Mark O. Gessner

Technische Universität Berlin | TUB · Institute of Ecology

Advances in analytical chemistry have facilitated the characterization of dissolved organic matter (DOM), which has improved understanding of DOM sources and transformations in surface waters. For urban waters, however, where DOM diversity is likely to be high, the interpretation of DOM signatures is hampered by a lack of information on the influen...

Local biodiversity patterns are expected to strongly reflect variation in topography, land use, dispersal boundaries, nutrient supplies, contaminant spread, management practices and other anthropogenic influences. Contrary to this expectation, studies focusing on specific taxa revealed a biodiversity homogenization effect in areas subjected to long...

Microbes play a critical role in plant litter decomposition and influence the fate of carbon in rivers and riparian zones. When decomposing low‐nutrient plant litter, microbes acquire nitrogen (N) and phosphorus (P) from the environment (i.e., nutrient immobilization), and this process is potentially sensitive to nutrient loading and changing clima...

Global freshwater biodiversity is declining dramatically, and meeting the challenges of this crisis requires bold goals and the mobilisation of substantial resources. While the reasons are varied, investments in both research and conservation of freshwater biodiversity lag far behind those in the terrestrial and marine realms. Inspired by a global...

The cover image is based on the Viewpoint A global agenda for advancing freshwater biodiversity research by Alain Maasri et al., https://doi.org/10.1111/ele.13931. Image Credit: Solvin Zankl. image

Local biodiversity patterns are expected to strongly reflect variation in topography, land use, dispersal boundaries, nutrient supplies, contaminant spread, management practices and other anthropogenic influences. In contrast, studies focusing on specific taxa revealed a biodiversity homogenization effect in areas subjected to long-term intensive i...

The biodiversity–ecosystem functioning concept asserts that processes in ecosystems are markedly influenced by species richness and other facets of biodiversity. However, biodiversity–ecosystem functioning studies have been largely restricted to single ecosystems, ignoring the importance of functional links – such as the exchange of matter, energy,...

Changes in land use and agricultural intensification threaten biodiversity and ecosystem functioning of small water bodies. We studied 67 kettle holes (KH) in an agricultural landscape in northeastern Germany using landscape-scale metatranscriptomics, to understand the responses of active bacterial, archaeal, and eukaryotic communities, to land-use...

Advances in analytical chemistry have facilitated the characterization of dissolved organic matter (DOM), which has improved understanding of DOM sources and transformations in surface waters. For urban waters, however, where DOM diversity is likely high, the interpretation of DOM signatures is hampered by a lack of basic information. Here we explo...

Light pollution is an environmental stressor of global extent that is growing exponentially in area and intensity. Artificial skyglow, a form of light pollution with large range, is hypothesized to have environmental impact at ecosystem level. However, testing the impact of skyglow at large scales and in a controlled fashion under in situ condition...

Considerable theoretical work predicts that intraspecific trait variation can have profound ecological consequences by altering species interactions. Because of their high flexibility, behavioral traits may be especially relevant in mediating how species respond to one another, thus affecting food web dynamics and ecosystem functioning. However, em...

The commercial use and spread of silver nanoparticles (AgNPs) in freshwaters have greatly increased over the last decade. Both AgNPs and ionic silver (Ag⁺) released from nanoparticles are toxic to organisms and compromise ecosystem processes such as leaf litter decomposition. Yet little is known about how AgNPs affect multitrophic systems of intera...

Light pollution is an environmental stressor of global extent that is growing exponentially in area and intensity. Artificial skyglow, a form of light pollution with large range, is hypothesized to have environmental impact at ecosystem level. However, testing the impact of skyglow at large scales and in a controlled fashion under in situ condition...

Changes in land use and agricultural intensification threaten biodiversity and ecosystem functioning of small water bodies. We studied 67 kettle holes (KH) in an agricultural landscape in northeastern Germany using landscape-scale metatranscriptomics, to understand the responses of active communities across the three domains of life, Bacteria, Arch...

Understanding ecological patterns and processes at the global scale is becoming increasingly important in view of the rapid pace of environmental change and consequent impacts on ecosystems. This chapter reviews current knowledge about how plant litter decomposition—a key stream ecosystem process—and its major biotic and abiotic drivers vary global...

The relationship between detritivore diversity and decomposition can provide information on how biogeochemical cycles are affected by ongoing rates of extinction, but such evidence has come mostly from local studies and microcosm experiments. We conducted a globally distributed experiment (38 streams across 23 countries in 6 continents) using stand...

Loadings of colored dissolved organic matter (cDOM) and nutrients affect lake ecosystem functioning in opposite ways, rendering assessments of combined effects challenging. We used the “ecosystem metabolome” as a conceptual framework to overcome this problem by characterizing the chemically diverse pool of DOM in lakes. The underlying rationale is...

Running waters contribute substantially to global carbon fluxes through decomposition of terrestrial plant litter by aquatic microorganisms and detritivores. Diversity of this litter may influence instream decomposition globally in ways that are not yet understood. We investigated latitudinal differences in decomposition of litter mixtures of low a...

Running waters contribute substantially to global carbon fluxes through decomposition of terrestrial plant litter by aquatic microorganisms and detritivores. Diversity of this litter may influence instream decomposition globally in ways that are not yet understood. We investigated latitudinal differences in decomposition of litter mixtures of low a...

Freshwater biodiversity is declining dramatically, and the current biodiversity crisis requires defining bold goals and mobilizing substantial resources to meet the challenges. While the reasons are varied, both research and conservation of freshwater biodiversity lag far behind efforts in the terrestrial and marine realms. We identify fifteen pres...

The diversity and composition of biological communities in ecosystems is typically linked to land use. Consequently, intensive agriculture has a strong influence on these patterns, including a reduction and homogenization of species diversity. Kettle holes (KH; also known as potholes) are small water bodies (<1 ha) typical to formerly glaciated lan...

Freshwater biodiversity is declining dramatically, and the current biodiversity crisis requires defining bold goals and mobilizing substantial resources to meet the challenges. While the reasons are varied, both research and conservation of freshwater biodiversity lag far behind efforts in the terrestrial and marine realms. We identify fifteen pres...

Despite advances in conceptual understanding, single-stressor abatement approaches remain common in the management of fresh waters, even though they can produce unexpected ecological responses when multiple stressors interact. Here we identify limitations restricting the development of multiple-stressor management strategies and address these, brid...

Climate and land-use change drive a suite of stressors that shape ecosystems and interact to yield complex ecological responses, i.e. additive, antagonistic and synergistic effects. Currently we know little about the spatial scale relevant for the outcome of such interactions and about effect sizes. This knowledge gap needs to be filled to underpin...

Fungi play an important role as microbial decomposers of plant litter in streams, forests, grasslands and various other terrestrial and freshwater environments. The most basic parameter to assess their quantitative importance in these ecosystems is fungal biomass. Consequently, various approaches have been used over the past decades to estimate fun...

Bacterial abundance and biomass are fundamental variables to elucidate the role of bacteria in ecosystem processes such as litter decomposition. Multiple approaches have been used to quantify bacteria in different environments. This chapter presents a method based on cell counts to determine bacterial abundance and biomass associated with decomposi...

Fungi are key components in the decomposition of plant litter in aquatic environments. Therefore, estimates of rates of fungal growth and biomass production associated with decaying litter are important in assessing the importance of fungi in ecosystems. This chapter describes a method for estimating rates of fungal growth and production. Pieces of...

Lignin and cellulose are the two most abundant polymers in the biosphere. Conferring toughness and tensile strength to plant tissues, they can account for more than half of the total leaf dry mass and an even larger fraction in wood. The recalcitrance of lignin, in particular, means that lignin concentrations are critical in determining the nutriti...

Lipids are a major class of biomolecules in plant tissues. They stand out by their high energetic content and the fact that some lipids, or constituents thereof such as certain unsaturated fatty acids, are essential to many consumers, including detritivorous invertebrates. This chapter presents the sulphophosphovanillin assay, a spectrophotometric...

Condensed tannins, also known as proanthocyanidins, are a diverse class of widespread polyphenolic secondary metabolites produced by plants. The putative ecological functions are manifold. Prominent is the chemical defence of plant tissues, suggesting that condensed tannins can also be an important factor affecting litter decomposition, including t...

Temperature is a key environmental factor controlling rates of litter decomposition in streams and other ecosystems. Normalizing decomposition rates for temperature not only enables assessments of the importance of temperature effects but also facilitates comparisons of potential other controlling factors. This chapter describes procedures to achie...

Bacterial secondary production (BSP) can be a significant fraction of total microbial production associated with decomposing litter in aquatic environments. Quantifying production rates is hence important for addressing many ecological questions. This chapter describes a method for estimating rates of bacterial production and growth rates by measur...

The spatial and temporal context in which plant litter decomposes is a critical consideration when selecting methods to study litter decomposition. Some plants, such as emergent macrophytes, do not abscise leaves, and their shoots may remain standing for extended periods, such that plant biomass begins decomposition in an upright aerial position. T...

The growing proliferation of silver nanoparticles (AgNPs) calls for detailed information on ecotoxicological effects, particularly on diverse communities and key ecosystem processes where impacts remain poorly known. This includes the decomposition of plant litter by fungi and bacteria in streams. Impacts are likely to depend on community compositi...

The neonicotinoid imidacloprid (IMI) is one of the most extensively applied neuro-active insecticides worldwide and continues to enter surface waters in many countries despite a recent ban for outdoor use in the EU. Yet little is known about ecotoxicological effects on non-target benthic freshwater species exposed to environmentally relevant concen...

This edited volume is an extensive collection of methods for investigating plant litter dynamics in ecosystems. Particular emphasis is placed on litter decomposition in streams and rivers. The presented methods range from analyses of chemical and physical litter properties to the taxonomic and functional characterization of microbial decomposers, b...

Freshwaters including adjacent floodplains, as well as coastal waters are among the global hotspots of biological diversity. They are also among the most threatened ecosystems on Earth, and yet receive much less attention than terrestrial and marine ecosystems. Not only does the dramatic decline in freshwater biodiversity affect all levels of biolo...

Browning caused by colored dissolved organic matter is predicted to have large effects on aquatic ecosystems. However, there is limited experimental evidence about direct and indirect effects of browning on zooplankton in complex field settings. We used a combination of an ecosystem‐scale enclosure experiment and laboratory incubations to test how...

“Research for the Future of our Freshwaters“ is IGB’s guiding principle. This involves giving objective and evidence-based information and advice to policymakers, authorities, associations, industry, educational institutions and the public. Within the institute’s publication series called IGB Outlines, which includes the IGB Policy Brief, IGB disse...

Das Biodiversitätsmonitoring in Deutschland ist disziplinär und institutionell stark fragmentiert ‐ mit der Folge, dass weder der Zustand der Biodiversität noch ihre Entwicklungstrends einheitlich abgebildet werden. Das wäre jedoch die Voraussetzung, damit Deutschland dem Biodiversitätsverlust gezielt entgegentreten sowie seinen nationalen und inte...

Intermittent rivers and ephemeral streams (IRES) may represent over half the global stream network, but their contribution to respiration and carbon dioxide (CO2) emissions is largely undetermined. In particular, little is known about the variability and drivers of respiration in IRES sediments upon rewetting, which could result in large pulses of...

Global urbanization trends impose major alterations on surface waters. This includes impacts on ecosystem functioning that can involve feedbacks on climate through changes in rates of greenhouse gas emissions. The combination of high nutrient supply and shallow depth typical of urban freshwaters is particularly conducive to high rates of methane (C...

Evolutionary history and adaptation to climate shape plant traits. Some include leaf traits that influence litter quality. Thus, evolutionary history should affect litter decomposition, a crucial ecosystem process. In addition, litter decomposition is directly influenced by climate. We consequently expect plant phylogeny, adaptation and climate to...

Across a landscape, aquatic-terrestrial interfaces within and between ecosystems are hotspots of organic matter (OM) mineralization. These interfaces are characterized by sharp spatio-temporal changes in environmental conditions, which affect OM properties and thus control OM mineralization and other transformation processes. Consequently, the exte...

Living Water - Research Agenda on Biodiversity of Inland and Coastal Waters

Rates of leaf litter decomposition in streams are strongly influenced both by inorganic nutrients dissolved in stream water and by litter traits such as lignin, nitrogen (N) and phosphorus (P) concentrations. As a result, decomposition rates of different leaf species can show contrasting responses to stream nutrient enrichment resulting from human...

The Earth’s subsurface represents a complex electrochemical environment that contains many electro-active chemical compounds that are relevant for a wide array of biologically driven ecosystem processes. Concentrations of many of these electro-active compounds within Earth’s subsurface environments fluctuate during the day and over seasons. This ha...

The Earth's subsurface represents a complex electrochemical environment that contains many electro-active chemical compounds that are relevant for a wide array of biologically driven ecosystem processes. Concentrations of many of these electro-active compounds within Earth's subsurface environments fluctuate during the day and over seasons. This ha...

Global patterns of biodiversity have emerged for soil microorganisms, plants and animals, and the extraordinary significance of microbial functions in ecosystems is also well established. Virtually unknown, however, are large-scale patterns of microbial diversity in freshwaters, although these aquatic ecosystems are hotspots of biodiversity and bio...

River ecosystems receive and process vast quantities of terrestrial organic carbon, the fate of which depends strongly on microbial activity. Variation in and controls of processing rates, however, are poorly characterized at the global scale. In response, we used a peer-sourced research network and a highly standardized carbon processing assay to...

River ecosystems receive and process vast quantities of terrestrial organic carbon, the fate of which depends strongly on microbial activity. Variation in and controls of processing rates, however, are poorly characterized at the global scale. In response, we used a peer-sourced research network and a highly standardized carbon processing assay to...

River ecosystems receive and process vast quantities of terrestrial organic carbon, the fate of which depends strongly on microbial activity. Variation in and controls of processing rates, however, are poorly characterized at the global scale. In response, we used a peer-sourced research network and a highly standardized carbon processing assay to...

River ecosystems receive and process vast quantities of terrestrial organic carbon, the fate of which depends strongly on microbial activity. Variation in and controls of processing rates, however, are poorly characterized at the global scale. In response, we used a peer-sourced research network and a highly standardized carbon processing assay to...

Climate change and human pressures are changing the global distribution and extent of intermittent rivers and ephemeral streams (IRES), which comprise half of the global river network area. IRES are characterized by periods of flow cessation, during which channel substrates accumulate and undergo physico‐chemical changes (preconditioning), and peri...

Weltweit nimmt die nächtliche Helligkeit durch künstliche Beleuchtung rasant zu. Je nach Wolkendichte und ‐höhe kann sie Nachtlandschaften weiträumig erhellen. Diese Lichtverschmutzung prägt Lebensräume in und um Gewässer nicht nur durch die veränderte Lichtstärke, sondern auch durch die Veränderung der spektralen Zusammensetzung, Beleuchtungshäufi...

The enrichment of ecosystems by nutrients such as nitrogen (N) and phosphorus (P) has important ecological consequences. This includes effects on plant litter decomposition in forest soils and forested headwater streams, where fungi play a pivotal role. However, our understanding of nutrient relationships on fungal communities associated with decom...

Perennial rivers and streams make a disproportionate contribution to global carbon (C) cycling. However, the contribution of intermittent rivers and ephemeral streams (IRES),which sometimes cease to flow and can dry completely, is largely ignored although theymay represent over half the global river network. Substantial amounts of terrestrialplant...

In the version of this Article originally published, the affiliation for M. I. Arce was incorrect; it should have been: ⁵Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB), Berlin, Germany. This has now been corrected in the online versions of the Article.

Perennial rivers and streams make a disproportionate contribution to global carbon (C) cycling. However, the contribution of intermittent rivers and ephemeral streams (IRES), which sometimes cease to flow and can dry completely, is largely ignored although they may represent over half the global river network. Substantial amounts of terrestrial pla...

Silver nanoparticles (AgNP) are widely used as antimicrobial agents. During their life cycle, some of the AgNP are released into natural environments, where chronic exposure to them can continue to cause harmful effects on microorganism. However, very little is known about long-term impacts on important ecosystem compartments such as periphyton, a...