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Beta diversity can provide insights into the processes that regulate communities subjected to frequent disturbances, such as flood pulses, which control biodiversity in floodplains. However, little is known about which processes structure beta diversity of amphibians in floodplains. Here, we tested the influence of flood pulses on the richness, composition, and beta diversity of amphibians in Amazonian floodplain environments. We also evaluated indicator species for each environment. We established linear transects in three environments: low várzea, high várzea, and macrophyte rafts. Species richness decreased and beta diversity increased according to the susceptibility of habitats to flood pulses. Indicator species differed among environments according to forest succession promoted by the flood pulse. The decrease in species richness between high and low várzea is due to non-random extinctions. The higher rates of species turnover between várzeas and macrophyte rafts are driven by the colonization of species adapted to open areas. Our results highlight that the maintenance of complex environments is needed to protect biodiversity in floodplains.

Due to their small size, planktonic marine microorganisms have large dispersal capacity in the global ocean. However, it is not known how epibenthic microalgae disperse across long distances because they are generally associated with a substrate. In this study, we examined a long-term data series (∼50 yr) of microalgal composition from a coastal station in southeast Australia for the presence of epibenthic dinoflagellates in the plankton. In addition, we collected drifting macrophytes (i.e. macroalgae and seagrass) and plastic debris from the East Australian Current, identified the associated microalgal assemblage, assessed their viability, and used phylogenetic analyses to taxonomically identify cryptic harmful epibenthic dinoflagellate species. We found no occurrences of epibenthic dinoflagellates from the genera Gambierdiscus, Fukuyoa, Ostreopsis, and Coolia at the long-term coastal station, concluding that entrainment of cells in ocean currents is an unlikely mechanism for transport of these taxa. The epibenthic microalgal communities associated with macrophyte rafts and plastic debris were primarily comprised of diatom taxa. However, intact cells of potentially harmful epibenthic dinoflagellates from the genera Coolia, Amphidinium, and Prorocentrum were also observed, and their viability was confirmed by division of isolated cells and establishment into clonal cultures. Phylogenetic analyses confirmed the presence of C. palmyrensis on a drifting Sargassum sp. raft, the first report of this potentially harmful epibenthic species in temperate Australian waters. This study shows that epibenthic dinoflagellates can attach to, and remain viable, when associated with macrophyte fragments that drift in the open ocean, therefore revealing rafting as a potential vector for dispersal of these organisms.

Recent reports of illegal small-scale alluvial gold mining activities (locally called garimpo ) by miners working on rafts in the Paraíba do Sul River (PSR) and in one of its tributaries (Muriaé River (MR)) have raised concerns about Hg contamination. This study aimed to evaluate the impact of garimpo activities on Hg contamination in three environmental compartments. Water, sediment, and aquatic macrophytes ( Pistia stratiotes ) were sampled during the rainy season in PSR, forming a 106-km transect from the point where garimpo rafts were seen and/or seized by the Federal Police. They were also sampled in the MR. Total and dissolved mercury (Hg) concentrations in water and total Hg in the suspended particulate matter (SPM) sampled in the PSR increased by 1.7, 1.5, and 2.1 times at the points where the rafts were seen compared to the point immediately upstream. In the MR, Hg concentrations were higher than those in the PSR, but most values in the environmental compartments were below the safe limits (174–486 ng∙g −1 , threshold and probable effect level, respectively), with the exception of Hg in the SPM of one of the MR sampling points (256 ng∙g −1 ) and the mining tailings (197 ng∙g −1 ). Sediment granulometry was exponentially associated with Hg concentrations in the sediment ( R 2  = 0.75, p  < 0.0001) and is also essential to understand the physical impacts of garimpo on PSR. Future studies should focus on assessing the seasonal variability of Hg concentrations in the studied compartments, especially if garimpo is identified during the dry season.

Aquatic macrophytes add structural complexity to the environment, which influences fish species. The structure of macrophytes rafts can vary depending on the hydrological cycle and space availability. Thus, the objective of the present study was to evaluate which predictors associated with environmental conditions, composition of macrophyte species and spatial factors can affect fish communities in different hydrological regimes. The study was carried out in oxbow lakes in the Amazon, in the middle Purus River, Amazonas, Brazil. Samples of fish and macrophytes were collected during the flood, receding and drought periods, and environmental variables were measured in all macrophytes rafts. Partial redundancy analysis was applied to quantify the relative contribution of environmental variables, macrophyte composition and spatial factors in the fish community. Our study revealed that environmental conditions and macrophyte species composition, and both spatially structured as well, were the main factors that explained changes in fish composition in floating meadows of oxbow lakes. Corroborating our predictions, the variations in the fish communities were explained mainly by niche-based processes, including environmental conditions and macrophyte species composition as an environmental component, which varied over the hydrological cycle. The spatial component was more important during flooding, environmental conditions during receding, and macrophyte species composition during the drought hydrological regime. However, the shared explanations that indicated a spatially structured environment, both for environmental conditions and for composition of macrophytes, were greater during all hydrological regimes, also supporting our prediction.

Most models predicting changes to species distributions under future climate scenarios ignore dispersal processes, despite their importance in determining community structure in both terrestrial and aquatic systems (‘supply-side ecology’). In the marine environment, facilitation of long-distance dispersal of coastal organisms by macrophytic rafts may be severely modified by climate impacts on raft supply, quality, and persistence, and on transport processes. Increasing storminess in the coastal zone, higher water temperatures, and changes in water circulation represent some of the key mechanisms that will directly affect rafts, while increases in herbivore metabolism due to higher water temperatures are likely to indirectly reduce raft longevity through raft consumption. Accurate predictions of climate impacts on coastal biodiversity will be contingent on resolution of factors influencing rafting so that this and other dispersal mechanisms can be incorporated into species distribution models.

Thompson Pond, a bog lake in Pine Plains, New York, has flora indicative of both ombrotrophic and minerotrophic conditions. Distinct community types within this wetland system include a peripheral moat, hummock swamp, floating vegetation mats, peat rafts, aquatic floating-leaved and submergent macrophytes, and open water. A false-bottom of unconsolidated peat overlies the lake bed. Vegetation composition is typically diverse in such lakes, which support species of both acidic and calcareous habitat affinities. We repeated a 1973–74 survey to assess changes in wetland flora after four decades. The recent survey yielded 218 vascular plant species, representing 66 families and 134 genera. The largest genus was Carex with 26 species. Forty species from the original survey were not relocated, and 97 species were found in the recent survey that had not been found in the original survey. Eriocaulon aquaticum, usually associated with oligotrophic waters, was common in the original survey and not found in the recent survey. Aerial photos were used to calculate the change in vegetation cover, revealing that floating vegetation mats and peat rafts expanded between 1970 and 2016. Nutrient loading from agricultural and residential land use within the watershed, in addition to the installation of a dam across the lake's surface water outlet have likely contributed to the floristic and community structure changes seen in Thompson Pond.

Large rivers have played a prominent role in biogeographic theory for their potential to act as barriers for the dispersal of terrestrial organisms,and therefore be involved in the generation of species diversity (Brown & Lomolino 1998). In this paper, we document the potential role of macrophyte rafts as a mechanism by which Amazonian rivers could act as dispersal agents rather than barriers, transferring organisms across banks and possibly across very large distances. These vectors could therefore act against speciation and towards homogenization of the local biota.

During the winter months, the application of large quantities of glycol based anti- and deicers to aircraft and runways poses a serious threat to receiving waters because of their toxicity and BOD effect. The orthodox approach has been to store runoff waters in aerated lagoons before discharge to receiving waters or to sewage treatment works. In the development of a pollution control strategy for Heathrow Airport Ltd. (HAL), a combination of alternative methods for treatment are being considered, and amongst these is the use of constructed wetlands on a pilot scale. Results from this study indicate that most constructed wetland plants and substrate micro-organism populations throughout the beds are not adversely affected by airport runoff or exposure to shock-loads of glycols at initial total concentrations of 1180mg/l and 632mg/l in the subsurface and surface flow reedbeds respectively. Apart from Typha spp, the aquatic macrophytes have adapted well to the exposure to airport runoff. Glycol removal efficiencies have improved as the beds have matured, and average removal efficiencies of 78% for the sub-surface system and 54% for the surface system have been recorded. Complimentary monitoring of substrate micro-organism populations prior to and after glycol dosings have shown that aerobic microbial groups of bacteria, fungi and actinomyctes, are present in higher numbers (103–107 CFU/g substrate dry weight) than their anaerobic counterparts (103–105 CFU/g substrate dry weight). In the laboratory, studies have shown fungi and bacteria to be most tolerant of glycol, with several strains able to utilise these compounds.