Distribution And Bioavailability Of Colloidal Organic Matter In Lake Taihu

Taihu lake is the third largest freshwater lake in China as well as an important freshwater resource in the middle and lower reaches of the Yangtze River.At present,excessive input of nutrients such as nitrogen and phosphorus in the basin has led to frequent outbreaks of Taihu Lake blooms.Colloidal substances are ubiquitous in natural water bodies,and a large number of colloidal particles affect the inorganic and organic matter in water bodies through the adsorption-desorption process,then affecting the community structure of phyto-plankton.This thesis takes Taihu Lake and its northern river courses as the research object.Using cross-flow ultrfiltration system to concentrate the colloidal solution.To obtain the origin and distribution of the natural colloids in Taihu lake,the distribution of colloidal CDOM and colloidal amino acids in Taihu lake and it river courses were studied in spatial and temporal.The spatial and temporal distribution and composition characteristics of CDOM in Taihu lake and its river courses were analyzed by Three-Dimensional Fluorescence Spectrum,and the spatial and temporal distribution and composition characteristics of amino acids in Taihu lake and its river courses were analyzed by Sykam amino acid analyzer.Microcystis aeruginosa cultured in the medium with different gradient colloidal concentration,and the bioavailability of colloid was analyzed by Phyto-Pam and cell count methods.The main results were as follows:(1)The spatial distribution of CDOM absorption coefficient in Taihu lake shows that the CDOM absorption coefficient in the entrance of Taihu lake and its inflow rivers are significantly higher than the center of Taihu lake,and in the algae-type zone is higher than the grace-type zone.Indicating that inflow river has a significant input effect on the CDOM of the Taihu lake.The whole lake showes a strong peak of proteinlike fluorescent components,mainly based on protein-like D peaks.The fluorescence intensity of humic-like was higher in the inflow rivers and estuaries,while protein-like components were the main ingredient in the center of lake and the algae-type zone,indicating that these areas are less affected by inflow rivers and mainly input by algae degradation.(2)The spatial distribution of amino acid content in Taihu Lake shows that the content of the amino acids in the river are higher than its river courses,and the content of amino acids in lake area are higher than that of river courses.Indicating that the content of amino acid in river courses is affected by both external input and biodegradation.Basic amino acids are the main amino acids in Taihu lake which is difficult to degrade.The content of acidic amino acids in the center of Taihu and inflow rivers are higher than that in the estuary,that is,the acidic amino acids has been degraded before reaching the center of Taihu lake,and the changes of amino acid content in the center Taihu was consistent with the seasonal change.Indicates that the increase of amino acid content in the center of Taihu is mainly due to the increase of endogenous organic matter.The content of amino acids in the inflow river was higher than that in the estuary,and the content in the center of lake was haigher than that in estuary.Indicating that the input of amino acids in the estuary were mainly from inflow river.(3)The content of nitrogen and phosphorus in the colloid is higher.The content of N and P in the colloid treatment is higher than that in the control group.Compared with the non-sterile colloid,the sterilized colloid can significantly promote the growth of Microcystis aeruginosa.The number of cells in microcystis aeruginosa treated with 20% sterilized colloid concentrate was 7 times that of the control group,and the Chla content was 3 times that of the control group.However,the higher concentration not means the better growth of microcystis aeru-ginosa.Through the culture experiment of different gradient,it can be found that the treatment with 20% colloid concentration is more favorable for photosynthesis of microcystis aeruginosa,the growth of microcystis aeruginosa with 50% colloid concentration wsa preferably.In conclusion,the inflow river and estuary of the lake are mainly affected by external input,and the lake-bay and center of the lake are dominated by biogenic sources.Colloidal organic matter has a significant promotion effect on the growth of Microcystis aeruginosa,but the mechanism of promotion needs further study.The bioavailability study of colloids provides theoretical support for the mechanism of cyanobacterial blooms.