Asynchronous multitrophic level regime shifts show resilience to lake browning.

Lake browning is widespread due to increased supply of dissolved organic carbon under climate warming and nitrogen deposition. However, multitrophic level responses to lake browning are poorly understood. Our study aims to explore such responses across multitrophic levels based on sedimentary records of diatoms, chrysophyte stomatocysts and chironomids in a remote headwater lake in the Three Gorges Reservoir region, central China. Although all biotic proxies were analysed in the same core, the timing of shifts in chironomids (1886 ± 18 CE) preceded that in chrysophyte stomatocysts (∼1914 ± 10 CE) and diatoms (∼1941 ± 6 CE). Shifts in biotic communities were closely linked to rising temperature, δ15N depletion (a proxy for nitrogen deposition), δ13C enrichment (a proxy for littoral moss expansion), as well as biotic interactions, whereas the relative importance of the driving forces varied among the three biotic groups. Our results suggest that the zoobenthos grazing effect might be more important than bottom-up pathways in humic environments. Additionally, the coexistence of benthic, littoral and pelagic algae after the 1950s suggested that mixotrophic chrysophytes could reduce lake browning through heterotrophic processes and sustain the ecological equilibrium between littoral, pelagic and benthic productivity. Therefore, lake browning ecosystem regime shifts require analyses of multiple trophic levels. Our results suggest that heterotrophy may become more important in lake ecosystem carbon cycling with water brownification in Mulong Lake, as well as similar montane lakes.

Algae from Cr-containing infiltrate bioremediation for valorised chemical production - Seasonal availability, composition, and screening studies on hydrothermal conversion.

Integrating bioremediation of toxic wastewater with value-added production is increasing interest, but - due to some essential problems - it is hardly applied in industrial practice. The aim of the study was an annual observation of the taxonomic and biochemical composition of various Cr-resistant algal communities grown in the existing Cr-containing infiltrate treatment system, selection of the most suitable algal biomass for infiltrates bioremediation and chromium-loaded algae conversion under mild subcritical conditions. Considering continuous availability and relatively constant chemical composition, Cladophora sp. was selected for utilisation in the chromium bioremediation system, simultaneously as a waste biomass source suitable for hydrothermal conversion. Screening studies conducted in a continuous pilot plant confirmed the possibility of selective extraction of saccharides and their separation from the metals remaining in the solid residual. The negligible concentration of metals in the obtained sugar-rich aqueous phase is essential for its further use in biotechnological processes.

Exploring a unique water ecosystem under long-term exposure to hexavalent chromium - An in situ study of natural diatom (Bacillariophyceae) communities.

This paper reports the third in a series of three studies of a unique aquatic phytobial consortium that developed in a polluted ditch situated near an old chromium waste landfill. The ditch is a specific ecological niche having increased loads of several chemical compounds, including extreme hexavalent chromium concentrations up to two thousand times the allowed limit (0.02 mg dm-3 in Poland) in the more polluted section B; the moderate concentrations in section A are twice the limit. We focus on the microscopic algae group of diatoms, one of the most important components of the phytobial consortium, and continue our novel attempt to analyze the bioremediation potential of the entire consortium under those environmental conditions. We used numerical methods to analyze differences in diatom biodiversity between sections A and B, and assessed the relations between diatoms and selected water chemistry properties, including hexavalent chromium, chlorides and sulphates, the latter two known to positively influence the resistance of algae to the impact of hexavalent chromium. We noted 37 diatom taxa in section A of the ditch and 30 in section B. The most frequently observed diatoms were cosmopolitan taxa and/or characteristic taxa of saline waters. Sulphates were the most important factor influencing the diatom composition in the ditch, explaining 52% of the total variability, followed by chlorides (30%) and hexavalent chromium (9%). Gomphonema acuminatum, Melosira varians and Nitzschia frustulum var. frustulum were found to be most resistant to hexavalent chromium and were selected for further experimental studies on their biotechnological usefulness.

Natural community of macroalgae from chromium-contaminated site for effective remediation of Cr(VI)-containing leachates.

The natural macroalgal community, which developed in the unique and extremely Cr(VI)-polluted aquatic reservoir situated near a historical chromium-waste landfill, was studied in order to recognize the main mechanisms of Cr(VI) detoxification by the algal species. The conducted taxonomic analysis revealed mixed composition of the filamentous forms of algae and showed that three species of Tribonema, namely T. vulgare, T. microchloron and T. viride, which have not been studied before with regard to the mechanisms of Cr(VI) removal, are likely responsible for the effective bioremediation of this highly Cr(VI)-polluted habitat. The studied algal community, with the ability to grow in extremely high concentrations of Cr(VI), i.e. up to ca. 6150 times the upper limit for surface water, exhibited hyperaccumulative properties for chromium (max 16230 mg/kg dry weight) under the given environmental conditions. We found that the main mechanism of Cr(VI) detoxification was reduction followed by Cr(III) biosorption - feasibly by ion exchange and complexation mechanisms - and that the excellent efficiency of chromium reduction under the given, unfavorable weakly alkaline conditions indicates the biological origin of this process. It was concluded that the examined reservoir inhabited by the algal community can be used, after some modifications, as a simple cost-effective "bioreactor" allowing the reduction of chromium concentration to the desired level. Moreover, the conducted studies are also essential to obtain in-depth knowledge and should also be helpful in the relevance of the community for its further application as a potential biosorbent of Cr(VI) on a global scale.

Unique biocenosis as a foundation to develop a phytobial consortium for effective bioremediation of Cr(VI)-polluted waters and sediments.

This paper analyzes a unique, aquatic phytobial biocenosis that has been forming naturally for over 20 years and operating as a filter for Cr(VI)-polluted groundwater. Our study presents a thorough taxonomic analysis of the biocenosis, including filamentous algae, vascular plants, and microbiome, together with the analysis of Cr accumulation levels, bioconcentration factors and other environmentally-significant parameters: siderophore production by bacteria, biomass growth of the plants or winter hardiness. Among 67 species identified in the investigated reservoir, 13 species were indicated as particularly useful in the bioremediation of Cr(VI)-polluted water and sediment. Moreover, three species of filamentous algae, Tribonema sp., and three easily culturable bacterial species were for the first time shown as resistant to Cr concentration up to 123 mg/dm3, i.e. 6150 times over the permissible level. The work presents a modern holistic phytobial consortium indispensable for the remediation of Cr(VI)-contaminated aquatic environment in temperate zones worldwide.

Cyanotoxin cylindrospermopsin producers and the catalytic decomposition process: A review.

Cylindrospermopsin (CYN) is a toxic secondary metabolite produced by several freshwater species of cyanobacteria. Its high chemical stability and wide biological activity pose a series of threats for human and animal morbidity and mortality. The biggest risk of CYN exposure for human organism comes from the consumption of contaminated water, fish or seafood. Very important for effective monitoring of the occurrence of CYN in aquatic environment is accurate identification of cyanobacteria species, that are potentially able to synthesize CYN. In this review we collect data about the discovery of CYN production in cyanobacteria and present the morphological changes between all its producers. Additionally we set together the results describing the catalytic decomposition of CYN.