梯级水库运行对沉积物氮形态时空分布的影响——澜沧江和怒江对比研究

Temporal and spatial variations of sedimentary nitrogen forms in the Lancang River and Nu River.

为探究梯级水库运行对河流沉积物氮形态时空分布的影响,分别在枯水期和汛期对澜沧江和怒江沿程表层沉积物进行跟踪监测,并利用分级连续浸取分离法得到了离子可交换态氮(IEF-N),弱酸可浸取态氮(WAEF-N),强碱可浸取态氮(SAEF-N)和强氧化剂可浸取态氮(SOEF-N)等四种沉积物氮形态.结果表明:(1)怒江和澜沧江自然河流段可转化态氮(TTN)含量略低于水库段,沿程分布含量范围512.2~1548.5mg/L,同时期4种可转化态氮形态分布规律基本一致,枯水期SOEF-N>WAEF-N>SAEF-N>IEF-N,含量范围分别为486.6~1424.8,3.3~83.1,1.4~88.8和1.2~10.7mg/kg;汛期WAEF-N>SOEF-N>SAEF-N>IEF-N,含量范围分别为360.7~755.7,42.8~656.2,6.8~394.3和35.8~153.6mg/kg;(2)梯级水库运行导致有机质富集,颗粒物粒径变小,对WAEF-N的释放有抑制作用;梯级水库运行导致水库段沉积物粒径变小,而SOEF-N主要分布在细颗粒中,致使沉积物的矿化作用受到抑制,有机氮含量得到累积;水库段由于有机质含量的累积,IEF-N含量逐步升高;自然河道段表层沉积物基本以氧化环境为主,沉积物中SAEF-N更易释放,而在水库段基本处在弱还原或者还原环境下,导致SAEF-N累积在沉积物.

In order to investigate the effects of cascade reservoirs on the temporal and spatial distributions of nitrogen forms along rivers,the sediment samples along Lancang River and Nu River were collected and analyzed during dry and flood seasons,respectively.The sedimentary nitrogen forms,including ion-exchangeable nitrogen(IEF-N),weak-acid leachable nitrogen(WAEF-N),strong alkaline extractable nitrogen(SAEF-N),and strong oxidant extractable nitrogen(SOEF-N),were measured with fractional continuous leaching separation method.The results showed that the content of transformable nitrogen(TTN)in free-flowing reaches of these two rivers was slightly lower than that in the reservoirs,ranging from 512.2 to 1548.5mg/L,and the distribution patterns of four types of transformable nitrogen were basically the same in the same season,following the order of SOEF-N>WAEF-N>SAEF-N>IEF-N in the dry season,and their content ranges were 486.6~1424.8,3.3~83.1,1.4~88.8 and 1.2~10.7mg/kg,respectively;but the order changed to WAEF-N>SOEF-N>SAEF-N>IEF-N in flood season,and the content ranges were 360.7~755.7,42.8~656.2,6.8~394.3 and 35.8~153.6mg/kg,respectively.And the cascade reservoirs operation might inhibit the release of WAEF-N due to the enrichment of organic matter and the reduction of particle size.As SOEF-N was mainly contained in fine particles,the sediments with smaller grain sizes might inhibit the mineralization of sediments and result in an accumulation of organic nitrogen.Due to the accumulation of organic matter in reservoirs,the content of IEF-N increased gradually.Moreover,in the free-flowing reaches,the surface sediments were basically in oxidation state,and SAEF-N was easier to release from the sediments;while in the reservoirs where the sediments were in weak reduction or reduction state,the SAEF-N was contained and accumulated in sediments.