Global regionalized characterization factors for phosphorus and nitrogen impacts on freshwater fish biodiversity.

Inefficient global nutrient (i.e., phosphorus (P) and nitrogen (N)) management leads to an increase in nutrient delivery to freshwater and coastal ecosystems and induces eutrophication in these aquatic environments. This process threatens the various species inhabiting these ecosystems. In this study, we developed regionalized characterization factors (CFs) for freshwater eutrophication at 0.5 × 0.5-degree resolution, considering different fates for direct emissions to freshwater, diffuse emissions, and increased erosion due to agricultural land use. The CFs were provided for global and regional species loss of freshwater fish. CFs for global species loss were quantified by integrating global extinction probabilities. Results showed that the CFs for P and N impacts on freshwater fish are higher in densely populated regions that encompass either large lakes or the headwaters of large rivers. Focusing on nutrient-limited areas increases country-level CFs in 51.9 % of the countries for P and 49.5 % of the countries for N compared to not considering nutrient limitation. This study highlights the relevance of considering freshwater eutrophication impacts via both P and N emissions and identifying the limiting nutrient when performing life cycle impact assessments.

Costs and benefits of synthetic nitrogen for global cereal production in 2015 and in 2050 under contrasting scenarios.

Cereals are the most important global staple crop and use more than half of global cropland and synthetic nitrogen (N) fertilizer. While this synthetic N may feed half of the current global population, it has led to a massive increase in reactive N loss to the environment, causing a suite of impacts, offsetting the benefits of N fertilizers for food security and agricultural economy. To address these complex issues, the NBCalCer model was developed to quantify the global effects of N input on crop yields, N budgets and environmental impacts and to assess the associated social benefits and costs. Three Shared Socioeconomic Pathway scenarios (SSPs) were considered with decreasing N agri-environmental ambitions, through contrasting climate and N policy ambitions: sustainability (SSP1H), middle-of-the-road (SSP2M) and fossil-fueled development (SSP5L). In the base year the contribution of synthetic N fertilizer to global cereal production was 44 %. Global modelled grain yield was projected to increase under all scenarios while the use of synthetic N fertilizer decreases under all scenarios except SSP5L. The total N surplus was projected to be reduced up to 20 % under SSP1H but to increase under SSP5L. The Benefit-Cost-Ratio (BCR) was calculated as the ratio between the market benefit of increased grain production by synthetic N and the summed cost of fertilizer purchase and the external cost of the N losses. In base year the BCR was well above one in all regions, but in 2050 under SSP1H and SSP5L decreased to below one in most regions. Given the concerns about food security, environmental quality and its interaction with biodiversity loss, human health and climate change, the new paradigm for global cereal production is producing sufficient food with minimum N pollution. Our results indicate that achieving this goal would require a massive change in global volume and distribution of synthetic N.

Surface-Water Nitrate Exposure to World Populations Has Expanded and Intensified during 1970-2010.

Excessive nitrate in surface waters deteriorates the water quality and threatens human health. Human activities have caused increased nitrate concentrations in global surface waters over the past 50 years. An assessment of the long-term trajectory of surface-water nitrate exposure to world populations and the associated potential health risks is imperative but lacking. Here, we used global spatially explicit data on surface-water nitrate concentrations and population density, in combination with thresholds for health risks from epidemiological studies, to quantify the long-term changes in surface-water nitrate exposure to world populations at multiple spatial scales. During 1970-2010, global populations potentially affected by acute health risks associated with surface-water nitrate exposure increased from 6 to 60 million persons per year, while populations at potential chronic health risks increased from 169 to 1361 million persons per year. Potential acute risks have increasingly affected Asian countries. Populations potentially affected by chronic risks shifted from dominance by high-income countries (in Europe and North America) to middle-income countries (in Asia and Africa). To mitigate adverse health effects associated with surface-water nitrate exposure, anthropogenic nitrogen inputs to natural environments should be drastically reduced. International and national standards of maximum nitrate contamination may need to be lowered.

Inland Waters Increasingly Produce and Emit Nitrous Oxide.

Nitrous oxide (N2O) is a long-lived greenhouse gas and currently contributes ∼10% to global greenhouse warming. Studies have suggested that inland waters are a large and growing global N2O source, but whether, how, where, when, and why inland-water N2O emissions changed in the Anthropocene remains unclear. Here, we quantify global N2O formation, transport, and emission along the aquatic continuum and their changes using a spatially explicit, mechanistic, coupled biogeochemistry-hydrology model. The global inland-water N2O emission increased from 0.4 to 1.3 Tg N yr-1 during 1900-2010 due to (1) growing N2O inputs mainly from groundwater and (2) increased inland-water N2O production, largely in reservoirs. Inland waters currently contribute 7 (5-10)% to global total N2O emissions. The highest inland-water N2O emissions are typically in and downstream of reservoirs and areas with high population density and intensive agricultural activities in eastern and southern Asia, southeastern North America, and Europe. The expected continuing excessive use of nutrients, dam construction, and development of suboxic conditions in aging reservoirs imply persisting high inland-water N2O emissions.

Nitrogen from agriculture and temperature as the major drivers of deoxygenation in the central Bohai Sea.

Agricultural N losses strongly dominate the N delivery (average 72 % of total N delivery to rivers in the period 1980-2010) in the rivers discharging into the Bohai Sea, a semi-enclosed marginal sea, which has been suffering from eutrophication and deoxygenation since the 1980s. In this paper we investigate the relationship between N loading and deoxygenation in the Bohai Sea, and consequences of future N loading scenarios. Using modeling for the period 1980-2010, the contributions of different oxygen consumption processes were quantified and the main controlling mechanisms of summer bottom dissolved oxygen (DO) evolution in the central Bohai Sea were determined. Model results show that the water column stratification during summer impeded the DO exchange between oxygenated surface water and oxygen-poor bottom water. Water column oxygen consumption (60 % of total oxygen consumption) was strongly correlated with elevated nutrient loading, while nutrient imbalances (increasing N:P ratios) enhanced harmful algal bloom proliferation. Future scenarios show that deoxygenation may be reduced in all scenarios owing to increasing agricultural efficiency, manure recycling and wastewater treatment. However, even in the sustainable development scenario SSP1, nutrient discharges in 2050 will still exceed the 1980 levels, and with further enhancement of water stratification due to climate warming, the risk of summer hypoxia in bottom waters may persist in the coming decades.

Effects of Nitrogen Emissions on Fish Species Richness across the World's Freshwater Ecoregions.

The increasing application of synthetic fertilizer has tripled nitrogen (N) inputs over the 20th century. N enrichment decreases water quality and threatens aquatic species such as fish through eutrophication and toxicity. However, the impacts of N on freshwater ecosystems are typically neglected in life cycle assessment (LCA). Due to the variety of environmental conditions and species compositions, the response of species to N emissions differs among ecoregions, requiring a regionalized effect assessment. Our study tackled this issue by establishing regionalized species sensitivity distributions (SSDs) of freshwater fish against N concentrations for 367 ecoregions and 48 combinations of realms and major habitat types globally. Subsequently, effect factors (EFs) were derived for LCA to assess the effects of N on fish species richness at a 0.5 degree × 0.5 degree resolution. Results show good SSD fits for all of the ecoregions that contain sufficient data and similar patterns for average and marginal EFs. The SSDs highlight strong effects on species richness due to high N concentrations in the tropical zone and the vulnerability of cold regions. Our study revealed the regional differences in sensitivities of freshwater ecosystems against N content in great spatial detail and can be used to assess more precisely and comprehensively nutrient-induced impacts in LCA.

Hindcasting harmful algal bloom risk due to land-based nutrient pollution in the Eastern Chinese coastal seas.

Harmful algal blooms (HABs) have been increasing in frequency, areal extent and duration due to the large increase in nutrient inputs from land-based sources to coastal seas, and cause significant economic losses. In this study, we used the "watershed-coast-continuum" concept to explore the effects of land-based nutrient pollution on HAB development in the Eastern Chinese coastal seas (ECCS). Results from the coupling of a watershed nutrient model and a coast hydrodynamic-biogeochemical model show that between the 1980s and 2000s, the risk of diatom blooms and dinoflagellate blooms increased by 158% and 127%, respectively. The spatial expansion of HAB risk caused by dinoflagellates is larger than that of diatoms. The simulated suitability of the habitat for bloom of Aureococcus anophagefferens, a pico-plankton of non-diatom or dinoflagellate, in the Bohai Sea is consistent with observations spatially and temporally. To halt further nutrient accumulation in the ECCS, reductions of dissolved inorganic nitrogen (DIN) (16%) and dissolved inorganic phosphorus (DIP) (33%) loading are required. To improve the situation of distorted DIN:DIP ratios, even larger reductions of DIN are required, especially in the Bohai Sea. Our approach is a feasible way to predict the risk of HABs under the pressure of increasing anthropogenic nutrient pollution in coastal waters.

The impact of phosphorus on projected Sub-Saharan Africa food security futures.

Sub-Saharan Africa must urgently improve food security. Phosphorus availability is one of the major barriers to this due to low historical agricultural use. Shared socioeconomic pathways (SSPs) indicate that only a sustainable (SSP1) or a fossil fuelled future (SSP5) can improve food security (in terms of price, availability, and risk of hunger) whilst nationalistic (SSP3) and unequal (SSP4) pathways worsen food security. Furthermore, sustainable SSP1 requires limited cropland expansion and low phosphorus use whilst the nationalistic SSP3 is as environmentally damaging as the fossil fuelled pathway. The middle of the road future (SSP2) maintains today's inadequate food security levels only by using approximately 440 million tonnes of phosphate rock. Whilst this is within the current global reserve estimates the market price alone for a commonly used fertiliser (DAP) would cost US$ 130 ± 25 billion for agriculture over the period 2020 to 2050 and the farmgate price could be two to five times higher due to additional costs (e.g. transport, taxation etc.). Thus, to improve food security, economic growth within a sustainability context (SSP1) and the avoidance of nationalist ideology (SSP3) should be prioritised.

Exploring Spatially Explicit Changes in Carbon Budgets of Global River Basins during the 20th Century.

Rivers play an important role in the global carbon (C) cycle. However, it remains unknown how long-term river C fluxes change because of climate, land-use, and other environmental changes. Here, we investigated the spatiotemporal variations in global freshwater C cycling in the 20th century using the mechanistic IMAGE-Dynamic Global Nutrient Model extended with the Dynamic In-Stream Chemistry Carbon module (DISC-CARBON) that couples river basin hydrology, environmental conditions, and C delivery with C flows from headwaters to mouths. The results show heterogeneous spatial distribution of dissolved inorganic carbon (DIC) concentrations in global inland waters with the lowest concentrations in the tropics and highest concentrations in the Arctic and semiarid and arid regions. Dissolved organic carbon (DOC) concentrations are less than 10 mg C/L in most global inland waters and are generally high in high-latitude basins. Increasing global C inputs, burial, and CO2 emissions reported in the literature are confirmed by DISC-CARBON. Global river C export to oceans has been stable around 0.9 Pg yr-1. The long-term changes and spatial patterns of concentrations and fluxes of different C forms in the global river network unfold the combined influence of the lithology, climate, and hydrology of river basins, terrestrial and biological C sources, in-stream C transformations, and human interferences such as damming.

More efficient phosphorus use can avoid cropland expansion.

Global projections indicate that approximately 500 Mha of new arable land will be required to meet crop demand by 2050. Applying a dynamic phosphorus (P) pool simulator under different socioeconomic scenarios, we find that cropland expansion can be avoided with less than 7% additional cumulative P fertilizer over 2006-2050 when comparing with cropland expansion scenarios, mostly targeted at nutrient-depleted soils of sub-Saharan Africa. Additional P fertilizer would replenish P withdrawn from crop production, thereby allowing higher productivity levels. We also show that further agronomic improvements such as those that allow for better (legacy) P use in soils could reduce both P outflows to freshwater and coastal ecosystems and the overall demand for P fertilizer.

Aquaculture Production is a Large, Spatially Concentrated Source of Nutrients in Chinese Freshwater and Coastal Seas.

As Chinese aquaculture production accounts for over half of the global aquaculture production and has increased by 50% since 2006, there is growing concern about eutrophication caused by aquaculture in China. This paper presents a model-based estimate of nutrient flows in China's aquaculture system during 2006-2017 using provincial scale data, to spatially distribute nutrient loads with a 0.5° resolution. The results indicate that with the increase in fish and shellfish production from 30 to 47 million tonnes (Mt) during 2006-2017, the nitrogen (N) release increased from 1.0 to 1.6 Mt/year and that of phosphorus (P) from 0.1 to 0.2 Mt/year. Nutrient release from freshwater aquaculture was concentrated in Guangdong, Jiangsu, and Hubei, and that from mariculture in Shandong, Fujian, and Guangdong. Aquaculture is an important strongly concentrated nutrient source in both freshwater and marine environments. Its nutrient release is >20% of total nutrient inputs to freshwater environments in some provinces, and nutrients from mariculture are comparable to river nutrient export to Chinese coastal seas. Aquaculture production and nutrient excretions are now comparable to those of livestock production systems in China and need to be accounted for when analyzing causes of eutrophication and harmful algal blooms and possible mitigation strategies.

Future global pig production systems according to the Shared Socioeconomic Pathways.

Global pork production has increased fourfold over the last 50 years and is expected to continue growing during the next three decades. This may have considerable implications for feed use, land requirements, and nitrogen emissions. To analyze the development of the pig production sector at the scale of world regions, we developed the IMAGE-Pig model to describe changes in feed demand, feed conversion ratios (FCRs), nitrogen use efficiency (NUE) and nitrogen excretion for backyard, intermediate and intensive systems during the past few decades as a basis to explore future scenarios. For each region and production system, total production, productive characteristics and dietary compositions were defined for the 1970-2005 period. The results show that due to the growing pork production total feed demand has increased by a factor of two (from 229 to 471Tg DM). This is despite the improvement of FCRs during the 1970-2005 period, which has reduced the feed use per kg of product. The increase of nitrogen use efficiency was slower than the improvement of FCRs due to increasing protein content in the feed rations. As a result, total N excretion increased by more than a factor of two in the 1970-2005 period (from 4.6 to 11.1 Tg N/year). For the period up to 2050, the Shared Socio-economic Pathways (SSPs) provide information on levels of human consumption, technical development and environmental awareness. The sustainability of pig production systems for the coming decades will be based not only on the expected efficiency improvements at the level of animal breeds, but also on four additional pillars: (i) use of alternative feed sources not competing with human food, (ii) reduction of the crude protein content in rations, (iii) the proper use of slurries as fertilizers through coupling of crop and livestock production and (iv) moderation of the human pork consumption.

Exploring spatiotemporal changes of the Yangtze River (Changjiang) nitrogen and phosphorus sources, retention and export to the East China Sea and Yellow Sea.

Nitrogen (N) and phosphorus (P) flows from land to sea in the Yangtze River basin were simulated for the period 1900-2010, by combining models for hydrology, nutrient input to surface water, and an in-stream retention. This study reveals that the basin-wide nutrient budget, delivery to surface water, and in-stream retention increased during this period. Since 2004, the Three Gorges Reservoir has contributed 5% and 7% of N and P basin-wide retention, respectively. With the dramatic rise in nutrient delivery, even this additional retention was insufficient to prevent an increase of riverine export from 337 Gg N yr-1 and 58 Gg P yr-1 (N:P molar ratio = 13) to 5896 Gg N yr-1 and 381 Gg P yr-1 (N:P molar ratio = 35) to the East China Sea and Yellow Sea (ECSYS). The midstream and upstream subbasins dominate the N and P exports to the ECSYS, respectively, due to various human activities along the river. Our spatially explicit nutrient source allocation can aid in the strategic targeting of nutrient reduction policies. We posit that these should focus on improving the agricultural fertilizer and manure use efficiency in the upstream and midstream and better urban wastewater management in the downstream subbasin.

Erratum: FLO1K, global maps of mean, maximum and minimum annual streamflow at 1 km resolution from 1960 through 2015.

This corrects the article DOI: 10.1038/sdata.2018.52.

FLO1K, global maps of mean, maximum and minimum annual streamflow at 1 km resolution from 1960 through 2015.

Streamflow data is highly relevant for a variety of socio-economic as well as ecological analyses or applications, but a high-resolution global streamflow dataset is yet lacking. We created FLO1K, a consistent streamflow dataset at a resolution of 30 arc seconds (~1 km) and global coverage. FLO1K comprises mean, maximum and minimum annual flow for each year in the period 1960-2015, provided as spatially continuous gridded layers. We mapped streamflow by means of artificial neural networks (ANNs) regression. An ensemble of ANNs were fitted on monthly streamflow observations from 6600 monitoring stations worldwide, i.e., minimum and maximum annual flows represent the lowest and highest mean monthly flows for a given year. As covariates we used the upstream-catchment physiography (area, surface slope, elevation) and year-specific climatic variables (precipitation, temperature, potential evapotranspiration, aridity index and seasonality indices). Confronting the maps with independent data indicated good agreement (R2 values up to 91%). FLO1K delivers essential data for freshwater ecology and water resources analyses at a global scale and yet high spatial resolution.

Socio-environmental consideration of phosphorus flows in the urban sanitation chain of contrasting cities.

Understanding how cities can transform organic waste into a valuable resource is critical to urban sustainability. The capture and recycling of phosphorus (P), and other essential nutrients, from human excreta is particularly important as an alternative organic fertilizer source for agriculture. However, the complex set of socio-environmental factors influencing urban human excreta management is not yet sufficiently integrated into sustainable P research. Here, we synthesize information about the pathways P can take through urban sanitation systems along with barriers and facilitators to P recycling across cities. We examine five case study cities by using a sanitation chains approach: Accra, Ghana; Buenos Aires, Argentina; Beijing, China; Baltimore, USA; and London, England. Our cross-city comparison shows that London and Baltimore recycle a larger percentage of P from human excreta back to agricultural lands than other cities, and that there is a large diversity in socio-environmental factors that affect the patterns of recycling observed across cities. Our research highlights conditions that may be "necessary but not sufficient" for P recycling, including access to capital resources. Path dependencies of large sanitation infrastructure investments in the Global North contrast with rapidly urbanizing cities in the Global South, which present opportunities for alternative sanitation development pathways. Understanding such city-specific social and environmental barriers to P recycling options could help address multiple interacting societal objectives related to sanitation and provide options for satisfying global agricultural nutrient demand.

Losses of Ammonia and Nitrate from Agriculture and Their Effect on Nitrogen Recovery in the European Union and the United States between 1900 and 2050.

Historical trends and levels of nitrogen (N) budgets and emissions to air and water in the European Union and the United States are markedly different. Agro-environmental policy approaches also differ, with emphasis on voluntary or incentive-based schemes in the United States versus a more regulatory approach in the European Union. This paper explores the implications of these differences for attaining long-term policy targets for air and water quality. Nutrient surplus problems were more severe in the European Union than in the United States during the 1970s and 1980s. The EU Nitrates and National Emission Ceilings directives contributed to decreases in fertilizer use, N surplus, and ammonia (NH) emissions, whereas in the United States they stabilized, although NH emissions are still increasing. These differences were analyzed using statistical data for 1900-2005 and the global IMAGE model. IMAGE could reproduce NH emissions and soil N surpluses at different scales (European Union and United States, country and state) and N loads in the Rhine and Mississippi. The regulation-driven changes during the past 25 yr in the European Union have reduced public concerns and have brought agricultural N loads to the aquatic environment closer to US levels. Despite differences in agro-environmental policies and agricultural structure (more N-fixing soybean and more spatially separated feed and livestock production in the United States than in the European Union), current N use efficiency in US and EU crop production is similar. IMAGE projections for the IAASTD-baseline scenario indicate that N loading to the environment in 2050 will be similar to current levels. In the United States, environmental N loads will remain substantially smaller than in the European Union, whereas agricultural production in 2050 in the United States will increase by 30% relative to 2005, as compared with an increase of 8% in the European Union. However, in the United States, even rigorous mitigation with maximum recycling of manure N and a 25% reduction in fertilizer use will not achieve the policy target to halve the N export to the Gulf of Mexico.

Exploring global changes in nitrogen and phosphorus cycles in agriculture induced by livestock production over the 1900-2050 period.

Crop-livestock production systems are the largest cause of human alteration of the global nitrogen (N) and phosphorus (P) cycles. Our comprehensive spatially explicit inventory of N and P budgets in livestock and crop production systems shows that in the beginning of the 20th century, nutrient budgets were either balanced or surpluses were small; between 1900 and 1950, global soil N surplus almost doubled to 36 trillion grams (Tg) · y(-1) and P surplus increased by a factor of 8 to 2 Tg · y(-1). Between 1950 and 2000, the global surplus increased to 138 Tg · y(-1) of N and 11 Tg · y(-1) of P. Most surplus N is an environmental loss; surplus P is lost by runoff or accumulates as residual soil P. The International Assessment of Agricultural Knowledge, Science, and Technology for Development scenario portrays a world with a further increasing global crop (+82% for 2000-2050) and livestock production (+115%); despite rapidly increasing recovery in crop (+35% N recovery and +6% P recovery) and livestock (+35% N and P recovery) production, global nutrient surpluses continue to increase (+23% N and +54% P), and in this period, surpluses also increase in Africa (+49% N and +236% P) and Latin America (+75% N and +120% P). Alternative management of livestock production systems shows that combinations of intensification, better integration of animal manure in crop production, and matching N and P supply to livestock requirements can effectively reduce nutrient flows. A shift in human diets, with poultry or pork replacing beef, can reduce nutrient flows in countries with intensive ruminant production.