Núria Perujo, Helmholtz Centre for Environmental Research – UFZ, Germany
nuria.perujo-buxeda@ufz.de
Anna Freixa, Catalan Institute for Water Research (ICRA), Spain

Aquatic microorganisms have been affected – and will continue to be so – by global climate change and their responses are a growing concern for aquatic ecosystems. We understand global climate change as the set of climatic alterations in temperature and precipitation patterns as well as an increased frequency of extreme climate events. Microbial biofilms that develop on riverbed surfaces (i.e. sediments, cobbles, leaves, etc.) are key players of freshwater ecosystems as they are the base of trophic networks and due to their small size and fast generation time they respond very quickly to environmental changes. The main goal of the session is to understand how microbial biofilms respond to climate change and their potential to act as early warning indicators of ecosystem health. This session calls for contributions on the effects of climate change on microbial aquatic biofilms, including microbial community composition, functional diversity, phenotypic microbial traits, biofilm functioning and physiological responses. Original field studies of biofilms across biogeographical regions, experiments that manipulate global-change-related variables, and modelling studies using microbial variables as proxies of ecosystem health are welcome. In an increasingly changing future, knowing how microbial communities – and their functions – respond to it will help us to predict the impacts of global change in freshwater ecosystems.

Rebecca North, University of Missouri, MO, USA
northr@missouri.edu
Mindy Morales, University of Vermont, VT, USA

The world-wide increase in frequency, biomass, duration, and distribution of cyanobacteria harmful algal blooms (cyanoHABs) suggests conditions are becoming more favorable for their growth. Eutrophication is the most parsimonious explanation; increased nutrients are fertilizing phytoplankton and allowing cyanobacteria- superior competitors- to “win.” In remote regions, however, increasing incidences of cyanoHABs are seemingly disconnected from nutrient inputs. We are finding cyanobacteria at unexpected times (e.g., winter) and places (e.g., oligotrophic lakes). We also find weak relationships between traditional water quality parameters and cyanotoxin concentrations. The goal of this session is to explore alternative drivers of cyanoHABs and their toxins. We encourage contributions that extend the traditional nutrient-focused understanding of cyanoHAB ecology. Contributions can include studies at the field scale, lab, modelling, and predictive studies, which investigate both basic and applied research questions related to freshwater cyanoHABs in a range of study systems including lakes, reservoirs, streams, rivers, estuaries, and ponds. Contributions should encourage us to remove our nutrient-centric blinders and question assumptions of when and where to expect cyanoHABs and associated cyanotoxins.

Xiufeng Zhang, Jinan University, China
wetlandxfz@163.com
Lars Rudstam, Cornell University, NY, USA

The goal of many biomanipulations is to reduce the abundance of planktivorous fish, either by addition of piscivorous fish or by manually removing or reducing the biomass of undesired fish. The method was originally intended to reduce grazing pressure on zooplankton, thereby increasing grazing pressure on phytoplankton by zooplankton, especially Daphnia, to increase water clarity and promote the growth of aquatic macrophytes. Biomanipulation has become a commonly used technique for improving water quality of lakes and reservoirs after external nutrient load reduction. From a management point of view, biomanipulation is likely to be most successful in the long term in shallow eutrophic lakes. With decades of successful applications as a method for lake restoration, its popularity is increasing in the Northern Hemisphere. However, the effectiveness is questionable in tropical and subtropical regions because Daphnia are less abundant and planktivorous fish may be omnivores and can produce eggs all year round making them harder to control. In addition, large phytoplankton in some eutrophic conditions are difficult to handle by the zooplankton, including Daphnia. Furthermore, in the scenario of global climate warming, biological invasion and the enhancing human activities, the percentage of omnivorous fish increases, which may lead to reduced control of zooplankton on phytoplankton. So, the success of biomanipulation may be challenged also in the temperate zone. In this special session we wish to promote cross-continent comparisons of grazing manipulation-based biotechnology for restoration of eutrophic waters. We encourage contributions discussing results from field studies, experiments, models, and theoretical analyses.

Katrin Attermeyer, WasserCluster Lunz, Austria 
katrin.attermeyer@wcl.ac.at                                                                                
Scott D. Tiegs, Oakland University, MI, USA
tiegs@oakland.edu
Maximilian Lau, TU Bergakademie Freiberg, Germany
Eric Benbow, Michigan State University, MI, USA
Gwendoline David, Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB), Germany
Mark O. Gessner, Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB), Germany

Inland waters receive, process, and transport large amounts of organic matter in dissolved (DOM) and particulate (POM) form. Both fractions are important components in biogeochemical cycles but contribute differently to carbon and nutrient cycling through specific forms of transport, use by organisms, transformation and mineralization. POM comprises plant and animal remains (e.g. leaf litter, large wood, carcasses) and flocs, faeces, and other fine organic particles. The diversity of DOM and colloidal organic matter, although less obvious, is at least equally high. Furthermore, evidence is emerging that POM and DOM interact in inland waters, which can critically affect ecosystem functions such as carbon mineralization and burial. However, the distinct roles of processes, reactions and interactions of DOM and POM, as well as the consequences for the transformation and removal of carbon and nutrients in inland waters has not been widely acknowledged. Against this backdrop, this session aims at highlighting the particulate and dissolved world of aquatic organic matter. We invite contributions focusing on DOM and POM composition, decomposition and dynamics, microbial communities attached to litter and other organic particles, as well as their functioning, with the overarching goal of bringing together researchers from diverse backgrounds to exchange concepts and insights.

Christopher Bellas, University of Innsbruck, Austria
christopher.bellas@uibk.ac.at
Christian Wurzbacher, Technical University of Munich, Germany
c.wurzbacher@tum.de
Maiko Kagami, Yokohama National University, Japan
Julia Reiss, University of Roehampton, UK
julia.reiss@roehampton.ac.uk

Organisms that are invisible to the naked eye are the most abundant component of any freshwater community. These tiny organisms span domains and phyla and include viruses, prokaryotes and eukaryotes such as aquatic fungi. Microscopically small organisms do not only exceed macroscopic eukaryotes in terms of their numbers by far, they are also extremely biodiverse and contribute substantially to energy flows in freshwater ecosystems. For example, recent studies have detected several new groups of viruses in lakes and rivers, demonstrating that we still do not know their full diversity and the implications of virus infection for freshwater bacterial and microeukaryotic populations. Free-living freshwater bacteria are ubiquitous in freshwater systems all over the world and a main driver of ecosystem processes such as organic matter decomposition. They are a basal food source in the microbial food web and an important component fuelling freshwater food webs as a whole. In the same vein, aquatic fungi are very important as parasites and saprophytes in aquatic food webs. Freshwaters are subject to global change and hence it is vital to capture the biodiversity and function of these different microbes that underpin freshwater ecosystems.

Sebastian Sobek, Uppsala University, Sweden
sebastian.sobek@ebc.uu.se

Raquel Mendonça, Federal University of Juiz de Fora, Brazil
fm.raquel@yahoo.com.br

Sediments are a metabolically highly active compartment of freshwater systems, and the cycling of organic matter in inland water sediments largely affect the global carbon cycle and the climate. Organic carbon burial in sediments removes carbon to long-term storage in the geosphere, and therefore has a cooling effect on climate. On the other hand, organic matter degradation in sediments produces greenhouse gases (carbon dioxide, methane, nitrous oxide), which has a warming effect on climate. Despite the global significance of these fluxes, freshwater sediments remain poorly understood. While past studies have provided insights into many aspects of sediment organic matter cycling (e.g. the effectiveness of organic carbon burial, the extent of methane ebullition and oxidation, the magnitude of nitrous oxide production, the effect of drying-rewetting cycles), most of these insights are based on the small scale of individual lakes or sediment cores. The application of this small-scale knowledge at larger scales (regionally or globally) remains a challenge, and requires verification from other systems. In addition, the potential anthropogenic perturbation to sediment organic matter cycling in inland waters is currently unknown. Here we invite presentations and discussions with an empirical and theoretical focus related to freshwater sediments and their dual role as carbon sinks and sources of greenhouse gases. We welcome contributions reporting field measurements, laboratory experiments and modelling, and spanning spatial scales from individual sediment cores to the globe.

Zhe Li, Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, China
lizhe@cigit.ac.cn
Mina Bizic, Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB), Germany
mina.bizic@igb-berlin.de
Bertram Boehrer, Helmholtz Centre for Environmental Research – UFZ, Germany
Yves Prairie, Université de Québec à Montréal, QC, Canada
Hans-Peter Grossart, Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB), Germany
hanspeter.grossart@igb-berlin.de

Gases and their release from inland waters have recently received great interests in limnological research since they constitute key players in the carbon cycle: released gases such as carbon dioxide and methane are the most important contributors to the current greenhouse effect. However, the relevance of gases goes far beyond this. Oxygen is a central agent for the metabolism of higher organisms, while carbon dioxide is a requirement for photosynthesis. Some lakes store immense amounts of gas which, when suddenly released, threatens animals and humans on land. Degassing due to instantaneous pressure change and strong turbulence mixing upon discharge from reservoirs not only results in significant emissions of methane, but also causes oversaturated dissolved gases in water, threatening downstream biological communities. In addition, there is emerging evidence that several biological mechanisms can contribute to oxic methane production. This challenges our further understanding of interactions between inland waters and the atmosphere, in particular under global climate change scenarios. Presentations will cover a wide range of topics, such as the nature of gas production via microbial processes, transport of gases, solubility, ebullition, diffusive exchange at the air-water interface and gas tracing. Furthermore, presentations of methodological development or the application of novel methods ranging from micro-scale experiments to upscaling exercises will be included in this session.

Maria Dittrich, University of Toronto, ON, Canada
m.dittrich@utoronto.ca
Michael Hupfer, Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB), Germany
Man Xiao, Nanjing Institute of Geography & Limnology, Chinese Academy of Sciences, China
m.xiao@griffith.edu.au
David Hamilton, Australian Rivers Institute, Griffith University, QLD, Australia
Michele Burford, Australian Rivers Institute, Griffith University, QLD, Australia
Ingrid Chorus, Private address (ex Federal Environment Agency), Germany
ingrid.chorus@gmail.com
Hans Paerl, University of North Carolina at Chapel Hill, NC, USA

Our understanding of cellular stoichiometry and genetic regulation of nutrient uptake is growing. So is our frustration not only about insufficient control of nutrient loading, but also about situations in which external loads have been reduced, but internal loads remain significant. To control them effectively, we need an understanding of biogeochemical processes in sediments and methods to manipulate them. Also, where blooms occur, cellular nutrient uptake mechanisms and nutrient allocation within the cell are important for understanding drivers of species dominance and – for nitrogen – levels of cyanopeptide occurrence. Nitrogen can also have a critical role for limiting phytoplankton biomass. Explicitly including nitrogen in bloom control strategies therefore needs more attention. With 3 blocks of on-site and 7 pre-recorded on-line presentations, supported by 6 posters, this session addresses the mechanisms that drive both cellular responses to nutrients and nutrient releases from sediments. From this information we aim to discuss and derive options for more effective eutrophication control, including a stronger focus on the management of nitrogen loads. We intend to collect input from participants to discuss hypotheses and to develop strategies for more effective eutrophication management.

Xuexiu Chang, University of Windsor, OT, Canada
xchang@uwindsor.ca
Rainer Kurmayer, University of Innsbruck, Austria

Cyanobacterial harmful algal blooms (cHABs) are infamous for their adverse impacts on water quality and human health, which is caused by the many bioactive metabolites that cHABs produce including well-known toxins such as microcystins, anatoxin-a and saxitoxins. However, the impact that lesser known metabolites have on other organisms is poorly understood. Their benefit for ecological fitness and ecological diversification in cHAB communities is not yet understood. Molecular tools enable studying populations or communities focusing on genotypes with and without the genes for the production of specific metabolites relative to conditions for their growth and dominance. Our aim with this session is to collate the current state of knowledge from this novel research on the genetic basis of cyanotoxins and ecology. This session welcomes presentations that contribute to elucidating factors impacting the genetic regulation of cyanobacterial bioactive metabolites and their possible role on the ecological or evolutionary success of genotypes in cHAB communities.