Microbial Dynamics of an Epilithic Mat Community in a High Alpine Stream

Studies were conducted to examine interrelationships between the heterotrophic and phototrophic populations within an epilithic community in the outlet stream of a high alpine lake. Levels of nitrates, phosphates, and total organic compounds in the lake were consistently near the lower limits of detectability. Microscopic examination of the community by phase-contrast light microscopy and scanning electron microscopy revealed diatoms, filamentous algae, and bacteria embedded within a dense gelatinous matrix. Chlorophyll a and primary productivity measurements had peak values in early August, with subsequent declines. Bacterial heterotrophic activity, as measured by V_max, turnover rate, and relative activity, increased significantly as the phototrophic community declined. This trend in heterotrophic activity was not accompanied by an increase in total bacterial numbers as determined by epi-illuminated fluorescence microscopy. These results suggest that the phototrophic community responded to changes in, or interactions among, various chemical and physical factors throughout the study period. The catabolic activity of the sessile bacteria appeared to be positively influenced by changes in the mat environment resulting from the decline of the phototrophic populations.     

Effects of Acid Stress on Aerobic Decomposition of Algal and Aquatic Macrophyte Detritus: Direct Comparison in a Radiocarbon Assay

Radiolabeled phytoplankton and macrophyte lignocelluloses were incubated at pHs 4 and 7 in water from a naturally acidic freshwater wetland (Okefenokee Swamp; ambient pH, 3.8 to 4.2), a freshwater reservoir (L-Lake; pH 6.7 to 7.2), and a marine marsh (Sapelo Island; pH ~7.8). The data suggest that acidity is an important factor in explaining the lower decomposition rates of algae in Okefenokee Swamp water relative to L-Lake or Sapelo Island water. The decomposition of algal substrate was less sensitive to low pH (~5 to 35% inhibition) than was the decomposition of lignocellulose (~30 to 70% inhibition). These substrate-dependent differences were greater and more consistent in salt marsh than in L-lake incubations. In both freshwater sites, the extent to which decomposition was suppressed by acidity was greater for green algal substrate than for mixed diatom or blue-green algal (cyanobacteria) substrates. The use of different bases to adjust pH or incubation in a defined saltwater medium had no significant effect on substrate-dependent differences. Although pH differences with lignocellulose were larger in marine incubations, amendment of lakewater with marine bacteria or with calcium, known to stabilize exoenzymes in soils, did not magnify the sensitivity of decomposition to acid stress.     

Recurring Seasonal Dynamics of Microbial Communities in Stream Habitats

Recurring seasonal patterns of microbial distribution and abundance in three third-order temperate streams within the southeast Pennsylvania Piedmont were observed over 4 years. Populations associated with streambed sediments and rocks (epilithon) were identified using terminal restriction length polymorphism (tRFLP) and sequencing of 16S rRNA genes selectively amplified with primers for the bacterial domain. Analyses of the relative magnitudes of tRFLP peak areas by using nonmetric multidimensional scaling resolved clear seasonal trends in epilithic and sediment populations. Oscillations between two dominant groups of epilithic genotypes, explaining 86% of the seasonal variation in the data set, were correlated with temperature and dissolved organic carbon. Sequences affiliated with epilithic phototrophs (cyanobacteria and diatom chloroplasts), a Rhodoferax sp., and a Bacillus species clustered in the summer, whereas sequences most closely related to “Betaproteobacteria” (putative Burkholderia sp.), and a putative cyanobacterium clustered in the fall/spring. The sediment genotypes also clustered into two groups, and these explained 85% of seasonal variation but correlated only with temperature. A summer tRFLP pattern was characterized by prevalence of “Betaproteobacteria,” “Gammaproteobacteria,” and a Bacillus sp., whereas the winter/spring pattern was characterized by phylotypes most closely related to “Firmicutes,” “Gammaproteobacteria,” and “Nitrospirae.” A close association between these headwater streams and their watersheds was suggested by the recovery of sequences related to microbial populations provisionally attributed to not only freshwaters but also terrestrial habitats.     

Detritus Quality Controls Macrophyte Decomposition under Different Nutrient Concentrations in a Eutrophic Shallow Lake, North China

Macrophyte decomposition is important for carbon and nutrient cycling in lake ecosystems. Currently, little is known about how this process responds to detritus quality and water nutrient conditions in eutrophic shallow lakes in which incomplete decomposition of detritus accelerates the lake terrestrialization process. In this study, we investigated the effects of detritus quality and water nutrient concentrations on macrophyte decomposition in Lake Baiyangdian, China, by analyzing the decomposition of three major aquatic plants at three sites with different pollution intensities (low, medium, and high pollution sites). Detritus quality refers to detritus nutrient contents as well as C∶N, C∶P, and N∶P mass ratios in this study. Effects of detritus mixtures were tested by combining pairs of representative macrophytes at ratios of 75∶25, 50∶50 and 25∶75 (mass basis). The results indicate that the influence of species types on decomposition was stronger than that of site conditions. Correlation analysis showed that mass losses at the end of the experimental period were significantly controlled by initial detritus chemistry, especially by the initial phosphorus (P) content, carbon to nitrogen (C∶N), and carbon to phosphorus (C∶P) mass ratios in the detritus. The decomposition processes were also influenced by water chemistry. The NO(3)-N and NH(4)-N concentrations in the lake water retarded detritus mass loss at the low and high pollution sites, respectively. Net P mineralization in detritus was observed at all sites and detritus P release at the high pollution site was slower than at the other two sites. Nonadditive effects of mixtures tended to be species specific due to the different nutrient contents in each species. Results suggest that the nonadditive effects varied significantly among different sites, indicating that interactions between the detritus quality in species mixtures and site water chemistry may be another driver controlling decomposition in eutrophic shallow lakes.     

A Three Years' Study of Life Cycle,Population Dynamics and Production of Asellus aquaticus L. in a Macrophyte Rich Stream

Populations of A. aquaticus were sampled quantitatively in 1979–82 at two localities in the river Suså which has a slope of <1 m km⁻¹ and large variations in macrophyte biomass, discharge and stream velocity. The latter two differed significantly between years. A. aquaticus had (1)−2 life cycles per year and summer and winter cohort production intervals of 85 and 290 days. Populations of A. aquaticus varied between 0 and 28,000 ind. m⁻² with an exponential increase in the spring and an exponential decrease in the autumn-winter. The A. aquaticus rate of decrease varied between 0.62 and 5.61 % d⁻¹ and increased with increasing rate of elimination of the macrophyte biomass Differences between the two localities were due to differences in physical heterogeneity. Production varied between 2.8 and 9.1 g DW m⁻² yr⁻¹ and between 12.9 and 55 g DW m⁻² yr⁻¹ at the two localities and P/B ratios were 7.4–9.9 yr⁻¹. Physical limitations are thought to be most important for the populations of A. aquaticus in the Suså, and the macrophyte biomass played an important role in modifying the physical environment. Differences between streams and lake populations are discussed.     

Comparisons of Macrophyte Breakdown,Associated Plant Chemistry,and Macroinvertebrates in a Wastewater Dominated Stream

Replacement of native macrophyte species with exotic or invasive ones affects the quality of detritus entering streams and can alter nutrient cycles and community structure in aquatic ecosystems. Decomposition of air‐dried native hardstem bulrush (Schoenoplectus acutus), invasive southern cattail (Typha domingensis), and exotic common reed (Phragmites australis) were studied in an urban stream (Las Vegas, Nevada, USA) using litter bags. Samples were analyzed for dry mass, lignin, nutrients, trace elements, and macroinvertebrates. Litter type and sediment deposited on plant material influenced material loss. Trace elements arsenic and selenium increased in plant material to concentrations considered marginal for ecosystem contamination by exposure day 76. Mercury increases were inconsistent across plant species and did not exceed limits. Bulrush decomposed faster, and tended to have higher selenium concentrations, than did invasive southern cattail and exotic common reed. Macroinvertebrate communities colonizing litter bags were similar across plant litter types, but differed from mesh‐only bags and samples collected with a kick‐net. Macroinvertebrate exclusion resulted in significantly lower loss rates, but functional feeding groups such as shredders were not associated with decomposition differences. The caddisfly, Smicridea, physically modified stem material and aided in processing, but microbes appeared most important in biological material breakdown. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Litter Breakdown and Microbial Succession on Two Submerged Leaf Species in a Small Forested Stream

Microbial succession during leaf breakdown was investigated in a small forested stream in west-central Georgia, USA, using multiple culture-independent techniques. Red maple (Acer rubrum) and water oak (Quercus nigra) leaf litter were incubated in situ for 128 days, and litter breakdown was quantified by ash-free dry mass (AFDM) method and microbial assemblage composition using phospholipid fatty acid analysis (PLFA), ribosomal intergenic spacer analysis (RISA), denaturing gradient gel electrophoresis (DGGE), and bar-coded next-generation sequencing of 16S rRNA gene amplicons. Leaf breakdown was faster for red maple than water oak. PLFA revealed a significant time effect on microbial lipid profiles for both leaf species. Microbial assemblages on maple contained a higher relative abundance of bacterial lipids than oak, and oak microbial assemblages contained higher relative abundance of fungal lipids than maple. RISA showed that incubation time was more important in structuring bacterial assemblages than leaf physicochemistry. DGGE profiles revealed high variability in bacterial assemblages over time, and sequencing of DGGE-resolved amplicons indicated several taxa present on degrading litter. Next-generation sequencing revealed temporal shifts in dominant taxa within the phylum Proteobacteria, whereas γ-Proteobacteria dominated pre-immersion and α- and β-Proteobacteria dominated after 1 month of instream incubation; the latter groups contain taxa that are predicted to be capable of using organic material to fuel further breakdown. Our results suggest that incubation time is more important than leaf species physicochemistry in influencing leaf litter microbial assemblage composition, and indicate the need for investigation into seasonal and temporal dynamics of leaf litter microbial assemblage succession.     

Relationships Between Abundance of Insects and Standing Crop of Coarse Detritus in a Pennsylvania Stream

Relationships between insect abundance and standing crop of coarse detritus, which was estimated both volumetrically and gravimetrically, were studied in a second-order stream (Little Sugar Creek, Pennsylvania) between June 1977 and June 1978. For individual taxa, coefficients of determination (R²) for relationships between insect abundance and standing crop of detritus were significant (P≦0.05) in 39% (by volume) and 32% (by weight) of the cases. Deposit feeding collectors accounted for only 41% of the significant R² values. For total fauna, R² values were significant (P≦0.05) on 7 of the 11 dates (by volume) and on 8 of the 11 dates (by weight).     

Strong Indirect Effects of a Submersed Aquatic Macrophyte, Vallisneria americana, on Bacterioplankton Densities in a Mesotrophic Lake

Phytoplankton and allochthonous matter are important sources of dissolved organic carbon (DOC) for planktonic bacteria in aquatic ecosystems. But in small temperate lakes, aquatic macrophytes may also be an important source of DOC, as well as a source or sink for inorganic nutrients. We conducted micro- and mesocosm studies to investigate the possible effects of an actively growing macrophyte, Vallisneria americana, on bacterial growth and water chemistry in mesotrophic Calder Lake. A first microcosm (1 L) study conducted under high ambient NH ₄ ⁺ levels (NH ₄ ⁺ 10 µM) demonstrated that macrophytes had a positive effect on bacterial densities through release of DOC and P. A second microcosm experiment, conducted under NH ₄ ⁺ -depleted conditions (NH ₄ ⁺ < 10 µM), examined interactive effects of macrophytes and their sediments on bacterial growth and water chemistry. Non-rooted macrophytes had negative effects on bacterial numbers, while rooted macrophytes had no significant effects, despite significant increases in DOC and P. A 70-L mesocosm experiment manipulated macrophytes, as well as N and P supply under surplus NH ₄ ⁺ conditions (NH ₄ ⁺ 10 µM), and measured effects on bacterial growth, Chl a concentrations, and water chemistry. Bacterial growth and Chl a concentrations declined with macrophyte additions, while bacterial densities increased with P addition (with or without N). Results suggest that the submersed macrophyte Vallisneria exerts a strong but indirect effect on bacteria by modifying nutrient conditions and/or suppressing phytoplankton. Effects of living macrophytes differed with ambient nutrient conditions: under NH ₄ ⁺ -surplus conditions, submersed macrophytes stimulated bacterioplankton through release of DOC or P, but in NH ₄ ⁺ -depleted conditions, the influence of Vallisneria was negative or neutral. Effects of living macrophytes on planktonic bacteria were apparently mediated by the macrophytes use and/or release of nutrients, as well as through possible effects on phytoplankton production.     

Fine Scale Patterns in Microbial Extracellular Enzyme Activity during Leaf Litter Decomposition in a Stream and its Floodplain

Microorganisms mediate the decomposition of leaf-litter through the release of extracellular enzymes. The surfaces of decomposing leaves are both chemically and physically heterogeneous, and spatial patterns in microbial enzyme activity on the litter surface should provide insights into fine-scale patterns of leaf-litter decomposition. Platanus occidentalis leaves were collected from the floodplain of a third-order stream in northern Mississippi, enclosed in individual litter bags, and placed in the stream channel and in the floodplain. Replicate leaves were collected approximately monthly over a 9-month period and assayed for spatial variation in microbial extracellular enzyme activity and rates of organic matter (OM) decomposition. Spatial variation in enzyme activity was measured by sampling 96 small discs (5-mm diameter) cut from each leaf. Discs were assayed for the activity of enzymes involved in lignin (oxidative enzymes) and cellulose (β-glucosidase, cellobiohydrolase) degradation. Rates of OM loss were greater in the stream than the floodplain. Activities of all enzymes displayed high variability in both environments, with severalfold differences across individual leaves, and replicate leaves varied greatly in their distribution of activities. Geostatistical analysis revealed no clear patterns in spatial distribution of activity over time or among replicates, and replicate leaves were highly variable. These results show that fine-scale spatial heterogeneity occurs on decomposing leaves, but the level of spatial variability varies among individual leaves at the measured spatial scales. This study is the first to use geostatistical analyses to analyze landscape patterns of microbial activity on decomposing leaf litter and in conjunction with studies of the microbial community composition and/or substrate characteristics, should provide key insights into the function of these processes.     

Seasonal Changes in the Quantity and Nitrogen Content of Coarse Detritus in a Southern Ontario Stream

Seasonal changes in standing crop of coarse, benthic detritus at five locations across a second-order stream were studied between May 1971 and May 1972. Standing crop near the banks varied seasonally with highest quantities in the autumn and winter, whereas near midstream seasonal changes in standing crop were negligible. Mean annual standing crop was 747 g/m² (ash-free dry weight) near the banks and 225 g/m² (AFDW) at midstream. Deposition experiments showed that standing crops of detritus came to equilibrium in 2–3 days at midstream and in about one week near the banks. Nitrogen content of coarse detritus, which ranged between 0.65 and 3.51% (AFDW), did not vary seasonally but was significantly greater near the banks than at midstream.     

Dominance of Epiphytic Filamentous Thiothrix spp. on an Aquatic Macrophyte in a Hydrothermal Vent Flume in Sedge Bay, Yellowstone Lake, Wyoming

Sublacustrine hydrothermal vents, geysers, and fumaroles impart regions of Yellowstone Lake with distinctive chemical compositions that generate unique freshwater habitats and support diverse microbial life. Some microbial communities within Sedge Bay manifest themselves as accumulations of white-colored films on the surfaces of aquatic macrophytes located within the hydrothermal flow of vents. It was hypothesized that the white films were the product of microbial growth, particularly sulfur-oxidizing bacteria. An investigation of the relevant biological compounds in the vent waters was conducted. Microscopy, non-culture molecular techniques, and phylogenetic analysis were used to assay the bacterial diversity associated with the films. Microscopic analysis of the white films revealed the presence of long filaments (>200 μm) that contained sulfur granules. Filaments with these characteristics were not detected on the normal macrophyte samples. Nucleic acids were extracted from the surface of macrophyte coated with the white film (SB1, SB2) and from the surface of an uncoated macrophyte (SC). 16S ribosomal (rRNA) genes were amplified with the polymerase chain reaction (PCR) and cloned. Amplified ribosomal DNA restriction analysis (ARDRA) was used to examine 100 clones from each library and identify unique phylotypes. S_Chao1 and the Shannon Index, mathematical measures of richness and heterogeneity, were employed to assess the ARDRA pattern diversity of each sample. The SC community contained 50 unique phylotypes, predominantly cyanobacteria and proteobacteria, and was the most heterogeneous. SB1 and SB2 communities were less heterogeneous and dominated by Thiothrix. Dilution to extinction PCR conducted with specific primers indicated that the relative abundance of Thiothrix 16S rRNA gene copies in all three samples were similar. However, reduced sulfur compounds from the vent resulted in a more narrow habitat that supported the sulfur-oxidizing Thiothrix in the white film to the exclusion of cyanobacteria and other proteobacteria found on the normal macrophyte. The majority of 16S rRNA gene sequences obtained in this study displayed similarities ≤98% to any known sequence in public data bases which suggests an abundance of new bacterial species in Sedge Bay.     

Leaf Litter Dynamics and Its Use by Invertebrates in a High‐Altitude Tropical Andean Stream

This study evaluates litter dynamics and its relation to macroinvertebrate communities (assemblages and feeding habits) at Piburja stream (3300 m, Ecuador). Annual litterfall (216 g AFDM/m²) was not related to rainfall, but differed significantly between months. Transport of Coarse Particulate Organic Matter (CPOM) did not differ between seasons, but retention was higher during the dry season. Thus, CPOM standing stock was higher in the dry (125.28 g AFDM/m²) compared to the wet season (12.27 g AFDM/m²). Macroinvertebrate richness and diversity were positively related to Coarse Benthic Organic Matter (CBOM) especially during the wet season. Gut content analysis revealed that, regardless of season, CPOM and Fine Particulate Organic Matter (FPOM) were the most important food items in the diet of most invertebrate taxa, including those that are not considered shredders or gathering collectors in the literature. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Leaf Decomposition and Stream Macroinvertebrate Colonisation of Japanese Knotweed,an Invasive Plant Species

Japanese knotweed (Fallopia japonica Houtt. Ronse Decrane ) is a highly invasive exotic plant that forms monocultures in riparian areas, effectively reducing plant diversity. This change in riparian plant composition alters the allocthonous input of leaf litter into adjacent streams. A field experiment was completed to understand how leaf decomposition and macroinvertebrate colonisation associated with the incorporation of exotic leaf litter. Leaf packs of Japanese knotweed, native alder (Alnus incana L.), native cottonwood (Populus trichocarpa Torr . and Gray ), and two additional mixed pack types (alder and cottonwood; alder, cottonwood, and Japanese knotweed) were placed into a 50 m stream reach in Clear Creek, Idaho, and removed over a three‐month period. Leaf decomposition and macroinvertebrate assemblages were similar between leaf types, despite differences in nitrogen and phosphorus content. The diversity of leaf types within a given leaf pack also had no effect on leaf decomposition or macroinvertebrate dynamics. These findings suggest that allochthonous inputs of Japanese knotweed fulfill a detrital function similar to that of native leaf litter. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Q-RT-PCR for Assessing Archaea, Bacteria, and Fungi During Leaf Decomposition in a Stream

Leaf disks of Tilia cordata were exposed for up to 5 weeks in a first-order stream in Nova Scotia, Canada. The exponential decay rate k was 0.008 day(-1). Ergosterol levels increased linearly to a maximum of 134 mug g(-1) dry leaf mass. Release of conidia peaked at 700 day(-1) mg(-1) on leaves that had been exposed for 3 weeks; after 5 weeks, it declined to 15 mg(-1). In total, 23 taxa of aquatic hyphomycetes were distinguished. Anguillospora filiformis contributed over 76% of the conidia during weeks 1, 2, and 3, and 16.5% in week 5. Three sets of primers specific for Bacteria, Archaea, and Fungi were applied in quantitative real-time polymerase chain reaction (Q-RT-PCR) to estimate relative DNA amounts. Archaeal DNA was consistently present at low levels. Bacterial and fungal DNA peaked between weeks 2 and 3, and declined in week 5. With the exception of week 1, fungal DNA exceeded bacterial DNA by between 12 and 110%.     

The Influence of Pack Size and Position,Leaf Type,and Shredder Access on the Processing Rate of Atherosperma moschatum Leaves in an Australian Cool Temperate Rainforest Stream

Factors affecting the processing rate of packs of southern sassafras (Atherosperma moschatum) leaves were investigated in an Australian cool temperate rainforest stream pool. Processing rate was strongly influenced by pack weight fitting a linear inverse relationship. Processing was not significantly (p>0.05) affected by whether the packs were placed on bricks or free on the stream bed. Free packs, but not packs on bricks, were processed more rapidly near the bank than in midstream (p = 0.050). Packs placed in 300 μm mesh bags, with one side unsealed were processed at the same rate as packs attached to bricks or free on the stream bed, but packs in sealed 300 μm mesh bags were processed significantly more slowly (p<10⁻⁴). Abscissed leaves were processed significantly more slowly than fresh leaves (p<10⁻⁵) and at a rate not significantly different to leaves sealed in mesh bags (p = 0.197). There was no consistent pattern of difference between processing rates in summer and winter. The results indicate that the size of litter packs may be a more important factor in influencing processing rate estimates than the method of attachment of the packs. The slow rate of processing of abscissed leaves compared with fresh leaves indicates that they were at most, slightly influenced by stream shredders. The absence of a consistent pattern of difference between summer and winter processing rates is consistent with the results of previous litter processing studies from southeastern Australia although no clear causal factor can be identified.     

Sequestration,Phytoreduction, and Phytooxidation of Halogenated Organic Chemicals by Aquatic and Terrestrial Plants

Laboratory data from plant-mediated transformation of chlorinated and brominated alkanes, alkenes, and chlorinated pesticides, including phytotransformation data from field plants currently used in phytoremediation of trichloroethylene (TCE), were reviewed for the purpose of identifying important phytoprocesses and their respective roles in phytoremediation of halogenated organic compounds (HOCs). The results of the laboratory experiments indicated that the initial very rapid removal of hydrophobic HOCs from water or the gas phase by aquatic and terrestrial plants is primarily due to sequestration. The amount of HOC sequestered is controlled by the plant species and the physicochemical properties (e.g., K_ow, aqueous solubility, volatility) of the contaminant. Phytodegradation studies conducted in both the gas and aqueous phases indicated that hexachloroethane (HCA) is dechlorinated to the same metabolites by sterilized and axenically cultivated aquatic plants and an isolated plant dehalogenase factor. Similar results were obtained in experiments conducted with o,p'-DDT and p,p'-DDT in aqueous solution. The sterilized and axenically cultivated aquatic plants also oxidized HCA to similar chloroacetic acids. The metabolism of HOCs to the corresponding oxidative and reductive transformation products identified in the plant rhizosphere, stems, and leaves suggested that more than one pathway, requiring different enzymes, may be involved in phytotransformation reactions. Four phytoprocesses (mechanisms) were found to be important in the removal of the probe HOCs from water by aquatic plants, namely, (1) rapid sequestration by partitioning to the lipophilic plant cuticles; (2) phytoreduction to less halogenated metabolites; (3) phytooxidation to haloethanols, haloacetic acids, and unidentified metabolites; and (4) assimilation into the plant tissues as nonphytotoxic products, presumably produced by covalent binding with the plant tissues. Laboratory and field data indicate that the distribution of metabolites of perchloroethylene (PCE) and TCE in cottonwood and willow trees is determined by the growth stage or age of these vascular plants, the plant species, and the duration of exposure to the compound. For terrestrial plants, the predominant phytoprocesses by which HOCs are attenuated in the environment include sequestration, rhizodegradation, uptake, phytodegradation, and phytovolatilization. Using PCE as a model chlorinated organic solvent, possible phytotransformation pathways are proposed to account for the different metabolites identified in the rhizosphere and tissues of laboratory and field plants. The proposed pathways also combine phytoreduction reactions that occur in plant tissues and are likely catalyzed by plant dehalogenase(s) for example, enzyme(s) such as glutathione-S-transferase and Fe-S clusters in chloroplast ferredoxin, with phytooxidation and covalent binding (phytoassimilation) reactions mediated by oxidative-enzymes (possibly cytochrome P-450 with monooxygenase activity, glutathione or laccase). Depending on the characteristics of the field site, the phytoprocesses identified in this study are vital in the design and implementation of phytoremediation of halogenated organic contaminants.     

Environmental Factors as Predictors of Aquatic Macrophyte Richness and Composition in Wetlands of Southern Brazil

The main goal of this study was to determine how much variation in macrophyte richness and composition is explained by wetland area, altitude, water conductivity, and nitrate and total phosphorus concentrations in wetlands in southern Brazil, and to compare these variations in two wetland subsystems (palustrine and lacustrine). A total of 126 wetlands were sampled distributed in two subsystems: 87 palustrine and 39 lacustrine wetlands. A total of 153 species of aquatic macrophytes was found in wetlands of southern Brazil and the mean number of macrophyte species per site was 8.7 (range 1–23). From the variables tested, the altitude and area were the only predictor of macrophyte richness and explained 23.1% of variation in richness. The two first axes generated by CCA explained only 4.4% of the variation in the aquatic macrophytes distribution. The macrophyte richness was similar across lacustrine and palustrine subsystems. While altitude, area and conductivity explained 33.2% of variation in macrophyte richness in the palustrine subsystem, none of the variables were associated with macrophyte richness in the studied lacustrine wetlands.     

Technical Note: Phytoremediation of Hg and Cd from Industrial Effluents using an Aquatic Free Floating Macrophyte Azolla Pinnata

The level of heavy metal pollution in Singrauli, an industrial region in India, was assessed and the phytoremediation capacity of a small water fern, Azolla pinnata R.Br (Azollaceae), was observed to purify waters polluted by two heavy metals, i.e., mercury (Hg) and cadmium (Cd) under a microcosm condition. Azolla pinnata is endemic to India and is an abundant and easy-growing free-floating water fern usually found in the rice fields, polluted ponds, and reservoirs of India. The fern was grown in 24 40-L aquariums containing Hg²⁺ and Cd²⁺ ions each in concentrations of 0.5, 1.0, and 3.0 mgL^?1 during the course of this study. The study revealed an inhibition of Azolla pinnata growth by 27.0–33.9% with the highest in the presence of Hg (II) ions at 0.5 mgL^?1 in comparison to the control. After 13 days of the experiment, metal contents in the solution were decreased up to 70–94%. In the tissues of Azolla pinnata, the concentration of selected heavy metals during investigation was recorded between 310 and 740 mgKg^?1 dry mass, with the highest level found for Cd (II) treatment at 3.0 mgL^?1 containing a metal solution.