Isotopic characteristics and source analysis of atmospheric ammonia during agricultural periods in the Xichuan area of the Danjiangkou Reservoir

Nitrogen deposition is an important means of exogenous nitrogen input in reservoir water.Agricultural activities around the reservoir lead to a sharp increase in the concentration of ammonia in the atmosphere,which poses a threat to the reservoir water body.Clarifying the contribution of agricultural ammonia release to atmospheric NH_(x)(gaseous NH_(3)and particulate NH_(4)^(+)),in the reservoir area can provide a theoretical foundation for local reactive nitrogen control.We collected atmospheric NH_(3)and NH_(4)^(+)samples during the agricultural periods and analyzed the isotopic characteristics of atmospheric NH_(x)and the contribution rates of different ammonia sources in the Xichuan area of the Danjiangkou Reservoir.The results showed that the initialδ~(15)N values of NH_(3)(-30.0‰to–7.2‰)and particulate NH_(4)^(+)(–33‰to+4.9‰for finer and coarser particles,respectively)are different,and their contribution ratios from dissimilar ammonia sources are also different,among which NH_(4)^(+)is more susceptible to meteorological factors.However,since the atmospheric NH_(x)in the Xichuan area is mainly gaseous NH_(3),the final sources of atmospheric ammonia nitrogen source depend on gaseous NH_(3).Agricultural sources(59%-74%)were the main NH_(3)sources in this area.Among them,the fertilizer use emission was dominant;it had the highest contribution rate in summer during the agricultural period and a more prominent impact in areas with less human interference.Reasonable regulation of the application of high-ammonia releasing fertilizer,especially during the agricultural period in summer,is an effective way to reduce the threat of atmospheric ammonia to water health.

Nitrification performance of nitrifying bacteria immobilized in waterborne polyurethane at low ammonia nitrogen concentrations

Suspended and waterborne polyurethane immobilized nitrifying bacteria have been adopted for evaluating the effects of environmental changes, such as temperature, dissolved oxygen （DO） concentration and pH, on nitrification characteristics under conditions of low ammonia concentrations. The results showed that nitrification was prone to complete with increasing pH, DO and temperature. Sensitivity analysis demonstrated the effects of temperature and pH on nitrification feature of suspended bacteria were slightly greater than those of immobilized nitrifying bacteria. Immobilized cells could achieve complete nitrification at low ammonia concentrations when DO was sufficient. Continuous experiments were carried out to discuss the removal of ammonia nitrogen from synthetic micropollute source water with the ammonia concentration of about 1mg/L using immobilized nitrifying bacteria pellets in an up-flow inner circulation reactor under different hydraulic retention times （HRT）. The continuous removal rate remains above 80% even under HRT 30 min. The results verified that the waterborne polyurethane immobilized nitrifying bacteria pellets had great potential applications for micro-pollution source water treatment.