| The Haihe Basin is located in the most economically important area of China. Due to the rapid development of the economy and the society and the urbanization speeding up, as well as the shortage of the natural water resources in the basin, it has been one of the basins with the extreme drought and serious pollution in China, especially with the pollution of NH4+-N. Fuyang River is a typical river of Haihe Basin. Therefore, researching the characteristics of the nitrogen pollution is important to remedying contaminated river and restoring the destroyed ecological systems. Besides, as one of the elements of biological organisms, the biogeochemical cycles of N in the ecosystem of river is closely related to the problem of its pollution.This study focused on the nitrogen contamination of Fuyang River. By analyzing the occurrence form and spatial distribution characteristics in the water body and surface sediments, the actuality and characteristics of the nitrogen pollution were revealed. The typical samples of every section of the river were chosen to analyze the vertical distribution and the composition of speciation of the inorganic nitrogen in the overlying and interstitial water. And the diffusion fluxes and annual load were estimated, with which we might figure out its impact on overlying water quality from the emissions from the exogenous pollutions and the inner release from sediment. Then according to the abnormally high NH4+-N. in Fuyang River, to reveal migration and transformation of NH4+-N, the ammonification rate, PNR (potential nitrification rate) and the adsorption-desorption characteristics of NH4+N were studied. The major results are as follows:(1) The average concentration of TN was 24.95mg/L in the surface water, which was higher than the standard values of the environmental quality standards for Chinese surface water; the average content of TN was 2902.02mg/kg in the sediment, reaching the heavy contamination of sediment evaluation standard for the EPA. In the surface water, the major occurrence form of N was DIN, among which NH4+-N accounted for about 83.6% of DIN was the main contaminant. As to the surface sediment, organic nitrogen was the main existence form. It accounts for 89.02% of TN. However, the same to the water, NH4+-N was the main form of DIN in the sediment. The correlation analysis showed that the different forms of N and the physicochemical properties can have influence on the content and the distribution of every form of N in the surface water and sediment. In addition, the speciation and content between the water and the sediment can also be influenced by each other.(2) The occurrence form of DIN was also put on the NH4+-N, which accounted for 96.4%,94.2% of DIN, respectively. In the vertical scale, the concentration of NH4+-N、NO3--N and NO2--N kept stable with the increasing of the depth in the overlying water, on the contrary, they fluctuated significantly in the pore water. And NH4+-N and NO3--N reached the maximum within the range from 0 to 10 cm. In addition, due to the instability of NO2--N, it presented obvious volatility in pore water. In the spatial scale, the most serious pollution of DIN was also in the Shijiazhuang section in the overlying and pore water. The diffusion fluxes and the annual load of the DIN in the water-sediment surface had obvious spatial heterogeneity. As to the diffusion fluxes, the every form of DIN showed the inconsistency characteristics of "source" and "sink" except NO2--N, which spread from the sediment to the water. The phenomenon showed that the sediment had the potential risk of nitrogen release. In the Shijiazhuang section, the diffusion fluxes of ammonia nitrogen reached -42.18 mg/(m2·d) and the annual load of the external pollution was 101.62 t/a. Therefore, the endogenous load cannot be ignored as well as the control of exogenous emissions with governing the Fuyang River.(3) The average of the ammonification rate and PNR were 4.30μg N/(g·h) and 0.152μg N/(g·h), respectively. And the ammonification rates is about 28 times more than PNR. Compared with other studies, the rates varies in a comparatively large range and had obvious differences in different section. The hyperbolic diffusion model and the amended Elovich model can explain the ammonia nitrogen adsorption dynamics in the sediment. And the process of the adsorption dynamics contained two phases:fast and slow adsorption. And the former completed in the top 120 min, and then gradually to reach adsorption equilibrium. At low concentrations, the NH4+-N adsorption isotherms curves were fitted to Henry equation and simulate. The adsorption-desorption equilibrium concentration varied from 0.55 to 26.15mg/L. The background adsorption of the sediment was between 429.10 and 1162.60 mg/kg. Except S07, the NH4+-N adsorption isotherms curves were fitted to Langmuir model while Freundlich model can’t describe the results. The maximum adsorption of NH4+-N ranged from 429.10 to 1162.60 mg/kg. The desorption characteristics of NH4+-N were similar to the adsorption in the sediment of Fuyang River, but they needed 6h to reach the desorption equilibrium. The desorption kinetics of NH4+-N in the sediment surface was well simulated by the first-order kinetic equation, except S07. Besides, the equilibrium amount of the released NH4+-N was between 36.50 and 400.59mg/kg. The equilibrium of desorption was related to the TN, NH4+-N and C/N in the sediment. |
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