Floating-leaved Plants Research Articles

Decomposition of exotic versus native aquatic plant litter in a lake littoral zone: Stoichiometry and life form analyses

The decomposition rates and stoichiometric characteristics of many aquatic plants remain unclear, and our understanding of material flow and nutrient cycles within freshwater ecosystems is limited. In this study, an in-situ experiment involving 23 aquatic plants (16 native and 7 exotic species) was carried out via the litter bag method for 63 days, during which time the mass loss and nutrient content (carbon (C), nitrogen (N), and phosphorus (P)) of plants were measured. Floating-leaved plants exhibited the highest decomposition rate (0.038 ± 0.002 day−1), followed by submerged plants and free-floating plants (0.029 ± 0.002 day−1), and emergent plants had the lowest decomposition rate (0.019 ± 0.001 day−1). Mass loss by aquatic plants correlated with stoichiometric characteristics; the decomposition rate increased with an increasing P content and with a decreasing C content, C:N ratio, and C:P ratio. Notably, the decomposition rate of submerged exotic plants (0.044 ± 0.002 day−1) significantly exceeded that of native plants (0.026 ± 0.004 day−1), while the decomposition rate of emergent exotic plants was 55 ± 4 % higher than that of native plants. The decomposition rates of floating-leaved and free-floating plants did not significantly differ between the native and exotic species. During decomposition, emergent plants displayed an increase in C content and a decrease in N content, contrary to patterns observed in other life forms. The P content decreased for submerged (128 ± 7 %), emergent (90 ± 5 %), floating-leaved (104 ± 6 %), and free-floating plants (32 ± 6 %). Exotic plants released more C and P but accumulated more N than did native plants. In conclusion, the decomposition of aquatic plants is closely linked to litter quality and influences nutrient cycling in freshwater ecosystems. Given these findings, the invasion of the littoral zone by submerged and emergent exotic plants deserves further attention.

Effects of select herbicides for management of American lotus, white waterlily, and watershield

Literature describing effective control measures for the floating-leaved plants American lotus (Nelumbo lutea Willd.), white waterlily (Nymphaea odorata Aiton), and watershield (Brasenia schreberi J.F. Gmel.) is minimal as these are usually considered as desirable species. However, floating-leaved plants can cause ecological, economic, and social problems when undergoing demographic expansions, usually following alterations of natural hydrologic cycles. Therefore, a mesocosm trial was conducted to determine the potential of foliar applications of seven aquatic herbicides to reduce abundance of the three target species at maximum and half-maximum label rates. Three of the herbicides (glyphosate, imazamox, and florpyrauxifen-benzyl) provided short- and long-term suppression (.75% reduction) of white waterlily and watershield leaf density or biomass. As a followup trial, field work was conducted using glyphosate, imazamox, and florpyrauxifen-benzyl to determine plant response to these herbicides in a natural setting. All herbicides resulted in long-term (52 wk after treatment) leaf density reduction of white waterlily (64 to 100% reduction) and watershield (46 to 75% reduction; except 2.83 kg ae ha 1 glyphosate) in field sites while the abundance of American lotus increased. Reduction of white waterlily and watershield may have reduced competition thereby favoring higher abundance of lotus. Regardless, long-term (52-wk) reduction of white waterlily and watershield suggest the potential for these herbicides as operational management tools for nuisance populations of these species. Future work should evaluate chemical techniques for control of American lotus, where both timing of leaf emergence and potential interactions with other plant species must be considered in the design of those studies.

An overview of oxygen transport in plants: diffusion and convection.

The movement of gases within plants is crucial for species that live in flood-prone areas with limited soil oxygen. These plants adapt to hypoxia/anoxia not by using oxygen more efficiently, but by ensuring a steady oxygen supply to their cells. Wetland plants typically form gas-filled spaces (aerenchyma) in their tissues, providing a low-resistance pathway for gas movement between shoots and roots, especially when the shoots are above water, and the roots are submerged. Oxygen movement in plant roots is mainly through diffusion. However, in certain species, such as emergent and floating-leaved plants, pressurized flows can also facilitate the movement of gases within their stems and rhizomes. Three types of pressurized (convective) flows have been identified: humidity-induced pressurization (positive pressure), thermal osmosis (positive pressure with air flow against the heat gradient), and venturi-induced suction (negative pressure) caused by wind passing over broken culms. A clear diel variation in pressurized flows exists, with higher pressures and flows during the day and negligible pressures and flows during the night. This article discusses some key aspects of these mechanisms for oxygen movement.

Performance of unoccupied aerial application systems for aquatic weed management: Two novel case studies

AbstractUnoccupied aerial application systems (UAAS) are gaining popularity for weed management to increase applicator safety and to deliver herbicide treatments where treatment sites limit ground-based spray equipment. Several studies have documented UAAS application strategies and procedures for weed control in terrestrial settings, yet literature describing remote spray technology for use in aquatics remains limited. Currently, applicators seek guidance for UAAS deployment for aquatic weed management to overcome site access restrictions, deal with environmental limitations, and improve ground-based applicator safety in hazardous treatment scenarios. In the present case studies, we evaluate a consumer-available UAAS to deliver the herbicide, florpyrauxifen-benzyl, as both foliar and directed in-water spray applications. The first case study showed that the invasive floating-leaved plant, yellow floating heart, was controlled 80% to 99% by 6 wk after treatment (WAT) following UAAS foliar herbicide treatments. The second case study demonstrated that UAAS directed in-water herbicide application reduced variable-leaf watermilfoil visible plant material by 94% at 5 WAT. Likewise, directed in-water applications from UAAS eliminated the need to deploy watercraft, which improved overall operational efficiency. Data from both case studies indicate that UAAS can provide an effective and efficient treatment strategy for floating-leaved and submersed plant control among common herbicide treatment scenarios. Future integration of UAAS in aquatic weed control programs is encouraged, especially among smaller treatment sites (≤4 ha) or where access limits traditional spray operations.

Allometric relationships between leaf and petiole traits across 31 floating-leaved plants reveal a different adaptation pattern from terrestrial plants.

Allometric scaling between stomata and xylem for terrestrial woody plants is a widely observed pattern that may be constrained by water transport. Floating-leaved plants, a particular life form of aquatic plants, have leaves in direct contact with both air and water and a poorly developed xylem that may not be limited by water supply as for terrestrial plants. However, whether such an allometric scaling relationship still exists in floating-leaved plants has not been explored. We analysed 31 floating-leaved species/varieties with a range in leaf area covering six orders of magnitude. For all 31 floating-leaved plants, we studied the allometric relationships between leaf area and petiole transverse area, and between total stomatal area and petiole vascular area. The slopes of both relationships were similar to the slope of the allometric relationship (1.23) between total stomatal area and xylem area of 53 terrestrial plants. However, for ten of them with xylem that can be clearly defined, the strong positive relationship between total stomatal area and petiole xylem area had a significantly smaller slope than that of terrestrial plants (0.64 vs. 1.23). Furthermore, after considering phylogeny, the scaling relationships between total stomatal area and petiole traits in floating-leaved plants remained significant. We speculated that for floating-leaved plants, the hyperallometric relationship (slope >1) between the construction of leaf/stoma and petiole was promoted by the high demand for photosynthesis and thus more leaves/stomata. While the hypoallometric relationship (slope <1) between stomatal and xylem area was related more to hydraulic processes, the selection pressure on stomata was lower than xylem of floating-leaved plants. Allometric relationships among the hydraulic traits on water transport of aquatic plants are the result of natural selection to achieve maximum carbon gain, which is similar to terrestrial plants.

Effects of Macrobenthos Relative to Floating-Leaved Plants on the Wintering Shorebird Assemblages at Shengjin Lake, China

In shallow lakes, floating-leaved plants can produce dense lakebeds that dramatically alter freshwater ecosystems and impact macrobenthic communities. Shorebirds are morphologically diverse and utilize different foraging strategies; they can partition food resources to achieve coexistence due to differences in food availability. In this study, we defined shorebird foraging guilds using a principal component analysis and explained differences in shorebird composition in terms of food availability by comparing macrobenthic and shorebird communities in Euryale ferox artificial planting areas, Trapa spp. natural growth areas, and control areas. The Mantel test and a Spearman analysis were used to correlate macrobenthic taxa with shorebird foraging guilds. We recorded four different macrobenthic taxa in the three study areas, including insects, gastropods, oligochaetes, and bivalves. Fifteen species belonging to three shorebird families were recorded across the three study areas. Our results suggest that floating-leaved plants are an important cause of differences in macrobenthic communities, and epifaunal macrobenthos (insects and gastropods) and infaunal macrobenthos (oligochaetes and bivalves) take on different patterns of diversity composition in different habitats. The macrobenthic and shorebird communities were potentially coherent. Different shorebird foraging guilds were limited by food availability and thus correlated differently with different macrobenthos. Therefore, differences in macrobenthic communities relative to floating-leaved plants can affect shorebird assemblages by affecting the availability of food resources.

Self-Purification Mode of Still-Water Ponds in Urban Parks Based on In Situ Ecological Remediation Design

Still-water ponds in urban parks are often eutrophic; hence, these ponds are typically at risk of algal blooms, which have a negative impact on landscapes and visitor experiences. Instead of adopting the current mainstream methods of ex situ ecological remediation with flowing water bodies, such as the construction of a circulating filtration system or an artificial wetland system around the pond, this research adopted in situ ecological remediation in still-water ponds to suppress algal blooms. The plan was implemented through a small-scale engineering design and plant configuration inside the pond. Using six still-water ponds in Beijing Yu Park as experimental sites, different mini-engineering designs and plant configurations were implemented at different ponds to perform comparative experiments, and the water quality of each pond was monitored for three consecutive years. By summarizing the variation in key water quality indices for each pond, we found that a mini-engineering design of “multilevel” pond revetments and lakebeds combined with a “multilayer” aquatic macrophyte configuration of floating-leaved plants, emergent plants, and submerged plants could effectively inhibit algal blooms. Thus, an effective ecological self-purification model and corresponding landscape design principles for still-water ponds in urban parks were proposed.

Genome-Wide Analysis of the Growth-Regulating Factor (GRF) Family in Aquatic Plants and Their Roles in the ABA-Induced Turion Formation of Spirodela polyrhiza.

Growth-regulating factors (GRFs) are plant-specific transcription factors that play essential roles in regulating plant growth and stress response. The GRF gene families have been described in several terrestrial plants, but a comprehensive analysis of these genes in diverse aquatic species has not been reported yet. In this study, we identified 130 GRF genes in 13 aquatic plants, including floating plants (Azolla filiculoides, Wolffia australiana, Lemna minuta, Spirodela intermedia, and Spirodela polyrhiza), floating-leaved plants (Nymphaea colorata and Euryale ferox), submersed plants (Zostera marina, Ceratophyllum demersum, Aldrovanda vesiculosa, and Utricularia gibba), an emergent plant (Nelumbo nucifera), and an amphibious plant (Cladopus chinensis). The gene structures, motifs, and cis-acting regulatory elements of these genes were analyzed. Phylogenetic analysis divided these GRFs into five clusters, and ABRE cis-elements were highly enriched in the promoter region of the GRFs in floating plants. We found that abscisic acid (ABA) is efficient at inducing the turion of Spirodela polyrhiza (giant duckweed), accompanied by the fluctuated expression of SpGRF genes in their fronds. Our results provide information about the GRF gene family in aquatic species and lay the foundation for future studies on the functions of these genes.

The influence of macrophyte ecological groups on food web components of temperate freshwater lakes

Aquatic macrophyte taxonomic composition, species abundance and cover determine the physical structure, complexity and heterogeneity of aquatic habitats – the structuring role of macrophytes. These traits influence richness, distribution, feeding and strength of the relationships between food web communities in lakes. The aim of this study was to determine how lakes with different dominating macrophyte ecological groups affect planktonic food web components, emphasising the influence on young of year (YOY) fish and large (≥1 +) fish community. We hypothesised that different dominating macrophyte ecological groups have different structural effects on food web components and YOY fish growth, abundance and feeding. Studied lakes categorised into three different macrophyte ecological groups – lakes dominated by emergent, floating+floating-leaved or submerged vegetation. We found that all dominating ecological groups had a strong influence on plankton communities (except heterotrophic bacterioplankton and nanoflagellates), YOY fish and large fish. Floating-leaved plant dominance was positively related to planktonic food web structure and YOY fish weight, length, abundance and the consumption of zooplankton as a prey of all major species of YOY fishes. Larger fish tended to favour the presence of emergent vegetation. This conclusion has important implications for local managers and conservationists in respect to the maintenance and protection of littoral habitats and fish resources.

Ventilation Systems in Wetland Plant Species

Molecular oxygen and carbon dioxide may be limited for aquatic plants, but they have various mechanisms for acquiring these gases from the atmosphere, soil, or metabolic processes. The most common adaptations of aquatic plants involve various aerenchymatic structures, which occur in various organs, and enable the throughflow of gases. These gases can be transferred in emergent plants by molecular diffusion, pressurized gas flow, and Venturi-induced convection. In submerged species, the direct exchange of gases between submerged above-ground tissues and water occurs, as well as the transfer of gases via aerenchyma. Photosynthetic O2 streams to the rhizosphere, while soil CO2 streams towards leaves where it may be used for photosynthesis. In floating-leaved plants anchored in the anoxic sediment, two strategies have developed. In water lilies, air enters through the stomata of young leaves, and streams through channels towards rhizomes and roots, and back through older leaves, while in lotus, two-way flow in separate air canals in the petioles occurs. In Nypa Steck palm, aeration takes place via leaf bases with lenticels. Mangroves solve the problem of oxygen shortage with root structures such as pneumatophores, knee roots, and stilt roots. Some grasses have layers of air on hydrophobic leaf surfaces, which can improve the exchange of gases during submergence. Air spaces in wetland species also facilitate the release of greenhouse gases, with CH4 and N2O released from anoxic soil, which has important implications for global warming.

Aquatic macrophyte fluctuations since the 1900s in the third largest Chinese freshwater lake (Lake Taihu): Evidences, drivers and management implications

Diverse aquatic macrophyte communities represent an essential component of healthy shallow lake ecosystems, and information on changes in macrophytes abundance and composition is crucial for restoration initiatives and management. However, the long-term dynamics of aquatic macrophyte communities are poorly understood for most subtropical freshwater lakes. This study used macrophyte surveys from 1960 to 2014 alongside plant macrofossil and pollen remains deposited in the sediment to reconstruct, macrophyte community change over the two centuries in the southeastern bay of Lake Taihu, China. Plant macrofossils efficiently captured the main historical recorded macrophyte species, including four unrecorded submerged taxa (Vallisneria spinulosa, Zannichellia palustris, Nitella sp., and Chara sp.) by the monitoring surveys. Aquatic pollen failed to reflect the main species composition in the bay, but provided additional information on species with no macrofossils and few seeds, especially the floating-leaved and free-floating taxa (e.g., Nymphoides and Azolla). We conducted a constrained incremental sum of squares cluster analysis and a multiple factor analysis (MFA) to the macrophyte community in the core and identified three major changes over the past century, with a shift from Potamogeton malaianus (pre-1960), to Vallisneria natans, P. malaianus, Potamogeton maackianus, and charophyte species (1960–1998), followed by the proliferation of pollutant-resistant species Ceratophyllum demersum and Myriophyllum spicatum, as well as the floating-leaved plant Nymphoides (post-1998). MFA also clearly elucidated the relationships between macrophyte shifts and changes in various environmental stressors (i.e., cladocerans, particle size spectra and geochemical data). The results confirmed our hypothesis, which stated that hydrological alterations and increased nutrient inputs, driven by the increasing anthropogenic pressures were likely the main drivers of the alteration in the macrophyte composition and succession in the bay. Our study provides a unique perspective on the pre-disturbance macrophyte community composition of Eastern Lake Taihu, thereby offering useful information not only for lake managers in the Yangtze region, but also for the global decision-making for the eutrophication and restoration of large shallow lakes.

Methane emission of a lake aquaculture farm and its response to ecological restoration

Enclosure lake aquaculture causes lake eutrophication and emits CH4 to the atmosphere. So far, little is known about the rate of CH4 emission from lake aquaculture and about how ecological restoration (or aquaculture abandonment) affects the emission. In this study, the eddy covariance (EC) technique was deployed to quantify the CH4 flux in an enclosure lake aquaculture farm and to investigate the flux response to ecological restoration. The lake site under aquaculture farming emitted 36.0 g C-CH4 m−2 yr−1 to the atmosphere, an amount that is comparable to the global mean value of semi-intensive aquaculture systems. The annual CH4 emission decreased from the pre-restoration level by 34% and 37% to 23.7 and 22.8 g C-CH4 m−2 yr−1 in the first and second year of ecological restoration, respectively, but was still much higher than that at a reference lake site not impacted by aquaculture farming (6.12 g C-CH4 m−2 yr−1). The high emission values after aquaculture abandonment suggest that aquafeed input in the decades of farming may have caused accumulation of a large amount of organic carbon in the sediment that continues to fuel CH4 production and that it may take a long time for the system to recover to a natural state. After aquaculture abandonment, floating-leaved plants expanded rapidly within the EC flux footprint, resulting in a high net ecosystem productivity (NEP) in the growing season. These plants appeared to be able to transport CH4 to the atmosphere through aerenchyma tissues and stomata.

The Use of Constructed Wetland for Mitigating Nitrogen and Phosphorus from Agricultural Runoff: A Review

The loss of nitrogen and phosphate fertilizers in agricultural runoff is a global environmental problem, attracting worldwide attention. In the last decades, the constructed wetland has been increasingly used for mitigating the loss of nitrogen and phosphate from agricultural runoff, while the substrate, plants, and wetland structure design remain far from clearly understood. In this paper, the optimum substrates and plant species were identified by reviewing their treatment capacity from the related studies. Specifically, the top three suitable substrates are gravel, zeolite, and slag. In terms of the plant species, emergent plants are the most widely used in the constructed wetlands. Eleocharis dulcis, Typha orientalis, and Scirpus validus are the top three optimum emergent plant species. Submerged plants (Hydrilla verticillata, Ceratophyllum demersum, and Vallisneria natans), free-floating plants (Eichhornia crassipes and Lemna minor), and floating-leaved plants (Nymphaea tetragona and Trapa bispinosa) are also promoted. Moreover, the site selection methods for constructed wetland were put forward. Because the existing research results have not reached an agreement on the controversial issue, more studies are still needed to draw a clear conclusion of effective structure design of constructed wetlands. This review has provided some recommendations for substrate, plant species, and site selections for the constructed wetlands to reduce nutrients from agricultural runoff.

The Bowati in Kordofan, Sudan: Unique Aquatic Ecosystems of a Non-Nilotic In-Land Delta

This paper describes the unique in-land, non-Nilotic delta of Wadi El Galla, a seasonal water course which originates in the Nuba Mountains of Kordofan region and terminates in a chain of small ponds each known locally as a Bouta (pl Bowati). The Bowati are inhabited by a community of aquatic plants forming a wide spectrum ranging from small true (Euophytes) to large woody trees. The euophytes encountered were grouped into six categories. The free-floating species were represented by the small Lemna purpusilla Torr. and the larger Pistia stratiotes L. while only one submerged species was found: Ottelia alismoides (Planch.) Welp. One suspended species was found, Utricularia stellaris L. F. Three species of the floating-leaved plants were encountered namely, Nymphaea lotus L., N. micrantha Guill. & Perrott and Nymphoides nilotica (Kotschy & Peyr.) Léonard. The emergent Limnophyton obtusifolium (L.) Miq. was very prominent in all the Bowat constituting with N. lotus the two dominant species. Trailing from the Bouta edge and forming thick mats on the open water is Neptunia oleracea Lour., a member of the Fabaceae family. Within these euophytes and towering to over ten meters is the woody tree Mitragyna inermis Kuntze. Some of herbaceous plants are a source of food for the local community such as the bulbils of Nymphaea micrantha. These meagrely studied ecosystems are under threat from natural and anthropogenic factors. The former are the recurrent drought, climate change, and the latter are due to urbanization, overexploitation and oil activities. There is an urgent need for delineating and mapping the geomorphology, drainage patterns of Al Muglad in-land delta as well as the number and sites of the Bowati. The taxonomy of the aquatic species, their nutritive and medicinal values are other areas of research. Within such a context, a concerted national and international endeavour is called for to conserve these unique ecosystems and conceivably, declaring them as protected sites.

Variations in stable carbon isotopes in different components of aquatic macrophytes from Taihu Lake, China

Understanding the fractionation mechanism and factors controlling carbon isotopes (δ13C) in macrophytes is significant for studying the biogeochemical carbon cycle and changes in nutrients within lakes. However, whether the environmental implications of δ13C are different in the different components (α-cellulose, holocellulose and whole sample) of macrophytes is unclear. In this paper, the δ13C composition of different macrophytes tissue components in Taihu Lake was analysed on spatial and temporal scales. The effects of aquatic environmental variables on the δ13C values of macrophytes were also explored. The results showed that emergent plants have the most negative stable carbon isotope signals, with a mean value (±SD) of −27.85‰ ± 0.95‰. Submerged macrophytes have large variations with significantly more positive δ13C values (−15.19‰ ± 3.08‰). The δ13C values of floating-leaved plants (−25.32‰ ± 1.02‰) fall between those of the two groups above. In the one-way analysis of variance (ANOVA), the different components (α-cellulose, holocellulose and whole sample) of δ13C exhibited significant differences (p-value <0.01) among the three groups of macrophytes. However, there was no significant seasonal difference in the δ13C of macrophytes. In addition, the δ13C of macrophytes in rivers were lighter than those in lakes. Correlation analyses indicated that the water pH was the main factor affecting δ13C variability in macrophytes. The δ13C values of α-cellulose showed stronger sensitivity to environmental variation than did those of the whole samples and holocellulose. Hence, it is necessary to extract α-cellulose when using the δ13C of aquatic macrophytes to study the changes in lake ecological environments. These results provided a theoretical reference and experimental data support for a modern process of using δ13C in macrophytes for palaeoenvironmental changes.

Linkages between Macrophyte Functional Traits and Water Quality: Insights from a Study in Freshwater Lakes of Greece

Freshwater ecologists have shown increased interest in assessing biotic responses to environmental change using functional community characteristics. With this article, we investigate the potential of using functional traits of the aquatic plants to assess eutrophication in freshwater lakes. To this end we collected macrophyte and physicochemical data from thirteen lakes in Greece and we applied a trait-based analysis to first identify discrete groups of macrophytes that share common functional traits and then to assess preliminary responses of these groups to water quality gradients. We allocated 11 traits that cover mostly growth form and morphological characteristics to a total of 33 macrophyte species. RLQ and fourth corner analysis were employed to explore potential relationships between species, trait composition and environmental gradients. In addition, a hierarchical cluster analysis was conducted to discriminate groups of plants that share common trait characteristics and then the position of the groups along the environmental gradients was assessed. The results showed total phosphorus, chlorophyll-a, conductivity, pH and Secchi disk depth as main drivers of the environmental gradients. Hierarchical cluster analysis showed a clear separation of macrophyte assemblages with discrete functional characteristics that appeared to associate with different environmental drivers. Thus, rooted submerged plants were related with higher Secchi disk depth, conductivity and alkalinity whereas rooted floating-leaved plants showed a preference for enriched waters with phosphorus and nitrogen. In addition, free-floating plants were related positively with nitrogen and increased pH. Although we did not identify specific trait patterns with environmental drivers, our findings indicate a differentiation of macrophytes based on their functional characteristics along water quality gradients. Overall, the presented results are encouraging for conducting future monitoring studies in lakes focused on the functional plant trait composition, as expanding the current approach to additional lakes and using quantifiable functional characteristics will provide more insight about the potential of trait-based approaches as ecological assessment systems.

The vegetation of the small rivers of Novosibirsk Region (a syntaxonomic essay)

Information on the aquatic and semiaquatic vegetation of the major watercourses of West Siberia is relatively scarce, while this of small rivers is practically absent. There are 430 rivers whose length exceeds 10 km within the Novosibirsk Region. The aim of our work was to study the phytocenotic diversity of their aquatic and semiaquatic vegetation. 130 geobotanical relevés were performed by the authors in July–August 2003–2005. The object was aquatic communities formed by true aquatic (submergent and floating-leaved) plants and semiaquatic ones with emergent plants and these of water′s edge. In total 10 watercourses were studied (Table 1): 2–3 in each of five geomorphologic regions within the forest-steppe zone (Table 2). The upper, middle and lower courses (Fig. 1, Table 1) with the length of 2–2.5 km were studied in each case to ensure the 4–5 repetition of main elements (stream pools and ridges) that would give a reliable information on their flora and vegetation. The sample plots were selected above the settlements, whenever possible in sites with no to intensive anthropogenic impact. The data were collected according to J. Braun-Blanquet (1964) approach. The relevés were done on the sample plot of 100 m2 placed in the most homogeneous part of the community or, in case of its smaller area, within the natural boundaries. The following scale was used for abundance estimation: r — the species is extremely rare; + — rare, small cover; 1 — the number of individuals is large, the cover is small or individuals are sparse, but the cover is large; 2 —cover of 5–25 %; 3 — 26–50 %; 4 — 51–75 %; 5 — more than 75 %. The date on water depth, transparency (on a white Secchi disk with a diameter of 30 cm), temperature and the flow rate were obtained. The soil mechanical composition and color, the degree and nature of anthropogenic impact on vegetation and river banks were quantified. Water samples for general chemical analysis were taken in the middle course of each river. Computer programs TURBOVEG and MEGATAB (Hennekens, 1996) were used for database. The syntaxonomic affiliation of phytocenoses was determined using modern literature (Bobrov, Chemeris, 2006; Vegetace..., 2011; Chepinoga, 2015; Landucci et al. 2015; Mucina et al., 2016, etc.). 36 associations and 3 communities belonging to 12 alliances, 9 orders, and 5 classes have been identified (Tables 3–14, Fig. 2–9). Such great syntaxonomic diversity is determined by the significant ecotopic variety, the variability of substrates, the wide range of water flow rates and the different water trophicity. For comparison, 26 associations, 13 variants, 2 communities were identified in the study of 50 rivers of Lithuania (Sinkyavichene, 1992); altogether 84 associations are known for the Upper Volga region as a whole (Bob­rov, Chemeris, 2006), while 45 ones were recorded previously in 130 watercourses of this region (Bobrov, 1999). Information on small river macroalgae cenoses in the study area is partially reflected in the paper published earlier (Bobrov et al., 2005).

Selenium removal and biotransformation in a floating-leaved macrophyte system

Selenium (Se) is an essential micronutrient for animals with a relatively narrow margin between essentiality and toxicity. To evaluate Se removal efficiency by a constructed wetland treatment system and its potential eco-risk, a floating-leaved macrophyte system was constructed, consisting of three main trophic levels. Over 21-d treatment, water Se concentration was gradually reduced by 40.40%, while 24.03% and 74.41% of the removed Se were found in the plant Nymphoides sp. and sediment, respectively. Among plant tissues, roots accumulated the highest Se level, although the greatest total Se was found in stems, followed by leaves, roots and rhizomes. X-ray absorption spectroscopy revealed that 82.65% of the absorbed selenite by the plants was biotransformed to other forms, as organo-Se species accounted for 45.38% of the Se retained in the sediment, which was primarily responsible for the entry of Se into the detritus food chain. The proportion of organo-Se compounds increased with trophic levels from sediments to fish, indicating, instead of direct uptake of selenite, the food chain transfer and biotransformation of Se may serve as a key exposure route for Se in aquatic organisms. When exposed to organo-Se compounds, i.e., SeCys and SeMet, the plants, shrimp and fish tended to accumulate more Se. However, the greater trophic transfer factor was obtained for selenate, leading to higher Se levels accumulated in fish. Overall, in addition to key mechanisms involved in Se removal, our research also provides a much better understanding of the potential eco-risk that may be posed by the floating-leaved plant system for bioremediation of Se via food chain transfer and biotransformation, paving the way for a low eco-toxic treatment system for Se remediation.

Comparison of radioactive and stable cesium uptake in aquatic macrophytes affected by the Fukushima Dai-ichi Nuclear Power Plant accident

Concentrations of 134+137Cs and 133Cs in aquatic macrophytes, water, and sediment were measured in samples collected from Fukushima Prefecture, Japan. The concentrations of 137Cs in submerged and floating-leaved plants were higher than the values for emergent plants according to their main Cs uptake mode. The geometric mean water-to-plant concentration ratio for 137Cs and 133Cs was comparable observed in submerged and floating-leaved plants, while the geometric mean sediment-to-plant concentration ratio for 137Cs in emergent plants was higher than that of 133Cs, which suggest that the mobility of Fukushima accident-derived 137Cs is not in steady state 4–5 years after the accident.

ZOOPLANKTON COMMUNITY BEFORE AND AFTER NUTRIENT DIVERSION AND REVETMENT CONSTRUCTION IN LAKE FUKAMI-IKE, JAPAN

Lake Fukami-ike is a small eutrophic lake, to improve the water quality of the lake, a lakemanagement project was carried out in 1992. This project involved nutrient diversion and revetmentconstruction along the lake shore. A biotope was built near the lake in 2000. As a result, although the inorganicnitrogen in the lake decreased considerably, chlorophyll-a (phytoplankton) increased slightly. The zooplanktoncommunity in the lake before the project in 1978-1979 predominantly comprised large-sized species (about 1.8mm), however, small-sized species (about 0.1-0.2 mm) were dominant after in 2013-2015. The reason for thedecrease of the large-sized zooplankton was thought to be the possibility of losing habitat space because aquaticmacrophytes of the littoral zone were filled up when revetment construction built in 1992. We compared thebody length and composition of zooplankton community between the lake (nearly emergent plants on the lakeshore) and the biotope (emergent and floating-leaved plant cover). Large-sized zooplankton (about 0.9-1.2mm) were dominant in the biotope, and size distribution did not differ in 1978-1979. The presence of developedaquatic macrophytes was suggested to promote the survival of large zooplankton.