Enhancement Of Microcystis On The Denitrification At The Sediment-water Interface

Enrichment of nutrients?nitrogen and phosphorus?makes lakes eutrophic,and leads to cyanobacteria blooms further.However,lakes do not always respond to the input of nitrogen passively;they can remove nitrogen through biological denitrification.With the requirement of anoxic condition,biological denitrification occurs at the sediment-water interface mainly.At present,research on the lake eutrophication is mainly about how nitrogen and phosphorus determine the abundance and composition of cyanobacteria,harmful effects of cyanobacteria blooms and how to control harmful algae blooms,but it is less known how cyanobacteria affects the nitrogen cycling of lakes,especially denitrification at the sediment-water interface.So experiments about the interaction between cyanobacteria and sediment-water interface were carried out firstly,then effects of Microcystis on the denitrification at the sediment-water interface was studied;further the feasibility of using pressurized Microcystis and Microcystis under nitrogen-limited cultivation as carbon source for denitrification at the sediment-water interface was investigated.This research is importantly valuable to utilization of cyanobacteria and lake eutrophication control.Major results of this research are as follows:1)Not only can live Microcystis reduce dissolved oxygen at the sediment-water interface,but also can release much carbon?13.93 mg TOC/mg Chl a?and little nitrogen?0.18 mg DTN/mg Chl a?,which are helpful to biological denitrification at the sediment-water interface.2)Microcystis?live and dead?favors the process of denitrification at the sediment-water interface and when concentration of Microcystis is higher,NO_x^--N declines more quickly.The rate constants of NO_x^--N declining were 1.06,1.14,1.40times higher than the control,respectively,with Microcystis densities of 0.2,0.4,0.8 mg Chl a L^-1.3)Microcystis under nitrogen-limited cultivation can favor the process of denitrification at the sediment-water interface too.Concentration of Microcystis under nitrogen-limited cultivation is higher,and DTN declines more quickly.When both Microcystis under nitrogen-limited cultivation and Microcystis under nitrogen-sufficient cultivation were 100mg·L^-1,the rate constants of DTN declining were 0.951,0.423 d^-1and the removal rates of DTN were 99.3%,66.7%,respectively.The enhancing effect of Microcystis under nitrogen-limited cultivation was similar to glucose,and better than Microcystis under nitrogen-sufficient cultivation.4)Pressurized Microcystis can enhance denitrification at the sediment-water interface and enhancing effect increases with Microcystis densities.The removal rates of DTN were 1.63,2.08,2.1times higher than the control,respectively,with pressurized Microcystis densities of 0.37,0.75,1.12 mg Chl a L^-1.in lab-scale,pressurized Microcystis collected from lakes can enhance denitrification at the sediment-water interface,too.