Characteristics Of Organic Nitrogen Deposition And Its Effects On Photosynthetic Physiology Of Typical Diatoms In Xichuan Reservoir Area

Nitrogen cycle,a most important nature element,is crucial in biogeochemical cycle system.Nitrogen deposition is central to the nitrogen input in the earth ecosystem.Excessive nitrogen deposition poses an important challenge to function of terrestrial aquatic ecosystem.Although organic nitrogen has long been known to be a quantitatively significant component of atmospheric nitrogen deposition,but its component characteristics are unknown,which limits the research on the algae physiology and ecology effects of organic nitrogen deposition.The"Small Pacific Reservoir Area",a first-class water quality protection area of the water source of the middle route of the South-to-North Water Transfer Project,which is taken as the research object.In this study,the methods of field sampling,simulation experiment and indoor test were combined conducted to systematically study the dry/wet deposition flux of dissolved organic nitrogen(DON)in reservoir area,clarify the component of organic nitrogen deposition compounds,and study the effects of components on the growth and photosynthetic physiology of dominant diatoms in reservoir area,explore the regional variation from multi-functional land in flux and composition,and reveal the impact of organic nitrogen deposition on the water ecosystem of reservoir area.The results will provide theoretical support to control nitrogen pollution in the reservoir area,which are as follow:(1)The DON deposition flux was 23.57 kg/(hm~2·a),accounting for 41.99%of the dissolved total nitrogen(DTN)deposition flux.The DON deposition in Xichuan reservoir area is mainly dry deposition,dry deposition accounted for 71.18%of DON.In dry deposition,the DON deposition is more sensitive to land type,showing the characteristics of high in winter and spring while low in summer and autumn.There is a significant positive correlation between DON and rainfall in wet deposition.The DON deposition flux is consistent with seasonal rainfall,showing the characteristics of high in summer and autumn while low in winter and spring.(2)The urea nitrogen(Urea-N)deposition flux is 4.81 kg/(hm~2·a),accounts for20.41%of DON.Urea-N deposition changes significantly with time and space.The Urea-N deposition flux in spring and summer is higher than that in winter and autumn.The Urea-N deposition of agricultural cultivated land is higher than that of other monitoring stations.Agricultural activities and rainfall played an important role in Urea-N deposition.(3)The deposition flux of dissolved total amino acids(DTAA)is 6.33 kg/(hm~2·a),accounting for 26.86%of DON.Among them,the dry deposition accounted for 69.04%of DTAA.Dissolved combined amino acids(DCAA)accounted for 78.01%of the DTAA deposition in Xichuan reservoir area.The seasonal difference of the DTAA deposition flux was large,which was the largest in summer,followed by spring and autumn,and the lowest in winter.In terms of single amino acid components,the DCAA are mainly glutamate and histidine,and the dissolved free amino acids(DFAA)are mainly glutamate,histidine and lysine.(4)Ten kinds of organic amines were quantitatively detected in the atmospheric particle samples collected in five nitrogen deposition monitoring stations,namely dimethylamine,diethylamine,propylamine,n-butylamine,pyrrolidine,di-n-butylamine,n-methylaniline,2-ethylaniline,anisidine and 4-ethylaniline.The total concentration of10 organic amines accounted for 4.01%of DON,of which diethylamine was the highest,reaching 0.71%,4-ethylaniline,pyrrolidine,propylamine and n-butylamine were0.4%-0.56%,dimethylamine,di-n-butylamine and N-methylaniline were 0.2%-0.36%.The concentration of organic amines has significant seasonal differences.The total concentration of organic amines is the highest in spring,followed by autumn,and the total concentration of organic amines is lower in summer and winter.(5)Organic nitrogen had a significant effect on the growth and photosynthetic physiology of cyclotella and stephanodiscus hantzschii.When the mixed organic nitrogen,urea-N and amino acid were used as the only nitrogen source of cyclotella and stephanodiscus hantzschii respectively,the mixed organic nitrogen nutrition was more conducive to the growth of cyclotella and stephanodiscus hantzschii.The response of cyclotella and stephanodiscus hantzschii to mixed organic nitrogen is higher,especially the stephanodiscus hantzschii.High concentration nitrogen source corresponds to high specific growth rate,which is more suitable for high nutrient nitrogen environment.We can monitor the level of organic nitrogen deposition in the reservoir area by monitoring the cell density and other related parameters of cyclotella and stephanodiscus hantzschii in the water.86 figures,5 tables and 193 references.