Denitrification Mechanism And Its Influencing Factors In Ponds Of Tianmu Lake Basin In The Upper Reaches Of Taihu Lake

Due to the unique hilly landform and rainfall scour,Tianmu Lake Basin is located in the upper reaches of Taihu Lake,and numerous different types of ponds are formed in the basin,and are polluted by nitrogen in different degrees.Denitrification is one of the effective ways to remove nitrogen permanently,and it is also the main way to remove nitrogen in the water body of the ditch and pond.In view of the lack of understanding of denitrification process in small water bodies such as ditch pond water,it is important to systematically study the seasonal variation law,quantitative denitrification rate and the main influencing factors affecting denitrification,which is of great significance to understand the nitrogen removal function and accurately evaluate the nitrogen source of water pollution.In this paper,tea garden pond,village pond,forest pond and culture pond were selected as the research objects.The production rate and main influencing factors of nitrogen in the final product of denitrification and denitrification were determined by MIMS through field sampling and indoor culture.The main research results are as follows（1）The water quality and sedimentary physical indexes of different types of ponds in Tianmu Lake Basin are analyzed.The results showed that the physical and chemical indexes of the gully pond had obvious seasonal changes,among which,the trend of physical indicators was basically the same,and the concentrations of different nitrogen in different ponds varied with the seasons.The highest concentration of total nitrogen and nitrate nitrogen is tea garden pond,the highest concentration of ammonia nitrogen is village pond,and the proportion of nitrogen components in different ponds is different.The highest average concentration of nitrogen in the sediments of the gully pond is the tea garden pond,while the highest of the total phosphorus and carbon concentration is the culture pond.The study of the physical and chemical characteristics of the water body and deposition in the gully pond provides support for the subsequent study of denitrification influencing factors.（2）The experiment of 24-hour culture was carried out in the field.The nitrogen production concentration and culture time were linear regression to get the nitrogen concentration change rate of different ponds.The denitrification rate of the ditch and pond was obtained under indoor conditions by linear regression of nitrogen production concentration and culture time.The denitrification rate of the pond was obtained under indoor conditions,among which the denitrification rate of tea garden pond,village pond and culture pond was 91.28μmol/（m²·h）,77.15μmol/（m²·h）and59.77μmol/（m²·h）.The denitrification and denitrification rate of tea garden pond was obtained by adding different concentration of nitrate solution.After comparison,it was found that there was a certain nitrogen saturation effect in the denitrification of tea garden pond.The sediment treatment group of Goutang containing different ¹⁵N drugs was set up.N₂production in denitrification and anaerobic ammonium oxidation in different ponds was measured by ¹⁵N isotope tracer method combined with coupling calculation The results showed that the contribution rate of denitrification and denitrification at different sites was above 63%.（3）Based on the field data of the denitrification rate of tea garden pond,village pond and forest pond,the results show that the denitrification rate of tea garden pond varies from 76.54 to 94.60μmol/（m²·h）,the change range of denitrification rate is23.52 to 57.72μmol/（m²·h）,and the denitrification rate of the forest pond is 8.36 to13.57μmol/（m²·h）;the denitrification rate has obvious seasonal variation range The denitrification rate of Lintang and village pond is much higher than that in autumn,while that of tea garden pond is larger than that in summer.The experiment analysis was carried out on the diurnal change of denitrification,among which:the groundwaterΔN concentration and denitrification rate were higher than the surface water concentration,which indicated that the denitrification process of different water bodies in different areas of the same ditch and pond showed different rules,and the diurnal change did have a significant influence on denitrification process.Through analysis,the main water indexes affecting denitrification in Goutang are water temperature,do,nitrate nitrogen and nitrous nitrogen;sediment indexes include p H,bulk density,ammonia nitrogen and carbon index,among which the main influencing factors of denitrification in tea garden pond are nitrous nitrogen,and the concentration of nitrous nitrogen is positively correlated with denitrification rate;the main influencing factors of denitrification in village pond are do and water temperature,do concentration and denitrification rate The main factors of denitrification in forest pond were do,total nitrogen and nitrate nitrogen,do was negatively correlated with denitrification rate,and total nitrogen and nitrate nitrogen were positively correlated with denitrification rate.