Reducing the Phytoplankton Biomass to Promote the Growth of Submerged Macrophytes by Introducing Artificial Aquatic Plants in Shallow Eutrophic Waters

Abstract

Harmful cyanobacterial blooms frequently occur in shallow eutrophic lakes and usually cause the decline of submerged vegetation. Therefore, artificial aquatic plants (AAPs) were introduced into enclosures in the eutrophic Dianchi Lake to investigate whether or not they could reduce cyanobacterial blooms and promote the growth of submerged macrophytes. On the 60th day after the AAPs were installed, the turbidity, total nitrogen (TN), total phosphorous (TP), and the cell density of phytoplankton (especially cyanobacteria) of the treated enclosures were significantly reduced as compared with the control enclosures. The adsorption and absorption of the subsequently formed periphyton biofilms attached to the AAPs effectively decreased nutrient levels in the water. Moreover, the microbial diversity and structure in the water changed with the development of periphyton biofilms, showing that the dominant planktonic algae shifted from Cyanophyta to Chlorophyta. The biodiversity of both planktonic and attached bacterial communities in the periphyton biofilm also gradually increased with time, and were higher than those of the control enclosures. The transplanted submerged macrophyte (Elodea nuttallii) in treated enclosures recovered effectively and reached 50% coverage in one month while those in the control enclosures failed to grow. The application of AAPs with incubated periphyton presents an environmentally-friendly and effective solution for reducing nutrients and controlling the biomass of phytoplankton, thereby promoting the restoration of submerged macrophytes in shallow eutrophic waters. co-precipitated phosphorus into the sediment [12]. Inorganic compounds in marl have been used to immobilize nutrients on the sediment surface, thus reducing nutrient concentrations in the water [13]. However, the aforementioned methodologies often have some effect on the original aquatic ecosystem, including changes in pH or salinity, which may threaten life in the lake [14]. Other measures have been applied to control the cyanobacterial blooms directly. Algaecides such as organic bromide, copper sulphate, and hydrogen peroxide have mostly been used to control large-scale cyanobacterial bloom as an emergency method, but these may result in an unsafe aquatic ecosystem and easily induce secondary pollution [15].Periphyton is an assemblage of freshwater organisms mainly composed of photoautotrophic algae, heterotrophic, and chemoautotrophic bacteria, fungi, protozoans, metazoans and viruses, which attach to submerged surfaces [16]. Periphyton plays a crucial role in nutrient cycling and in supporting food webs and it has an excellent ability to degrade pollutants in aquatic environments [17]. Previous studies have utilized biofilms to remove nitrogen and phosphorus from wastewater and to biodegrade other hazardous contaminants [18,19]. Moreover, microbial communities are easily incorporated into bioreactors, which result in efficient bioremediation operations [20]. Additionally, the microbial compositions of periphyton are derived fr...

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