Assessing risks of algal blooms in water transfer based on algal growth potential.

Water transfer is an effective way to solve the unequal distribution of water resources to meet the needs of urban residents and industry. Annual wet weight data indicated that there may be algal blooms during water transfer. We explored the ecological risk of water transfer from Xiashan to the Jihongtan reservoir through algae growth potential (AGP) tests. The results showed that the Jihongtan reservoir had certain self-regulation abilities. When the total dissolved phosphorus (TDP) concentration was not more than 0.04 mg/L, the risk of algal bloom was low. When the N/P ratio (by mass) was less than 40, the ecological imbalance of algal growth may be caused. When the N/P ratio was 20, it was the best environment for algal growth. Under the current nutrient condition of the Jihongtan reservoir, the volume of ecological safety threshold in water transfer was 60% of the Jihongtan reservoir's capacity. If the nutrient level was further increased, the water transfer threshold would rise to 75%. In addition, water transfer may cause the homogenization of water quality and accelerate the eutrophication process of reservoirs. Regarding risk assessment, we believe that controlling nitrogen and phosphorus are more consistent with the natural evolution of reservoirs than controlling phosphorus alone for solving the problem of eutrophication.

The integrative effect of periphyton biofilm and tape grass (Vallisneria natans) on internal loading of shallow eutrophic lakes.

The response of periphyton biofilm and the submerged macrophyte tape grass (Vallisneria natans) to internal loading from eutrophic lake sediments were evaluated in microcosms. The sediments from the littoral zone and center of a lake were selected to carry out the microcosm experiment. To determine how the differences in the periphyton biofilm and V. natans growth alone or in combination, we measured changes in water quality, growth, and TP in the periphyton biofilm and V. natans in microcosms containing these sediments. The results showed that the average daily TN and TP removal rates were 32.6 and 35.4%, respectively, in the microcosms containing the lake center sediments by V. natans and the periphyton biofilm. The presence of the periphyton biofilm and V. natans increased the pH, dissolved oxygen, and redox potential and decreased the conductivity in the overlying water in all treatments. Compared to the state before the treatments, V. natans grew well, with a significant increase in biomass (3.1- to 5.5-fold growth) and TP amount (5.1- to 8.8-fold) in all treatments after 48 days. However, the growth of V. natans that combined with the periphyton biofilm was better than that of V. natans alone, as reflected by the dry weight, chlorophyll a content, malondialdehyde content, and TP amount. In conclusion, the periphyton biofilm was beneficial for the growth of V. natans, and the appropriate combination of V. natans and periphyton biofilm would be a potential method for the ecological restoration of eutrophic lakes.

Removal and retention of phosphorus by periphyton from wastewater with high organic load.

The total phosphorus (TP) removal efficiency from organic wastewater (pig farm and distillery wastewater) were estimated by using filamentous green algae (FGA) and benthic algal mats (BAM) treatment systems under laboratory conditions, and the contents of periphyton phosphorus fractions were determined by using a sequential extraction. The removal rates of TP reached 59-78% within the first 8 days of all treatment systems and could achieve average 80% during 30 day period, and the phosphorus removal rates by using BAM was higher than that of FGA. The ability of retention TP of periphyton enhanced gradually, the BAM TP contents were higher than that of FGA, the highest TP concentrations of BAM and FGA were 26.24 and 10.52 mg P g(-1)·dry weight. Inorganic phosphorus (IP) always exceeded 67.5% of TP, but the organic phosphorus fraction only made up less than 20% of TP. The calcium-binding phosphorus (Ca-P) was the dominant fraction and its relative contribution to TP was more than 40%. The TP was also strongly and positively correlated with the IP and Ca-P (p < 0.01) in periphyton. It showed that the periphyton had a potential ability of rapid phosphorus removing and remarkable retention from wastewater with high load phosphorus.