Trading offspring for survival: high duckweed cover decreases reproductive potential and stimulates elongation in the submerged macrophyte Chara globularis Thuillier

Compact blankets of free-floating plants generate stressful aquatic environments. The response of submerged macrophytes remains largely elusive. Will they rush toward the light or rather speed up reproductive efforts and escape using propagules—the macrophyte equivalent of lifeboats? We studied the effects of complete duckweed (Lemna minor) cover on growth and reproductive fitness of macroalga Chara globularis in a pond mesocosm experiment. C. globularis growing in Lemna-covered plots lost biomass and developed longer internodes, indicating an elongative reflex to escape stress. Densities of reproductive organs per biomass unit evolved positively in open plots and negatively in covered plots, suggesting a trade-off between reproductive effort and vegetative elongation. Reproductive potential correlated significantly with incident radiation. Lemna cover, however, did not affect oospore rain—at least within the limited time span of propagule trapping. C. globularis thus displayed an ability to modify phenology in response to floating plant stress, allocating resources to internodes instead of gametangia. Nevertheless, duckweed dominance clearly suppressed the overall reproductive performance of C. globularis. The regenerative capacity of many submerged macrophytes will likely suffer from increased floating plant dominance due to global warming—unless efforts are made to reduce nutrient levels in vulnerable waterbodies.

Removing Nutrients from Crab-Breeding Wastewater by a Floating Plant–Effective Microorganism Bed

Effective microorganism treatment, a low-cost and remediation measure that with no secondary pollution, was conducted in aquaculture wastewater. Unfortunately, effective microorganism erosion caused by the momentum of water flow under in situ conditions limits the treatment effect. In the channel test, a floating plant bed coupled with the effective microorganism was used to treat crab-breeding wastewater. This study explored the effect of plant coverage and hydraulic loading on aquaculture wastewater purification in the floating plant bed–effective microorganism coupled system. The results show that the effect of the coupled treatment effect is much better than pure microorganism treatment. The pollutant degradation coefficient has a significantly positive correlation with the length of the floating plant bed. A plant coverage rate of 30% and effluent hydraulic loading of 1.0 m3/m2·day are optimum floating plant bed–effective microorganism test conditions. Once the coverage rate exceeded 30%, the increase in the CODMn removal efficiency was not clear. At the same time, the high plant coverage inhibited the oxygen capacity in the water body, which directly led to a decrease in the degradation ability of organic matter by the plant. The biology–ecology coupled technology proposed in this study overcame the shortcomings of the easy-to-lose effective microorganism during the traditional unfixed process and improved the stability of the processing system. It strengthened the crab-breeding wastewater remediation effect. For an in situ application, the artificial restoration system 1 km in length was efficient, and the discharge met the standard at the end of the river.

Living with floating vegetation invasions

Invasions of water bodies by floating vegetation, including water hyacinth (Eichhornia crassipes), are a huge global problem for fisheries, hydropower generation, and transportation. We analyzed floating plant coverage on 20 reservoirs across the world’s tropics and subtropics, using > 30 year time-series of LANDSAT remote-sensing imagery. Despite decades of costly weed control, floating invasion severity is increasing. Floating plant coverage correlates with expanding urban land cover in catchments, implicating urban nutrient sources as plausible drivers. Floating vegetation invasions have undeniable societal costs, but also provide benefits. Water hyacinths efficiently absorb nutrients from eutrophic waters, mitigating nutrient pollution problems. When washed up on shores, plants may become compost, increasing soil fertility. The biomass is increasingly used as a renewable biofuel. We propose a more nuanced perspective on these invasions moving away from futile eradication attempts towards an ecosystem management strategy that minimizes negative impacts while integrating potential social and environmental benefits.

Effects and Mechanisms of Calcium Ion Addition on Lead Removal from Water by Eichhornia crassipes

Karst water is rich in calcium ions (Ca2+) and exhibits poor metal availability and low biodegradation efficiency. This study sought to analyze the effects and mechanisms of Ca2+ on lead (Pb) removal and absorption by Eichhornia crassipes (a floating plant common in karst areas). Moreover, the morphology and functional groups of E. crassipes in water were characterized via SEM, and FTIR. The results demonstrated that the removal rate of Pb in karst water (85.31%) was higher than that in non-karst water (77.04%); however, the Pb bioconcentration amount (BCA) in E. crassipes roots in karst water (1763 mg/kg) was lower than that in non-karst water (2143 mg/kg). With increased Ca2+ concentrations (60, 80, and 100 mg/L) in karst water, the Pb removal rate increased (85.31%, 88.87%, and 92.44%), the Pb BCA decreased (1763, 1317, and 1095 mg/kg), and the Ca BCA increased (6801, 6955, and 9368 mg/kg), which was attributed to PbCO3 and PbSO4 precipitation and competitive Ca and Pb absorption. High Ca2+ concentrations increased the strength of cation exchange, alleviated the fracture degree of fibrous roots, reduced the atrophy of vascular bundles, protected the cell wall, promoted C–O combined with Pb, enhanced the strength of O‒H, SO42−, C=O, and reduced the oxidization of alkynyl acetylene bonds.