Effect of aquatic macrophyte growth on landscape water quality improvement

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.

Egeria densa organic extracts: an eco-friendly approach to suppress Microcystis aeruginosa growth through allelopathy

Macrophytes play a significant role in shaping plankton communities by shading, controlling water turbulence, and nutrient availability, while also producing allelochemicals causing varying effects on different organisms. Many researchers have shown that when live macrophytes are present, they inhibit cyanobacteria. However, their widespread use is often limited due to numerous concerns, including invasive characteristics. This study focused on the applicability of Egeria densa extracts to suppress Microcystis aeruginosa. We employed pure water and dimethyl sulfoxide, to obtain compounds from E. densa. The results revealed that E. densa aqueous extracts stimulated M. aeruginosa growth, whereas organic extracts exhibited suppression. Specifically, at low concentrations of organics extracts (0.5 and 1 g/L), after day 4, the growth inhibition was confirmed by significantly higher (p < 0.05) stress levels shown in cells treated with low concentrations. The highest inhibition rate of 32% was observed at 0.5 g/L. However, high concentrations of organic extracts (3 and 6 g/L), showed increased growth compared with control. These results suggest that high concentrations of organic extracts from E. densa potentially suppress allelochemical-induced M. aeruginosa inhibition due to high nutrient availability. In comparison with an aqueous solvent, the use of organic solvent seems to be more effective in efficiently extracting allelochemicals from E. densa.

The contribution of sediment desiccation and rewetting process to eutrophication in the presence and absence of emergent macrophytes

The purpose of current study was to investigate the effects of sediment desiccation on nutrient dynamics and eutrophication in wetlands during the presence or absence of wiry and sturdy rooted emergent macrophytes, based on the hypothesis that sediment desiccation negatively correlated with plants nutrient uptake abilities and positively with nutrients fluxes at sediment-water interface. Growth of four emergent macrophytes, including two wiry rooted plants, i.e., Alocasia cucullata and Aglaonema commutatum, and two sturdy rooted plants, i.e., Cannabis indica and Acorus calamus, were grown and investigated in dried-rewetted sediments (DS) and constantly wet sediments (WS), respectively, for 6 months. The findings revealed that sediment drying and rewetting process significantly decreased the diffusion of overlying nutrient into sediment and the particle size density, porosity, and nutrients' repository ability in DS treatments, while the sediment bulk density and mineralization of organic macronutrients increased. Compared to WS treatments, the DS treatments impaired plant growth, root biomass, shoot biomass, and stimulated higher fluxes of ammonium nitrogen ([Formula: see text]-N, 0.042-0.081 mg m ^{- 2} d ^{- 1}) and phosphate (P[Formula: see text] 0.009-0.030 mg m^-2 d^-1) at sediment-water interface upon rewetting. The higher internal release of macronutrients and dissolved organic carbon (DOC) from DS led to the higher chlorophyll-a (Chl-a) concentrations (34.47-21.28 to 41.76-33.36 μg L^-1) in their water column than in the water column of WS. The wiry rooted plants with higher root biomass displayed lower internal release of [Formula: see text]-N, PO₄³-P and DOC and water column Chl-a concentrations than the sturdy rooted plants in two sediment types. Root biomass of plants correlated positively with TN (63-87%) and TP (56-78%) removal percentages from WS and DS. These results demonstrated that sediment desiccation process reduced plant growth and enhanced internal loading of nutrients and consequently accelerated eutrophication in these wetlands.

The influence of flow rates and water depth gradients on the growth process of submerged macrophytes and the biomass composition of the phytoplankton assemblage in eutrophic water: an analysis based on submerged macrophytes photosynthesis parameters

Submerged macrophytes and phytoplankton assemblage play significant roles in the functioning of aquatic ecosystems. An experiment was carried out in Beijing in order to further evaluate the environmental factors that affect the growth of submerged macrophytes and phytoplankton assemblage. Submerged macrophytes (i.e., Vallisneria natans, Hydrilla verticillata, and Ceratophyllum demersum) constructed the growth system with some controllable influencing factors (i.e., the flow rate and water depth gradient). The flow rates were set separately as 4 L/h (1#), 6 L/h (2#), and 12 L/h (3#), while the water depth gradient was of 0.5-1.7 m in eutrophic water. Generally, all macrophytes could grow normally in the experiment, and the system could maintain and improve the effluent quality. The average removal rates of NH3-N, COD, NO3-N, TN, and TP were about 90%, 33%, 65%, 45%, and 40%, respectively. Seen from the results of the water depth gradient experiments, it is indicated that Vallisneria natans grows better in shallow water (0.5 m) and moderate shallow water (0.7 m) area, with an average relative growth rate (ARGA) of 57%. Hydrilla verticillata and Ceratophyllum demersum grow better in moderate deep water (1.2 m) and deep water (1.7 m) area (ARGA of 66% and 64%, respectively). Results of the flow rate experiments showed that the moderate flow rate (6 L/h) was the best for those three macrophytes' growth. As the fitting results of the rapid light curves (RLCs) showed that the utilization of light and the tolerance to strong light were different for these macrophytes, if they are ranked in the order of the utilization and the tolerance from strong to weak, they are Hydrilla verticillata, Ceratophyllum demersum, and Vallisneria natans. Microbial analyses indicated that the overall system diversity of the experimental groups have been improved after cultivation of macrophytes. However, the accumulated Cyanobacteria caused by the low flow rate (1#) would lead to the suppression of microbial organics decomposition and nutrient metabolism in the macrophytes. To sum up, the results of this study provided theoretical guidance and technical support for the restoration of submerged macrophytes in eutrophic water.

Nitrogen Metabolism in Acorus calamus L. Leaves Induced Changes in Response to Microcystin-LR at Environmentally Relevant Concentrations

Acorus calamus L., a semiaquatic plant with a high capacity to remove nitrogen and phosphorus from polluted water, is a potential candidate plant for use in the restoration of eutrophic aquatic ecosystems. However, it is not clear how microcystins (MCs), commonly found in eutrophic water, influence plant growth since the effects of MCs are likely to be dose and species dependent. The present study aimed to investigate the regulation of nitrogen metabolism, a key metabolic process related to plant growth, in the leaves of A. calamus L. exposed to microcystin-leucine-arginine (MC-LR) (1.0-29.8 µg/L). Nitrate (NO₃^-) uptake, assimilation and transformation was stimulated in the leaves of A. calamus L. when exposed to 1.0 µg/L MC-LR through the elevation of nitrate reductase (NR), glutamine synthetase (GS), glutamate synthase (GOGAT), glutamic-pyruvic transaminase (GPT), and glutamic-oxaloacetic transaminase (GOT) activity. Conversely, MC-LR inhibited nitrogen metabolism by decreasing NO₃^- uptake and the activities of enzymes related to nitrogen metabolism following exposure to MC-LR (9.9-29.8 µg/L) for 30 days, while, ammonium nitrogen (NH₄⁺) content and glutamate dehydrogenase (GDH) activity increased significantly (p < 0.05, LSD test), when compared with the control group. Chronic exposure to MC-LR (9.9-29.8 µg/L) negatively influenced nitrogen metabolism in A. calamus L. leaves, which suggested that it may not be a suitable candidate species for use in the restoration of eutrophic aquatic ecosystems containing MC-LR at concentrations ≥ 9.9 µg/L.