| Nitrogen cycle plays an important roles in global material circulation and it has became the one of the research focus in biogeochemical cycle. The concentration and distribution of nitrogen in aquatic ecosystem directly influence the quality of water. Sediment is a significant place of nutrient elements' transformation,accumulation and regeneration. Nitrogen transformation in sediment also plays the important roles in nitrogen cycle process. In this paper,24 surface sediments samples from 6 different regions(Wuhai,Linhe,Qianqi,Baotou,Tuoxian,Laoniuwan) of Yellow River in Inner Mongolia were investigated with field sampling under simulation environmental condition. Samples were collected in three season of spring (2013),autumn(2013,2014) and summer(2015). The properties and microbial biomass of overlying water and sediments, nitrogen forms in sediments and the characteristics of nitrate nitrogen adsorption and desorption form sediments were studied in this paper.The results show that:(1)The content of TN in surface sediments from Yellow River is between 127.28 mg·kg-1?1034.60 mg·kg-1,with an average of 354.99 mg·kg-1. The maximum concentration was observed in Wuhai of 2015 summer,while the minimum concentration was discovered in Laoniuwan of 2014 autumn. Generally,the content of TN in autumn and summer is higher than in spring.(2)The content of TTN in surface sediments from Yellow River is between 50.23 mg·kg-1?345.83 mg·kg-1,with an average of 144.35 mg·kg-1. The highest values and lowest values were observed in Baotou of 2015 summer and Tuoxian of 2013 autumn.The average content of four different forms of TTN was in the order as OSF-N(95.35 mg·kg-1)> IMOF-N(29.36 mg·kg-1)> IEF-N(15.40 mg·kg-1)> CF-N(4.24 mg·kg-1). The content of OSF-N was obviously higher than the others and the content of CF-N was the lowest. In the term of seasonal change,the content of TTN on surface sediments was in the order as autumn> summer>spring. It has a colse relation between the content of TTN and the properties of sediment.The content of different forms of TTN has a positive correlation between TTN,TN,OM and CEC.(3)Adsorption kinetics of nitrate nitrogen in surface sediments followed Lagergren second- order adsorption kinetics model.The adsorption capacity in summer is higher than autumn,the lowest adsorption capacity is in spring. The factors of the season changes in adsorption capacity are many-sided and complex. The environmental conditions,the aquatic organisms,microbial biomass were all related to the adsorption capacity.(4)Adsorption isotherm of nitrate nitrogen in surface sediments from Yellow River in Inner Mongolia can described by Langmuir isotherm model.The fitting relation coefficient R2 ranged 0.9999.The maximum adsorbed amount was 75.7576 mg·kg-1?98.3284 mg·kg-1,with an average in 89.6791 mg·kg-1.The highest and lowest values discovered in Laoniuwan of 2015 summer and Tuoxian of 2013 spring. In the term of seasonal change, the Qmax was in the order as summer(91.7445 mg·kg-1)> autumn(89.1530 mg·kg-1) >spring(88.6659 mg·kg-1).The adsorption fitting parameters (Qmax?Qe)has a negative correlation with the properties of sediment(CEC?TN?NO3--N) and it has a positive correlation with the content of nitrifying bacteria.(5)The adsorption-desorption equilibrium concentrations reflects the adsorption capacity.The content of NO3--N in the overlying water (1.2390 mg·L-1)is higher than The average equilibrium concentrations of surface sediments(0.1070 mg·L-1).Therefore,he surface sediments of Yellow River adsorb NO3--N from the overlying water.(6)The NO3--N adsorption on the surface sediment from the Yellow River was an irreversible reaction, obviously. The part of NO3--N can be released gradually from the Yellow River sediment in certain condition,and the others was seldom reversible. |
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