The Distribution And Release Characteristics Of Nitrogen And Phosphorus In The Sediments Of Liaohe River In Jilin Province

With widely public concern, nitrogen and phosphorus are important pollutants andthe limiting nutrients of eutrophication in aquatic environments. Sediment has apooling effect for nitrogen and phosphorus pollutants in water, and is carrier and vaultin the mobilility and transformation of nitrogen and phosphorus in aquatic ecosystems.So sediment plays an important role in the geochemical cycle of nitrogen andphosphorus. After dissolved oxygen content, redox potential, pH and concentrationsof nitrogen and phosphorus changing, the nitrogen and phosphorus pollutants in thesediments may release into water.In order to further study the water pollution characteristics of Liaohe River in JilinProvince, total nitrogen, total phosphorus, organic matter and phosphate forms in10sampling sediments in this catchment were investigated. Based on these investigations,the release progresses of ammonia nitrogen and dissolved phosphate from sedimentwere simulated under laboratory conditions. The effects of pH values on the release ofammonia nitrogen and dissolved phosphate from sediment were also studied bymanually controlling pH values. Finally， the effects of sediment resuspensionconditions on phosphorus content in overlying water and the phosphorus fractions insediment were studied, and soils from related sampling sites nearby were also studiedas a control experiment.The results showed that the concentrations of total nitrogen, total phosphorus andorganic matter were different in vary spatial location of the sampling sites. They werehigher in the sediments of the Yangmu Reservoir and the Tiaozhihe River, a LiaoRiver tributary. And they were lower in other sediments of Liao River and itstributaries. These were related to external pollutants input, water quality andhydrological condition. There were significantly correlation among total nitrogen,total phosphorus and organic matter. The concentrations of exchangeable P, Al-boundP and Fe-bound P were low, and Ca-bound P, organic phosphorus and residualphosphorus were the main forms of total phosphorus.The release characteristics of ammonia nitrogen and phosphate from sedimentswere obviously different. The sediment gradually released ammonia nitrogen until abalance was reached. The sediment first released a large mount of phosphate in a shorttime, and then the sediment absorbed the phosphate from water, finally the sediment turned to release phosphate. The release processes were influenced by microbialactivities and dissolved oxygen content. Both the acidic and alkaline conditionspromoted the release of ammonia from sediment, because H+and OH-could bedirectly reacted with ammonia nitrogen in sediment. Acidic condition was alsofavored for the release of dissolved phosphate, owing to the stability of Ca-bound Pchanged by pH, and causing the release of Ca-bound P from sediment.Sediment resuspension made phosphorus in the sediments release into overlyingwater, the concentrations of dissolved phosphate and suspended particulate matterincreased in overlying water. The forms of phosphorus in sediment redistributed,easily releasing forms of phosphorus were occupied by difficult releasing forms ofphosphorus. The changes of phosphorus forms in the sediments after the suspensionwere: the contents of exchangeable P, Al-bound P and Fe-bound P and organicphosphorus in sediments obviously increased, as sediment adsorbed soluble inorganicand organic phosphorous in overlying water after resuspension. But Fe-bound P andorganic phosphorus after the third day became decreasing, which were influenced bydissolved oxygen decline in sediment, diffusion of pore water and agitation ofoverlying water. Resuspension conditions promoted the release of Ca-bound P fromsediments. Residual phosphorus became the most forms of phosphorus in thesediments, which was related to the distribution of residual phosphorus in thesediment particles of different particle size.