Submerged Macrophyte Species Research Articles

How Do Different Growth Forms of Winter Submerged Macrophytes Species Respond to Underwater Light Quality in a Mesocosm Study?

Underwater light is a key factor that affects the growth of submerged macrophytes. However, the responses of different growth forms of submerged macrophytes to light quality remain unclear. The morphological, physiological, photosynthetic, and stoichiometric responses of erect Potamogeton crispus (P. crispus) and low-canopy Elodea nuttallii (E. nuttallii) to six different light qualities (white light, R/B = 1:8, 1: 4, 1:1, 4:1, 8:1) were studied by a control experiment. (1) No significant differences were observed in the germination number, leaf length, and leaf width of P. crispus under different light qualities (p > 0.05). Both P. crispus and E. nuttallii produced greater plant heights, more leaves and branches under more red light (4:1, 8:1), which was beneficial for the extension of leaves. Under white light, the germination number of P. crispus, adventitious roots of E. nuttallii, and branch number of P. crispus and E. nuttallii were the lowest. (2) Compared to red light, more blue light (1:4, 1:8) was more conducive to the synthesis of photosynthetic pigments. However, excessive blue and red light was not conducive to the accumulation of pigments. The result of malondialdehyde showed that the physiological stress induced by blue light in P. crispus and E. nuttallii was stronger. (3) The N:P, C:N, and C:P ratios of P. crispus and E. nuttallii were higher under more red light, which was beneficial for the synthesis of nutrients in two submerged macrophy; however, the contents of TN and TP in E. nuttallii were higher under more blue light. Two different growth forms of submerged macrophytes grew better under red light, and better adapted to the eutrophic water dominated by red light. However, for aquatic restoration, other submerged macrophytes need to be supplemented after the water quality is improved.

Functional traits of exotic submerged macrophytes mediate diversity-invasibility relationship in freshwater communities under eutrophication

Plant diversity may respond differently in terms of whether it can drive plant invasions in freshwater ecosystem. Linkages and interactions between diversity and invasibility have not been clearly resolved, and it is unclear how nutrient enrichment (e.g., eutrophication) will affect this relationship. As a key predictor of plant growth, the ability of functional traits to mediate trade-offs in the diversity-invasibility relationship is unknown. Here, we conducted a series of experiments to determine the role of exotic plant functional traits in the diversity-invasibility relationship of submerged macrophyte communities under eutrophication. We selected common native and exotic submerged macrophytes in the subtropics to construct different diverse submerged macrophyte communities to simulate invasion. Meanwhile, to test the adaptability and importance of functional traits, we experimentally verified the differences in functional traits between exotic and native species. Our results showed a positive correlation between native plant diversity and community invasibility. Moreover, the invader's performance was predominantly determined by functional traits of exotic species, such as plant biomass and tissue nutrients, which were significantly altered by species diversity. Furthermore, our results suggested that functional traits contribute significantly more to the invasiveness of exotic submerged macrophytes than the other factors to which they are subjected. Plant functional traits can mediate the diversity–invasibility relationship because of the higher intrinsic dominance of exotic submerged macrophyte species. In summary, our study revealed diversity-invasibility relationship in submerged macrophyte communities and highlighted functional traits as key drivers of invasion of high-risk exotic submerged macrophyte species. Although previous studies have elucidated the importance of functional trait studies for plant invasions, our study provides the only current evidence demonstrating the important role of invaders' functional traits in mediating the diversity-invasibility relationship. This novel perspective offers valuable insights into the management and control of invasive aquatic plants.

Characteristics of Epiphytic Bacterial Community on Submerged Macrophytes in Water Environment Supplemented with Reclaimed Water

Biofilms attached to submerged macrophytes play an important role in improving the water quality of the water environment supplemented with reclaimed water. In order to explore the effects of reclaimed water quality and submerged macrophyte species on the characteristics of an epiphytic bacterial community, different types of submerged macrophytes were selected as research objects in this study. 16S rRNA high-throughput sequencing technology was used on the epiphytic bacteria and the surrounding environmental samples to analyze the bacterial community structure and functional genes. The results showed that approximately 20%-35% of the nitrogen and phosphorus nutrients were absorbed and utilized in the water environment supplemented with reclaimed water. However, the COD, turbidity, and chroma of the downstream water were significantly increased. The bacterial community of the biofilms attached to submerged macrophytes was significantly different from that in the surrounding environment (soil, sediment, and water body) and in the activated sludge that was treated by reclaimed water. In terms of bacterial community diversity, the richness and diversity were significantly lower than those of soil and sediment but higher than those of plankton bacteria in water. In terms of bacterial community composition, dominant genera and corresponding abundances were also different from those of other samples. The main dominant bacterial genera were Sphingomonas, Aeromonas, Pseudomonas, and Acinetobacter, accounting for 7%-40%, respectively. Both macrophyte species and the quality of reclaimed water (BOD5, TN, NH4+-N, and TP) could affect the bacterial community. However, the effect of water quality of the bacterial community was greater than that of macrophytes species. Additionally, the quality of reclaimed water also affected the abundance of functional genes in the bacterial community, and the relative abundance of nitrogen and phosphorus cycling functional genes was higher in areas with higher nitrogen and phosphorus concentrations.

Phosphorus stoichiometric homeostasis of submerged macrophytes and associations with interspecific interactions and community stability in Erhai Lake, China

According to stoichiometric homeostasis theory, eutrophication is expected to increase the dominance of submerged macrophytes with low homeostatic regulation coefficients (H) relative to those with high H values, ultimately reducing macrophyte community stability. However, empirical evidence supporting this hypothesis is limited. In this study, we conducted a three-year tracking survey (seven sampling events) at 81 locations across three regions of Erhai Lake. We assessed the H values of submerged macrophyte species, revealing significant H values for phosphorus (P) and strong associations of HP values (range: 1.58–2.94) with species and community stability. Moreover, in plots simultaneously containing the dominant high-HP species, Potamogeton maackianus, and its low-HP counterpart, Ceratophyllum demersum, we explored the relationships among eutrophication, interspecific interaction shifts, and community dynamics. As the environmental P concentration increased, the dominance of P. maackianus decreased, while that of C. demersum increased. This shift coincided with reductions in community HP and stability. Our study underpins the effectiveness of H values for forecasting interspecific interactions among submerged macrophytes, thereby clarifying how eutrophication contributes to the decline in stability of the submerged macrophyte community.

Introduction of Native Submerged Macrophytes to Restore Biodiversity in Streams.

Streams are biodiversity hotspots that provide numerous ecosystem services. Safeguarding this biodiversity is crucial to uphold sustainable ecosystem functioning and to ensure the continuation of these ecosystem services in the future. However, in recent decades, streams have witnessed a disproportionate decline in biodiversity compared to other ecosystems, and are currently considered among the most threatened ecosystems worldwide. This is the result of the combined effect of a multitude of stressors. For freshwater systems in general, these have been classified into five main pressures: water pollution, overexploitation, habitat degradation and destruction, alien invasive species, and hydromorphological pressures. On top of these direct stressors, the effects of global processes like environmental and climate change must be considered. The intricate and interconnected nature of various stressors affecting streams has made it challenging to formulate effective policies and management strategies. As a result, restoration efforts have not always been successful in creating a large-scale shift towards a better ecological status. In order to achieve an improved status in these systems, situation-specific management strategies tailored to specific stressor combinations may be needed. In this paper, we examine the potential of introducing native submerged macrophyte species to advance the restoration of stream ecosystems. Through successful introductions, we anticipate positive ecological outcomes, including enhanced water quality and increased biodiversity. This research is significant, as the potential success in restoring stream biodiversity not only represents progress in ecological understanding but also offers valuable insights for future restoration and management strategies for these vital ecosystems.

Do submerged macrophyte species influence crustacean zooplankton functional group richness and their resource use efficiency in the low-light environment?

During the high grazing of epiphytic zooplankton in submerged macrophyte beds, the changes in crustacean zooplankton functional groups are crucial for stabilizing a clear water state in shallow lakes. However, submerged macrophytes often experience low-light stress due to many ecological processes. It is unclear whether submerged macrophytes alter the zooplankton functional group and their resource use efficiency in the low-light environment. We conducted two mesocosm experiments involving the treatments of low-light and submerged macrophyte species (Vallisneria natans and Potamogeton maackianus). The results show that abiotic factors (e.g., light) were the most important variables in explaining the change in the zooplankton community. Specifically, zooplankton functional group (i.e., pelagic species, plant-associated species, and substrate scrapers) richness and zooplankton species diversity decreased with the decreasing light intensity, especially for low substrate scraper abundance. In addition, structural equation models showed that low-light stress reduced zooplankton resource use efficiency by reducing zooplankton functional group richness and species diversity. Compared to species diversity, zooplankton functional group richness had a greater influence on their resource use efficiency (Zp/Chl-a) in the low-light environment. Our results suggest that the low-light stress reduced zooplankton resource use efficiency by changing their functional group richness. Moreover, the abundance of substrate scrapers shaken from V. natans was higher than that from P. maackianus. Therefore, submerged macrophyte species influence crustacean zooplankton functional group richness and their resource use efficiency in the low-light environment. Selecting appropriate aquatic plant species to assure the high diversity of zooplankton should be considered when conducting lake restoration using submerged macrophytes.

The distribution of submerged macrophytes in response to intense solar radiation and salinity reveals hydrogen peroxide as an abiotic stress indicator

The feasible condition for submerged macrophyte growth is hard to understand as many environmental factors contribute to establishing macrophyte distribution with different intensities generating excess reactive oxygen species (ROS). Among various kinds of ROS, hydrogen peroxide (H2O2) is relatively stable and can be measured accurately. Thus, for the quantification of submerged macrophyte species, H2O2 can be used to evaluate their distribution in a lake. Submerged macrophytes, such as Potamogeton anguillanus, were abundant in Lake Shinji. The largest biomass distribution was around 1.35 m deep, under low solar radiation intensity, and nearly no biomass was found less than 0.3 m deep, where solar radiation was high. Tissue H2O2 concentrations varied in response to the diurnal photosynthetically active radiation (PAR) intensity, which was followed by antioxidant activities, though slightly delayed. Laboratory experiments were conducted with different PAR intensities or salinity concentrations. A stable level of H2O2 was maintained up to about 200 μmol m−2 s−1 of PAR for 30 days, followed by a gradual increase as PAR increased. The H2O2 concentration increased with higher salinity. A change in Chlorophyll a (Chl-a) concentration is associated with an altering H2O2 concentration, following a unique negative relationship with H2O2 concentration. If H2O2 exceeded 45 μmol/gFW, the homeostasis collapsed, and H2O2 and Chl-a significantly declined afterward. The above findings indicate that H2O2 has a negative effect on the physiological condition of the plant. The increase in H2O2 concentration was prevented by antioxidant activities, which elevated with increasing H2O2 concentration.

Effects of water depth on the biomass of two dominant submerged macrophyte species in floodplain lakes during flood and dry seasons

Floodplain lakes share characteristics of both deep and shallow lakes throughout any given year. Seasonal fluctuations in their water depth drive changes in nutrients and total primary productivity, which directly and indirectly affect submerged macrophyte biomass. To investigate how water depth and environmental variables affect submerged macrophyte biomass, we surveyed six sub-lakes in the Poyang Lake floodplain, China, during the flood and dry seasons of 2021. Dominant submerged macrophytes include Vallisneria spinulosa and Hydrilla verticillata. The effect of water depth on the biomass of these macrophytes varied between the flood and dry seasons. In the flood season, there was a direct effect of water depth on biomass, while in the dry season only an indirect effect was observed. During the flood season, the direct effect of water depth on the biomass of V. spinulosa was less than the indirect effect, with water depth primarily affecting the total nitrogen, total phosphorus and water column transparency. Water depth directly, positively affected H. verticillata biomass, with this effect being greater than the indirect effect by affecting the carbon, nitrogen and phosphorus content in the water column and sediment. During the dry season, water depth affected H. verticillata biomass indirectly through sediment carbon and nitrogen content, while for V. spinulosa, the effect on biomass was indirect through carbon content of the sediment and water column. The main environmental variables affecting submerged macrophyte biomass in the Poyang Lake floodplain during the flood and dry seasons, and the mechanisms through which water depth affects dominant submerged macrophyte biomass, are identified. An understanding of these variables and mechanisms will enable improved management and restoration of wetland.

Diversity and interaction of bacterial and microeukaryotic communities in sediments planted with different submerged macrophytes: Responses to decabromodiphenyl ether

Although various persistent organic pollutants (POPs) can affect microbial communities and functions in aquatic ecosystems, little is known about how bacteria and microeukaryotes respond to the POPs in sediments planted with different submerged macrophytes. Here, a 60-day microcosm experiment was carried out to investigate the changes in the diversity and interaction of bacterial and microeukaryotic communities in sediments collected from Taihu lake, either with decabromodiphenyl ether (BDE-209) own or combined with two common submerged macrophyte species (Vallisneria natans and Hydrilla verticillate). The results showed that BDE-209 significantly decreased the bacterial α-diversity but increased the microeukaryotic one. In sediments planted with submerged macrophytes, the negative effect of BDE-209 on bacterial diversity was weakened, and its positive effect on microeukaryotic one was strengthened. Co-occurrence network analysis revealed that the negative relationship was dominant in bacterial and microeukaryotic communities, while the cooperative relationship between microbial species was increased in planted sediments. Among nine keystone species, one belonging to bacterial family Thermoanaerobaculaceae was enriched by BDE-209, and others were inhibited. Notably, such inhibition was weakened, and the stimulation was enhanced in planted sediments. Together, these observations indicate that the responses of bacteria and microeukaryotes to BDE-209 are different, and their communities under BDE-209 contamination are more stable in sediments planted with submerged macrophytes. Moreover, the effects of plant species on the microbial responses to BDE-209 need to be explored by more specific field studies in the future.

Biodiversity buffers the impact of eutrophication on ecosystem functioning of submerged macrophytes on the Yunnan-Guizhou Plateau, Southwest China

Increasing eutrophication poses a considerable threat to freshwater ecosystems, which are closely associated with human well-being. As important functional entities for freshwater ecosystems, submerged macrophytes have suffered rapidly decline with eutrophication. However, it is unclear whether and how submerged macrophytes maintain their ecological functions under increasing eutrophication stress and the underlying patterns in the process. In the current study, we conducted an extensive survey of submerged macrophytes in 49 lakes and reservoirs (67% of them are eutrophic) on the Yunnan-Guizhou Plateau of southwestern China to reveal the relationship between submerged macrophyte biodiversity and ecosystem functioning (BEF) under eutrophication stress. Results showed that submerged macrophytes species richness, functional diversity (FD), and β diversity had positive effects on ecosystem functioning, even under eutrophication. Functional diversity was a stronger predictor of community biomass than species richness and β diversity, while species richness explained higher coverage variability than FD and β diversity. This suggests that species richness was a reliable indicator when valid functional traits cannot be collected in considering specific ecological process. With increasing eutrophication in water bodies, the mechanisms underlying biodiversity-ecosystem functioning evolved from “niche complementarity” to “selection effects”, as evidenced by decreased species turnover and increased nestedness. Furthermore, the relative growth rate, specific leaf area, and ramet size in trade-off of community functional composition became smaller along eutrophication while flowering duration and shoot height became longer.This study contributes to a better understanding of positive BEF in freshwater ecosystems, despite increasing anthropogenic impacts. Protecting the environment remained the effective way to protect biodiversity and corresponding ecological functions and services. It will be important to consider different facets of biodiversity on ecosystem functioning in future studies to improve effective management plans.

Diatom community composition on submerged macrophyte species from an Ontario (Canada) lake.

The introduction of invasive macrophyte species can affect submerged macrophyte community composition and abundance, which in turn can alter the functions of lake ecosystems. Knowing when and how invasive macrophytes arrive and spread can help disentangle the effects of invasive species from other stressors on lake ecosystems. This requires a long-term (decades) perspective of macrophyte community composition, which is rarely available. An alternative is paleolimnological inferences of macrophyte community composition from fossil diatom assemblages, which requires knowledge of epiphytic diatom communities. Here, we investigated the epiphytic diatom community composition of three common submerged macrophyte species (Chara sp., Potamogeton robbinsii, and the invasive Myriophyllum spicatum) in a typical temperate, mixed forest lake, Chandos Lake, Ontario, Canada, to provide a basis for future paleolimnological research. Non-parametric, multivariate analysis of variance indicated a statistically significant difference in the epiphytic diatom communities of different macrophyte species, despite principal components analysis showing some overlap among the diatom communities. Diatom community composition of all macrophytes had abundant Achnanthidium minutissimum and Cocconeis placentula. Generalized linear models and univariate analysis of variance identified six diatoms (Encyonopsis microcephala, Epithemia turgida, Gomphonema parvulius, Navicula gerloffi, Rhopalodia gibba, and Rossithidium anastasiae) that were significantly different among macrophyte species. Although it remains uncertain whether these differences are sufficient to infer historical macrophyte community composition from epiphytic diatom fossil assemblages, our results indicate the potential of such an approach and offer suggestions for future research.

Eutrophication drives regime shift via changes in stoichiometric homeostasis-based submerged macrophyte assemblages

Homeostasis for phosphorus (HP) in submerged macrophytes may influence the susceptibility of lakes to regime shifts; however, the mechanisms linking submerged macrophyte HP to regime shifts remain unclear. We conducted an in situ mesocosm experiment to compare the dynamic responses of a high-HP species, Potamogeton maackianus, and a low-HP species, Hydrilla verticillata, to different phosphorus (P) level gradients, as well as their effects on phytoplankton inhibition. The biomass of P. maackianus under mesotrophic P (MP; P concentration 0.05 mg L−1) and eutrophic P (EP; P concentration 0.10 mg L−1) conditions was either non-significantly different from, or lower than that under oligotrophic P conditions (OP; P concentration under detection limit of 0.01 mg L−1). Conversely, H. verticillata biomass under EP was significantly higher than that under MP on day 90, whereas it died under OP. This variable response of submerged macrophyte species to P level gradients increased the relative growth advantage of H. verticillata compared to P. maackianus during eutrophication. The inhibition ratio of phytoplankton (IRP) for P. maackianus was ~15 times higher than that for H. verticillata under EP. Our study demonstrated a trend that submerged macrophyte assemblage IRP increased along with its assemblage HP. Thus, the changes in submerged macrophyte assemblages from high-HP species-dominance to low-HP species-dominance would erode its phytoplankton inhibition capacity, and further promote the regime shift from a clear-water state to a turbid state. Our results advance the regime shift theory from an ecological stoichiometry perspective and highlight the importance of high-HP submerged macrophyte species in the restoration of eutrophic lakes.

14C AND OTHER RADIONUCLIDES IN THE ENVIRONMENT IN THE BORDER REGION OF LITHUANIA BEFORE THE START OF THE BELARUSIAN NUCLEAR POWER PLANT OPERATION

ABSTRACTIn this paper, we analyze the background activity of anthropogenic radionuclides (14C, 3H, 137Cs, and 239,240Pu), emphasizing 14C content, in terrestrial and aquatic ecosystems in the Lithuanian border region before the commissioning of a new nuclear power plant in Belarus (BelNPP). In terrestrial samples, the 14C concentration varied insignificantly—from 98.6 ± 0.7 to 102.2 ± 0.8 pMC, which is close to the 14C level in atmospheric CO2. In aquatic samples, the 14C concentration varied within wide limits from 76.9 ± 0.7 to 99.6 ± 0.6 pMC, depending on the ecological group of macrophytes. Various ecological groups of macrophytes have experienced the influence of a freshwater reservoir effect. This lowest 14C content in submerged macrophyte species, within the limits of uncertainty, was very close to the specific activity of 14C in DIC (78.6 ± 0.6 pMC) in the water of the Neris River. The background 14C values, together with the data on 3H, 137Cs and 239,240Pu obtained in this study, can be used in the future to assess the contribution of the BelNPP conventional radioactive effluents to the levels of 14C and other radionuclides in terrestrial and aquatic ecosystems of the transboundary region of Belarus and Lithuania.

The effect of trait‐based diversity on productivity results mainly from intraspecific trait variability in the macrophyte community

Abstract Trait‐based methods are key to understanding the biodiversity–productivity relationship (BPR) of macrophyte communities. Community‐weighted mean traits (i.e., community trait structure) have been proven to have more influence on macrophyte community productivity than species richness. However, the underlying mechanism by which community trait structure variation affects macrophyte community productivity along an environmental gradient is still not well understood. A mesocosm experiment was used to investigate how community trait structure shapes macrophyte community productivity along the water depth gradient. Three submerged macrophyte species (Myriophyllum spicatum, Vallisneria natans and Potamogeton malaianus) were assembled into all possible combinations (one, two and three species per community) at three different water depths (1, 2.5 and 4 m). We fitted the relationships between community‐weighted mean traits and community productivity, and between species richness and community productivity as a comparison. We compared functional traits under different water depths and species composition at the species and community levels and disentangled the community trait structure into species turnover and intraspecific trait variability effects. The results showed that community trait structure had various influences on macrophyte community productivity, which was based on traits per se. However, species richness had a non‐significant impact on macrophyte community productivity. Water depth had a significant impact on most traits of the three species at the species level, whereas both water depth and species composition had significant impacts on community trait structure which was mainly affected by intraspecific trait variability along the water depth gradient. Our findings highlight the importance of considering intraspecific trait variability and species turnover under water depth gradients to understand the relationship between trait‐based biodiversity and productivity.

Antidote or Trojan horse for submerged macrophytes: Role of microplastics in copper toxicity in aquatic environments

Due to their unique surface structures and physicochemical properties, microplastics (MPs) can adsorb other contaminants, thus impacting their toxicity and fate in aquatic ecosystems. In the present study, the adsorption and transportation of copper ions (Cu2+) in polyethylene (PE, 5 and 150 μm) and their combined effects on four submerged macrophyte species were assessed. Results demonstrated that the addition of PE reduced the Cu2+ concentration in copper sulfate (CuSO4) solution and the adsorption of Cu2+ in PE (10 mg/L) increased with CuSO4 concentration (100–600 μmol/L). PE alone exhibited no inhibitory effects on macrophytes, while Cu2+ showed fatal toxicity toward the macrophytes. However, the combination of PE and Cu2+ showed lower inhibitory effects on macrophytes and the toxicity attenuation varied among species. Additionally, PE may act as a carrier (like a Trojan horse) for the environmental transfer of Cu2+, thereby hosting Cu2+ toxicity against macrophytes in the imported environment. Our findings indicate that PE acts as both an antidote to and carrier of Cu2+ toxicity in macrophytes. This study should help in clarifying the combined effects and risk assessments of MPs and heavy metals in future studies.

Multiple-stressor exposure of aquatic food webs: Nitrate and warming modulate the effect of pesticides

Shallow lakes provide essential ecological and environmental services but are exposed to multiple stressors, including agricultural runoff (ARO) and climate warming, which may act on different target receptors disrupting their normal functioning. We performed a microcosm experiment to determine the individual and combined effects of three stressors—pesticides, nitrate and climate warming—on two trophic levels representative of communities found in shallow lakes. We used three submerged macrophyte species (Myriophyllum spicatum, Potamogeton perfoliatus, Elodea nuttallii), eight benthic or pelagic microalgal species and three primary consumer species (Daphnia magna, Lymnaea stagnalis, Dreissena polymorpha) with different feeding preferences for benthic and pelagic primary producers. Eight different treatments consisted of a control, only nitrate, a pesticide cocktail, and a combination of nitrate and pesticides representing ARO, each replicated at ambient temperature and +3.5°C, mimicking climate warming. Pesticides negatively affected all functional groups except phytoplankton, which increased. Warming and nitrate modified these effects. Strong but opposite pesticide and warming effects on Myriophyllum drove the response of the total macrophyte biomass. Nitrate significantly suppressed Myriophyllum final biomass, but not overall macrophyte and microalgal biomass. Nitrate and pesticides in combination caused a macrophyte decline, and the system tipped towards phytoplankton dominance. Strong synergistic or even reversed stressor interaction effects were observed for macrophytes or periphyton. We emphasize the need for more complex community- and ecosystem-level studies incorporating multiple stressor scenarios to define safe operating spaces.

Effects of two submerged macrophyte species on microbes and metazoans in rooftop water-storage ponds with different labile carbon loadings

Nature-based solutions including rooftop-water storage ponds are increasingly adopted in cities as new eco-designs to address climate change issues, such as water scarcity and storm-water runoff. Macrophytes may be valuable additions for treating stored rooftop waters and provisioning other services, including aquaponics, esthetic and wildlife-conservation values. However, the efficacy of macrophyte treatments has not been tested with influxes of different labile carbon loadings such as those occurring in storms. Moreover, little is known about how macrophytes affect communities of metazoans and microbes, including protozoans, which are key players in the water-treatment process. Here, we experimentally investigated the effectiveness of two widely distributed macrophytes, Ceratophyllum demersum and Egeria densa, for treating drained rooftop water fed with two types of leaf litter, namely Quercus robur (high C lability) and Quercus rubra (low C lability). C. demersum was better than E. densa at reducing water conductivity (by 10 ̶ 40 µS/cm), TDS (by 10–18 mg/L), DOC (by 4–5 mg/L) and at increasing water transparency (by 4–9%), water O2 levels (by 19–27%) and daylight pH (by 0.9–1.3) compared to leaf-litter only microcosms after 30 days. Each treatment developed a different community of algae, protozoa and metazoa. Greater plant mass and epiphytic chlorophyll-a suggested that C. demersum was better at providing supporting habitat than E. densa. The two macrophytes did not differ in detritus accumulation, but E. densa was more prone to develop filamentous bacteria, which cause sludge bulking in water-treatment systems. Our study highlights the superior capacity of C. demersum and the usefulness of whole-ecosystem experiments in choosing the most adequate macrophyte species for nature-based engineered solutions.

Evaluation of eutrophication level changes in Baiyangdian Lake based on multiple biological groups

Baiyangdian Lake is the largest shallow lake in the North China Plain. Due to the increases in upstream water consumption in recent decades, the amount of natural water entering the lake has decreased, resulting in a significant drop in the water level of Baiyangdian Lake. Severe eutrophication has occurred in Baiyangdian Lake owing to the discharge of domestic sewage around the sub-lakes. With the establishment of the Xiong'an New Area in 2017, the importance of environmental governance and protection of Baiyangdian Lake has been unprecedentedly increased. The implementation of ecological water supplement from upstream reservoirs and other basins has significantly increased water level of Baiyangdian Lake. Moreover, domestic sewage from surrounding rural areas was collected. In order to understand the current state of water quality in Baiyangdian Lake, and to evaluate the effects of the previous water replenishment and pollution control projects, we investigated water physicochemical variables and aquatic organisms of Baiyangdian Lake in August 2019. We evaluated water quality status of Baiyangdian Lake based on water quality, phytoplankton, zooplankton and macrozoobenthos, by comparing with the evaluation based on the survey data in 2010. In addition, submerged macrophytes were used to evaluate the water ecological status. The results showed that the water quality state of Baiyangdian Lake in 2019 was greatly improved compared with 2010. Among them, total phosphorus concentration decreased by 88.6%, total nitrogen concentration decreased by 83.9%, chlorophyll a concentration decreased by 47.8%, and the Seechi depth increased by 43.4%. The diversity of zooplankton and macrozoobenthos were significantly increased, the density of phytoplankton was significantly reduced, the dominant species of phytoplankton changed from a general highly eutrophic type to a eutrophic type, and the distribution of the clean-type submerged macrophytes was narrowed. The evaluation methods based on submerged macrophytes species and based on zooplankton diversity were not suitable for water quality evaluation in Baiyangdian Lake. In the early stage, the pollution source of Baiyangdian Lake was concentrated in the west, which led to lower water quality. Nowadays, due to the water replenishment from the west, north and south, the hydrodynamic conditions changed significantly. In the west, pollution control projects were carried out, and the spatial distribution of water quality in Baiyangdian Lake are showing a characteristics of homogenization.

Evaluating aquatic macrophytes for removing erythromycin from contaminated water: floating or submerged?

Water contamination by antibiotics is an emerging global problem, with impacts on both public health and the environment. Erythromycin has been encountered in bodies of water throughout the world, which demands the development of efficient remediation technologies. We investigated the physiological responses and phytoremediation capacity of four species of aquatic macrophytes, two floating (Salvinia molesta and Lemna minor) and two submerged (Myriophyllum aquaticum and Rotala rotundifolia). The plants were exposed to relevant environmental concentrations of erythromycin (0 and 1.7 µg l−1) in artificially contaminated water for seven days. Physiological evaluations evidenced the ability of that antibiotic to promote oxidative events in those plants, such as the activation of antioxidant enzymes (ascorbate peroxidase and/or catalase). S. molesta exposed to erythromycin demonstrated accumulations of hydrogen peroxide and oxidative damage (lipid peroxidation) that was reflected in growth reductions. The erythromycin removal efficiency of floating plants varied from 9 to 12%, while submerged species varied from 31 to 44%. As such, submerged macrophyte species demonstrated the most efficient removal of erythromycin from contaminated waters, and are therefore more indicated for antibiotic phytoremediation projects.

Depth distribution of three submerged macrophytes under water level fluctuations in a large plateau lake

Submerged plants are crucial for maintaining a clear water state in lakes, and their distribution area is usually determined by the lowest distribution boundary (LDB). However, LDBs of submerged macrophytes often exhibit species differences and vary with seasonal water level fluctuations. In this study, we carried out a three-year field investigation to compare differences in the LDBs of three submerged macrophyte species (i.e., Vallisneria natans, Ceratophyllum demersum, and Potamogeton maackianus) and explore their distinct determinants. We assumed that LDB differences would exist among the three species and that water level (WL) would be a key environmental driver of LDB dynamics, with an association between the LDBs of submerged macrophytes and water level fluctuations. Indeed, our results showed significant seasonal differences between C. demersum and V. natans in the period of September - May, with mean annual values in the order (low to high) V. natans, C. demersum, and P. maackianus. Furthermore, water level was a major driving force of the LDB dynamics of the three species. Changes in the LDBs of the three species in response to water level fluctuations could be divided into three periods: i.e., recovery growth period (April to June), stress tolerance period (July to September), and recession period (October to following March). This study not only clarifies the impact of water level on submerged macrophyte growth and distribution, but also has larger practical implications for the ecological restoration and management of large deep lakes.