Dag Olav Hessen

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• PhD
• Professor (Full) at University of Oslo

Human activities have more than doubled the amount of nitrogen (N) circulating in the biosphere. One major pathway of this anthropogenic N input into ecosystems has been increased regional deposition from the atmosphere. Here we show that atmospheric N deposition increased the stoichiometric ratio of N and phosphorus (P) in lakes in Norway, Sweden,...

Lakes experience anthropogenically-forced changes that may initiate ecosystem feedbacks, in some cases reaching tipping points beyond which impacts become hard to reverse. Lakes are also important players in the global climate by ventilating a large share of terrestrial carbon back to the atmosphere as greenhouse gases, and will likely provide subs...

Lakes and ponds experience anthropogenically forced changes that may be non-linear and sometimes initiate ecosystem feedbacks leading to tipping points beyond which impacts become hard to reverse. In many cases climate change is a key driver, sometimes in concert with other stressors. Lakes are also important players in the global climate by ventil...

Climate change is anticipated to cause species to shift their ranges upward and poleward, yet space for tracking suitable habitat conditions may be limited for range‐restricted species at the highest elevations and latitudes of the globe. Consequently, range‐restricted species inhabiting Arctic freshwater ecosystems, where global warming is most pr...

Redox conditions, influenced by the availability of oxygen, are expected to dictate the rate of CO2 and CH4 production and to shape the composition and metabolism of microbial communities. Here, we use thawing permafrost peat in thermokarst water under a gradient of initial O2 concentrations to experimentally cover the variability in redox conditio...

The study highlights the critical role of CDOM in coastal light attenuation and its impact on primary production (PP). We investigated the spectral attenuation of light due to water, phytoplankton pigments, detritus and coloured dissolved organic matter (CDOM) along a salinity gradient in the outer Oslofjord, Norway. By examining the effects of the...

Globally, locally, and regionally, there are different patterns of biotic diversity and community composition reflecting past evolutionary history shaped by differences in niches, productivity, climate, and other ambient factors, as well as migration barriers. Historically, humans have impacted and eroded these biotic patterns, notably by the impac...

Aim Glaciers cover considerable portion of land and host diverse life forms from single‐celled organisms to invertebrates. However, the determinants of diversity and community composition of these organisms remain underexplored. This study addresses the biogeography, population connectivity and dispersal of these organisms, especially critical in u...

Climate tipping points are a topic of growing interest in climate research and a frequent communication tool in the media to warn of dangerous climate change. Despite indications that several climate tipping points may already be triggered within 1.5 to 2 °C warming above pre-industrial levels, there is limited research about the public understandi...

Well into the Anthropocene, the double threat of increasing greenhouse gases and deteriorating nature pose a fundamental new challenge in our history as a species. Humans are evolutionarily, psychologically, socially, and politically quite unprepared to face it, yet we will not escape confronting it. It is easy to answer why we need to act. Anthrop...

Tipping points in the Earth system could be passed within the Paris Agreement's temperature goal range (1.5 • C-2 • C). Tipping processes are a feature of complex Earth system dynamics that present major governance challenges not addressed by existing global governance institutions. The common governance toolkit is a poor match for dealing with tip...

Respiration of lipids by copepods during diapause (overwintering dormancy) contributes to ocean carbon sequestration via the seasonal lipid pump (SLP). Parameterizing this flux in predictive models requires a mechanistic understanding of how life history adaptation in copepods shapes their timing of exit from diapause. We investigate the optimal ph...

This study investigates the optical properties of coloured dissolved organic matter (CDOM) along a salinity gradient from the Glomma river to the outer Oslofjord. The research aims to determine the spectral, isotopic, and quantitative changes in CDOM across this gradient. Key findings indicate that total organic carbon (TOC) concentrations display...

This chapter is about the new modes of in vitro fertilisation (IVF) and possible evolutionary outcomes of this via changed pre- and postzygotic selection regimes and well as cultural evolution impacts related to IVF

At high latitudes, the suitable window for timing reproductive events is particularly narrow, promoting tight synchrony between trophic levels. Climate change may disrupt this synchrony due to diverging responses to temperature between, for example, the early life stages of higher trophic levels and their food resources. Evidence for this is equivo...

Any scientific career is a mix of planning and stochastic events, often with a fair share of the latter. I illustrate this by the evolution of my own career. Ecosystem studies of food webs under the impact of eutrophication (Master), and carbon cycling in DOC (Dissolved Organic Carbon)-rich lakes (PhD) led me to elemental ratios in organisms and th...

Zooplankton community composition of northern lakes is changing due to the interactive effects of climate change and recovery from acidification, yet limited data are available to assess these changes combined. Here, we built a database using archives of temperature, water chemistry and zooplankton data from 60 Scandinavian lakes that represent bro...

The macroecological drivers of freshwater diversity are accredited geographical, spatial and climatic variables, but also to productivity, ecosystem age and landscape history. Locally diversity is also influenced by the dispersal ability of species. Here we evaluated how spatial and climatic variables influence species richness and macroecological...

The state of affairs So, where do we stand currently? With the current trajectories of greenhouse gas emissions and ecosystem degradation, the planet is at risk of encountering serious local or regional feedback points in the Earth systems. These are driven by escalating feedback processes, which may ultimately – although, fortunately, this is unli...

The increased export of terrestrial dissolved organic matter (terrDOM) to coastal marine ecosystems may affect local filter feeders and the local food web via the altered uptake of organic material and associated contaminants. To compare terrDOM to marine DOM (marDOM) as contaminant vectors to coastal biota, we exposed blue mussels (Mytilus sp.) to...

Climate tipping points are a topic of growing interest in climate research as well as a frequent communication tool in the media to warn of dangerous climate change. Despite indications that several climate tipping points may be triggered within the Paris Agreement temperature range of 1.5 °C to well below 2 °C warming above pre-industrial levels,...

Temperature anomalies and changes in the diurnal temperature range (DTR) are expected to pose physiological challenges to biota; hence, both spatial and temporal variations in DTR provide important insights into temperature-induced stress in humans, animals, and vegetation. Furthermore, vegetation could dampen temperature variability. Here, we use...

The symposium focused on the interrelations between climate change and biocultural loss.

Due to climate warming, ice sheets around the world are losing mass, contributing to changes across terrestrial landscapes on decadal time spans. However, landscape repercussions on climate are poorly constrained mostly due to limited knowledge on microbial responses to deglaciation. Here, we reveal the genomic succession from chemolithotrophy to p...

An overview with text, photo and papers of the CBA activities, research on carbon cycling and climate change in boreal and permafrost ecosystems

The extractive industry consumes vast amounts of energy and is a major contributor to greenhouse gas (GHG) emissions. However, its climatic impacts have not yet been fully accounted for. In this study, we estimated the GHG emissions from extractive activities globally with a focus on China, and assessed the main emission drivers. In addition, we pr...

Never before has humanity placed its stamp on the planet in ways even remotely comparable to the situation now. A fifth into the twenty-first century, human ‘domination’ of the Earth is such that the term Anthropocene has become widespread as a label for the present time; a nomenclature which would, if widely adopted, make the Holocene (which began...

Ensuring global food security and environmental sustainability is dependent upon the contribution of the world's hundred million smallholder farms, but the contributions of smallholder farms to global agricultural greenhouse gas (GHG) emissions have been understudied. We developed a localized agricultural life cycle assessment (LCA) database to cal...

Changes in land use, afforestation, reduced acidification, and climate are causing increased terrestrial primary production and vegetation density in the boreal zone. This greening on land contributes to increased exports of natural organic matter that have made inland waters become browner. The brown freshwater ultimately drains to the coast, but...

In recent years, unexplained declines in lake total phosphorus (TP) concentrations have been observed at northern latitudes (> 42°N latitude) where most of the world's lakes are found. We compiled data from 389 lakes in Fennoscandia and eastern North America to investigate the effects of climate on lake TP concentrations. Synchrony in year-to-year...

Browning of Fennoscandian boreal lakes is raising concerns for negative ecosystem impacts as well as reduced drinking water quality. Declined sulfur deposition and warmer climate, along with afforestation, other climate impacts and less outfield grazing, have resulted in increased fluxes of Total Organic Carbon (TOC) from catchments to freshwater,...

The flourishing logistics in both developed and emerging economies leads to huge greenhouse gas (GHG) emissions, however, the emission fluxes are poorly constrained. Here, we constructed a spatial network of logistic GHG emissions based on multi-source big data at continental scale. GHG emissions related to logistics transportation reached 112.14 M...

Lakes are significant players for the global climate since they sequester terrestrially derived dissolved organic carbon (DOC), and emit greenhouse gases like CO2 to the atmosphere. However, the differences in environmental drivers of CO2 concentrations are not well constrained along latitudinal and thus climate gradients. Our aim here is to provid...

Mating strategies are key components in the fitness of organisms, and notably in birds the occurrence of monogamy versus polygyny has attracted wide interest. We address this by a very comprehensive dataset (2899 breeding events spanning the years 1978–2019) of the white‐throated dipper Cinclus cinclus. Though the mating system of this species has...

Global surface temperature has been setting new record highs in the recent decades, imposing increasing environmental challenges for societies and ecosystems worldwide. Global warming rates of the 20th century have been documented by a number of studies, nevertheless, the warming rates in the most recent decades in the 21st century are of particula...

Boreal lakes are the most abundant lakes on Earth. Changes in acid rain deposition, climate, and catchment land use have increased lateral fluxes of terrestrial dissolved organic matter (DOM), resulting in a widespread browning of boreal freshwaters. This browning affects the aqueous communities and ecosystem processes, and boost emissions of the g...

Due to climate warming, ice sheets around the world are losing mass, contributing to changes in runoff, loads of nutrients and organic carbon to recipient lakes and rivers, and on a longer time span to greening of terrestrial landscapes. These changes are expected to affect microbial communities and the release of greenhouse gases from these system...

ARCTIC-BIODIVER is a multidisciplinary project among collaborative research groups of Europe and North America. It aims to facilitate baseline information on freshwater biodiversity as well as development of biodiversity scenarios at national and circumpolar scales. In a multi-site space-for-time field study in Arctic and sub-Arctic regions we inve...

Global change affects gross primary production (GPP) in benthic and pelagic habitats of northern lakes by influencing catchment characteristics and lake water biogeochemistry. However, how changes in key environmental drivers manifest and impact total (i.e., benthic + pelagic) GPP and the partitioning of total GPP between habitats represented by th...

Copepods are a critical component of ocean ecosystems, providing an important link between phytoplankton and higher trophic levels as well as regulating biogeochemical cycles of carbon (C) and nutrients. Lipid-rich animals overwinter in deep waters where their respiration may sequester a similar quantity of C as that due to sinking detritus. This ‘...

Net Ecosystem Production (NEP) of forests is the net carbon dioxide (CO2) fluxes between land and the atmosphere due to forests' biogeochemical processes. NEP varies with natural drivers such as precipitation, air temperature, solar radiation, plant functional type (PFT), and soil texture, which affect the gross primary production and ecosystem res...

Humans are shaped by evolution through natural selection, as are all species. While evolution is central to all biological processes, the key stage for competition and selection is reproduction, which encompasses various events from courtship and mating to fertilization and pregnancy. In humans, IVF is used to aid the intrinsically inefficient repr...

Humans are shaped by evolution through natural selection, as are all species. While evolution is central to all biological processes, the key stage for competition and selection is reproduction, which encompasses various events from courtship and mating to fertilization and pregnancy. In humans, IVF is used to aid the intrinsically inefficient repr...

It is increasingly evident that climate sustainability depends not only on societal actions and responses, but also on ecosystem functioning and responses. The capacity of global ecosystems to provide services such as sequestering carbon and regulating hydrology is being strongly reduced both by climate change itself and by unprecedented rates of e...

Universities and, more broadly, higher education institutions (HEIs), need to use the knowledge they produce and their education of new professionals, to help solve some of the world´s greatest problems, as addressed by the Sustainable Development Goals (SDGs) set out by the United Nations (UN). Humanity is facing unprecedented challenges, most str...

a UNESCO report

Climate and land-use changes are leading to impacts on individual ecosystems as well as shifts in transfer dynamics between interconnected systems. At the land-ocean interface, changes in riverine inputs of organic matter (OM) and nutrients have the potential to lead to shifts in coastal carbon and nutrient cycling with consequences for ecosystem s...

The natural basis for tourism is changing: several factors are coworking Ingress Samtidig som turisme er sårbart for en rekke effekter av klimaendringer, så er turisme i seg selv en viktig pådriver både for klimaendringer og naturslitasje. Den naturbaserte turismen i Norge har derfor et behov for en baerekraftig tilpasning til klimaendringer. I den...

ARCTIC-BIODIVER is a large and multidisciplinary collaboration among research groups of Europe and North America that aims to facilitate development of biodiversity scenarios at national and circumpolar scales. In this poster, we present the extent and geographic distribution of a dataset of >100 lakes and streams covering broad latitudinal and eco...

Ecological association studies often assume monotonicity such as between biodiversity and environmental properties although there is growing evidence that nonmonotonic relations dominate in nature. Here, we apply machine-learning algorithms to reveal the nonmonotonic association between microbial diversity and an anthropogenic-induced large-scale c...

Dissolved Natural Organic Matter (DNOM) is a heterogeneous mixture of partly degraded, oxidised and resynthesised organic compounds of terrestrial or aquatic origin. In the boreal biome, it plays a central role in element cycling and practically all biogeochemical processes governing the physico-chemistry of surface waters. Because it plays a centr...

Climate change and other anthropogenic stressors have led to long-term changes in the thermal structure, including surface temperatures, deepwater temperatures, and vertical thermal gradients, in many lakes around the world. Though many studies highlight warming of surface water temperatures in lakes worldwide, less is known about long-term trends...

The ability of communities to withstand stress or maintain their species composition over extended periods of environmental changes is a matter of major concern. Here, we utilize a dataset where microcrustacean communities were related to water chemistry in 82 boreal‐alpine lakes over a 50‐yr time span (1968 and 2016), with the same person involved...

Lake surfaces are warming worldwide, raising concerns about lake organism responses to thermal habitat changes. Species may cope with temperature increases by shifting their seasonality or their depth to track suitable thermal habitats, but these responses may be constrained by ecological interactions, life histories or limiting resources. Here we...

Climate change is one of the most important threats to aquatic biodiversity worldwide, but especially in Arctic freshwaters, where it is expected to cause changes in mean water temperatures, catchment properties and water quality. Climate-driven changes in inputs of nutrients and organic matter from the catchment are expected to affect community c...

Assessments of diversity in Arctic freshwaters generally focus on structural diversity, i.e., the number and composition of taxa at local or regional scales. However, changes in community structure may not result in alterations to ecosystem function if there is strong niche overlap among taxa, leading to functional redundancy. In Arctic freshwaters...

Marine phytoplankton play a central role in supporting life in the oceans and profoundly affect global biogeochemical cycles. Previous studies have revealed positive effects of sea‐surface temperature (SST) on phytoplankton in terms of chlorophyll a concentrations (Chla) in high latitude oceans, while negative effects prevail in tropical and midlat...

Marine copepods are ubiquitous and play important roles in sustaining fish stocks, nutrient cycling, and carbon sequestration in deep waters. Our ability to represent these tiny animals in ocean biogeochemical models is hindered by an incomplete understanding of how the quantity and quality of food influence their growth. Using a state-of-the-art m...

Ecological memory (EM) recognizes the importance of previous stress encounters in promoting community tolerance and thereby enhances ecosystem stability, provided that gained tolerances are preserved during non-stress periods. Drawing from this concept, we hypothesized that the recruitment of tolerant species can be facilitated by imposing an initi...

Ecological association studies often assume monotonicity such as between biodiversity and environmental properties although there is growing evidence that non-monotonic relations dominate in nature. Here we apply machine learning algorithms to reveal the non-monotonic association between microbial diversity and an anthropogenic induced large scale...

Aquatic plant nutrient concentrations provide important information to characterise their role in nutrient retention and turnover in aquatic ecosystems. While large standing biomass of aquatic plants is typically found in nutrient-rich localities, it may also occur in oligotrophic ecosystems. Juncus bulbosus is able to form massive stands even in v...

These days many gyms and fitness centers are closed to reduce transmission of the SARS-CoV-2 virus in society. The gym is an environment rich in microorganisms, and careful hygiene is a necessity to keep infections at bay. Exercise centers strive for better hygiene compliance among their members. This effort has become essential in light of the cur...

Globally, lake surface water temperatures have warmed rapidly relative to air temperature, but changes in deepwater temperatures and vertical thermal structure are still largely unknown. We have compiled the most comprehensive data set to date of long-term (1970-2009) summertime vertical temperature profiles in lakes across the world to examine tre...

[This corrects the article DOI: 10.3389/fmicb.2020.569879.].

In aquatic environments, prey perceive predator threats by chemical cues called kairomones, which can induce changes in their morphology, life histories, and behavior. Predator‐induced defenses have allowed for prey, such as Daphnia pulex, to avert capture by common invertebrate predators, such as Chaoborus sp. larvae. However, the influence of add...

The current trend of increasing input of terrestrially derived dissolved organic carbon (DOC) to boreal freshwater systems is causing increased levels of carbon dioxide (CO2) supersaturation and degassing. Phosphorus (P) is often the most limiting nutrient for bacterial growth and would thus be expected to increase overall mineralization rates and...

Many boreal lakes are experiencing an increase in concentrations of terrestrially derived dissolved organic matter (DOM)-a process commonly labeled "browning." Browning affects microbial and photochemical mineraliza-tion of DOM, and causes increased light attenuation and hence reduced photosynthesis. Consequently, browning regulates lake heterotrop...

Understanding the factors that control the growth of heterotrophic organisms is central to predicting food web interactions and biogeochemical cycling within ecosystems. We present a new framework, Geometric Stoichiometry (GS), that unifies the disciplines of Nutritional Geometry (NG) and Ecological Stoichiometry (ES) by extending the equations of...

Covariation in species richness and community structure across taxonomical groups (cross‐taxon congruence) has practical consequences for the identification of biodiversity surrogates and proxies, as well as theoretical ramifications for understanding the mechanisms maintaining and sustaining biodiversity. We found there to exist a high cross‐taxon...

Acquisition of tolerance to an environmental stressor can result in organisms displaying slower growth after stress release. While well-grounded in the theory, empirical evidence of trade-off between stress tolerance and organism fitness is scarce and blurred by the interaction with different environmental factors. Here, we report the effects of wa...

Inducible defenses against predators are widespread among plants and animals. For example, some Daphnia species form neckteeth against predatory larvae of the dipteran genus Chaoborus. Though thoroughly studied in D. pulex, knowledge about neckteeth in other Daphnia species is limited. The occurrence of this trait in the D. longispina species compl...

Loss of diversity, burning forests, rising oceans, storms and heat waves: some fear all this could lead to humanity’s extinction. But the majority here in the privileged north seem to think that it will sort itself out and that there is little we can do about the matter anyway. We face threatening and complex problems – and a wealth of contradictor...

What does “belonging to nature” mean today and how can children and young people be inspired to experience this? What basic dilemmas and challenges arise between the requirement for critical thinking on the one side, and the experience of belonging and coexisting in nature on the other? In this article we will scrutinize the ideal of rational argum...

A collected volum of papers that discuss freedom from a broad range of perspectives; published as part of the bicentenary for the Norwegian Constitution, 1814-2014. Texts in Norwegian.