[Temporal and Spatial Distribution Characteristics and Difference Analysis of Nitrogen and Phosphorus in Daihai Lake].

Based on the historical monitoring survey data from 2018 to 2019, the temporal and spatial distribution characteristics and main influencing factors of nitrogen and phosphorus in the overlying water in Daihai Lake were analyzed, and the differences of the temporal and spatial distribution were discussed. The results showed that the content of total nitrogen and total phosphorus in the overlying water was at a high level, especially the total nitrogen content was obviously higher than that in other lakes in China. The content of total nitrogen ranged from 3.29 mg·L-1 to 4.99 mg·L-1, with a mean value of (3.93±0.33) mg·L-1; the content of total phosphorus ranged from 0.063 mg·L-1 to 0.163 mg·L-1, with a mean value of (0.111±0.023) mg·L-1. In spring and summer, the content of total nitrogen and total phosphorus in the overlying deep water from the middle of the lake was significantly higher than that in the surrounding area. In autumn, the contents decreased from east to west, and in winter, the contents in the shallow water of the southern area were higher than that in the northern area. Nitrogen and phosphorus in the overlying water were mainly in the dissolved state, and the proportions of total dissolved nitrogen and phosphorus were 86.62% and 77.84%, respectively. The dissolved nitrogen was dominated by nitrate, whereas dissolved phosphorus was dominated by organic phosphorus. The concentration of lake water and the release of endogenous nutrient salts are the main reasons for the high total nitrogen and phosphorus. To prevent further deterioration of water quality, it is suggested to carry out endogenous treatment and ecological restoration in combination with engineering measures.

[Critical collapse pressure of gas vesicles in six strains of cyanobacteria].

Two methods including filtration (vacuity is 0.02 MPa) and centrifugation ( < 500 r/min) were applied to concentrate algal biomass, and capillary compression tube and the concentrated algae suspensions, critical pressure distribution of gas vesicles in six cyanobacteria were also investigated. The results showed that unicellular Microcystis aeruginosa cells couldn't be concentrated effectively by filtration or centrifugation, but colony of Microcystis wesenbergii and Microcystis flosaquae, and filament of Planktothrix mougeotii could be concentrated by centrifugation and filtration respectively. Both filtration and centrifugation had a negligibly impact on gas vesicles content of cells, and the loss of gas vesicles was lower than 7%. The mean critical pressure values of five strains Microcystis were very close, which ranged from 0.64 to 0.67 MPa, and the mean critical pressure of P. mougeotii was 0.715 MPa. All of the six cyanobacteria were isolated from three shallow lakes, and their mean critical pressure values were lower than those cyanobacteria that inhabit in deep lakes or reservoirs. At the same condition of illumination density and temperature, turgor pressures of two unicellular Microcystis were higher than those of colonial Microcystis.

[Effects of EDTA and iron on growth and competition of Microcystis aeruginosa and Scenedesmus quadricauda].

Not only population density of phytoplankton but also its community structure were influenced by iron limitation. The growth and competition of a cyanobacterium Microcystis aeruginosa and a green alga Scenedesmus quadricauda at different iron and EDTA concentrations were investigated using batch cultures. The results showed that the growth of M. aeruginosa was significantly inhibited whereas S. quadricauda wasn't when EDTA at high concentrations (> or = 13.5 micromol/L), and consequently, it favored the dominance of S. quadricauda. Moreover, increasing iron concentration from 3 micromol/L to 18 micromol/L could greatly alleviate the growth inhibition of M. aeruginosa while increasing concentration of other microelements e.g. B, Mn, Zn, Cu, Mo didn't. These results suggest that high EDTA concentration decreases iron availability for M. aeruginosa, but not for S. quadricauda. The reason that the two algae respond to high EDTA concentrations differently is that their adsorption strategies for iron should be different.

[Dynamic studies on the effect of nutrients on the growth of Microcystis aeruginosa].

The effects of nitrogen and phosphorus on the growth of Microcystis aeruginosa were investigated by using the Monod equation. The semi-saturation constants of Microcystis aeruginosa to TP (KsP) and TN (KsN) were calculated. The results show that KsN is higher than KsP. This indicates that the effect of TP on the growth of Microcystis aeruginos is further more significant than that of TN. Further analysis finds that extant quantity (X) and special growth rate (micro) of Microcystis aeruginosa increase with TP or TN, and there exists a point of inflection. When the concentrations of TP and TN ranged from 0.005mg/L to 0.2mg/L and from 0.01mg/L to 2mg/L respectively with TP or TN as the single limiting substrate, the growth rate of Microcystis aeruginosa increased rapidly. Because Microcystis aeruginosa exhibits different affinity with TP and TN (according to the semi-saturation constants), the effect of N/P ratio on the growth of Microcystis aeruginosa does not demonstrate at a constant value. No constant ratio can be used to determine the limiting nutrient elements on the growth of Microcystis aeruginosa in any aquatic environment. The effect of N/P ratio on the growth of Microcystis aeruginosa depends on both the N and P concentrations and the N/P ratio.