Study On The Environmental Behavior Of Dissolved Organic Nitrogen And Carbon In Paddy Water In Upper Reach Of Huangpu River Basin

Dissolved organic nitrogen (DON) and Dissolved organic carbon(DOC) are very active and important chemical components in paddysystems. DON, DOC are not only important source of rice nutrients butalso organic pollution when are discharged into water.The upper reachof Huangpu river basin is the main rice producing area, DON, DOCrealeased from rice field put a direct threat to water quality of Shanghaiwater source. Based on the lysimeter method, the content distributionand microbial degradation characteristics of DON, DOC under twofertilization treatments (Chemical Treatment, CT; Mixed Treatment,MT) in water environment of rice field were determined, and addingmicrobial agents were used to be a source control of DON, DOC fromrice field. The research has important scientific significance andapplication value to control organic nitrogen and carbon emissions andreduce organic pollution in Shanghai water source. The main resultsare as follows:1. Through the analysis of the content of DON, DOC in surface water,section water, runoff and leakage water, the behavior of DON, DOC inrice field under different fertilization treatments, were determined. Theresults showed that MT had better self-restraint ability than CT insurface water and section water; The first half month was criticalperiod to prevent nitrogen and carbon loss when they reached95.8%TN loss and67.2%TC loss; Both fertilization treatments had the sametrends of nitrogen and carbon concentration, which had a rapid increaseand decrease in first7days after fertilization, then stabilized slowly;TN, DON flux under MT were49.5%,19.5%lower than which under CT, and TC and DOC flux under MT were slightly lower than whichunder CT by0.8%and5.8%, which means MT could control organicnitrogen loss, but has little effect on C flux in rice field.2. The content analysises of DON, DOC in paddy soil solution inbaking state under different fertilization treatments were conducted.The results showed that nitrogen concentration in soil solution hadsignificant differences among different depths (P<0.05), and TN andDON concentration in0~10cm soil was significantly lower than otherdepths. The range of ratio of DON/TN was63.1%~79.9%in differentdepths. The ratios of DOC/TC increased when depths deepened, andwere21.1%~25.1%under MT. The ratios decreased slowly withdeepened depths and were18.9%~20.0%under CT. The results of thecorrelation analysis revealed that DON concentration in soil solutionhad positive correlation with organic matter content and TN in soil inboth fertilization treatments (R2=0.936,0.960); DOC concentration insoil solution had significant positive correlation with organic mattercontent and TC in soil (R2=0.939,0.913).3. Composition analysis of DON, DOC in paddy soil solution underdifferent fertilization treatmentsThe compositions of DOM (DON, DOC) in different depths wereas followed:CT:0~10cm: a, b, c;10~20cm: b, c;20~30cm: b, c;MT0~10cm: b, c;10~20cm: b, c:20~30cm: b, c, da, b, c, d are the results of HPLC-MS.The possible results of identifications were as followed:a:3-(4-thiazolyl)-L-alanine, b:2-Phenylbenzimidazole-5-sulfonicacid, c:4-(2,4-difluorophenyl)-3-nitrobenzene carbaldehyde, d:fendizoic acid.4. The method of PCR-DGGE was applied to analysis the indigenousmicrobial community in paddy soil. Fertilization had comparativelylarge influence on0~20cm soil, and the similarity of microbialcommunity composition was0.75between two fertilization treatments.MT had higher microbial diversity index and microbial evenness indexthan CT in10~20cm and20~30cm. Bands selected for DNA sequencing were mainly related to Escherichia coli,Ruminococcusalbus.5. Through the in situ microorganisms, microbial degradationexperiments of leakage water and soil solution in baking state wereconducted to determined microbial degradation characteristics of DON,DOC in water environment of rice field under different fertilizationtreatments. The material of degradation experiment I were the mixtureof leakage water of1~7d after fertilization, and the material ofdegradation experiment II were the mixture of leakage water of8~25dafter fertilization. The results showed that the biodegradable ratiounder MT was higher than CT. DOC was more stable than DON, andfertilization had affected DON more than DOC. Compared to theresults of leakage water degradation experiments, the biodegradableratio of soil solution degradation experiment was lower. DON, DOC inwater environment of rice field had high biodegradability, andmicrobial degradation could be used to control organic nitrogen andcarbon loss.6. Microbial agents were added to control DON, DOC loss in waterenvironment of rice field. Microbial agent had little impact on nitrogenin runoff of rice field, but could raise carbon concentration up.Microbial agent could control nitrogen loss in leakage water, butexcessive number of microbial agent could also lead more nitrogen loss.Microbial agent had little impact on TC content in leakage water, but1time microbial agent could reduce DOC content. Microbial agent hadlittle impact on DOC content in soil solution in baking state, but couldreduce DON content. The results showed that MT and addingmicrobial agent could both control organic pollution from rice field,and the treatment of MT adding1time microbial agent was the mosteffective.