Distribution Characteristics And Flux Analysis Of Soil Nitrogen And Organic Matter In The Water-Fluctuating Zone Of Danjiangkou Reservoir

Danjiangkou Reservoir is used as the water source of the Middle Route P roject of South-to-North Water Transfer.Its water quality safety affects the wat er safety of cities along the Mid-route Project.The water-fluctuating zone is a n important part of the reservoir ecosystem.It is a source of sediment,organic matter,agricultural fertilizer,domestic sewage and other pollution sources.The last barrier of the water body in the area is that during the period from the f lood of the reservoir to the dryness of the reservoir,the organic matter and nit rogen in the soil of the water-fluctuating zone are transferred and transformed in the overlying water,soil,and atmosphere through physical,chemical,and bi ological processes,affecting the water quality of the reservoir area.Therefore,studying and analyzing the distribution characteristics and fluxes of soil organic matter and nitrogen in the water-fluctuation zone will play an important practi cal role in further studying and analyzing the geochemical cycle of nutrient ele ments in the ecosystem of the reservoir area and protecting the water quality o f the reservoir.This paper mainly analyzes the soil physical and chemical char acteristics,the correlation between organic matter and nitrogen,and their distrib ution characteristics at different times,different soil types,and different regions during the flooding-drying period of Danjiangkou Reservoir from 2018 to 2019.And through mathematical models,the organic matter and nitrogen fluxes in d ifferent periods are estimated.The main conclusions are as follows:(1)The temperature of the soil in the Danjiangkou Reservoir’s fluctuating zone changes with the seasons,and its pH value is generally neutral and slight ly alkaline,fluctuating between 5.3 and 8;the moisture content is between 6% and 79%,of which Most of them are in the range of 20% to 50%,and they are in a relatively high range,and the flood period is slightly higher than the dry period.The electrical conductivity varies greatly between different regions,and generally varies between 42.5 ~ 625 uS / cm.As time changes,there is an upward trend.The particle size of the soil is generally expressed as powder> sand> cohesive.The proportion of powder is between 20% and 73%,which ha s a high proportion.The proportion of clay is the smallest,2% ~ 23%.XC1,NY9 HJ14,HJ14 and HJ15 are sandy loam soils,and the remaining monitorin g areas are all silt loam soils.(2)The average content of organic matter in different soil types is represe nted by powdery loam soil> sandy loam soil,and the average content of organ ic matter in different areas is represented by Nanyang> Xichuan> Hanjiang Riv er.During the flood period,the soil organic matter content in the drawdown z one fluctuated to a certain extent,and remained stable overall During the dryin g period,as the amount of drying time prolongs,the content of organic substa nces in the falling zone increases significantly.The problems of human activiti es and agricultural production in the fallout zone during the dry season led to the accumulation of soil organic matter in the fallout zone.(3)The total nitrogen content of the soil in the fluctuating zone gradually decreases at any time during the flooding period.During the drying period,the total nitrogen content slightly increases with the extension of time.From the perspective of the overall process of flooding-drying,the total nitrogen content There is a relatively obvious increase.The content distribution of inorganic nitr ogen in the study area is inversely proportional to the soil particle size.The c ontent is generally stable during the flooding period and slightly decreases duri ng the drying period.From the analysis of the flooding-falling period process,due to the initial period of the drying period,Affected by agricultural activities,inorganic nitrogen is accumulating in the soil.From a spatial perspective,Nan yang’s main reservoir area is significantly affected by agricultural non-point sou rces.The nitrogen content of all forms is higher than the average content of the overall reservoir area.It is the main area that affects the nitrogen content l evel in the reservoir area.The water level during the flood period When rising,the potential eutrophication risk of the water body in its water-fluctuatinging zone is greatest.Correlation analysis shows that organic matter is significantly correlated with various forms of nitrogen(P <0.01),total nitrogen is significant ly positively correlated with water content and electrical conductivity(P <0.01),and organic nitrogen is significantly positively correlated with water content a nd electrical conductivity(P <0.01).Nitrate nitrogen was significantly positively correlated with water content and electrical conductivity(P <0.01),and ammo nia nitrogen was significantly positively correlated with inorganic nitrogen(P <0.01).(4)During the flooding period,the organic matter flux S_OM flooding per iod =-307285 t,the total nitrogen flux S_N flooding period =-7779 t,during t he drying period,the organic matter flux S_OM falling period = 585333 t,the total nitrogen flux S_N falling Dry period = 6941 t.During the flooding-drying cycle from 2018 to 2019,the total amount of soil organic matter in the Danjia ngkou Reservoir’s fluctuating zone increased by 278049 t,and nitrogen decrease d by 838 t.