Anthropogenically-derived nitrogen input to the northern Indian Ocean has increased significantly in recent decades, based on both observational and model-derived estimates. This external nutrient source is supplied by atmospheric deposition and riverine fluxes, and has the potential to affect the vulnerable biogeochemical systems of the Arabian Sea and Bay of Bengal, influencing productivity and oceanic production of the greenhouse-gas nitrous-oxide (N2O). We summarize current estimates of this external nitrogen source to the northern Indian Ocean from observations and models, highlight implications for regional marine N2O emissions using model-based analyses, and make recommendations for measurement and model needs to improve current estimates and future predictions of this impact. Current observationally-derived estimates of deposition and riverine nitrogen inputs are limited by sparse measurements and uncertainties on accurate characterization of nitrogen species composition. Ocean model assessments of the impact of external nitrogen sources on regional marine N2O production in the northern Indian Ocean estimate potentially significant changes but also have large associated uncertainties. We recommend an integrated program of basin-wide measurements combined with high-resolution modeling and more detailed characterization of nitrogen-cycle process to address these uncertainties and improve current estimates and predictions.

We model future trends in river export of nutrients to the Bay of Bengal, and the sources of this pollution. We focus on total nitrogen (TN), total phosphorus (TP), and dissolved silica (DSi) inputs to the Bay of Bengal Large Marine Ecosystem (BOB LME) in the years 2000, 2030, and 2050. In 2000, rivers exported 7.1 Tg N and 1.5 Tg P to the BOB LME. Three rivers (Ganges, Godavari, Irrawaddy) account for 75–80% of the total river export of N and P. For 2050, we calculate an increase in river export of N to 8.6 Tg, while P export stabilizes at the 2000 level. Future trends are the net effect of increasing river export of dissolved N (by 40%) and P (by 80%), and decreasing river export of particulate N and P. The increases in dissolved N and P loads are associated primarily with increased N and P losses from agriculture and sewage systems. The decreasing export of particulate N and P is associated with damming of rivers and increased human water consumption. There are large differences in nutrient export among rivers. Rivers draining into the western BOB LME generally export more N and P than eastern BOB LME rivers. Most N and P in western BOB LME rivers are from anthropogenic sources. Future increases in dissolved inorganic N and P (DIN and DIP) export can be large for individual rivers: up to more than a factor of five for DIP and more than a doubling for DIN. The calculated nutrient export ratios (N and P relative to DSi) indicate an increasing risk for blooms of non-siliceous algal species, which can potentially produce toxins and otherwise disrupt coastal ecosystems. Our results indicate that basin-specific management may be the most effective approach towards reducing the risk of coastal eutrophication in the BOB LME.

How can nitrogen emissions be reduced and reused to reduce pressure on ecosystems?

We report a new synthesis of best estimates of the inputs of fixed nitrogen to the world ocean via atmospheric deposition and compare this to fluvial inputs and dinitrogen fixation. We evaluate the scale of human perturbation of these fluxes. Fluvial inputs dominate inputs to the continental shelf, and we estimate that about 75% of this fluvial nitrogen escapes from the shelf to the open ocean. Biological dinitrogen fixation is the main external source of nitrogen to the open ocean, i.e., beyond the continental shelf. Atmospheric deposition is the primary mechanism by which land-based nitrogen inputs, and hence human perturbations of the nitrogen cycle, reach the open ocean. We estimate that anthropogenic inputs are currently leading to an increase in overall ocean carbon sequestration of similar to 0.4% (equivalent to an uptake of 0.15 Pg Cyr(-1) and less than the Duce et al. (2008) estimate). The resulting reduction in climate change forcing from this ocean CO2 uptake is offset to a small extent by an increase in ocean N2O emissions. We identify four important feedbacks in the ocean atmosphere nitrogen system that need to be better quantified to improve our understanding of the perturbation of ocean biogeochemistry by atmospheric nitrogen inputs. These feedbacks are recycling of (1) ammonia and (2) organic nitrogen from the ocean to the atmosphere and back, (3) the suppression of nitrogen fixation by increased nitrogen concentrations in surface waters from atmospheric deposition, and (4) increased loss of nitrogen from the ocean by denitrification due to increased productivity stimulated by atmospheric inputs.

The 'Anthropocene' is now being used as a conceptual frame by different communities and in a variety of contexts to understand the evolving human environment relationship. However, as we argue in this paper, the notion of an Anthropos, or 'humanity', as global, unified 'geological force' threatens to mask the diversity and differences in the actual conditions and impacts of humankind, and does not do justice to the diversity of local and regional contexts. For this reason, we interpret in this article the notion of an Anthropocene in a more context-dependent, localized and social understanding. We do this through illustrating examples from four issue domains, selected for their variation in terms of spatial and temporal scale, systems of governance and functional interdependencies: nitrogen cycle distortion (in particular as it relates to food security); ocean acidification; urbanization; and wildfires. Based on this analysis, we systematically address the consequences of the lens of the Anthropocene for the governance of social-ecological systems, focusing on the multi-level, functional and sectoral organization of governance, and possible redefinitions of governance systems and policy domains. We conclude that the notion of the Anthropocene, once seen in light of social inequalities and regional differences, allows for novel analysis of issue-based problems in the context of a global understanding, in both academic and political terms. This makes it a useful concept to help leverage and (re-)focus our efforts in a more innovative and effective way to transition towards sustainability. (C) 2015 The Authors. Published by Elsevier Ltd.

Coastal resource management initiatives in recent years have moved towards ecosystem approaches such as embodied by Large Marine Ecosystems (LMEs). In this study, land-based dissolved inorganic nitrogen (DIN) loading to LMEs was evaluated using a spatially-explicit river export model (Global NEWS 2) for the year 2000 conditions and for a current trends analysis for the year 2050. Watershed export was aggregated by LME to estimate total DIN load and attribution to diffuse and point sources including natural biological fixation, agricultural biological fixation, fertilizer, manure, atmospheric deposition and sewage. Biological fixation in natural landscapes was the primary source of DIN to many LMEs, but in most (73%) LMEs, over half of the total DIN load was related to anthropogenic sources. Most of the anthropogenic DIN load across LMEs was related to agricultural sources especially fertilizer and manure. Fertilizer was the primary source of DIN to LMEs in most of Europe and Asia, while manure was the primary source in most of Central and South America. Agricultural biological fixation, sewage and atmospheric deposition in general supported a minor fraction of the DIN exported to LMEs although each was a dominant source to a few LMEs. If current trends continue, DIN export to coastal systems by 2050 relative to 2000 is predicted to increase by approximately 40–45% from Africa, South America, South Asia and Oceania. Almost half of the total global increase in DIN is from South Asia. Relatively smaller increases are predicted for North America, with slight decreases in Australia and Europe.

The 'Anthropocene' concept provides a conceptual framework that encapsulates the current global situation in which society has an ever-greater dominating influence on Earth System functioning. Simulation models used to understand earth system dynamics provide early warning, scenario analysis and evaluation of environmental management and policies. This paper aims to assess the extent to which current models represent the Anthropocene and suggest ways forward. Current models do not fully reflect the typical characteristics of the Anthropocene, such as societal influences and interactions with natural processes, feedbacks and system dynamics, tele-connections, tipping points, thresholds and regime shifts. Based on an analysis of current model representations of Anthropocene dynamics, we identify ways to enhance the role of modeling tools to better help us understand Anthropocene dynamics and address sustainability issues arising from them. To explore sustainable futures ('safe and operating spaces'), social processes and anthropogenic drivers of biophysical processes must be incorporated, to allow for a spectrum of potential impacts and responses at different societal levels. In this context, model development can play a major role in reconciling the different epistemologies of the disciplines that need to collaborate to capture changes in the functioning of socio-ecological systems. Feedbacks between system functioning and underlying endogenous drivers should be represented, rather than assuming the drivers to be exogenous to the modelled system or stationary in time and space. While global scale assessments are important, the global scale dynamics need to be connected to local realities and vice versa. The diversity of stakeholders and potential questions requires a diversification of models, avoiding the convergence towards single models that are able to answer a wide range of questions, but without sufficient specificity. The novel concept of the Anthropocene can help to develop innovative model representations and model architectures that are better suited to assist in designing sustainable solutions targeted at the users of the models and model results. (C) 2015 The Authors. Published by Elsevier Ltd.

The maturing of Earth system science as a discipline has underpinned the development of concepts such as the Anthropocene and planetary boundaries. The International Geosphere–Biosphere Programme’s (IGBP) scientific and institutional history is deeply intertwined with the development of the concept of the Earth as a system as well as the discipline of Earth system science. Here we frame the broader programme of IGBP through its core projects and programme-level activities and illustrate this co-evolution. We identify and discuss three phases in the programme’s history. In its first phase beginning in 1986, IGBP focused on building international networks and global databases that were key to understanding Earth system component processes. In the early 2000s IGBP’s first major synthesis and associated activities promoted a more integrated view of the Earth system informed by greater emphasis on interdisciplinarity. Human actions were seen as an integral part of the Earth system and the concept of the Anthropocene came to the fore. In recent years IGBP has increased focus on sustainability and multifaceted engagement with policy processes. IGBP closed at the end of 2015 after three decades of coordinating international research on global change. The programme’s longevity points to its capacity to adapt its scientific and institutional structures to changing scientific and societal realities. Its history may offer lessons for the emerging Future Earth initiative as it seeks to rally international collaborative research around sustainability and solutions.

The development of human civilisations has occurred at a time of stable climate. This climate stability is now threatened by human activity. The rising global climate risk occurs at a decisive moment for world development. World nations are currently discussing a global development agenda consequent to the Millennium Development Goals (MDGs), which ends in 2015. It is increasingly possible to envisage a world where absolute poverty is largely eradicated within one generation and where ambitious goals on universal access and equal opportunities for dignified lives are adopted. These grand aspirations for a world population approaching or even exceeding nine billion in 2050 is threatened by substantial global environmental risks and by rising inequality. Research shows that development gains, in both rich and poor nations, can be undermined by social, economic and ecological problems caused by human-induced global environmental change. Climate risks, and associated changes in marine and terrestrial ecosystems that regulate the resilience of the climate system, are at the forefront of these global risks. We, as citizens with a strong engagement in Earth system science and socio-ecological dynamics, share the vision of a more equitable and prosperous future for the world, yet we also see threats to this future from shifts in climate and environmental processes. Without collaborative action now, our shared Earth system may not be able to sustainably support a large proportion of humanity in the decades ahead.

Dissolved organic nitrogen (DON) produced by the nitrogen-fixer Trichodesmium sp. has the potential to serve as a nitrogen source for the red tide dinoflagellate Karenia brevis. Dissolved organic matter (DOM) from laboratory cultures of Trichodesmium sp. was isolated, concentrated and then supplied as a nutrient source to K. brevis cells collected from the Gulf of Mexico. K. brevis abundance increased immediately after Trichodesmium sp. cellular exudate (TCE) addition, allowing the population to double within the first 24 h. There was rapid and complete utilization of the TCE DON as well as similar to 89% of the TCE dissolved organic phosphorus (DOP). Additionally, terminal restriction fragment length polymorphism (TRFLP) was used to assess the bacterial community response to the addition of TCE. The number of bacterial operational taxonomic units (OTUs) initially increased after the TCE DOM addition, but decreased as K. brevis reached its maximum abundance. Electrospray ionization mass spectrometry (ESI-MS) and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) were used to chemically characterize the DOM. Approximately 25% of compounds disappeared within the first 24 h, corresponding to the greatest increase in K. brevis abundance. Using FT-ICR MS, 391 DON and 219 DOP potentially bioavailable compounds were characterized. The bioavailable DON compounds were highly reduced and 44% had molar ratios indicative of lipid or protein-like compounds. The changes in DON concentration and compound composition show that Tricho desmium sp. provides a sufficient source of nitrogen to directly or indirectly support K. brevis blooms.

Atmospheric deposition of nitrogen (AD-N, as wet deposition and dry deposition), is a significant and growing source of biologically-available nitrogen (NOx, NH3/NH+4, and dissolved organic N (DON)) entering nitrogen-limited estuarine and coastal waters (jointly termed coastal). AD-N ranges from 400 to >1000 mg N m−2 yr−l, and represents from <10 to >40% of new N inputs in North American and European coastal waters downwind of emission sources. The relative contribution of AD-N to total external N loading depends on land use, watershed and airshed size, and hydrological and morphological characteristics (i.e., water retention time) of receiving waters. In heavily-impacted, N-sensitive waters, the ecological impacts of AD-N include accelerating primary production (eutrophication), which may yield a variety of negative impacts including increased algal bloom activity, toxicity, oxygen depletion (hypoxia) events, and food web alterations. Depending on their sources (i.e., agricultural, urban, industrial) certain forms of AD-N are increasing relative to others, leading to qualitative changes in deposition and biogeochemical response in receiving waters. Because phytoplankton and bacteria differentially utilize different forms of N, changes in the ratios of NH4+ to NOx and DON in AD-N may usher in community compositional changes. One example is intensive animal operations in Western Europe and the U.S. Mid-Atlantic States, which are linked to regionally elevated NH4+ deposition rates. Experimental evidence indicates that increasing levels of AD-NH4+ enhance primary production, while favoring growth of specific phytoplankton functional groups. In addition, AD (as well as other sources of new N) enrichment alters the stoichiometric nutrient ratio (N:P:Si) which may impact phytoplankton community composition and growth potentials. Both quantitative and qualitative changes in AD-N inputs may be linked to eutrophication and algal bloom dynamics.

This paper first describes the concept of, governance interest in, and criticism on planetary boundaries, specifically with respect to the nitrogen (N) cycle. These criticisms are then systematically evaluated. We argue that planetary N boundaries should include both the benefits and adverse impacts of reactive N (Nr) and the spatial variability of Nr impacts. We revise the planetary N boundary by considering the need to: first, avoid adverse impacts of elevated Nr emissions to water, air and soils, and second, feed the world population in an adequate way. The derivation of a planetary N boundary, in terms of anthropogenic fixation of di-nitrogen (N-2) is illustrated by first, identification of multiple threat N indicators and setting limits for them; second, back calculating N losses from critical limits for N indicators, while accounting for the spatial variability of these indicators and their exceedance; and third, back calculating N fixation rates from critical N losses. The derivation of the needed planetary N fixation is assessed from the global population, the recommended dietary N consumption per capita and the N use efficiency in the complete chain from N fixation to N consumption. The example applications show that the previously suggested planetary N boundary of 35 Tg N yr(-1) is too low in view of needed N fixation and also unnecessary low in view of most environmental impacts.