Submerged vegetation removal promotes shift of dominant phytoplankton functional groups in a eutrophic lake

Historical data indicate that the dominance of submerged plants in Dianchi Lake in the 1960 s was characterized by low algal density with dominance of non-toxic group J（Scenedesmus,Pediastrum,etc.）. The removal of submerged plants,which began in the 1970 s,resulted in the expansion of bloom-forming Microcystis（group M）. Laboratory experiments suggested that Microcystis aeruginosa was inclined to grow and develop at elevated temperatures. The growth of Scenedesmus obliquus was slower than that of co-cultivated M. aeruginosa in the absence of Ceratophyllum demersum,especially at higher temperatures. The existence of submerged plant C. demersum could inhibit the growth of the harmful algae M. aeruginosa and this inhibitory effect by C. demersum was enhanced with an increase in temperature. Instead,with C. demersum,the growth of S. obliquus was not inhibited,but the co-cultivated M. aeruginosa was eliminated in a short time. Combined with the historical data and laboratory experiments,it was indicated that the submerged plants might play important roles in the dominance of the non-toxic group J in the historical succession. Consequently,the introduction of the submerged plant such as C. demersum might alter the dominant phytoplankton functional groups from M to J and benefit the restoration of the eutrophic lake.

Removing nitrogen and phosphorus from simulated wastewater using algal biofilm technique

Algal biofilmtechnology is a new and advanced wastewater treatment method.Experimental study on removing nitrogen and phosphorus from simulated wastewater using algal biofilm under the continuous light of 3500 Lux in the batch and continuous systems was carried out in this paper to assess the performance of algal biofilm in removing nutrients.The results showed that the effect of removing nitrogen and phosphorus by algal biofilm was remarkable in the batch system.The removal efficiencies of total phosphorus(TP),total nitrogen(TN),ammonianitrogen(NH_(3)-N),and chemical oxygen demand(COD)reached 98.17%,86.58%,91.88%,and 97.11%,respectively.In the continuous system,hydraulic retention time(HRT)of 4 days was adopted;the effects of removing TP,TN,NH_(3)-N,and COD by algal biofilm were very stable.During a run of 24 days,the removal efficiencies of TP,TN,NH_(3)-N,and COD reached 95.38%,83.93%,82.38%,and 92.31%,respectively.This study demonstrates the feasibility of removing nitrogen and phosphorus from simulated wastewater using algal biofilm.