Nitrogen Forms And Adsorption/Desorption

As one of the major biogenic elements in water body, nitrogen influence the content of primary productivity of the water. Forms of nitrogen in the sediments directly affect the pathways that involved in biogeochemical cycles and the contribution of the nitrogen cycle. Therefore, in-depth study of chemical speciation, content and distribution of nitrogen in sediments, is premise to understand the biogeochemical cycle of nitrogen and their environmental effects in the aquatic ecosystem. This paper studies surface sediments of the Yellow River in Inner Mongolia. In spring and autumn, respectively collected sediments from6regions and studied the content of nitrogen forms and to explore its impact on spatial and temporal distribution mechanism. Simultaneously studied the characteristics of ammonia adsorption, desorption and release from the Yellow River sediments in laboratory simulated conditions.(1)The content of TN on Yellow River surface sediments in spring is between166.6mg/kg～310.33mg/kg, with an average of226.57mg/kg; content of TN in autumn range224.93mg/kg～723.33mg/kg, with an average of480.20mg/kg. There are significant differences in the seasonal distribution, TN content in autumn is much higher than in spring content.(2)The descending order of TTN average content in surface sediments is:Tuoketuo County> Wuhai> Wulateqianqi> Laoniuwan> Linhe> Baotou. The average content of each translate nitrogen on sediments is: OSF-N(184.41mg/kg)> IMOF-N(42.54mg/kg)> IEF-N(22.71mg/kg)> CF-N (5.65mg/kg). OSF-N is the main form of nitrogen and the highest concent form in sediments, accounting for62.90%of the TTN.(3)The species of nitrogen in sediments have obvious seasonal distribution, similar to TN, high in autumn arid low in spring. The average content of different forms of nitrogen in sediments were:TTN was184.41mg/kg; NTN was168.98mg/kg; EN was11.02mg/kg; MN was 6.10mg/kg; FN was66.46mg/kg. There was a significant positive correlation different forms of nitrogen and TN, physicochemical characteristics of sediments in level of p<0.01and p<0.05. The highest content of the three forms of exchangeable nitrogen is NH4-N, accounting for68.81%of the EN. NH4-N is the main form of nitrogen that exchange between the sediment-water interface. Secondly is NO3-N, accounting for28.67%of the EN; lowest content is NO2-N, only accounting for2.52%of EN. Dynamic equilibrium exists between the NH4-N, NO3-N and NO2-N, the three forms of nitrogen can be transformed into each other. The content of OM and CEC in sediments affect the content and distribution of NH4-N, NO3-N and NO2-N.(4) Adsorption isotherm of ammonia in surface sediments from the Yellow River in Inner Mongolia can described by Langmuir isotherm model and Freundlich isotherm model. The maximum amount of adsorption was416.67mg/kg～2000.00mg/kg, average as1018.48mg/kg; The Adsorption/desorption equilibrium concentration was1.00mg/L～2.03mg/L, average as1.61mg/L. Adsorption kinetics of ammonia in sediments consistent with Lagergren pseudo-first and pseudo-second adsorption rate equation. The sorption of ammonia is an irreversible reaction. The process of ammonia adsorption in sediment is the result of a complex interaction from physical and chemical reactions, it’s influenced by many factors. The capacity of the ammonia adsorption in sediments was mainly affected by the content of organic matter of sediments. As the TN and TP content will increase in pace with the increase of organic matter content, resulting in an increase in the capacity of ammonia adsorption in sediments.(5)The release kinetics of ammonia in sediment has a significant correlation with Lagergren pseudo-second kinetic equation. Obtained equilibrium release capacity (Se) was37.31mg/kg～57.47mg/kg. And the release capacity in autumn was significantly higher than in spring. Ability of release ammonia in sediment restricted mainly by the content of nutrients and organic matter. With increase of organic matter, TN and TP, the release capacity of ammonia is also increased accordingly.