Quantifying future sanitation scenarios and progress towards SDG targets in the shared socioeconomic pathways.

Two main targets of SDG 6 (Sustainable Development Goal), clean water and sanitation, are SDG 6.2, to achieve universal and equitable access to improved sanitation and to phase out unimproved sanitation (include pit latrines without a slab or platform, hanging latrines, bucket latrines and open defecation) and SDG 6.3, to halve the proportion of untreated wastewater by 2030. We compiled a global sanitation database for 200 countries. Starting from recent trends, we constructed a wide spectrum of contrasting future scenarios, i.e. the five Shared Socio-economic Pathways (SSP1-5) whereby the SSP2 scenario is 'middle of the road' scenario. The sanitation scenarios differ due to contrasting pathways for population growth and urbanization, economic growth and the SSP narratives. Our results indicate that it will be difficult to achieve the SDG 6 target. Target 6.2 on improved sanitation is expected to be achieved between 2070 and 2090 in SSP1, SSP2 and SSP5, while the target will not be achieved by 2100 in SSP3 and SSP4. Unimproved sanitation is projected to be phased out by 2070 in SSP1 and SSP5, or beyond 2100 in SSP3 and SSP4. The percentage of households with sewerage connection will be between 51% in SSP3 and 75% in SSP5 in 2050, and respectively 60% and 95% in 2100. Target SDG 6.3 on improving wastewater treatment will be reached by 2030 only in SSP1, followed by SSP2 and SSP5 between 2040 and 2050, while in SSP3 and SSP4 this target is not reached by 2100. The developments in wastewater treatment, expressed as percentage nutrient removal, showed an increase from 14% in 2015 to 45% in 2050 and 80% in 2100 in SSP1. But in SSP3, the global percentage is expected to have hardly changed by 2050 and have declined to 12% by 2100 due to the population growth in Sub-Saharan Africa. There is a major contrast between countries and regions. In the period between 2000 and 2015, although globally the percentage of people with unimproved sanitation declined, in 7% of the 200 countries the number of people with unimproved sanitation increased. Also, wastewater treatment globally improved, but in 16 countries it deteriorated. This inequality is particularly important in SSP3 and SSP4 where the lack of improved sanitation will continue till 2100.

From planetary to regional boundaries for agricultural nitrogen pollution.

Excessive agricultural nitrogen use causes environmental problems globally1, to an extent that it has been suggested that a safe planetary boundary has been exceeded2. Earlier estimates for the planetary nitrogen boundary3,4, however, did not account for the spatial variability in both ecosystems' sensitivity to nitrogen pollution and agricultural nitrogen losses. Here we use a spatially explicit model to establish regional boundaries for agricultural nitrogen surplus from thresholds for eutrophication of terrestrial and aquatic ecosystems and nitrate in groundwater. We estimate regional boundaries for agricultural nitrogen pollution and find both overuse and room for intensification of agricultural nitrogen. The aggregated global surplus boundary with respect to all thresholds is 43 megatonnes of nitrogen per year, which is 64 per cent lower than the current (2010) nitrogen surplus (119 megatonnes of nitrogen per year). Allowing the nitrogen surplus to increase to close yield gaps in regions where environmental thresholds are not exceeded lifts the planetary nitrogen boundary to 57 megatonnes of nitrogen per year. Feeding the world without trespassing regional and planetary nitrogen boundaries requires large increases in nitrogen use efficiencies accompanied by mitigation of non-agricultural nitrogen sources such as sewage water. This asks for coordinated action that recognizes the heterogeneity of agricultural systems, non-agricultural nitrogen losses and environmental vulnerabilities.

Global nitrogen and phosphorus in urban waste water based on the Shared Socio-economic pathways.

This paper presents global estimates of nutrient discharge from households to surface water based on the relationships between income and human emissions represented by protein consumption, degree of connection to sewerage systems, presence of wastewater treatment plants and their level of nutrient removal efficiency. These relationships were used to construct scenarios for discharge of nutrients with waste water based on the five Shared Socio-economic Pathways for the period from 1970 to 2050. The number of inhabitants connected to a sewerage system will increase by 2-4 billion people between 2010 and 2050. Despite the enhanced nutrient removal by wastewater treatment, which will increase by 10%-40% between 2010 and 2050, nutrient discharge to surface water will increase in all scenarios by 10%-70% (from 10.4 Tg nitrogen (N) in 2010 to 13.5-17.9 Tg N by 2050 and from 1.5 Tg phosphorus (P) in 2010 to 1.6-2.4 Tg P by 2050). In most developing countries, nutrient discharge to surface water will strongly increase over the next decades, and in developed countries it will stabilize or decrease slightly. A global decrease in nutrient discharge is possible only when wastewater treatment plants are extended with at least tertiary treatment in developing countries and with advanced treatment in the developed countries. In future urban areas that will be developed over the 2010-2050 period, options for recycling can be included in wastewater management systems. A separate collection system for urine can yield 15 Tg N yr-1 and 1.2 Tg P yr-1, which can be made available for recycling in agriculture. The SDG 6.3 about safely treated waste water by 2030 will be reached in the developed countries in 2030. In the developing countries, the goal will be reached by 2050 only under SSP1, SSP2 and SSP5.

Datasets of the phosphorus content in laundry and dishwasher detergents.

This data article provides the data of Phosphorus emissions from laundry and dishwasher detergents as part of the Phosphorus emissions from households. The household emissions are presented in the research article "Global nitrogen and phosphorus in urban waste water based on the Shared Socio-economic pathway" (van Puijenbroek et al., 2019) [1]. Laundry and dishwasher detergents are a major source of phosphorus loading of aquatic ecosystems in countries with a substantial use of laundry and dishwasher machines. In this article, datasets are presented with the global use of laundry and dishwasher detergents and the Phosphorus emissions due to laundry and dishwasher detergents. These results are presented for 10 world regions for 1970 and 2010, and for 2050 with 5 Shared Socio-economic Pathways. The outlook results for 2050 were based on the growth in income and population and on environmental policy for the introduction of Phosphorus free detergents.

Lessons from temporal and spatial patterns in global use of N and P fertilizer on cropland.

In recent decades farmers in high-income countries and China and India have built up a large reserve of residual soil P in cropland. This reserve can now be used by crops, and in high-income countries the use of mineral P fertilizer has recently been decreasing with even negative soil P budgets in Europe. In contrast to P, much of N surpluses are emitted to the environment via air and water and large quantities of N are transported in aquifers with long travel times (decades and longer). N fertilizer use in high-income countries has not been decreasing in recent years; increasing N use efficiency and utilization of accumulated residual soil P allowed continued increases in crop yields. However, there are ecological risks associated with the legacy of excessive nutrient mobilization in the 1970s and 1980s. Landscapes have a memory for N and P; N concentrations in many rivers do not respond to increased agricultural N use efficiency, and European water quality is threatened by rapidly increasing N:P ratios. Developing countries can avoid such problems by integrated management of N, P and other nutrients accounting for residual soil P, while avoiding legacies associated with the type of past or continuing mismanagement of high-income countries, China and India.

Negative global phosphorus budgets challenge sustainable intensification of grasslands.

Grasslands provide grass and fodder to sustain the growing need for ruminant meat and milk. Soil nutrients in grasslands are removed through withdrawal in these livestock products and through animal manure that originates from grasslands and is spread in croplands. This leads to loss of soil fertility, because globally most grasslands receive no mineral fertilizer. Here we show that phosphorus (P) inputs (mineral and organic) in global grasslands will have to increase more than fourfold in 2050 relative to 2005 to achieve an anticipated 80% increase in grass production (for milk and meat), while maintaining the soil P status. Combined with requirements for cropland, we estimate that mineral P fertilizer use must double by 2050 to sustain future crop and grassland production. Our findings point to the need to better understand the role of grasslands and their soil P status and their importance for global food security.

Global implementation of two shared socioeconomic pathways for future sanitation and wastewater flows.

Households are an important source of nutrient loading to surface water. Sewage systems without or with only primary wastewater treatment are major polluters of surface water. Future emission levels will depend on population growth, urbanisation, increases in income and investments in sanitation, sewage systems and wastewater treatment plants. This study presents the results for two possible shared socioeconomic pathways (SSPs). SSP1 is a scenario that includes improvement of wastewater treatment and SSP3 does not include such improvement, with fewer investments and a higher population growth. The main drivers for the nutrient emission model are population growth, income growth and urbanisation. Under the SSP1 scenario, 5.7 billion people will be connected to a sewage system and for SSP3 this is 5 billion. Nitrogen and phosphorus emissions increase by about 70% under both SSP scenarios, with the largest increase in SSP1. South Asia and Africa have the largest emission increases, in the developed countries decrease the nutrient emissions. The higher emission level poses a risk to ecosystem services.

Global trends and uncertainties in terrestrial denitrification and N2O emissions.

Soil nitrogen (N) budgets are used in a global, distributed flow-path model with 0.5° × 0.5° resolution, representing denitrification and N2O emissions from soils, groundwater and riparian zones for the period 1900-2000 and scenarios for the period 2000-2050 based on the Millennium Ecosystem Assessment. Total agricultural and natural N inputs from N fertilizers, animal manure, biological N2 fixation and atmospheric N deposition increased from 155 to 345 Tg N yr(-1) (Tg = teragram; 1 Tg = 10(12) g) between 1900 and 2000. Depending on the scenario, inputs are estimated to further increase to 408-510 Tg N yr(-1) by 2050. In the period 1900-2000, the soil N budget surplus (inputs minus withdrawal by plants) increased from 118 to 202 Tg yr(-1), and this may remain stable or further increase to 275 Tg yr(-1) by 2050, depending on the scenario. N2 production from denitrification increased from 52 to 96 Tg yr(-1) between 1900 and 2000, and N2O-N emissions from 10 to 12 Tg N yr(-1). The scenarios foresee a further increase to 142 Tg N2-N and 16 Tg N2O-N yr(-1) by 2050. Our results indicate that riparian buffer zones are an important source of N2O contributing an estimated 0.9 Tg N2O-N yr(-1) in 2000. Soils are key sites for denitrification and are much more important than groundwater and riparian zones in controlling the N flow to rivers and the oceans.

Exploring global Cryptosporidium emissions to surface water.

The protozoan parasite Cryptosporidium is a major cause of diarrhoea worldwide. This paper presents the first model-based inventory with 0.5 by 0.5 degree resolution of global Cryptosporidium emissions for the year 2000 from humans and animals to surface water. The model is based on nutrient distribution modelling, because the sources and transport of oocysts and nutrients to the surface water are comparable. Total emissions consist of point source emissions from wastewater and nonpoint source emissions by runoff of oocysts in manure from agricultural lands. Results indicate a global emission of 3 × 10(17) oocysts per year, with comparable contributions from point and nonpoint sources. Hot-spot areas for point sources are big cities in China, India and Latin America, while the area with the largest nonpoint source emissions is in China. Uncertainties in the model are large. Main areas for further study are (i) excretion rates of oocysts by humans and animals, (ii) emissions of humans not connected to sewage systems, and (iii) retention of oocysts to determine surface water pathogen concentrations rather than emissions. Our results are useful to health organisations to identify priority areas for further study and intervention.

Partial validation of the Dutch model for emission and transport of nutrients (STONE).

The Netherlands has to cope with large losses of N and P to groundwater and surface water. Agriculture is the dominant source of these nutrients, particularly with reference to nutrient excretion due to intensive animal husbandry in combination with fertilizer use. The Dutch government has recently launched a stricter eutrophication abatement policy to comply with the EC nitrate directive. The Dutch consensus model for N and P emission to groundwater and surface water (STONE) has been developed to evaluate the environmental benefits of abatement plans. Due to the possibly severe socioeconomic consequences of eutrophication abatement plans, it is of utmost importance that the model is thoroughly validated. Because STONE is applied on a nationwide scale, the model validation has also been carried out on this scale. For this purpose the model outputs were compared with lumped results from monitoring networks in the upper groundwater and in surface waters. About 13,000 recent point source observations of nitrate in the upper groundwater were available, along with several hundreds of observations showing N and P in local surface water systems. Comparison of observations from the different spatial scales available showed the issue of scale to be important. Scale issues will be addressed in the next stages of the validation study.

Global pollution of surface waters from point and nonpoint sources of nitrogen.

Global 0.5- by 0.5-degree resolution estimates are presented on the fate of nitrogen (N) stemming from point and nonpoint sources, including plant uptake, denitrification, leaching from the rooting zone, rapid flow through shallow groundwater, and slow flow through deep groundwater to riverine systems. Historical N inputs are used to describe the N flows in groundwater. For nonpoint N sources (agricultural and natural ecosystems), calculations are based on local hydrology, climate, geology, soils, climate and land use combined with data for 1995 on crop production, N inputs from N fertilizers and animal manure, and estimates for ammonia emissions, biological N fixation, and N deposition. For point sources, our estimates are based on population densities and human N emissions, sanitation, and treatment. The results provide a first insight into the magnitude of the N losses from soil-plant systems and point sources in various parts of the world, and the fate of N during transport in atmosphere, groundwater, and surface water. The contribution to the river N load by anthropogenic N pollution is dominant in many river basins in Europe, Asia, and North Africa. Our model results explain much of the variation in measured N export from different world river basins.