近百年来滇南双龙水库沉积物中氮的赋存特征变化

Nitrogen Forms in Sediments of Shuanglong Reservoir in Southern Dianchi over the Past Century

为研究沉积物中氮形态及其质量分数对湖库水体富营养化的影响,在滇南双龙水库采集沉积柱样,分析TN、TIN(可转化态氮)、IEF-N(离子交换态氮)、WAEF-N(弱酸浸取态氮)、SAEF-N(强碱可浸取态氮)、SOEF-N(强氧化剂可浸取态氮)质量分数的剖面特征.通过Pearson相关、RDA (冗余分析)和回归分析探讨沉积物理化性质对氮迁移转化的影响,并结合TLI (综合营养状态指数)和ON (有机氮)指标评估水库氮引起的富营养化程度.结果表明:①柱芯(70 cm)的沉积年代为1871—2011年.②沉积物中w(TN)范围为0.832~5.744 mg/g,其中w(IEF-N)和w(SAEF-N)范围分别为0.027~0.142和0.033~0.131 mg/g,且随深度的增加均呈下降趋势;w(WAEF-N)和w(SOEF-N)范围分别为0.044~0.108和0.114~0.586 mg/g,且随深度的增加均波动变化.③单因子分析表明,各形态氮质量分数与粒度呈负相关,与w(TOC)呈极显著正相关(P<0.01),pH与各形态氮(WAEF-N除外)质量分数存在极显著负相关;综合因子分析表明,各形态氮质量分数主要受w(TOC)和pH共同作用.④污染评价结果表明,沉积物中w(TN)和w(ON)较高,双龙水库长期处于中度富营养化水平.研究显示,沉积物中TIN的迁移转化和外源氮的输入会引起水库上覆水中氮质量分数的增加,进而加剧水库富营养化,需重点关注沉积物中氮的内源性释放及流域土壤侵蚀引起的氮外源输入.

In order to study the effect of the nitrogen form and mass percentage in sediments on water eutrophication,the vertical distribution of each nitrogen form (total nitrogen (TN),ion exchange nitrogen (IEF-N),weak acid extractable nitrogen (WAEF-N),strong alkali extractable nitrogen (SAEF-N) and strong oxidizer extractable nitrogen (SOEF-N)) in the sediments of Shuanglong Reservoir were analyzed. Pearson correlation analysis,redundancy analysis and regression analysis were used to examin the effects of physicochemical properties of the sediment on nitrogen transport and transformation. Eutrophication degree was evaluated by the trophic level index (TLI) and organic nitrogen (ON) index. The results show that: (1) The dating by the CRS model suggested that the age span of the 70 cm sediment core was from 1871 to 2011. (2) The TN,IEF-N and SAEF-N contents were 0. 832-5. 744,0. 027-0. 142 and 0. 033-0. 131 mg/g,respectively,which decreased with depth;the WAEF-N and SOEF-N contents were 0. 044-0. 108 and 0. 114-0. 586 mg/g,respectively,which fluctuated with depth. (3) Single factor analysis showed that the content of different nitrogen forms had a negative correlation with grain size,and an extremely significantly positive correlation with the content of organic carbon (TOC) (P <0. 01). The content of different nitrogen forms had an extremely significantly negative correlation with pH (except WAEF-N).Comprehensive factors analysis indicated that the content of different nitrogen forms were affected by the content of TOC and pH. (4) The contents of TN and ON were higher,and reservoir has been at a moderate eutrophication level for a long time. It is concluded that the migration and transformation of TIN in sediments and the input of exogenous nitrogen cause the increase of the nitrogen content in the overlying water,which further aggravated the eutrophication. It is necessary to focus on the endogenous release of nitrogen and exogenous input of nitrogen.