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      The Importance of Lake Sediments as a Pathway for Microcystin Dynamics in Shallow Eutrophic Lakes

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          Abstract

          Microcystins are toxins produced by cyanobacteria. They occur in aquatic systems across the world and their occurrence is expected to increase in frequency and magnitude. As microcystins are hazardous to humans and animals, it is essential to understand their fate in aquatic systems in order to control health risks. While the occurrence of microcystins in sediments has been widely reported, the factors influencing their occurrence, variability, and spatial distribution are not yet well understood. Especially in shallow lakes, which often develop large cyanobacterial blooms, the spatial variability of toxins in the sediments is a complex interplay between the spatial distribution of toxin producing cyanobacteria, local biological, physical and chemical processes, and the re-distribution of toxins in sediments through wind mixing. In this study, microcystin occurrence in lake sediment, and their relationship with biological and physicochemical variables were investigated in a shallow, eutrophic lake over five months. We found no significant difference in cyanobacterial biomass, temperature, pH, and salinity between the surface water and the water directly overlying the sediment (hereafter ‘overlying water’), indicating that the water column was well mixed. Microcystins were detected in all sediment samples, with concentrations ranging from 0.06 to 0.78 µg equivalent microcystin-LR/g sediments (dry mass). Microcystin concentration and cyanobacterial biomass in the sediment was different between sites in three out of five months, indicating that the spatial distribution was a complex interaction between local and mixing processes. A combination of total microcystins in the water, depth integrated cyanobacterial biomass in the water, cyanobacterial biomass in the sediment, and pH explained only 21.1% of the spatial variability of microcystins in the sediments. A more in-depth analysis that included variables representative of processes on smaller vertical or local scales, such as cyanobacterial biomass in the different layers and the two fractions of microcystins, increased the explained variability to 51.7%. This highlights that even in a well-mixed lake, local processes are important drivers of toxin variability. The present study emphasises the role of the interaction between water and sediments in the distribution of microcystins in aquatic systems as an important pathway which deserves further consideration.

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          Climate change: a catalyst for global expansion of harmful cyanobacterial blooms.

          Cyanobacteria are the Earth's oldest known oxygen-evolving photosynthetic microorganisms, and they have had major impacts on shaping our current atmosphere and biosphere. Their long evolutionary history has enabled cyanobacteria to develop survival strategies and persist as important primary producers during numerous geochemical and climatic changes that have taken place on Earth during the past 3.5 billion years. Today, some cyanobacterial species form massive surface growths or 'blooms' that produce toxins, cause oxygen depletion and alter food webs, posing a major threat to drinking and irrigation water supplies, fishing and recreational use of surface waters worldwide. These harmful cyanobacteria can take advantage of anthropogenically induced nutrient over-enrichment (eutrophication), and hydrologic modifications (water withdrawal, reservoir construction). Here, we review recent studies revealing that regional and global climatic change may benefit various species of harmful cyanobacteria by increasing their growth rates, dominance, persistence, geographic distributions and activity. Future climatic change scenarios predict rising temperatures, enhanced vertical stratification of aquatic ecosystems, and alterations in seasonal and interannual weather patterns (including droughts, storms, floods); these changes all favour harmful cyanobacterial blooms in eutrophic waters. Therefore, current mitigation and water management strategies, which are largely based on nutrient input and hydrologic controls, must also accommodate the environmental effects of global warming. © 2009 Society for Applied Microbiology and Blackwell Publishing Ltd.
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            Impacts of climate variability and future climate change on harmful algal blooms and human health

            Anthropogenically-derived increases in atmospheric greenhouse gas concentrations have been implicated in recent climate change, and are projected to substantially impact the climate on a global scale in the future. For marine and freshwater systems, increasing concentrations of greenhouse gases are expected to increase surface temperatures, lower pH, and cause changes to vertical mixing, upwelling, precipitation, and evaporation patterns. The potential consequences of these changes for harmful algal blooms (HABs) have received relatively little attention and are not well understood. Given the apparent increase in HABs around the world and the potential for greater problems as a result of climate change and ocean acidification, substantial research is needed to evaluate the direct and indirect associations between HABs, climate change, ocean acidification, and human health. This research will require a multidisciplinary approach utilizing expertise in climatology, oceanography, biology, epidemiology, and other disciplines. We review the interactions between selected patterns of large-scale climate variability and climate change, oceanic conditions, and harmful algae.
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              Extraction and high-performance liquid chromatographic method for the determination of microcystins in raw and treated waters.

              Increasing concern over the presence of microcystins (cyanobacterial/blue-green algal hepatotoxins) in water supplies has emphasized the need for a suitable analytical method. As many microcystins are known to exist, a method was developed that permits the determination of numerous variants by a single procedure. The method involves filtration to separate cyanobacterial cells from water, allowing intracellular and extracellular toxin levels to be assessed. The cellular components of the samples are extracted repeatedly in methanol, which was found to be the most versatile solvent tested for the extraction of microcystins. The efficiency of this extraction procedure was found to be independent of cell biomass. The filtered water was subjected to trace enrichment using a C18 solid-phase extraction cartridge, followed by identification and determination by photodiode-array high-performance liquid chromatography. The procedure was assessed using four water samples (two raw and two treated) spiked with a mixture of five microcystins and the cyanobacterial hepatotoxin nodularin. Recoveries of all but one microcystin were found to be good when spiked with concentrations as low as 250 ng l-1. The linearity and precision of the experimental procedure were assessed for five microcystins and nodularin. The proposed method permits rapid sample processing and determination of several microcystins.
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                Author and article information

                Contributors
                Role: Academic Editor
                Journal
                Toxins (Basel)
                Toxins (Basel)
                toxins
                Toxins
                MDPI
                2072-6651
                18 March 2015
                March 2015
                : 7
                : 3
                : 900-918
                Affiliations
                Aquatic Ecology and Ecosystem Studies, School of Civil, Environmental and Mining Engineering, the University of Western Australia, 35 Stirling Highway, M015, Crawley, WA 6009, Australia; E-Mails: haihong.song@ 123456research.uwa.edu.au (H.S.); liah.coggins@ 123456uwa.edu.au (L.X.C.); elke.reichwaldt@ 123456uwa.edu.au (E.S.R.)
                Author notes
                [†]

                These authors contributed equally to this work.

                [* ]Author to whom correspondence should be addressed; E-Mail: Anas.Ghadouani@ 123456uwa.edu.au ; Tel.: +61-8-6488-2687; Fax: +61-8-6488-1015.
                Article
                toxins-07-00900
                10.3390/toxins7030900
                4379532
                25793723
                a9c84712-4e02-4fde-a768-aab3d1112bbc
                © 2015 by the authors; licensee MDPI, Basel, Switzerland.

                This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution license ( http://creativecommons.org/licenses/by/4.0/).

                History
                : 15 December 2014
                : 05 March 2015
                Categories
                Article

                Molecular medicine
                cyanobacterial bloom,microcystins,cyanotoxins,cyanobacterial biomass,sediments,spatial variability,temporal variability

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