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This study presents research on the possibility of using lake macrophytes to create diagnostic and classification tools for trophically and morphologically diverse lakes. The diagnostic role of macrophytes was determined on the basis of the spatial and functional interrelationships of the various macrophyte groups, which include emergent, submerged, and floating species. In addition, an effort was made to reveal the morphometric features of the lakes that significantly affect the development of the distinguished macrophyte groups. The research was carried out comprehensively in the lakes of the Łęczna-Włodawa Lake District, a unique natural area due to the richness of hydrogenic areas. The lakes in the area are undergoing constant and rapid changes (despite the introduction of various forms of protection), which is reflected in the decreasing number of lakes and their eutrophication. Moreover, stoneworts, which are indicators of clean water, are disappearing from the lakes. The presence of specific groups of macrophytes led to the classification of these lakes as ecologically stable, meaning they are resistant to change and sustainable over time. The depth and surface area of the lakes were identified as the key morphometric features that most significantly influence the growth of macrophytes in eutrophic lakes, which were the most abundant in the study area. By analysing the consistent characteristics of macrophytes and lakes, four distinct classes were identified: emergent macrophyte dominated lakes, submerged macrophyte dominated lakes, low macrophyte density lakes, high macrophyte density lakes. The proposed classification can serve as a diagnostic framework for lakes, helping to identify them and improve our understanding of the changes occurring within these ecosystems.

BACKGROUND: According to the Intergovernmental Panel on Climate Change (IPCC) 2007, natural wetlands contribute 20-39 % to the global emission of methane. The range in the estimated percentage of the contribution of these systems to the total release of this greenhouse gas is large due to differences in the nature of the emitting vegetation including the soil microbiota that interfere with the production and consumption of methane. SCOPE: Methane is a dominant end-product of anaerobic mineralization processes. When all electron acceptors except carbon dioxide are used by the microbial community, methanogenesis is the ultimate pathway to mineralize organic carbon compounds. Emergent wetland plants play an important role in the emission of methane to the atmosphere. They produce the carbon necessary for the production of methane, but also facilitate the release of methane by the possession of a system of interconnected internal gas lacunas. Aquatic macrophytes are commonly adapted to oxygen-limited conditions as they prevail in flooded or waterlogged soils. By this system, oxygen is transported to the underground parts of the plants. Part of the oxygen transported downwards is released in the root zone, where it sustains a number of beneficial oxidation processes. Through the pores from which oxygen escapes from the plant into the root zone, methane can enter the plant aerenchyma system and subsequently be emitted into the atmosphere. Part of the oxygen released into the root zone can be used to oxidize methane before it enters the atmosphere. However, the oxygen can also be used to regenerate alternative electron acceptors. The continuous supply of alternative electron acceptors will diminish the role of methanogenesis in the anaerobic mineralization processes in the root zone and therefore repress the production and emission of methane. The role of alternative element cycles in the inhibition of methanogenesis is discussed. CONCLUSIONS: The role of the nitrogen cycle in repression of methane production is probably low. In contrast to wetlands particularly created for the purification of nitrogen-rich waste waters, concentrations of inorganic nitrogen compounds are low in the root zones in the growing season due to the nitrogen-consuming behaviour of the plant. Therefore, nitrate hardly competes with other electron acceptors for reduced organic compounds, and repression of methane oxidation by the presence of higher levels of ammonium will not be the case. The role of the iron cycle is likely to be important with respect to the repression of methane production and oxidation. Iron-reducing and iron-oxidizing bacteria are ubiquitous in the rhizosphere of wetland plants. The cycling of iron will be largely dependent on the size of the oxygen release in the root zone, which is likely to be different between different wetland plant species. The role of the sulfur cycle in repression of methane production is important in marine, sulfate-rich ecosystems, but might also play a role in freshwater systems where sufficient sulfate is available. Sulfate-reducing bacteria are omnipresent in freshwater ecosystems, but do not always react immediately to the supply of fresh sulfate. Hence, their role in the repression of methanogenesis is still to be proven in freshwater marshes.

In recent years, increasing attention has been given for reclamation and reuse of water (wastewater and stormwater) in the context of augmenting water supplies. Constructed wetland (CW) systems make use of natural substrates, plants, and microbes for decontamination of wastewater and stormwater. These nature-based water treatment systems are cost-effective and sustainable. This review critically analyzes the recent advances on the application of CW systems for removal of total suspended solids (TSS), various chemical (nutrients including total nitrogen and total phosphorus, heavy metals, and organics) and microbial pollutants ( Escherichia coli , enterococci, fecal coliforms, etc.) in wastewater and stormwater. Furthermore, the influence of key factors including CW configurations, substrates, vegetation, ambient temperature/seasonal changes, oxygen levels and hydraulic retention time on the performance of CW systems are discussed. Insights into various pollutant removal mechanisms, microbial diversity and modeling (kinetics, hydrological and mechanistic) are provided. CW systems show good performance for removal of diverse pollutants from wastewater and stormwater. The pollutant removal mechanisms include physical (sedimentation and filtration), chemical (sorption, complexation and precipitation) and biological (biodegradation, microbial transformation and microbial/plant assimilation) processes. The dominant microbial communities enriched in CW systems include nitrifiers, denitrifiers and organic biodegraders. The key knowledge gaps in the development of multifunctional CW systems are highlighted. We believe that this critical review would help urban planners, environmental engineers and managers with implementation of innovative strategies for wastewater and stormwater reclamation and reuse to alleviate water stress in urban areas and to contribute to environmental sustainability. Moreover, this review would help to optimize the performance of CW systems as well as to develop regulatory guidelines for installation, operation and maintenance of CW systems.

Aim: Spatial extent is inherently related to the potential roles of the main mechanisms structuring metacommunities. We examined the effects of varying spatial extent (ecological province, region and subregion) on the environmental and spatial components of variation in lake macrophyte communities. We also studied these effects separately for three macrophyte functional groups. Location: The US state of Minnesota. Methods: We examined average and heterogeneity differences in macrophyte community composition and environmental variation among the subregions of Minnesota using canonical analysis of principal coordinates (CAP) and homogeneity of multivariate dispersion (PERMDISP), respectively. We further used partial redundancy analysis (pRDA) to decompose variation in macrophyte community composition between environmental variables and spatial location at each spatial extent and geographical region. Spatial variables were derived using principal coordinates of neighbour matrices (PCNM) analysis. Results: CAP and PERMDISP analyses showed that the subregions differed both in average community composition and in the heterogeneity of community composition for all macrophyte taxa, for emergent and submerged macrophytes, but not for non-rooted macrophytes. We did not, however, find significant differences in overall environmental heterogeneity among the subregions. Variation partitioning using pRDAs showed that species sorting is more important than spatial processes for macrophytes, although these patterns were relatively weak. There was, however, much regional specificity, with the environmental and spatial fractions of community composition varying widely at different spatial extents, among different geographical regions and among functional groups. Contrary to our initial expectations, we did not find increasing spatial structuring and decreasing environmental control with increasing spatial extent. Main conclusions: Our findings indicate that, in macrophyte metacommunities, the relative contribution of spatial processes and environmental control varies rather unpredictably with spatial extent and geographical region. Our findings are thus of importance in advancing metacommunity ecology by showing that drawing wide-ranging conclusions based on a single spatial extent or a single geographical region may be unwise.

Plant zonation is conspicuous in wetlands. The cause is frequently assumed to be the direct physiological effects of physical factors (termed ‘stress’), however many experiments show that competition and facilitation also cause zonation patterns. We conducted a field experiment with freshwater marsh emergent plants to test the causes of zonation along a single stress gradient: flooding duration. We constructed an experimental wetland with ten flooding levels to ensure that the environmental conditions represented the full range of potential flooding levels, from never flooded to continually flooded. We planted ten common marsh plants with varied ecology along the flooding duration gradient. We grew them alone and in mixture for three years and measured changes in the minimum and maximum limits, the mode and the range of distribution, and interaction importance. The mode of distribution did not shift, whether species were grown alone or with neighbours. We found strong effects of competition under low flooding stress. We found no effects from facilitation under high flooding stress. Flooding duration alone controlled the lower limits of plants. The effects of competition were intense enough to eliminate half of the species within three growing seasons. Our experiment showed that competition and physical stresses, but not facilitation, controls the zonation of emergent macrophytes along a flooding duration gradient, at least in freshwater wetlands. Models guiding wetland restoration need to include competition as well as flood duration as causal factors, but not facilitation.

The roles mobile animals and abiotic processes play as vectors for resource transfers between ecosystems (“subsidies”) are well studied, but the idea that resources from animals with limited mobility may be transported across boundaries through intermediate taxa remains unexplored. Aquatic plants (“macrophytes”) are globally distributed and may mediate transfers of aquatic-derived nutrients from aggregations of aquatic animals to terrestrial ecosystems when consumed by terrestrial herbivores. We used mesocosms (94 × 44 cm) to test whether aquatic animal-generated biogeochemical hotspots increase growth and nutrient content in macrophytes using the macrophyte Justicia americana and freshwater mussels. Justicia americana biomass production increased and belowground biomass allocation changed with increasing mussel density. At high mussel density, water-column phosphorus increased and carbon: phosphorus ratios in J. americana tissues decreased. We deployed motion-sensing cameras to explore herbivory on J. americana growing along the margins of the Kiamichi River, Oklahoma, and documented feeding by large mammals (Odocoileus virginianus, Sus scrofa, and Bos taurus). Thus, biogeochemical hotspots generated by aquatic animal aggregations can promote macrophyte production that subsequently is transferred to terrestrial animals. More broadly, this suggests that reductions in aquatic animal biomass may have bottom-up impacts that indirectly affect terrestrial ecosystems via plant–animal interactions bridging ecosystem boundaries.

Decomposition of emergent macrophytes is now recognized as an internal nutrient source for shallow lakes. Temperate lakes always experience seasonal ice cover in winter, but the influences of emergent macrophytes decomposition on water quality have rarely been examined under ice. Here, we conducted an incubation experiment to investigate winter decomposition of two common emergent macrophytes species (Typha orientalis and Phragmites australis) and its influences on water quality in the Hengshui Lake, North China. Mesocosms simulating a lake ice regime were incubated in the field for 120 days in winter and were treated with and without plant material addition. Water quality was monitored through dissolved oxygen (DO), dissolved organic carbon (DOC), total nitrogen (TN), total phosphorus (TP), ammonium nitrogen (NH4-N), and nitrate nitrogen (NO3-N). We found that both species were significantly decomposed in winter and that the majority of mass loss occurred in the first 10 days of decomposition when the water surface of mesocosms were already frozen. The concentrations of DO rapidly dropped to values close to zero after plant material submergence. At the end of incubation, the concentrations of DOC, TN, and NO3-N in the mesocosms with plant material addition were significantly higher than initial concentrations. In contrast, the concentrations of DOC, TN, TP, NO3-N, and NH4-N in the mesocosms without plant material addition were equal to or less than initial concentrations. Our research suggests that winter decomposition of emergent macrophytes produces negative influences on water quality under ice that lasts for the whole winter.

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 ( NH 4 + –N, 0.042−0.081 mg m – 2 d – 1 ) and phosphate (P O 4 3 – – P , 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 NH 4 + –N, PO 4 3 –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.

In lacustrine wetlands connected to rivers, the changes in flood regimes caused by hydrological projects lead to changes in the community traits of dominant macrophytes and, consequently, influence the structure and function of wetland vegetation. However, community trait responses of macrophytes to the timing and duration of flood disturbance have been rarely quantified. In 2011–2019, we investigated plant species diversity, density, and biomass in three dominant macrophyte communities ( Carex brevicuspis C.B. Clarke, Miscanthus sacchariflorus (Maxim.) Hackel, and Polygonum hydropiper L.) through monthly field surveys in Dongting Lake wetlands. Partial least squares regressions were used to analyze how the variations in hydrological regimes affected plant community traits. Apparent inter-annual fluctuations in plant community traits were detected during 2011–2019. The species richness and Shannon index of diversity of Miscanthus and Polygonum communities increased, whereas the Shannon index of diversity of Carex community decreased. Variation in flooding had a greater effect on Polygonum and Carex community traits than on Miscanthus community traits. Flooding disturbed all plant communities, especially when the duration and timing varied. Shorter inundation periods caused the biomass of Miscanthus community to decline, and that of Carex and Polygonum communities to increase. Earlier flood recession caused the species richness and Shannon index of diversity of Polygonum and Miscanthus community to increase, and those of Carex community to decrease. These findings imply that shorter inundation durations and earlier flood recession generated by the operation of the Three Gorges Dam have changed the macrophyte growth pattern.

Constructed floating wetlands have been employed worldwide to treat effluents and to ameliorate water quality of water resources. However, the period of macrophyte establishment into the hydroponic functioning has not been specifically addressed. This paper reports root growth and nutrient removal of Typha domingensis and Schoenoplectus californicus in a floating structure without growth substrates over the period of 11 weeks of macrophyte establishment. The experiment was conducted in mesocosm with two replicas of each specie. Weekly batches were applied with three different concentrations of a synthetic effluent. Root growth was measured to evaluate the macrophyte adaptation. Physicochemical parameters were weekly monitored, and total nitrogen, nitrate, total phosphorus, and orthophosphate were quantified to assess nutrient removal. Both species have adapted to the floating structure, but T. domingensis presented superior root growth in relation to S. californicus . No significant differences were found during the application of first two synthetic solutions. As to solution 3, significant differences between input and output values were found to total phosphorus ( F = 9.948, df = 1, p = 0.008), nitrate ( F = 5.990, df = 1, p = 0.031), and total nitrogen ( F = 40.212, df = 1, p < 0.0001). Removal efficiency of T. domingensis ranged from 4 to 31% for total nitrogen and from 8 to 15% for total phosphorus. S. californicus , on the other hand, varied its removal efficiency from − 6 to 5% and 2 to 12% for total nitrogen and total phosphorus, respectively. Time period of macrophyte establishment varied between species, and it was an important factor that contributed to the increase of nutrient removal rates and root growth.