The integrative effect of periphyton biofilm and tape grass (Vallisneria natans) on internal loading of shallow eutrophic lakes

Enhancing water quality and ecosystems of reclaimed water-replenished river: A case study of Dongsha River, Beijing, China

The use of reclaimed water for urban river replenishment has raised concerns regarding its impact on water quality and aquatic ecosystems. This study aims to reveal the improvements seen in an urban river undergoing a practical water eco-remediation after being replenished with reclaimed water. A one-year monitoring of water quality, phytoplankton, and zooplankton was carried out in Dongsha River undergoing eco-remediation in Beijing, China. The results showed that compared to the unrestored river, the concentrations of COD, NH4+-N, TP, and TN decreased by 28.22 ± 7.88 %, 40.24 ± 11.77 %, 44.17 ± 17.29 %, and 28.66 ± 10.39 % in the restoration project area, respectively. The concentration of Chlorophyll-a in the restoration area was maintained below 40 μg/L. During summer, when algal growth is vigorous, the density of Cyanophyta in the unrestored river decreased from 46.84 × 104cells/L to 16.32 × 104cells/L in the restored area, while that of Chlorophyta decreased from 41.61 × 104cells/L to 11.87 × 104cells/L, a reduction of 65.16 % and 71.47 %, respectively. The dominant phytoplankton species were replaced with Bacillariophyta, such as Synedra sp. and Nitzschia sp., indicating that the restoration of aquatic plants reduces the risk of Cyanophyta blooms. Zooplankton species also changed in the restoration area, especially during summer. The density of pollution-tolerant Rotifer and Protozoa decreased by 31.06 % and 27.22 %, while the density of clean water indicating Cladocera increased by 101.19 %. We further calculated the diversity and evenness index of phytoplankton and zooplankton within and outside the restoration area. The results showed that the Shannon-Weaver index for phytoplankton and zooplankton in the restoration area was 2.1 and 1.91, which was higher than those in the river (1.84 and 1.82). This further confirmed that aquatic plant restoration has positive effects. This study can provide a practical reference and theoretical basis for the implementation of water ecological restoration projects in other reclaimed water rivers in China.

Long-term improvement of sediment in situ restoration and REDOX characteristics by Vallisneria natans coupling with carbon fiber

China is conducting ecological restoration work in urban water bodies. Under anoxic and anaerobic conditions, pollutants transform and produce odorous and black substances, deteriorating the water quality, which is a significant problem in urban water bodies. Vallisneria natans has received widespread attention for its applications in water treatment and restoration. However, the efficiency by which V. natans reduces water pollution and allows sediment remediation requires further improvement. Therefore, in this study, we investigated the effect of V. natans coupled with carbon fiber on the restoration of water bodies and sediment compared with the control group that grew V. natans without carbon fiber. The oxidation-reduction potential (ORP) was selected as the main evaluation index for the water and sediment. Dissolved oxygen in the water and total organic carbon and total nitrogen (TN) in the sediment were also evaluated. V. natans coupled with carbon fiber significantly increased the ORP; that of surface sediment increased by 50 % and that of the water body increased by 60 % compared with the sediment without any bioremediation. Chemical oxygen demand, total phosphorous, and TN in water decreased by 61.2 %, 22.9 %, and 48.3 %, respectively. These results indicate that planting V. natans with carbon fiber can reduce pollutants in water (including humus) and sediments, effectively improving ORP in water and sediment.

Effects of attapulgite on the growth status of submerged macrophytes Vallisneria spiralis and sediment microenvironment

The effects of raw attapulgite clay and thermally modified attapulgite clay on the growth status of submerged plant Vallisneria Spiralis (V. spiralis) and the microenvironment of sediment were first explored. The results demonstrated that the attapulgite could effectively promote the development of V. spiralis and improve plant stress resistance by enhancing the activity of antioxidant enzymes. The 10% addition of attapulgite clay increased the biomass of V. spiralis by 27%∼174%, and the promoted rate of raw attapulgite clay was 2∼5 times of modified attapulgite clay. The attapulgite increased redox potential in sediment (P < 0.05) and provided proper niches for organism propagation, further promoting the degradation of organic matter and nutrient metabolism in sediment. The value of Shannon, Chao, and Ace was 9.98, 4865.15, 5029.08 in the 10% modified attapulgite group, and 10.12, 4856.85, 4947.78 in the 20% raw attapulgite group, respectively, indicating that the attapulgite could increase the microbial diversity and abundance in sediment. Additionally, the nutrient elements, such as Ca, Na, S, Mg, K, Zn, and Mo, that dissolved from attapulgite may also promote the V. spiralis growth. This study provided an environment-friendly approach to facilitating submerged macrophyte restoration in the eutrophic lake ecosystem.

Combined toxic effects of perfluorooctanoic acid and microcystin-LR on submerged macrophytes and biofilms

Perfluorooctanoic acid (PFOA) and microcystin-LR (MCLR) are pervasive pollutants in surface waters that induce significant toxic effects on aquatic organisms. However, the combined environmental risk of PFOA and MCLR remains unclear. To assess the toxic effects of PFOA and MCLR on submerged macrophytes and biofilms, Vallisneria natans was exposed to different concentrations of PFOA and MCLR (0.01, 0.1, 1.0 and 10.0 μg L-1). Vallisneria natans was sensitive to high concentrations of MCLR (10 μg L-1): plants exposed to 10 μg L-1 of MCLR measured a biomass of 3.46 g, which was significantly lower than the 8.71 g of the control group. Additionally, antagonistic interactive effects were observed in plants exposed to combined PFOA and MCLR. Exposure to these pollutants adversely affected photosynthesis of the plants and triggered peroxidation that promoted peroxidase, superoxide dismutase and catalase activities, and increased malondialdehyde and glutathione concentrations. The total chlorophyll content was lower in the highest concentration of the combined treatment group (0.443 mg g-1) than in the control group (0.534 mg g-1). Peroxidase activity increased from 662.63 U mg-1 Pr to 1193.45 U mg-1 Pr with increasing PFOA concentrations. Metabolomics indicated that the stress tolerance of Vallisneria natans was improved via altered fatty acid metabolism, hormone metabolism and carbon metabolism. Furthermore, PFOA and MCLR influenced the abundance and structure of the microbial community in the biofilms of Vallisneria natans. The increased contents of autoinducer peptide and N-acylated homoserine lactone signaling molecules indicated that these pollutants altered the formation and function of the biofilm. These results expand our understanding of the combined effects of PFOA and MCLR in aquatic ecosystems.

Joint toxicity mechanisms of perfluorooctanoic acid and sulfadiazine on submerged macrophytes and periphytic biofilms

Hazardous chemicals, such as perfluoroalkyl substances (PFASs) and antibiotics, coexist in aquatic environments and pose a severe threat to aquatic organisms. However, research into the toxicity of these pollutants on submerged macrophytes and their periphyton is still limited. To assess their combined toxicity, Vallisneria natans (V. natans) was exposed to perfluorooctanoic acid (PFOA) and sulfadiazine (SD) at environmental concentrations. Photosynthetic parameters such as chlorophyll a, chlorophyll b, total chlorophyll, and carotenoids were lower in the SD exposure group, indicating that SD had a significant effect on the photosynthesis of aquatic plants. Single and combined exposures effectively induced antioxidant responses, with increases in superoxide dismutase, peroxidase activities, and ribulose-1,5-bisphosphate carboxylase concentrations, as well as malondialdehyde content. Accordingly, antagonistic toxicity was assessed between PFOA and SD. Furthermore, metabolomics revealed that V. natans improved stress tolerance through changes in enoic acid, palmitic acid, and palmitoleoyloxymyristic acid related to the fatty acid metabolism pathway responding to the coexisting pollutants. Additionally, PFOA and SD in combination induced more effects on the microbial community of biofilm. The alternation of α- and β-D-glucopyranose polysaccharides and the increased content of autoinducer peptides and N-acylated homoserine lactones indicated that PFOA and SD changed the structure and function of biofilm. These investigations provide a broader perspective and comprehensive analysis of the responses of aquatic plants and periphyton biofilms to PFAS and antibiotics in the environment.

Response of submerged macrophytes and biofilms to coexisting azithromycin and tetracycline: Antibiotic resistance genes removal, toxicity assessment and microbial properties

Antibiotics, such as azithromycin (AZ), tetracycline (TC), and their related antibiotic resistance genes (ARGs), create serious ecological risks to aquatic organisms. This study examined the response mechanisms of submerged macrophytes and periphytic biofilms to a mixture of AZ and TC pollution and determined the antibiotic removal efficiencies and fate of ARGs. The results showed that the plant-biofilm system had a significant capacity for removing both single and combined antibiotics with removal efficiencies of 93.06% ∼99.80% for AZ and 73.35% ∼97.74% for TC. Higher ARG (tetA, tetC, tetW, ermF, ermX, and ermB) abundances were observed in the biofilm, and subsequent exposure to the antibiotic mixture increased the abundances of these genes. Both single and combined antibiotics triggered antioxidant stress, but antagonistic effects were induced only with mixed AZ and TC exposure. Furthermore, the antibiotics changed the structural characteristics of extracellular polysaccharides and induced alterations in the structure of the biofilm microbial community. Increased N-acylated-l-homoserine lactone confirmed alternations in microbial quorum-sensing. The results extend the understanding of the fate of antibiotics and ARGs when aquatic plants and biofilms are exposed to antibiotic mixtures, as well as the organism's response mechanisms.

Growth and physiological responses in a submerged clonal aquatic plant and multiple-endpoint assessment under prolonged exposure to ciprofloxacin

Ciprofloxacin is ubiquitous and poses a potential threat to aquatic ecosystems. However, the comprehensive effect of prolonged ciprofloxacin exposure on the submerged clonal plant Vallisneria natans (Lour.) Hara remains unknown. Growth and physiological responses in V. natans exposed to ciprofloxacin at concentrations of 0, 0.05, 0.25, 1.25, 2.5, 5 and 10 mg/L were repeatedly evaluated on Days 7, 14, 28, 42 and 56. V. natans maintained good growth properties under 0.05-0.25 mg/L ciprofloxacin treatments, while the inhibition effect on plant growth induced by higher-concentration treatments increased over time. The IC50 values of ciprofloxacin for growth endpoints ranged from 1.6 mg/L to 5.3 mg/L and displayed time-dependent decreases. Pigment contents were significantly stimulated by ciprofloxacin on Day 7 but decreased to varying degrees as the exposure time was extended. Soluble protein and hydrogen peroxide content rose significantly over the first 14 days of treatment with 0.25-10 mg/L ciprofloxacin but decreased under 1.25-10 mg/L ciprofloxacin treatments since Day 28. Antioxidants including superoxide dismutase, catalase, guaiacol peroxidase, ascorbate peroxidase and proline functioned well in mitigating oxidative stress under different ciprofloxacin concentrations, lowering the comprehensive toxic effects of ciprofloxacin on V. natans during the period from Day 14 to Day 42, as evidenced by decreased IBR (integrated biomarker response) values. However, the toxic pressure of ciprofloxacin on V. natans peaked on Day 56. These findings suggest that exposure time can influence the responses of V. natans exposed to ciprofloxacin and that IBR can be employed to evaluate the integrated impacts of prolonged ciprofloxacin contamination in aquatic settings.

Mechanism of erythropoietin-induced M2 microglia polarization via Akt / Mtor / P70S6k signaling pathway in the treatment of brain injury in premature mice and its effect on biofilm

We investigated the mechanism of erythropoietin (EPO) in brain injury in premature mice based on Akt/mTOR/p70S6K signaling pathway. The brain injury model group of premature mice was obtained by intraperitoneal injection of lipopolysaccharide during pregnancy. Normal mice were taken as the control group. The model mice were divided into low-dose EPO (1,000 IU/kg, L-EPO), medium-dose EPO (2,500 IU/kg, M-EPO), and high-dose EPO groups (5,000 IU/kg, H-EPO) by intraperitoneal injection. The levels of malondialdehyde (MDA) and total superoxide dismutase (T-SOD) were detected. TUNEL staining and Western blotting were used to detect the differences in neuronal apoptosis index (AI), microglial polarization marker protein, and Akt/mTOR/p70S6K-related protein expression levels in each group. Compared with the control group, the protein levels of AI, MDA, Bax, and iNOS in the model, L-EPO, and M-EPO groups were significantly increased, while the T-SOD level and Bcl-2, ARG1, p-Akt, p-mTOR, and p-70S6K protein levels were significantly decreased (P < 0.05). Compared with the model group, AI, MAD levels and Bax, iNOS protein expression levels in L-EPO, M-EPO, and H-EPO groups were significantly decreased, while T-SOD level and Bcl-2, ARG1, p-Akt, p-mTOR, and p-70S6K protein levels were significantly increased. The changes were dose-dependent. In summary, EPO can activate microglia transformation from M1 to M2 through Akt/mTOR/p70S6K signaling pathway.

Interactions of Vallisneria natans and Iron-Oxidizing Bacteria Enhance Iron-Bound Phosphorus Formation in Eutrophic Lake Sediments

Submerged macrophyte restoration and in situ phosphorus (P) passivation are effective methods for the control of internal P loading from sediments. This study explored the synergistic effects of Vallisneria natans and iron (Fe)-oxidizing bacteria (IOB) on internal P loading from eutrophic freshwater lake sediments by taking into account Fe-bound P (FeP) formation and associated bacterial community structures. Sediment samples were prepared in glass tanks under four treatments, namely no V. natans planting or IOB inoculation (control), planting V. natans without IOB inoculation (Va), planting V. natans with IOB inoculation (Va-IOB), and planting V. natans with autoclaved IOB inoculation (Va-IOB[A]). Compared with the control, all three treatments with V. natans (Va, Va-IOB, and Va-IOB[A]) had significantly decreased organic matter contents and increased redox potential in sediments (p < 0.05), at the rapid growth and mature stages of V. natans. Planting V. natans with and without IOB inoculation also decreased the total P (TP) and Fe–P concentrations in sediments. Conversely, Fe³⁺ concentrations, Fe³⁺/Fe²⁺ ratios, and the proportions of Fe–P in TP all increased in sediments planted with V. natans, especially under the Va-IOB treatment (p < 0.05). Furthermore, bacterial community diversity increased in sediments due to the presence of V. natans. The relative abundances of IOB (including Acidovorax and Chlorobium) increased from the transplanting to the rapid growth stage of V. natans and then decreased afterwards. In the later stages, the relative abundances of IOB and their ratios to Fe-reducing bacteria were the highest under the Va-IOB treatment. Accordingly, synergistic interactions between V. natans and IOB could enhance Fe–P formation and reduce TP concentrations in eutrophic lake sediments by altering sediment physicochemical properties and Fe oxidation-related bacterial community structures.

Functional traits of submerged macrophytes in eutrophic shallow lakes affect their ecological functions

Trait-based approaches have been widely used to explore the relationships between submerged macrophytes and their surrounding environments. However, the effects of functional traits on ecological functions of submerged macrophytes in eutrophic lakes are still not well understood. Here, 1745 individuals of eight dominant submerged macrophyte species in 19 Yangtze floodplain lakes were collected and classified as needle-leaf (Myriophyllum spicatum, Ceratophyllum demersum, Stuckenia pectinatus, Najas minor) or flat-leaf (Vallisneria natans, Hydrilla verticillata, Potamogeton wrightii, Potamogeton maackianus) types according to photosynthetic trait-based cluster analysis. The flat-leaf type submerged macrophytes possessed greater photosynthetic (e.g. higher Fv/Fm) and morphological traits (e.g. higher SLA), while the needle-leaf types held greater stoichiometric traits (e.g. higher plant N/P). Moreover, the RDA analysis indicated that water depth (distribution depth of submerged macrophytes) was the key factor influencing functional traits of flat-leaf types, while it was water quality (e.g. WTP and WChl a) for the needle-leaf types. Furthermore, the flat-leaf types showed better performance in improving underwater light conditions (e.g. SD, K_d, Z_eu/WD and Red/Blue) and water quality (e.g. WChl a and TSM). Additionally, distribution depth (WD) of the flat-leaf types was shallower than the needle-leaf types in eutrophic shallow lakes along the middle-lower reaches of the Yangtze River. Our study highlights that functional traits of submerged macrophytes in eutrophic shallow lakes affect their ecological functions.

Combined toxic effects of anatoxin-a and microcystin-LR on submerged macrophytes and biofilms

Hazardous substances, such as anatoxin-a and microcystin-LR, are released into the aquatic environment during cyanobacterial blooms, causing significant ecological risk. To assess the toxic effects of anatoxin-a, microcystin-LR and their combined exposure on submerged macrophytes and biofilms, Vallisneria natans was exposed to solutions containing different concentrations of anatoxin-a and microcystin-LR (0.05-5.00 μg L^-1). Results showed that Vallisneria natans was sensitive to anatoxin-a of 0.05 μg L^-1, and antagonistic effects were induced at combined microcystin-LR and anatoxin-a exposure. Single and combined exposure effectively induced antioxidant responses such as promoted activities of superoxide dismutase, peroxidase and catalase, as well as increased glutathione S-transferase, glutathione and malondialdehyde content. In addition, anatoxin-a and microcystin-LR could also be absorbed by Vallisneria natans and trigger plant defense responses, generating increased concentrations of the phytohormones abscisic acid and strigolactones. Moreover, the abundances and structure of the microbial community in periphyton biofilms were altered by combined anatoxin-a and microcystin-LR exposure. The enhanced concentration of N-acylated-l-homoserine lactone indicated that the assessed cyanotoxins had a significant influence on quorum-sensing in biofilm microbial communities. These results demonstrated that anatoxin-a and microcystin-LR at environmentally relevant concentrations could disrupt homeostasis, induce effective defense mechanisms of Vallisneria natans and alter biofilms in aquatic ecosystems.

Response of submerged macrophytes and periphyton biofilm to water flow in eutrophic environment: Plant structural, physicochemical and microbial properties

The integrated effects of water flow on submerged macrophytes (Vallisneria natans) and leaf biofilms were comprehensively investigated in eutrophic microcosm. Changes in aquatic environmental factors were analyzed and water flow was found to elevate eutrophic water quality, especially in terms of TP removal. The removal efficiency of TP reached 78.95% in flowing water, which was more than 10-fold higher than in static water. Water flow altered the morphological and physiological characteristics of plants, decreasing the cell wall thickness and rate of photosynthesis, while promoting the accumulation of soluble sugar and protein in leaves. The starch content also increased with water flow, and significantly larger starch granules were observed in chloroplast. Furthermore, oxidative damage was evidenced by the consistently higher content of malondialdehyde in flowing water. Superoxide dismutase (SOD), peroxidase (POD) and Catalase (CAT) were induced in plants exposed to water flow, as an antioxidant stress response. The results of 16S rRNA high-throughput sequencing analysis showed that the structure of the biofilm microbial community changed in response to water flow. These results expand our understanding of the effects of water flow on submerged macrophytes and periphyton biofilms in eutrophic environments.

Response of submerged macrophytes and leaf biofilms to the decline phase of Microcystis aeruginosa: Antioxidant response, ultrastructure, microbial properties, and potential mechanism

Decaying cyanobacterial blooms carry a potential risk for submerged macrophyte and periphyton biofilms in aquatic environments. This study comprehensively studied the responses in growth, oxidative response, detoxification pathway, and ultrastructure characteristics of aquatic plants to Microcystis aeruginosa (M. aeruginosa) exudates and extracts released during the decline phase. Particular emphasis was placed on the variation of extracellular polymeric substances (EPS) and quorum-sensing signaling molecules. The results showed that superoxide dismutase, peroxidase, and glutathione S-transferase were significantly induced as antioxidant response, and the malondialdehyde content increased. Increased content of MC-LR (1.129 μg L^-1) and NH₄⁺-N (1.35 mg L^-1) were found in the decline phase of M. aeruginosa, which played a vital role in the damage to submerged plants. In addition, a change in the amount of osmiophilic granules and a variation of organelles and membranes was observed. A broad distribution of α-d-glucopyranose polysaccharides was dominant and aggregated into clusters in biofilm EPS in response to exposure to decaying M. aeruginosa. Furthermore, exposure to exudates and extracts changed the abundance and structure of the microbial biofilm community. Increased contents of N-acylated-L-homoserine lactone signal molecule might result in a variation of biofilm EPS production in response to decaying M. aeruginosa. These results expand the understanding of how submerged macrophyte and periphyton biofilms respond to environmental stress caused by exudates and extracts of decaying M. aeruginosa.

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

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.