Variation Of Nitrogen In Zhoucun Reservoir And The Analysis Of Driving Factors On The Nitrogen Decrease In The Early Stage Of The Thermal Stratification

The eutrophication of reservoirs and lakes is still exists,nitrogen has been the focus of the study as the main pollutant in water.In recent years,biological methods especially the aerobic denitrification to remove nitrogen has became a hot spot.The main area of Zhoucun reservoir was monitored regularly from August 2015 to July 2016 to studied the variation of nitrogen in the reservoir water,interstitial water and sediment,and the early stage of the thermal was selected to study the influence factors of nitrogen decrease in detail.At the same time,the fresh water and sediment in the reservoir in the early thermal stratification was collected to the synchronous experiment,to estimate the effect on nitrogen reduction of the aerobic denitrification in the water and sediment,and combined with three dimensional fluorescence spectrum technology to analyze the change characteristics of fluorescent organic matter in the aerobic denitrification process.The main research results and conclusions are as follows:(1)The Zhoucun reservoir belonged to the seasonal stratified reservoir,so the water temperature,dissolved oxygen,pH and chlorophyll in the reservoir had obvious seasonal changes.During the monitoring period,the concentration of total nitrogen in the surface and bottom water were between 0.48~2.43mg/L and 0.48~2.63mg/L respectively;the cocentration of total nitrogen in upper and lower sediment interstitial water were between 8.95~27.97mg/L and 13.01~25.25mg/L respectively;the concentration of total nitrogen in upper and lower sediment were between 3199.52~4477.29mg/kg and 591.95~2001.08mg/kg respectively.The variation of the total nitrogen concentration in water,interstitial water and sediment was mainly affected by the reservoir thermal stratification,rainfall and microbial activity.(2)In the early stage of thermal stratification,the total nitrogen in reservoir water decreased from 2.28mg/L to 1.04mg/L,the total nitrogen in surface sediments decreased from 4392mg/kg to 3611mg/kg,the input and output of nitrogen in the reservoir was analyzed at the same time.The results showed that the total amount of nitrogen in the main reservoir decreased.The temperature increased from 4.68℃ to 18.89 ℃,which improved the biological activity of water microorganism.The dissolved oxygen decreased from 12.53mg/L to 2.37mg/L,which improved the metabolic activity of aerobic microorganism.Organic matter was mainly composed of small molecules,which was beneficial to the absorption and utilization of microorganisms.The number of the aerobic denitrifier in this period were increased from 1.1×105cfu/L to 8.9×106cfu/L,which enhanced the denitrification and beneficial to the removal of nitrogen in reservoir,so the reduction of nitrogen in reservoirs was mainly due to aerobic denitrification.(3)In the experiment of synchronous simulation of nitrogen changes,the total nitrogen reduced from 2.28mg/L to 0.43mg/L,the removal rate was 80.31% in the experimental with water and sediment samples,the total nitrogen reduced from 2.28mg/L to 1.85mg/L,the removal rate was 18.86% in the experimental with water samples,so the proportion of nitrogen removal ratio of denitrification by aerobic denitrifying bacteria in water and sediments was generally 1:4,the denitrification in the surface sediment was an important factor of the reduction of nitrogen;the total nitrogen removal rate was 80.31% in the experimental with no shading and the total nitrogen removal rate was 78.33% in the experimental with the shading,so the algae in the water had little effect on the nitrogen concentration.(4)By using three-dimensional fluorescence spectroscopy combined with parallel factor analysis method,the study analyzed the characteristics of the organic matter in thee aerobic denitrification process,the results showed that the fluorescent substances were fulvic acid(coenzyme NADH),humic like and tryptophan(protein)respectively.The fluorescence intensity changes of coenzyme NADH was due to the blocked biological oxidation process and bacterial decay;the fluorescence intensity of humic acid did not change in the detection process;the fluorescence intensity of protein changed with the change of aerobic denitrifying bacteria in the experiment.