Distribution And Occurrence Characteristics Of Nitrogen Forms In Sediments Of The Qilihai Lagoon

Nitrogen exists in a complex form of sediment and is released in different proportions,that is,the effects of nitrogen on the eutrophication of lakes are different.In order to illustrate the distribution of nitrogen in the sediments and its effect on the environment,taking the Qilihai Lagoon sediments as the research object,using the grab sampler November 2015 acquisition of surface sediments（0¹0 cm）11 samples,of which seven of the Qilihai Lagoon coast 9 sites（1#,2#,3#,4#,5#,8#,9#,10#,11#）,lagoon center 2 sites（6#,7#）,columnar and collect 11 sites（0³0 cm）sediments.Sample collection immediately after loading into the polyethylene bag,exhaust air seal,4℃refrigerated storage,back to the laboratory reserve.Determination of the content of different forms of nitrogen in the laboratory using chemical extraction method,correlation analysis of sediment nitrogen speciation and median grain size,organic matter,and finally put forward about the Qilihai Lagoon proposed governance.Based on the above analysis and discussion,the following conclusions are made:（1）NTN in the surface sediment TN accounts for the major part,and the TTN that really participates in the geochemical cycle accounts for a small portion of the TN.The proportion of all forms of nitrogen in TTN is SOEF-N>WAEF-N>SAEF-N>IEF-N.（2）The nitrogen forms of surface sediments are affected by sediment sources,hydrodynamic effects,human factors,cofferdam aquaculture activities and other factors,showing different distributions.（3）According to the Guidelines for Environmental Quality Assessment,the single-factor environmental quality index assessment method and the comprehensive pollution assessment method were used to analyze the surface sediment contamination of lagoon.The results of the two assessments were consistent,indicating that most of the surface sediments in the Qilihai Lagoon were in safety level.However,it is necessary to effectively control the nutrient content in the waters near the southeast and mid-eastern waters in order to avoid eutrophication and affect the survival of other benthic species such as amphioxus.（4）The distributions of morphological N in surface sediments were significantly different from those of total organic carbon（TOC）and median diameter.There was a positive correlation between TN,SAEF-N and SOEF-N and TOC.The correlation between IEF-N and WAEF-N and TOC was not very obvious.SAEF-N and SOEF-N were dominated by NO₃^--N.The nitrification in this area may be more significant.（5）The content of TN in columnar sediments of lagoon is less than 15 cm,and no obvious changes are observed.It is only small-scale fluctuations.The variation range from 15 cm to 25 cm is relatively stable,and the variation between 25 cm and30 cm is relatively large.Affected by the depositional environment,the early diagenesis of sediments,and human activities,TN content gradually decreased with depth at each sampling site..Due to the strengthening of industrial and agricultural production activities in recent years and the significant increase in the amount of nitrogen input by humans to lakes and lakes,the nitrogen load in the Qilihai Lagoon has increased year by year.