Search Results (30)

Hydrilla, an invasive submerged macrophyte that is classified as a noxious weed in the U.S., can quickly spread into extensive monospecific infestations, excluding other native macrophytes and disrupting entire lake ecosystems. In Florida, infestation has increased tenfold in just three years, consuming over 60% of total management costs and requiring millions of dollars in annual control efforts. Traditional monitoring methods, such as field sampling, provide accurate localized assessments but are expensive and time-consuming. This study leverages Sentinel-2 satellite imagery, introducing the Submerged Aquatic Vegetation Index for Hydrilla (SVI_H), a novel three-band index utilizing the green (G, 560 nm), red-edge 1 (RE1, 705 nm), and shortwave infrared 1 (SWIR1, 1610 nm) bands to distinguish hydrilla from water and emergent aquatic vegetation (EAV) in two Florida lakes. The index, coupled with other vegetation indices, was validated using in situ measurements of hydrilla abundance levels, confirming its strong ability to accurately distinguish hydrilla. At the highest abundance level, SVI_H produced the highest Mathew correlation coefficients (MCCs), i.e., >0.86 for Lake Yale (2021), and >0.60 (2020) and >0.68 (2021) for Lake Apopka, using three thresholding methods. For Apopka (2022), other tested indices such as MFI and FAI yielded high MCC values along with high recall using incremental search threshold. However, these indices could not distinguish EAV from SAV in the eastern regions of Lakes Apopka and Yale, where EAV was dominant. These findings encourage the use of SVI_H for routine hydrilla detection and mapping, facilitating improved management, conservation efforts, and targeted herbicide applications. Full article

Submerged macrophytes are essential for the restoration of shallow lakes for maintaining clear-water conditions. The presence of fish can affect the nutrient cycles and the growth of submerged macrophytes in lakes. In this study, a 28-day mesocosm experiment was carried out with an herbivorous fish Ctenopharyngodon idella (CID) and an omni-benthivorous fish Carassius auratus (CAU) to investigate their effects on the growth of a submerged macrophyte Hydrilla verticillata and phosphorus (P) cycle in shallow lakes. The results showed that CID slowed down the growth of H. verticillata while CAU showed no significant effect. In overlying water, CID only increased the ammonium nitrogen (NH₃-N) concentration in the later stage due to excretion, while CAU elevated particulate phosphorus (PP) levels during the experiment through disturbance. Meanwhile, the radial oxygen loss and photosynthesis of H. verticillata in CAU might promote the formation of NaOH-P and HCl-P in the sediment, respectively. Changes in the water and sediment properties caused by CID and CAU can contribute to the increase in the eutrophication risk index (ERI). Our findings suggest that CID has the potential to be an indirect biological manipulation tool, while CAU should be controlled to minimize its negative impacts on the P cycle in lakes. Full article

Communities with high native species diversity tend to be less susceptible to the establishment of invasive species, especially in studies that test their local impact. This study investigated the impact of competition between native submerged aquatic macrophytes (SAMs) (Egeria najas and Egeria densa) and the exotic Hydrilla verticillata, recognized for its invasive potential in aquatic ecosystems, through a mesocosm experiment conducted over six months. Two treatments were evaluated: the intraspecific competition of H. verticillata and an interspecific competition involving all three species. The plants were cultivated under controlled conditions, with the foliar and subterranean biomass being monitored to analyze resource allocation patterns. The results showed that, under interspecific competition, the mean foliar biomass of H. verticillata was significantly higher compared to the intraspecific treatment, while the subterranean biomass was reduced in the presence of native species. We conclude that native species alter the biomass allocation pattern of the invader, favoring foliar structures over subterranean ones. Among the mechanisms of invasiveness, differential resource allocation represents an important strategy for the adaptation and competitiveness of invasive species influenced by environmental factors and resource competition. These findings contribute to the understanding of competitive interactions in aquatic ecosystems and have implications for the management and control of invasive species, highlighting the importance of promoting native diversity to mitigate invasibility. Future studies should investigate the impacts of reduced subterranean structures on the persistence and spread of submerged invasive species. Full article

Lake Trafford, a 600-ha subtropical lake in southwestern Florida, has suffered from over 50 years of cultural eutrophication, resulting in the invasion of Hydrilla verticillata and organic sediment accumulation due to herbicide treatments. This study aimed to assess the effects of dredging on nutrient dynamics. A pre-dredging nutrient budget, developed using land use models and climatic data, estimated nutrient loads of 190 kg d⁻¹ for total nitrogen (TN) and 18.6 kg d⁻¹ for total phosphorus (TP), with total maximum daily loads (TMDLs) of 70.4 kg d⁻¹ for TN and 4.15 kg d⁻¹ for TP. Post-dredging analysis, using detailed spatiotemporal data, showed higher nutrient loads of 274.3 kg d⁻¹ for TN and 24.2 kg d⁻¹ for TP. While dredging reduced legacy nutrient accumulation, it led to increased nutrient influx from groundwater, caused by the exposure of organic sediment, as evidenced by increased lake water electrical conductivity. These findings demonstrate the importance of conducting thorough pre-dredging assessments to mitigate unintended consequences, offering practical insights for managing nutrient loads and improving restoration strategies in eutrophic lakes. Full article

Submerged aquatic plants have potential applications in the phytoremediation of aquatic environments contaminated with arsenic (As). However, the role of epiphytic bacteria that grow on the surface of plants in As uptake and metabolism in plants has often been overlooked. An orthogonal experimental design with nine treatments, four factors, and three levels was conducted to inspect the effects of nitrogen (N, KNO₃, 2, 4, 10 mg/L), phosphorus (P, NaH₂PO₄·2H₂O, 0.02, 0.2, 1 mg/L), pH (6, 7, 9), and arsenate (As(V), Na₃AsO₄·12H₂O, 15, 75, 375 μg/L) on As accumulation and biotransformation in sterilized plants and to further explore the role of epiphytic bacteria in the metabolism of As by Hydrilla verticillata (L.f.) Royle. The results indicate that low N, intermediate P, and intermediate pH were beneficial for As accumulation (117.2 ± 62.2 μg/g DW) in sterilized plants, and epiphytic bacteria exhibited promotion (68%) in plants. High N promoted As absorption and transformation in non-sterilized plants but reduced As absorption in sterilized plants. Epiphytic bacteria in the medium showed significant As(III) oxidation, which was affected by environmental factors. These findings can promote remediation efficiency by regulating environmental factors for the phytoremediation of As-contaminated waters. Full article

Ecological restoration in dredging areas has attracted increasing attention. The reconstruction of a submerged plant ecosystem is an important method for aquatic ecosystem restoration. This study has systematically investigated the effect of biochar-improved sediment on the plant growth and decontamination efficiency of a constructed ecosystem. Microbial community composition and structure in the sediment were detected. The results showed that a supplement of 20 mg/g of biochar significantly increased the biomass of the submerged plants compared with other doses (0, 10, and 40 mg/g). The biomass and chlorophyll content were significantly inhibited by supplementing 40 mg/g of biochar. In the Ceratophyllum demersum L. system, TP and NH₄⁺-N concentrations were significantly lower after treatment with 20 mg/g of biochar compared to other doses. In Vallisneria spiralis L. and Hydrilla verticillata (L. f.) Royle systems, NH₄⁺-N, TP, and DO concentrations were significantly different among different biochar treatments. In general, 20 mg/g of biochar improved water quality in different submerged plant systems, while 40 mg/g of biochar had adverse effects on water quality, such as higher NH4⁺-N and TP concentrations. The dominant microbial community included Proteobacteria, Acidobacteria, Chloroflexi, Actinobacteriota, and Bacteroidota. The structure and function of microbial communities were different among submerged plants and biochar treatments. Our results proposed a construction strategy of submerged plants in the dredging area. Full article

Submerged macrophytes in eutrophic aquatic environments adapt to changes in ammonia nitrogen (NH₄-N) levels by modifying their levels of free amino acids (FAAs) and soluble carbohydrates (SCs). As symbionts of submerged macrophytes, epiphytic bacteria have obvious host specificity. In the present study, the interspecific differences in the FAA and SC contents of Hydrilla verticillata (Linn. f.) Roylep, Vallisneria natans Hara and Chara braunii Gmelin and their leaf epiphytic bacterial communities were assessed in response to increased NH₄-N concentrations. The results revealed that the response of the three submerged macrophytes to NH₄-N stress involved the consumption of SCs and the production of FAAs. The NH₄-N concentration had a greater impact on the variation in the FAA content, whereas the variation in the SC content was primarily influenced by the species. At the phylum level, the relative abundance of Nitrospirota on the leaves exhibited specific differences, with the order H. verticillata > V. natans > C. braunii. The dominant genera of epiphytic bacteria with denitrification effects on V. natans, H. verticillata and C. braunii leaves were Halomonas, Acinetobacter and Bacillus, respectively. When faced with NH₄-N stress, the variation in epiphytic bacterial populations associated with ammonia oxidation and denitrification among submerged macrophytes could contribute to their divergent responses to heightened nitrogen levels. Full article

The increasing use of herbicides in intelligent agricultural production is driven by the time-consuming nature of manual weeding, as well as its ephemeral effectiveness. However, herbicides like butachlor degrade slowly and can be washed away by rainwater, ultimately flowing into the farm ponds and posing risks to aquatic plants. To identify and recommend superior restoration strategies that effectively address the challenges posed by butachlor, we investigated the impacts of butachlor on the growth and physiology of four common aquatic plants (i.e., Hydrilla verticillata, Ceratophyllum demersum, Potamogeton maackianus, and Myriophyllum aquaticum) and their potential role in mitigating environmental damage by reducing residual herbicide levels. Our findings indicated that M. aquaticum was tolerant to butachlor, exhibiting higher growth rates than other species when exposed to various butachlor concentrations. However, the concentration of butachlor negatively impacted the growth of H. verticillata, C. demersum, and P. maackianus, with higher concentrations leading to more significant inhibitory effects. After a 15-day experimental period, aquatic plants reduced the butachlor residuals in culture mediums across concentrations of 0.5 mg/L, 1 mg/L, and 2 mg/L compared to non-plant controls. Our findings classified P. maackianus as butachlor-sensitive and M. aquaticum as butachlor-tolerant species. This investigation represents novel research aimed at elucidating the contrasting effects of different concentrations of butachlor on four common aquatic species in the agricultural multi-pond system. Full article

East Asia leads the global chemical industry, but environmental chemical risk in these countries is an emerging concern. Despite this, only a few native species that are representative of East Asian environments are listed as test species in international guidelines compared with those native to Europe and America. This review suggests that Zacco platypus, Misgurnus anguillicaudatus, Hydrilla verticillata, Neocaridina denticulata spp., and Scenedesmus obliquus, all resident to East Asia, are promising test species for ecotoxicity tests. The utility of these five species in environmental risk assessment (ERA) varies depending on their individual traits and the state of ecotoxicity research, indicating a need for different applications of each species according to ERA objectives. Furthermore, the traits of these five species can complement each other when assessing chemical effects under diverse exposure scenarios, suggesting they can form a versatile battery for ERA. This review also analyzes recent trends in ecotoxicity studies and proposes emerging research issues, such as the application of alternative test methods, comparative studies using model species, the identification of specific markers for test species, and performance of toxicity tests under environmentally relevant conditions. The information provided on the utility of the five species and alternative issues in toxicity tests could assist in selecting test species suited to study objectives for more effective ERA. Full article

Aquatic plant restoration is an important technique for the treatment of eutrophic water bodies. There are significant differences in pollutant removal efficiency among different combinations of aquatic plant species in eutrophic water bodies. Therefore, further research on the selection of suitable combinations of aquatic plant species is of great significance for the restoration of eutrophic water bodies. This study investigated the pollutant removal efficiency and bacterial community structure of three novel combinations of aquatic plants, including Lythraceae, Nymphaea, and Myriophyllum (LNM group), Lythraceae, Nymphaea, and Hydrilla verticillata (LNH group), and Lythraceae, Nymphaea, and Vallisneria (LNV group), as well as a control group (CK group). The components of the CK group were only sediment and culture water without any plants. The results show that on one hand, the LNH group had the highest removal rate of COD (90.29%); the LNV group exhibited the highest removal rates for NH₄⁺-N and TN, with removal rates of 61.20% and 82.94%, respectively; and there was no significant difference in the removal rate of TP among the experimental groups, except for the LNH group, which showed higher initial removal efficiency for TP. On the other hand, plant combinations had different impacts on the top 13 dominant microflora at the phylum level. Proteobacteria and Actinobacteria showed the highest removal efficiency for COD in the LNH group, while Verrucomicrobi, Chloroflex, and Acidobacteria showed higher removal efficiency for NH₄⁺-N and TN in the LNV and LNH groups. In summary, the three different combinations of aquatic plants exhibited distinct pollutant removal characteristics, significantly altered the structure of the microbial community, and provided a theoretical basis for their practical application in the restoration of eutrophic water bodies. Full article

Submerged macrophyes have been widely used to restore aquaculture ponds in recent years. Yet, whether the residual antibiotics in ponds will affect the remediation effect of submerged macrophyes, and the effect of different submerged macrophyes on the water and sediment in aquaculture ponds with antibiotic residues, is unclear. A microcosm experiment was carried out to study the interaction between three kinds of submerged macrophytes and their growing environment with antibiotic residues. Ceratophyllum demersum L. with no roots, Vallisneria spiralis L. with flourish roots, and Hydrilla verticillata L with little roots were chosen to be planted in the sediment added with enrofloxacin (ENR). The growth of submerged macrophytes, the changes of the overlying water and sediment characteristics, and the microbial community in the sediment were analyzed. The results showed that according to the growth rate and nutrients accumulation ability, V. spiralis with flourish roots performed best among the three submerged macrophytes. The concentrations of TOC, TP, NH₄⁺-N, and TN in the overlying water were 25.0%, 71.7%, 38.1%, and 24.8% lower in the V. spiralis treatment comparing with the control, respectively. The richness and diversity of the microorganisms in the sediment of V. spiralis treatment were significantly higher than those in the control, but this advantage was not obvious in the H. verticillata treatment. V. spiralis promoted the growth of Proteobacteria (22.8%) and inhibited the growth of Acidobacteria (32.1%) and Chloflexi (31.7%) in the rhizosphere sediment with ENR residue. The effects of the three submerged macrophytes on the removal of ENR from sediment were not reflected due to the limitation of water depth. Compared with C. demersum and H. verticillata, V. spiralis was more suitable for the remediation of the aquaculture ponds with ENR residue. Full article

Submerged macrophyte and periphyton are main primary producers which strongly interact with each other in clear water shallow lakes. In this study, the effects of genetic variation of the macrophyte species on periphyton biomass were studied in five submerged species. A two-year mesocosm study was conducted with four levels of genetic diversity (1, 4, 8 and 16 genotypes) for each submerged macrophyte, including 1600 individuals and 320 boxes in 20 mesocosms. Of the five submerged species, only Vallisneria spinulosa showed a positive correlation between its levels of genotype richness and the periphyton biomass. The correlation between genetic distance of genotypes and periphyton biomass was tested, which varied with the difference of seasons and species. In summary, we found that in freshwater mesocosms, the genetic diversity of submerged macrophytes may play a role in regulating the periphyton biomass, but the interaction between genetic diversity of macrophytes and periphyton biomass was not straightforward. This study will provide new insights into the interaction dynamics between the two primary producers in shallow lakes. Full article

A variety of remediation approaches have been applied to reduce the harm and diffusion of heavy metals in aquatic sediments; however, phytoremediation in co-contaminated soils is still not clear. In order to explore the phytoremediation of sediments contaminated by Cu and Pb, two submerged plants with different characteristics, Vallisneria natans and Hydrilla verticillata, were interplanted with Myriophyllum spicatum. By simulating a submerged plant ecological environment, medium-scale-simulated ecological remediation experiments were carried out. The results showed that the two planting patterns were effective in repairing the sediments in the Cu and Pb contaminated sediments. The intercropping of Myriophyllum spicatum and Vallisneria natans can be used as the plant stabilizer of Cu because of the TF > 1 and BCF < 1, and the intercropping with Hydrilla verticillata can regulate the enrichment efficiency of Myriophyllum spicatum. The removal rates of Cu and Pb in sediments reached 26.1% and 68.4%, respectively, under the two planting patterns. The risk grade of the restored sediments was RI < 150, indicating a low risk. Full article

Negative impacts from aquatic invasive plants in the United States include economic costs, loss of commercial and recreational use, and environmental damage. Simulation models are valuable tools for predicting the invasion potentials of species and for the management of existing infestations. We developed a spatially explicit, agent-based model representing the invasion, growth, and senescence of aquatic weeds as functions of day length, water temperature, water depth, and the response of aquatic weeds to biological control. As a case study to evaluate its potential utility, we parameterized the model to represent two historical invasions (1975–1983 and 2004–2007) of Hydrilla (Hydrilla verticillata (L. fil.) Royle) in Lake Conroe, Texas, USA, and their subsequent biological control using grass carp (Ctenopharyngodon idella). Results of several hypothetical alternative management schemes indicated that grass carp stocking densities needed to control Hydrilla infestation increased exponentially as the lag time between initial invasion and initial stocking increased, whereas stocking densities needed to control infestation decreased as the amount of time allowed to control the infestation increased. Predictions such as those produced by our model aid managers in developing proactive management plans for areas most likely to be invaded. Full article

The effects of harvesting intensity on the growth of Hydrilla verticillata (L. fil.) Royle as well as water quality were studied in controlled experiments to provide a reference for managing submerged vegetation and purifying the water. The results showed that harvesting had a significant effect on the recovery of shoot growth and H. verticillata height. The harvested group recovered completely or mostly after two harvests, but the recovery time was significantly longer than the control group. The final biomasses of the harvested groups (15%, 30%, 45%, 60%, and 75% harvested) decreased to 66.61%, 49.13%, 43.95%, 43.77%, and 29.94% of the control group, respectively. The greater the harvesting intensity, the fewer the winter buds. Harvesting reduced the number of H. verticillata branches. Repeated harvesting at medium and low intensities during the rapid growth of H. verticillata effectively improved the water quality and inhibited the propagation and growth of phytoplankton. These results show that harvesting controlled the growth of H. verticillata, and that medium and low harvesting intensities were best when considering water quality. Full article