Study On Nitrogen Form Distribution Characteristics And Exchange Flux In Water-level-fluctuating Zone Of Xiaowan Reservoir

The water-level-fluctuating zone is a special area where the water level of the reservoir is periodically exposed to the surface of the water due to seasonal fluctuations in the reservoir.As the interlaced zone of the water and land ecosystems,it is the material and energy transport in the ecosystem.Active zone of transformation.During the period of periodic water storage in the Xiao wan Reservoir area,the nitrogen,phosphorus,and organic matter in the soil of the fluctuating zone can be physically,biologically,and chemically exchanged with the overlying water through the interstitial water,thereby affecting the water quality of the overlying water.Moreover,as the last line of defense for pollutants entering the water body,the study of the distribution characteristics of nutrients in the water fall zone is of great significance for the control of water pollution.This paper mainly analyzes the nitrogen content and distribution characteristics of soils in the Xiaowan Reservoir area.The gap water concentration gradient method and the mass balance algorithm estimate the nitrogen exchange flux at the sediment-water interface of the Xiaowan Reservoir area,and use experiments The chamber culture method simulates the change of the exchange flux under different environmental conditions.The results are as follows:(1)Soil physical and chemical properties and nitrogen distribution characteristicsThe pH of soils and sediments in the subsidence zone of the Xiaowan Reservoir area was generally neutral or weakly alkaline.The soil particle size distribution is silt>clay>sand.With the increase of flooding time,the soil bulk density of the fading zone in the Xiaowan reservoir area showed an increasing trend.There is no significant difference in the organic matter content of each sampling point in the soil of the Xiaowan Reservoir in the vertical direction of the soil.The vertical overall performance is that the organic matter content gradually increases with the increase of inundation time,and the overall organic matter content of the flooding period is higher than that of the drying period.Contrary to organic matter,the content of total phosphorus is lower in the flooding period than in the drying period.The overall change trend of total nitrogen is similar to the change trend of organic matter,and it also shows that the content of the flooding period is higher than that of the drying period,and the longer the flooding period,the higher the total nitrogen content.Nitrogen of various forms as a whole showed strong oxidant exchangeable form(SOEF-N)>weak acid exchangeable form(WAEF-N)>strong oxidant exchangeable form(SAEF-N)>ion exchangeable form(IEF-N).And the nitrogen content of each form is shown in the flooding period is higher than the dry period.In the vertical direction,except for WAEF-N,which is un-flooded area>water-land junction area>flooded area,the other three forms of nitrogen are shown as flooded area>water-land junction area>unflooded area.(2)Nitrogen exchange flux at the sediment-water interface of the sinking zone of the Xiaowan reservoir areaNitrogen exchange flux in the fading zone of Xiaowan Reservoir area was estimated by interstitial water concentration cultivation method and mass balance algorithm.The result of interstitial water concentration cultivation method is that the average flux of ammonium nitrogen is 2.316mg/(m2·d),and the average flux of nitrate nitrogen is-0.044 mg/(m2·d);Amount-1.654mg/(m2·d),nitrogen flux during flooding period is 1.813 mg/(m2·d).The overall fading zone appears as a source of ammonium nitrogen and a sink of nitrate nitrogen,and as a sink of nitrogen during the dry-out period,and as a source of nitrogen during the flooding period.(3)Influence of different factors on nitrogen exchange fluxThe laboratory cultivation method was used to simulate the effect of different environmental conditions on the nitrogen exchange flux.The laboratory cultivation method obtained an average ammonium nitrogen flux of 19.275 mg/(m2·d)and an average nitrate nitrogen flux of-20.365 mg/(m2·d);With the increase of temperature,the ammonium nitrogen exchange flux in the sediments of the Xiaowan Reservoir fading zone keeps increasing.Flux is continuously decreasing in value and presents a negative value,with a tendency to change to the source.As the temperature rises,the sediment changes from the sink of inorganic nitrogen to the source.When the soil and sediments in the fluctuating zone are more acidic or alkaline,they are sinks of ammonium nitrogen,and when the soil and sediments in the fluctuating zone are neutral,they are the source.When soils and sediments in the fading zone are acidic,they are sinks of nitrate nitrogen,and when they are neutral or weakly alkaline,they are sources of nitrate nitrogen.The change trend of inorganic nitrogen is consistent with nitrate nitrogen.When the overlying water concentration is different,the ammonium nitrogen and nitrate nitrogen show a consistent trend,that is,as the overlying water concentration increases,the fading zone changes from a source of nitrogen nutrients to a sink.When the concentration of ammonium nitrogen in the overlying water is 0.52 mg/L,the fading zone realizes the transformation of ammonium nitrogen from source to sink.For nitrate nitrogen,the critical value is 1.307 mg/L.