沉积物氮形态与测定方法研究进展

Research progress on forms of nitrogen and determination in the sediments

长期以来,国内外学者对沉积物中氮进行了大量的研究,在氮生物地球化学循环和生态学效应方面取得了重要进展。然而,现有关于氮赋存形态的研究主要集中在总氮和无机氮方面,还不能深入阐明沉积物氮的生物和生态学机制。分析了沉积物和土壤氮赋存形态划分和测定方法的研究进展,研究表明:沉积物氮的形态划分与测定方法基本上还是借鉴了土壤氮的研究方法;无机态氮的研究多集中在可交换态氮方面,对固定铵的研究相对较少;在可交换态氮提取方法上并没有针对沉积物与土壤的差异进行必要的论证和改进,沉积物中可溶态氮对可交换态氮测定的影响还不明确;有机氮的测定方法基本上是经验方法,目前还无针对有机氮生态学效应的分类及测定方法;连续分级浸提方法从生态学效应的角度对沉积物氮的研究进行了有益的探索,为深入揭示氮的生态学机制提供了新的思路,但是此类方法目前还集中在国内学者的相关研究中。

Nitrogen（N） is generally recognized as one of the most critical nutrients to limit the river′s productivity in the aquatic ecosystem.The N in sediment is released into the overlying water making the sediment N content the most important factor in determining the N concentration in the water.Thus,N release from sediments may have a significant impact on aquatic systems.Researchers have recorded the N content in sediments starting in the 1960s.The N content in the upper layers of sediments was examined from some North American lakes and from marine sediments in the North Atlantic Ocean.Scholars have developed a large body of research on the levels of N in sediments and have made considerable progress in studying N cycling and the ecological effects of N.Recent research focused mainly on total N and inorganic N,the levels of which need to be determined when studying the background N content in sediments.However,this research has not explored the biological and ecological mechanisms of N cycling in sediments.The results also show not all N in sediments may be involved in N cycling,but instead,past results indicate that only a small part of N in sediments may be involved.Therefore,it is important to investigate forms in which N exists in sediments.In this paper,we analyzed both past research on the forms of N occurring in sediments and on analytical methods used to study the N content in sediments and soils.A review of the literature revealed the methods used in N classification and measurement in sediments closely followed the N analysis methods used in soil research but lagged behind when compared with the quality of N studies in soils.For inorganic N,most studies concentrated on exchangeable N,while few considered fixed N in ammonium.Exchangeable N compounds had been extracted from sediment samples yielding a variety of extractants while using a variety of extraction techniques.Choosing the most effective method to extract exchangeable N is still controversial.No systematic research has looked at the influence of extraction methods on the analysis of exchangeable N in sediments.The debated continues on whether to use fresh wet sediment or dried sediment in measuring the exchangeable N or other fractions of inorganic N.The effect of dissolved N on measuring exchangeable N is also uncertain.To determine N bioavailability in sediments,some domestic scholars employed the sequential extraction method used in the studies of marine sediments and lake sediments and N was divided into four fractions： ion-exchangeable forms,carbonate forms,iron-manganese oxide forms and organic matter-sulfide forms.The sequential extraction method provides new insights into the future study of N content in sediments.Although investigating the fractions of organic N in sediments is important,the measurement method used to measure organic N primarily has depended on the researchers＇ experience with the method,and no reliable method exists to determine organic N content in sediments.