Some urban rivers with slower flow rates receive more sewage,causing frequent blooms in river water bodies.During the growth and death process,algae will release a large amount of dissolved organic matter(DOM),which will affect the physical and chemical properties of the water environment,thereby affecting the bioavailability of pollutants in the water body.At present,the research on algal bloom mainly focuses on the areas where nutrients are collected,such as lakes,reservoirs and coastal waters.This is because the river water usually has rapid flow and turnover rate and it is not easy to accumulate nutrients.While the research on algal bloom in rivers,which is the channel of nutrient migration and transformation,is relatively less.Algae growth and death will release a lot of dissolved organic matter(DOM),which will affect the physical and chemical properties of the water environment,and then affect the heavy metals and other pollutants in the water.With the increasing impact of human activities on the water environment,algal blooms occur frequently in some rivers with slow flow velocity.Based on the field investigation,mathematical simulation and laboratory experiment,the characteristics of algal bloom in the typical slow flow channel Haihe River in the north of China and its influence on the bioavailability of dissolved organic matter(DOM)and heavy metals in the water body were studied.In conclusion,our study provides an ecological water regulation scheme to effectively prevent algal bloom,and offers new theoretical and technical support for controlling algal bloom outbreak in slow and stagnant rivers.Through the sampling monitoring in recent years,the main pollution factors of water quality in the main stream of Haihe River are TP,CODcr and NH3-N.The most abundant phytoplankton during algal bloom is cyanobacteria.According to the analysis of Tucker3 model,TN,TP,N/P and Chla all conform the nonlinear function of cubic polynomial.When N/P is lower than 10,the algae biomass increases,and the algae growth belongs to n limit with the increase of N/P value;when N/P>40,the algae biomass shows a decreasing or stable trend with the increase of N/P value,and the algae growth belongs to P limit.During the algal bloom,the proportion of NH3-N and NO3--N in the main stream of the Haihe River did not change significantly,while the concentration of Org-N showed a significant upward trend.According to the change characteristics of δ15N and δ180 of NO3--N in the water,as the content of NH3-N in the main stream of the Haihe River was relatively sufficient,the algae preferentially used the NH3-N in the water body to synthesize their own substances.Nitrogen was released into the water body by releasing Org-N and trace amount of NO3--N,which completed the conversion of NH3-N to Org-N,but the microbial effect of NH3-N and NO3--N in the water body was weak.After algal bloom,DOM content increased from 26.47mg/1 to 38.20mg/l,C/N ratio decreased from 18.51 to 6.39,and N/P ratio increased from 5.69 to 20.10.In general,the composition of DOM changed from a more complex variety of terrestrial source to a Mainly composition for algae endogenous.Algal bloom not only increased the content of DOM in water,but also changed its molecular weight,element composition and composition.After the outbreak of algal bloom,the composition of DOM changed from a complex variety of land-based sources to a relatively single algal source,which affected the bioavailability of pollutants in the water,and the bioavailability of Cu and Zn in the water decreased.With the outbreak of algal bloom,the half lethal concentration of Cu and Zn to Daphnia magna increased gradually,and the maximum and continuous reference concentrations increased significantly,about three times as much as before. |