Common Aquatic Macrophytes Research Articles

Investigating the Potential Effects of Microplastics on the Growth and Functional Traits in Two Aquatic Macrophytes (Myriophyllum spicatum and Phragmites australis) in Mesocosm Experiments

In the last decade, microplastics (MPs) have become a significant environmental pollutant with potential negative effects on aquatic biodiversity and ecosystems. This mesocosm study examined the effect of MPs on the growth and physiology of two common aquatic macrophytes (Myriophyllum spicatum and Phragmites australis), focusing on changes in biomass allocation and nutrient contents. We evaluated oxidative stress responses by measuring superoxide dismutase, malondialdehyde, soluble sugars, free amino acids, and glutamate synthetase activities for M. spicatum, and we assessed photosynthetic processes through metrics including Fv/Fm, electron transfer rate, and Y(II) for P. australis. Unlike most previous studies in plants, we found that the growth and all functional traits of these two plants were not significantly affected by the common MP type (polyethylene) at either low or high concentrations. Additionally, we have examined the impact of another type of MP (polystyrene) on P. australis, and no significant effect was observed. In conjunction with prior case studies, the majority of which demonstrated the toxic impacts of MPs, our research indicates that plants exhibit a species-specific response to MPs. In addition to the strong adaptation of widespread plants used in this study, the large experimental system and relative long-term treatment may also explain our negative results. Our study highlights the need to further investigate species-specific tolerances and adaptive responses to MPs to better understand their ecological impacts.

The characteristics and environmental significance of BVOCs released by aquatic macrophytes

Biogenic volatile organic compounds (BVOCs) emitted by plants serve crucial biological functions and potentially impact atmospheric environment and global carbon cycling. Despite their significance, BVOC emissions from aquatic macrophytes have been relatively understudied. In this study, for the first time we identified there were 68 major BVOCs released from 34 common aquatic macrophytes, and these compounds referred to alcohols, aldehydes, alkanes, alkenes, arenes, ethers, furans, ketones, phenol. For type of BVOC emissions from different life form and phylogenetic group of aquatic macrophytes, 34 of the 68 BVOCs from emergent and submerged macrophytes are classified into alkene and alcohol compounds, over 50% BVOCs from dicotyledon and monocotyledon belong to alcohol and arene compounds. Charophyte and pteridophyte emitted significantly fewer BVOCs than dicotyledon and monocotyledon, and each of them only released 12 BVOCs. These BVOCs may be of great importance for the growth and development of macrophytes, because many BVOCs, such as azulene, (E)-β-farnesene, and dimethyl sulfide are proved to play vital roles in plant growth, defense, and information transmission. Our results confirmed that both life form and phylogenetic group of aquatic macrophytes had significantly affected the BVOC emissions form macrophytes, and suggested that the intricate interplay of internal and external factors that shape BVOC emissions from aquatic macrophytes. Thus, further studies are urgently needed to investigate the influence factors and ecological function of BVOCs released by macrophytes within aquatic ecosystem.

Elodea Canadensis (Submerged Macrophyte of the Yenisei River) and Actinides: Properties, Accumulation, Regularities and Interactions

Radioactive contamination of the Yenisei River bottom and (including the contamination with actinides) is the result of long-term operation of the Mining and Chemical Combine, which manufactures plutonium for weapons. The study considers the behavior of a submerged macrophyte Elodea Canadensis, one of the most widely spread species of aquatic plants in the River Yenisei. The values of the accumulation coefficients obtained for 242Pu, 13100 ± 2100 L·kg-1, were close to the concentration factor for 241Am–17100 ± 4300 L·kg-1, obtained for the Elodea shoots. Studies on the potential adaptation of one of the common aquatic macrophytes Elodea canadensis when immersed in a medium containing actinide. It was found that almost all the studied 241Am and 242Pu do not show a clear external effect on the solid fragments of the plant (cell membranes). Thus, it was shown that Elodea canadensis is tolerant of anthropogenic radio nuclides that differ in nature, physico-chemical properties, etc.

In-situ anatomical and elemental response of aquatic macrophytes against nutrient enrichment in freshwater tropical lakes

Nutrient enrichment in lakes due to municipal wastewater discharge and agricultural run-off leads to excessive growth of algae and aquatic macrophytes leading to their altered trophic states. This paper presents the effect of wastewater-induced nutrient enrichment on the anatomical changes and elemental profiling in three common aquatic macrophytes of freshwater lakes in India’s Central Gangetic Plain. It is observed that with increase in trophic state, biomineral depositions are seen in the leaf anatomy of aquatic macrophytes. Elemental variations in free-floating (Eichhornia crassipes), submerged (Hydrilla verticillata) and emergent (Typha latifolia) macrophytes collected from three different lakes with different catchment characteristics and trophic state using EDS (Energy-Dispersive X-Ray Spectroscopy) spectra show that with increasing trophic state, elemental constituent in the aquatic macrophytes also increases. The rhizome of Eichhornia crassipes showed the formation of calcium oxalate crystals in SEM (Scanning Electron Microscope) images and EDS analysis. Among macrophytes, floating and submerged macrophytes show a greater number of elemental constituents as compared to the emergent macrophytes. The findings of this study show that the anatomical and elemental responses of macrophytes are dependent both on the water quality and trophic state of the lakes. In-situ responses of macrophytes are based on their tolerance level against the pollution load and environmental changes. This study has important implications for understanding the response mechanism of macrophytes with changing water quality and increasing trophic state, which may help in proper management of freshwater ecosystem.

The adaptive capabilities of Elodea canadensis under the influence of anthropogenic factors

Studies on the potential adaptation of one of the common aquatic macrophytes Elodea canadensis when immersed in a medium containing anthropogenic pollutants of various origins – metals (inorganic salts); organic salts, mineral acids; oil and its derivatives - water-soluble petrochemicals. It was found that almost all the studied pollutants do not show a clear external effect on the solid fragments of the plant (cell membranes). Thus, it was shown that Elodea canadensis is tolerant of anthropogenic pollutants that differ in nature, hazard class, physico-chemical properties, etc.

Dietary habits of the black-necked swan Cygnus melancoryphus(Birds: Anatidae) and variability of the aquatic macrophyte cover in the Río Cruces wetland, southern Chile.

The black-necked swan Cygnus melancoryphus is an aquatic herbivorous bird whose dietary habits depend on the dominance and accessibility of macrophyte banks in shallow areas of coastal and limnetic wetlands in southern South America. The swans from the Río Cruces wetland in southern Chile (ca. 39°S) feed mainly on the macrophyte Egeria densa from the water column between depths from less than 0,5 and 2,0 m. A micro- histological analysis of black-necked swan feces (N = 152) collected during six sampling occasions between 2012 and 2017 confirms the preferred consumption of E. densa and highlights the impact of temporal changes in the cover of these macrophytes on the swan’s diet. The dietary composition of black-necked swans appears as a reliable proxy for temporal changes in the distribution of the most common aquatic macrophytes in the Río Cruces wetland. These results highlight the importance of preserving shallow wetlands as the habitat for aquatic macrophytes that provide the main food source for these herbivorous water birds.

Interactive effects of road salt and sediment disturbance on the productivity of seven common aquatic macrophytes

Abstract Around the world, freshwater ecosystems are subjected to numerous stressors that can alter community composition in favour of stress‐tolerant species. Because combinations of stressors often result in non‐additive interactions, elucidating responses to isolated and combined stressors is important to understand the ecological responses to anthropogenic disturbance. In this study, we explored the responses of common macrophyte species to two stressors of increasing concern: elevated salinity from road salt applications and turbidity from human recreational activities and shoreline development. The independent and interactive effects of environmentally relevant salt concentrations and turbidity on macrophyte productivity have received little attention. We hypothesised that both stressors in isolation would reduce macrophyte productivity and that the two stressors combined will lead to a greater (i.e. synergistic) reduction in productivity. To test these hypotheses, we conducted dark‐ and light‐bottle experiments on seven species of native and invasive macrophytes under a factorial combination of three salt concentrations (0, 500 and 3,000 added mg Cl− L−1) and two turbidity conditions (clear and turbid via a disturbance to the sediment). On average, macrophytes exhibited reduced productivity in response to increased salt, but results were highly species‐specific. Several species exhibited a unimodal response to elevated salinity, whereas Elodea canadensis exhibited a positive response to the high‐salt treatment. Similarly, macrophytes exhibited an average reduction in productivity under turbid conditions, but analysis of species‐specific responses revealed both neutral and negative responses. Combining the two stresses yielded non‐additive responses for some species. Specifically, Myriophyllum spicatum appeared to suffer from the combination of salt and turbidity, whereas Elodea canadensis and Ceratophyllum demersum benefited from the combination. Our results suggest that increased anthropogenic disturbance of freshwater ecosystems can dramatically alter macrophyte species metabolism and might stimulate the growth of some species while deterring the growth of others.

Seasonal and spatial variation of aquatic macrophytes and phytoplankton community at El-Quanater El-Khayria River Nile, Egypt

In this study, the phytoplankton biomass and species composition in El-Quanater El-Khayria (River Nile, Egypt) was analyzed at four sampling sites on a program of a seasonally sampling and supported by measurements of different water variables as well as biomass production of most common aquatic macrophytes. The major species of aquatic macrophytes were two submerged species (Ceratophyllum demersum and Ceratophyllum submersum), two emergent (Polygonum tomentosum and spontaneum), and one free floating aquatic macrophyte (Eichhornia crassipes). Considerable seasonal variations in water quality as well as macrophytes biomass were found in the studied areas, which result in a variation of phytoplankton flora. A total of 235 phytoplankton species belonging to 7 classes was recorded, with higher numbers in autumn and winter compared to spring and summer. The maximum number of phytoplankton (7238 × 104 L−1 cells) was recorded in winter, however, the lowest one (96 × 104 L−1 cells) recorded in spring. Chlorophyceae was the dominant group, forming 56.96% of the total phytoplankton biomass followed by Bacillariophyceae (34.82%), Cyanophyceae (7.99%), Cryptophyceae (0.10%), Dinophyceae (0.096%), Chrysophyceae (0.03%) and Euglenophyceae (0.02%). Chlorophyll a values ranged from 9.77 µg L−1 to 69.81 µg L−1, with a considerable seasonal and spatial variation. All phytoplankton classes as well as, chlorophyll a was negatively correlated with all aquatic macrophytes species except for C. submersum which correlated positively with chlorophyll a and Cyanophyceae. In addition, it was positively correlated with pH, conductivity and dissolved oxygen.

Trace metal concentrations and their transfer from sediment to leaves of four common aquatic macrophytes.

In the present study, the concentrations of trace and alkali metals in leaves of four common helophytes, Sparganium erectum, Glyceria maxima, Phalaris arundinacea, and Phragmites australis, as well as in corresponding water and bottom sediments were investigated to ascertain plant bioaccumulation ability. Results showed that Mn and Fe were the most abundant trace metals in all plant species, while Co and Pb contents were the lowest. Leaves of species studied differed significantly in respect of element concentrations. The highest concentrations of Mg, Na, Fe, Mn, Cu, Pb, and Ni were noted in S. erectum while the highest contents of Co, Ca, Zn, and Cr in Phalaris arundinacea. Phragmites australis contained the lowest amounts of most elements. Concentrations of Co, Cr, Fe, and Mn in all species studied and Ni in all except for Phragmites australis were higher than natural for hydrophytes. The leaves/sediment ratio was more than unity for all alkali metals as well as for Cu and Mn in Phragmites australis; Cr, Co, and Zn in Phalaris arundinacea; Cr and Mn in S. erectum; and Cr in G. maxima. High enrichment factors and high levels of toxic metals in the species studied indicated a special ability of these plants to absorb and store certain non-essential metals and, consequently, their potential for phytoremediation of contaminated aquatic ecosystems.

Colonisation by fragments in six common aquatic macrophyte species

Vegetative reproduction is the most common form of propagation in aquatic macrophytes. Fragmentation and consecutive re-rooting of the fragments is one way in which new macrophyte colonies may establish. The success and frequency of this strategy depends on the species and the environment. This study tested how well six species are capable of colonising this way. Tested species are five of the most abundant species of Lake Balaton, where macrophyte recolonisation is still to take place after improving water quality and one potentially invasive species. Fragments of standardized length were examined for survival, rooting rates and length growth during five to six week experiments under laboratory conditions. Effects of species, shoot part (apical or mid-stem part) and seasonality on rooting probability were analysed with logistic regression. Effects on life-cycle were also examined, in terms of continuation of growth and of flowering or seed-set. Species differed significantly in rooting rates and growth, but not in survival rates. Egeria densa, Myriophyllum spicatum and Potamogeton perfoliatus showed the best colonisation properties (survival rates: 95 %, 84 % and 84 %; rooting rates: 88 %, 45 % and 65 %, respectively), while Potamogeton pectinatus colonised less successfully (survival rate: 91 %, rooting rate: 38 %). The annual Najas marina was the only species which frequently reached flowering (61 %), while fragmenting further, without much rooting (rooting rate: 5 %). The non-rooting Ceratophyllum demersum was least impacted by fragmentation and continued growth best, with survival rates of 100 %. Shoot part had a significant influence on rooting rate and length growth. Apical fragments had higher rooting rates and greater length growth than stem fragments, probably due to the action of their meristematic tissue. Differences in the three repetitions of the experiment may be attributable to seasonal changes in colonisation features. It is concluded that recolonisation by fragments might be an effective way for macrophyte populations to recover in Lake Balaton.

The Effect of Aquatic Plant Abundance on Shell Crushing Resistance in a Freshwater Snail

Most of the shell material in snails is composed of calcium carbonate but the organic shell matrix determines the properties of calcium carbonate crystals. It has been shown that the deposition of calcium carbonate is affected by the ingestion of organic compounds. We hypothesize that organic compounds not synthesized by the snails are important for shell strength and must be obtained from the diet. We tested this idea indirectly by evaluating whether the abundance of the organic matter that snails eat is related to the strength of their shells. We measured shell crushing resistance in the snail Mexipyrgus churinceanus and the abundance of the most common aquatic macrophyte, the water lily Nymphaea ampla, in ten bodies of water in the valley of Cuatro Ciénegas, Mexico. We used stable isotopes to test the assumption that these snails feed on water lily organic matter. We also measured other factors that can affect crushing resistance, such as the density of crushing predators, snail density, water pH, and the concentration of calcium and phosphorus in the water. The isotope analysis suggested that snails assimilate water lily organic matter that is metabolized by sediment bacteria. The variable that best explained the variation in crushing resistance found among sites was the local abundance of water lilies. We propose that the local amount of water lily organic matter provides organic compounds important in shell biomineralization, thus determining crushing resistance. Hence, we propose that a third trophic level could be important in the coevolution of snail defensive traits and predatory structures.

Morphological and Chemical Changes Induced by Herbivory in Three Common Aquatic Macrophytes

AbstractThe Dry Matter Content (DMC), the total phenolic content, the production of new branches and the plant fragmentation were compared in three macrophyte species (Elodea canadensis, Elodea nuttallii and Myriophyllum spicatum) exposed or not to snail herbivory. Grazing significantly reduced the DMC of M. spicatum and E. canadensis, but had no effect on the DMC of E. nuttallii. The phenolic contents of Elodea species were not modified by snail herbivory, whereas that of M. spicatum significantly increased when exposed to grazers. The number of new branches produced by M. spicatum and E. canadensis plants, and the fragmentation of E. canadensis also increased in response to herbivory.Chemical defences are therefore probably constitutive in Elodea and induced in M. spicatum, and morphological changes can be related to species growth form and synthesis of phenolic compounds. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Epiphytic bacterial community composition on two common submerged macrophytes in brackish water and freshwater

BackgroundPlants and their heterotrophic bacterial biofilm communities possibly strongly interact, especially in aquatic systems. We aimed to ascertain whether different macrophytes or their habitats determine bacterial community composition. We compared the composition of epiphytic bacteria on two common aquatic macrophytes, the macroalga Chara aspera Willd. and the angiosperm Myriophyllum spicatum L., in two habitats, freshwater (Lake Constance) and brackish water (Schaproder Bodden), using fluorescence in situ hybridization. The bacterial community composition was analysed based on habitat, plant species, and plant part.ResultsThe bacterial abundance was higher on plants from brackish water [5.3 × 107 cells (g dry mass)-1] than on plants from freshwater [1.3 × 107 cells (g dry mass)-1], with older shoots having a higher abundance. The organic content of freshwater plants was lower than that of brackish water plants (35 vs. 58%), and lower in C. aspera than in M. spicatum (41 vs. 52%). The content of nutrients, chlorophyll, total phenolic compounds, and anthocyanin differed in the plants and habitats. Especially the content of total phenolic compounds and anthocyanin was higher in M. spicatum, and in general higher in the freshwater than in the brackish water habitat. Members of the Cytophaga-Flavobacteria-Bacteroidetes group were abundant in all samples (5–35% of the total cell counts) and were especially dominant in M. spicatum samples. Alphaproteobacteria were the second major group (3–17% of the total cell counts). Betaproteobacteria, gammaproteobacteria, and actinomycetes were present in all samples (5 or 10% of the total cell counts). Planctomycetes were almost absent on M. spicatum in freshwater, but present on C. aspera in freshwater and on both plants in brackish water.ConclusionBacterial biofilm communities on the surface of aquatic plants might be influenced by the host plant and environmental factors. Distinct plant species, plant part and habitat specific differences in total cell counts and two bacterial groups (CFB, planctomycetes) support the combined impact of substrate (plant) and habitat on epiphytic bacterial community composition. The presence of polyphenols might explain the distinct bacterial community on freshwater M. spicatum compared to that of M. spicatum in brackish water and of C. aspera in both habitats.

The lethal and sublethal effects of the aquatic macrophyte Myriophyllum spicatum on Baltic littoral planktivores

Macrophyte architecture can structure predator-prey interactions, but it is the chemicals within the plant that may actually be lethal. We conducted aquarium experiments to study the effects of common aquatic macrophytes (Myriophyllum spicatum, Myriophyllum sibiricum, and Chara tomentosa) and a predator (perch, Perca fluviatilis) on the survival, habitat choice, swimming, and feeding activities of Baltic littoral planktivores, mysids Neomysis integer and Praunus flexuosus, and three-spined stickleback (Gasterosteus aculeatus) larvae. Chemicals excreted by M. spicatum in a dense patch caused high mortality (73% to 89%) in both mysid species but not in sticklebacks, whereas M. sibiricum and C. tomentosa had no lethal effects. In lower stem densities stickleback larvae and N. integer avoided M. spicatum even in the presence of predator signals, and M. spicatum lowered the swimming and feeding activities of stickleback larvae. Only P. flexuosus did not avoid M. spicatum vegetation. Areas occupied by M. spicatum seem to be highly unsuitable habitats for littoral mysids and three-spined stickleback larvae. Because M. spicatum is a dominant macrophyte in the study area and eutrophication further increases its abundance, it may strongly influence the occurrence and distribution of mysids and fish larvae in the littoral ecosystems of the Baltic Sea.

Allelopathic effects of the toxic cyanobacteriumMicrocystis aeruginosa on duckweed,Lemna gibba L.

Cyanotoxins are a group of compounds produced by cyanobacteria that can have severe physiological effects on other organisms, including humans. The potential allelopathic effects of Microcystis aeruginosa, a toxic cyanobacterium, on the duckweed plant, Lemna gibba L., were examined using three experimental methods: (1) a series of toxicity bioassays, (2) evaluation of toxin production by M. aeruginosa in the direct and indirect presence of L. gibba, and (3) inhibition of oxygen evolution in photosynthesis. The results showed that, first, there were no clear dose-dependent effects of the microcystin-LR standard or the toxic M. aeruginosa culture filtrate on any of the end points measured in the toxicity bioassays (plant and frond number, dry weight, growth rate, chlorophyll content; one-way ANOVA, p > 0.05). In those cases in which an EC(50) value could be obtained, chlorophyll a was the most sensitive end point, as it had the lowest EC(50) value (14.47 microg/L microcystin-LR) of all the end points. Second, the presence of L. gibba did not result in higher microcystin-LR production in the toxic M. aeruginosa culture. And, last, oxygen evolution was not affected in isolated chloroplasts exposed directly to microcystin-LR. Therefore, microcystins from the toxic cyanobacterium Microcystis aeruginosa do not appear to have an allelopathic effect on the common aquatic macrophyte Lemna gibba.

Decomposition dynamics of aquatic macrophytes in the lower Atchafalaya, a large floodplain river

Decomposition of aquatic macrophytes can considerably influence carbon cycling and energy flow in shallow freshwater aquatic ecosystems. The Atchafalaya River Basin (ARB) is a large floodplain river in southern Louisiana that experiences a seasonal floodpulse and is spatially composed of a mosaic of turbid riverine and stagnant backwater areas. During two seasons, winter and fall of 1995, we examined decomposition of four common aquatic macrophytes in the ARB: water hyacinth (Eichhornia crassipes), arrowhead (Sagittaria platyphylla), coontail (Ceratophyllum demersum) and hydrilla (Hydrilla verticillata). To determine decay rates, we used litter bags of two mesh sizes (5 mm and 0.25 mm) and analyzed data with a single exponential decay model. Analysis of decay rates established several trends for aquatic macrophyte decomposition in the ARB. First, macrophytes decayed faster in fall than winter due to the effect of increased temperature. Second, macroinvertebrates were the primary decomposers of macrophytes in riverine sites and microbes were the primary decomposers in backwater areas. These trends may have been related to decomposer-habitat interactions, with well-oxygenated riverine sites more hospitable to invertebrates and backwater areas more favorable to microbes because of high organic inputs and reduced flow. Decay rates for macrophytes, ranked from slowest to fastest, were E. crassipes<S. platyphylla<C. demersum<H. verticillata. Slower decomposition of E. crassipes was probably a result of microbial inhibition by the waxy-cutin outer layer and low nutritional value. The accelerated decomposition of C. demersum and H. verticillata was most likely a function of the large surface area of the highly dissected leaves. Macroinvertebrate numbers were twice as high in riverine sites compared to backwater sites. In the winter, amphipods Gammarus spp. and Hyallela azteca composed a large percentage of the total density on detritus. In the fall, Caenis sp. was prevalent in the backwater habitat and dipterans were abundant in the riverine site. We investigated the microbial component involved in the decomposition of E. crassipes and S. platyphylla and found that the highest microbial respiration rates occurred early in the winter at the backwater site. Bacterial density in the winter on E. crassipes and S. platyphylla averaged 1.4×106 cm-2 after two days and decreased to 2.0×105 cm-2 after 28 d. Our results emphasized the importance of the microbial community in the decomposition of macrophytes in the ARB, especially in backwater habitats and in the early stages of decay.

Characterization of Root-Associated Methanotrophs from Three Freshwater Macrophytes: Pontederia cordata , Sparganium eurycarpum , and Sagittaria latifolia

Root-associated methanotrophic bacteria were enriched from three common aquatic macrophytes: Pontederia cordata, Sparganium eurycarpum, and Sagittaria latifolia. At least seven distinct taxa belonging to groups I and II were identified and presumptively assigned to the genera Methylosinus, Methylocystis, Methylomonas, and Methylococcus. Four of these strains appeared to be novel on the basis of partial 16S ribosomal DNA sequence analysis. The root-methanotroph association did not appear to be highly specific, since multiple methanotrophs were isolated from each of the three plant species. Group II methanotrophs were isolated most frequently; though less common, group I isolates accounted for three of the seven distinct methanotrophs. Apparent K(m) values for methane uptake by representative cultures ranged from 3 to >17 muM; for five of the eight cultures examined, apparent K(m) values agreed well with apparent K(m) estimates for plant roots, suggesting that these strains may be representative of those active in situ.

In Situ Analyses of Methane Oxidation Associated with the Roots and Rhizomes of a Bur Reed, Sparganium eurycarpum, in a Maine Wetland

Methane oxidation associated with the belowground tissues of a common aquatic macrophyte, the burweed Sparganium eurycarpum, was assayed in situ by a chamber technique with acetylene or methyl fluoride as a methanotrophic inhibitor at a headspace concentration of 3 to 4%. Acetylene and methyl fluoride inhibited both methane oxidation and peat methanogenesis. However, inhibition of methanogenesis resulted in no obvious short-term effect on methane fluxes. Since neither inhibitor adversely affected plant metabolism and both inhibited methanotrophy equally well, acetylene was employed for routine assays because of its low cost and ease of use. Root-associated methanotrophy consumed a variable but significant fraction of the total potential methane flux; values varied between 1 and 58% (mean (plusmn) standard deviation, 27.0% (plusmn) 6.0%) with no consistent temporal or spatial pattern during late summer. The absolute amount of methane oxidized was not correlated with the total potential methane flux; this suggested that parameters other than methane availability (e.g., oxygen availability) controlled the rates of methane oxidation. Estimates of diffusive methane flux and oxidation at the peat surface indicated that methane emission occurred primarily through aboveground plant tissues; the absolute magnitude of methane oxidation was also greater in association with roots than at the peat surface. However, the relative extent of oxidation was greater at the latter locus.

Evaluation of some common aquatic macrophytes cultivated in enriched water as possible source of protein and biogas

The biomass production of three common aquatic macrophytes,viz. Azolla pinnata, Eichhornia crassipes andHydrilla verticillata, was high at the prevailing environmental conditions and by the enriched water of River Ganga. The biomass production ofAzolla andEichhornia was positively correlated with the orthophosphate phosphorus and nitrate-nitrogen concentrations of the enriched water. The biomass ofAzolla andHydrilla was positively correlated with the electrical conductivity of the water. The average yield of crude protein was highest in Azolla (8,520 kg.ha−1.yr−1), and somewhat lower inEichhornia (6,520 kg.ha−1.yr−1). The annual biogas production was highest inEichhornia (44,381 litres), and somewhat lower inAzolla (17,186 litres).