| The Huai River Basin is the most important grain production and core region of increase, which make up 18% of the total grain output in China. Up to 2020, The grain output in Henan province and Anhui province are expected to increase 1.5×1010kg and 1.0×1010kg respectively, which requires large usage of chemical fertilizers, leading to more serious nitrogen pollution. Unsaturated zone, as the link of the surface and underground, plays an irreplaceable role for retardanting, migration, adsorption and transformation of pollutants, which are always the hotspot and difficulty of academics around the world. In the present dissertation, unsaturated zone of the Huai River Basin was taken as the study object. By analyzing soil types, land use patterns, tillage types, etc., adsorption-desorption of ammonia nitrogen on soils, nitrification, denitrification, mineralization potential of unsaturated zone soil are studied, as well as vertical transformation and migration of nitrogen pollutant. The main results are as follows:(1) The soil types mainly included fluvo-aquic soils, vertisol, calcareous vertisol, cinnamon soils, Yellow-cinnamon soils, brown soils, yellow brown soils, etc. in Huaihe River Basin. The pH of surface and deep soils were neutral or slightly alkaline, and a few regions were slightly acidic. The OM content of surface soil were slightly higher than the deep soils, ranging from 0.3853% to 3.1637%. The main component of soil nitrogen was nitrate, ranging from 7.467 to 115.173mg. Contents of different forms of nitrogen in surface soils were higher than in deep soils, as surface soil accepts the replenishment of exogenous nitrogen firstly.(2) The isothermal of ammonia nitrogen on soil conforms to the linear relationship. Adsorption/desorption equilibrium concentration (ECo) and the maximum adsorption (qmax) of vertisol was the highest, while aeolian sandy soils was the lowest. A significant difference exists in ECo and qmax of different types of soil and different depth, ranging for 0.0075 to 3.0040mgL-1 and 249.4251 to 670.0524mg·kg-1 respectively. The isotherm adsorption experimental data under straw returning in fluvo-aquic soils and vertisol was best fitted in Langmuir isotherm equations. (The R2 ranged from 0.9472 to 0.9992.) Wheat straw and corn straw returning increased the ECo of fluvo-aquic soils, Henan Province, while had a small impact on vertisol in Suzhou, Anhui Province. On the contrary, qmax reduced evidently along with the amount of straw returning increased, showed that straw returning hindered the ammonia nitrogen adsorption on soil.(3) The changing of substrate, product with the time in the process of nitrification, denitrification and mineralization in tested soil can be fitted in First-order exponential decay/growth model(FOED/FOEG). By contrasting different soil type, mineralization potential of fluvo-aquic was the highest and that of vertisol was the lowest. Nitrification activity of fluvo-aquic and vertisol were the highest while that of other soil types differed slightly. Denitrification potential of different soil types were almost the same, while fluvo-aquic and vertisol were a little higher than that of others.(4) Leaching experiment in non-homogeneous soil column with adsorption-desorption, nitrification-denitrification-mineralization processes was carried out, and the results showed that:leakage of eight soil columns A-H(namely, fluvo-aquic soils in Zhongmou, calcareous vertisol in Xuchang, calcareous fluvo-aquic soils in Luohe, fluvo-aquic soils and drab fluvo-aquic soils in Fugou, fluvo-aquic soils in Xihua, aeolian sandy soils in Xinzheng and vertisol in Suzhou) were 4.2859mgN/kg,1.8304mgN/kg,2.8196mgN/kg,8.2383mgN/kg,3.3479mgN/kg, 18.0956mgN/kg,5.2659mgN/kg,3.8540mgN/kg, and the leakage rate is 20.4131%, 9.5034%,5.5852%,35.8346%,10.4914%,59.7183%,25.2921%,12.7301%, respectively. Soil Nitrogen leaching risk order in the eight region was:F> D> G>A >H>E>B>C, which mean that fluvo-aquic soils and aeolian sandy soils were more vulnerable. |
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