Effects of Diversity, Coverage and Biomass of Submerged Macrophytes on Nutrient Concentrations, Water Clarity and Phytoplankton Biomass in Two Restored Shallow Lakes

Purification Effect of Water Eutrophication Using the Mosaic System of Submerged-Emerged Plants and Growth Response

Aquatic plants play a crucial role in the sustainable management of eutrophic water bodies, serving as a valuable tool for water purification. However, the effectiveness of using aquatic plants for improving water quality is influenced by landscape considerations. In practical applications, challenges arise concerning low purification efficiency and compromised aesthetic appeal when utilizing plants for water purification. To address these issues, this study aimed to examine the impact of aquatic plants on the purification of simulated landscape water bodies, specifically focusing on the effectiveness of the mosaic system of submerged-emerged plants in remediating eutrophic water bodies. Our findings indicated that individual aquatic plants exhibited limited efficacy in pollutant (total nitrogen, total phosphorus, ammonia nitrogen, and chemical oxygen demand) removal. However, when combined in appropriate proportions, submerged plants could enhance species growth and improve the purification efficiency of polluted water bodies. Notably, the mosaic system of submerged-emerged plants neither significantly promoted nor inhibited the growth of each other, but it effectively removed pollutants from the simulated water bodies and inhibited turbidity increase. The comprehensive evaluation ranked the purification capacity as Canna indica-submerged plants combination (C + S) > Thalia dealbata-submerged plants combination (T + S) > Iris pseudacorus-submerged plants combination (I + S) > Lythrum salicaria-submerged plants combination (L + S). Both C + S and T + S configurations effectively mitigated the rise of water turbidity and offered appealing landscape benefits, making them viable options for practical applications in urban landscape water bodies. Our study highlights that a submerged-emerged mosaic combination is a means of water purification that combines landscape aesthetics and purification efficiency.

Biomanipulation as a strategy for minimizing ecological risks in river supplied with reclaimed water

Reclaimed water is an effective method for addressing water pollution and shortages. However, its use may contribute to the collapse of receiving water (algal blooms and eutrophication) owing to its unique characteristics. A three-year biomanipulation project was conducted in Beijing to investigate the structural changes, stability, and potential risks to aquatic ecosystems associated with the reuse of reclaimed water in rivers. During the biomanipulation, the proportion of Cyanophyta in the community structure of phytoplankton density in river supplied with reclaimed water decreased, and the community composition shifted from Cyanophyta and Chlorophyta to Chlorophyta and Bacillariophyta. The biomanipulation project increased the number of zoobenthos and fish species and significantly increased fish density. Despite the significant difference in aquatic organisms community structure, diversity index and community stability of aquatic organisms remained stable during the biomanipulation. Our study provides a strategy for minimizing the hazards of reclaimed water through biomanipulation by reconstructing the community structure of reclaimed water, thereby making it safe for large-scale reuse in rivers.

Dynamic Interception Effect of Internal and External Nitrogen and Phosphorus Migration of Ecological Ditches

The “ecological ditch” (eco-ditch) is an effective measure used to alleviate agricultural non-point-source pollution. However, information is lacking about the continuous transport characteristics of internal and external nitrogen and phosphorus in the interstitial water of the bottom mud of these ditches and overlying water under dynamic continuous inflow conditions. Understanding of the effect of matrix dams and microbial communities inside eco-ditches on the continuous transport characteristics of the N and P therein needs to be improved. To determine the interception effects of eco-ditches on the transfer of endogenous and exogenous N and P, an eco-ditch combining plants and a matrix dam was built to explore the transport distribution characteristics of N and P in the intermittent water and overlying water in the bottom of the eco-ditch and in the bottom of the soil ditch. We compared and analyzed the composition characteristics of the microbiological communities along the ecological and soil ditches. The research results showed that: (1) The concentration gradient between the interstitial water and the overlying water in the soil ditch is the main reason for the transport and diffusion of pollutants. However, in eco-ditches, the absorption function of plant roots and the differences between the structures of the microbial communities destroy the correlation of this concentration gradient diffusion, especially the effect on ammonium N; (2) a large number of mycelia adhere to the surface of the matrix dam in an eco-ditch, and are conducive to the adsorption and purification of pollutants in the water; (3) Proteobacteria, Chloroflexi, Actinomycetes, and Acidobacteria were the main bacterial groups in the ditches. The aquatic plants in the eco-ditch changed the microenvironment of the sediment, and both the microbial diversity and abundance along the eco-ditch were higher than in the soil ditch.