Influence Of The Lancang River Cascade Reservoir On The Distribution Of Nitrogen Forms In Sediments

The construction of cascade hydropower stations in the Lancang River Basin has changed the occurrence status of river sediments.The difference in nitrogen form distribution between natural rivers and rivers with cascade reservoirs and its influencing factors need to be clarified.This paper combines field in situ observation and other research methods to use the Lancang River The natural channel of the main channel of the Nu River is taken as the research area.Surface and columnar sediment samples are collected and the corresponding environmental factors are monitored.The difference in nitrogen form distribution between the surface layer and columnar deposits of the Lancang River and Nujiang River is analyzed and analyzed.The reasons for the difference in nitrogen form distribution are analyzed in conjunction with environmental factors.,Clarified the impact of the construction of cascade reservoirs on the nitrogen form of sediments and their occurrence environment,and reached the following main conclusions:(1)The particle size distribution of the Lancang River and the Nujiang River is quite different.The composition of the sediment particles of the Lancang River is mainly silt,clay,medium sand,fine sand,and very fine sand,mainly composed of fine particles,and the composition of the Nujiang sediment is mainly fine.Sand,medium sand,very fine sand and silt are mainly composed of coarse particles.Due to dam interception,the size of sediments in the cascade reservoirs of the Lancang River is the finest;on the sorting coefficient,the particle size of the natural river section of the Nu River and Lancang River The degree of uniformity is good,and some points of the reservoir section are excellent;on the skewness,the natural sections of the Nu River and Lancang River are both positively skewed,and the point sections of the reservoir section are negatively skewed;on the kurtosis,the natural river points and the reservoir section Compared with the points,the kurtosis of the points in the reservoir section tends to be medium(normal),while the natural river channels tend to be sharper.(2)The order of the content of transformable nitrogen in the surface sediments of the Nu River and Lancang River is: SOEF-N>WAEF-N>SAEF-N>IEF-N.The content and distribution of transformable nitrogen in the natural river sections of the Nu River and Lancang River The above is basically the same,but in the cascade reservoir section of the Lancang River,its distribution law is quite different from that of the natural section.Among the natural section,the content of IEF-N,SAEF-N,and SOEF-N is stable,while in the cascade reservoir section,IEF-The contents of N,SAEF-N and SOEF-N all increased in different degrees,while the contents of WAEF-N all showed a decreasing trend.(3)On the comparison of the nitrogen forms of surface sediments between the Nujiang River and the Lancang River,through single-factor analysis of variance,only the WAEF-N content of the Lancangjiang Reservoir section and its upstream natural river and the SAEFN content of the Lancangjiang Reservoir section and the Nujiang River have no significant difference.In comparison,the nitrogen content of the reservoir section and other natural channels showed significant differences.This shows that the distribution characteristics of nitrogen forms in sediments are very different between natural rivers and rivers with cascade reservoirs.(4)The columnar sediments of the Lancangjiang Reservoir are affected by different parameters due to the different characteristics of the sediments.The strong oxidant extracted nitrogen in Xiaowan in winter had a significant correlation with TOC,and showed a significant negative correlation.The ion exchange state of Manwan in summer was significantly positively correlated with TOC;the ion exchangeable state of Jinghong in winter was significantly positively correlated with p H,and summer Jinghong’s ionexchanged nitrogen was strongly positively and negatively correlated with strong alkali extracted nitrogen and p H,respectively;the ion-exchanged nitrogen in seedling seedlings in winter and the weak acid extractable nitrogen,the strong oxidant extracted state of Gongguoqiao,and The ion-exchanged nitrogen at the Jinghong site showed a significant correlation with ORP;meanwhile,the nitrogen extracted by the strong oxidant of Gongguoqiao in winter was significantly negatively correlated with the sand grains.There was a significant negative correlation.The nitrogen extracted from the strong oxidant at the tail of the seedlings had a significant positive correlation with the powder particles,and the ion-exchange nitrogen of Nuozhadu had a significant negative correlation with the sand particles.(5)There is mutual conversion between the four transformable nitrogen in the columnar sediments of the Lancang River.In winter,the ion-exchanged nitrogen is significantly related to the weak acid extracted nitrogen,and the weak acid extracted nitrogen is related to the strong alkaline extracted nitrogen and the strong alkaline extracted nitrogen.There is a significant relationship between nitrogen and ion-exchanged nitrogen,which indicates that these three nitrogen forms may have the same source and have the same biogeochemical characteristics,and there will be a certain degree of transformation between each other.In summer,only the strong oxidant extractable nitrogen is significantly related to the ionexchange state and the strong alkali extractable nitrogen,indicating that the strong oxidant extractable nitrogen may be similar to the other two nitrogen forms,and there will be transformations between them.At the same time,the content of nitrogen in the ion-exchange state and the strong alkali extracted state did increase in summer.(6)The storage capacity and storage time of different reservoirs are quite different,and these differences have a certain effect on the distribution of nitrogen forms in sediments.The content distribution of different nitrogen forms may have a certain relationship with the construction time of the reservoir and the relationship with the storage capacity.weak.The longer the construction time,the content of ion-exchanged nitrogen,strong oxidant extracted nitrogen,and total convertible nitrogen in the sediment will be correspondingly higher,while the content of weak acid extracted nitrogen will be lower,and the specific mechanism of action needs to continue the study.