The Study On Nitrogen Occurrence Characteristic In Water-Sediment System And Their Relationship With Algal Bloom In Chaohu Lake

We took the Chaohu water - sediment system as the main study by carrying out more than one-year on-site investigation and field simulation experiment.We studied the occurrence Characteristics of dissolved nitrogen in overlying water and pore water of sediments in Chaohu Lake,and estimated the diffusion flux of inorganic nitrogen at watersediment interface in different seasons.We improved the sequential extraction methods of nitrogen from sediments,and calissified nitrogen into free nitrogen,exchangeable nitrogen, acid hydrolysis nitrogen and residual nitrogen in sediments.We extracted different combination nitrogen from surface sediments and discussed the variations of nitrogen forms in water - sediment systems and also the correlation to algal biomass in the water.The results show that the Chla content of water begins to increase in May,and achieves the maxiumun in August in summer.Cyanobacteria dominate during algal bloom period.Algal recruitment and sedimentation exsist in the water column from May to Oct. Algae floating and sinking rate increases first and then decrease.Nitrogen occurrence varies over time in overlying water and interstitial wate.NH₄⁺-N keeps up the proliferation from the sediment pore water to overlying water,NO₃^-- N proliferates from the sediment to overlying water and from the overlying water to sediment.The total nitrogen of surface 2cm sediments maximizes in winter and minimizes in summer.Free nitrogen forms, exchangeable nitrogen forms and acid hydrolysis nitrogen forms of surface sediments vary with seasons.The order of nitrogen forms follow by acid hydrolysis N＞exchangeable N＞residual N＞free N.The Chla content and NH₄⁺-N of overlying water has a significant correlation in the winter and spring(P＜0.01).The Chla content and NO₃^--N has a significant correlation in summer and winter(P＜0.05).The Chla and NH₄⁺-N,DTN of the interstitial water has a significant correlation(P＜0.01).