,南四湖上下级湖区表层沉积物中除SAEF-N外,TN及各形态N含量差异显著且上级湖明显高于下级湖区;下级湖表层沉积物中TTN占TN含量的比列明显高于上级湖;南四湖沉积物中N元素成分主要结合在沉积物中的细粒黏土成分中;南四湖上覆水中TN和NH4+-N与表层沉积物中TN和各形态N没有表现出显著的正相关关系,这说明南四湖湖水中的N元素主要来源于入湖河流;沉积物中的氮磷比在1.5～4.5,低于Redfield指数,上覆水中的氮磷比为13.7～24.1,高于Redfield指数,进一步说明南四湖目前水体中的N、P元素主要来自于入湖河流;沉积物中的TN含量在近10 a间下降很大且P仍然是南四湖湖最主要的限制性营养元素。

In this study, different nitrogen forms in the seven surface sediments of Nansi Lake were separated by means of sequential extraction, and their contents, distribution characteristics and related factors were analyzed. The transfera- ble nitrogen can be divided into four forms, the ion exchangeable form （IEF-N）, weak acid extractable form （WAEF- N）, strong alkaline extractable form（SAEF-N） and strong oxidant extractable form（SOEF-N） and their contents, dis- tribution characteristics and influencing factors were analyzed. The results indicated that the content of total nitrogen and different translate nitrogen fractions（ except SAEF-N） in the upper Nansi Lake was higher than the lower lake district. The ratio of TTN and TN in the lower lake was higher than the upper Nansi Lake. Nitrogen mainly combined with grained sediments in Nansi Lake. There were no significance correlation of TN and NH4 ~ -N between sediments and wa- ter, which proved that most of the nitrogen came from its main inflow rivers. As a result, the N/P ratio in sediments was only about 1.5 -4. 5 below the Redfield index, while the N/P ratio in water was 13.7 -24. 1 higher than Redfield index, which farther illustrated that the nitrogen and phosphorus came from its main inflow rivers. Although the concen- tration of TN has greatly decreased in the last decade, phosphorus was the most restricting nutritious element. Key words： Nansi Lake; surface sediment; nitrogen form; distribution characteristic ; N/P