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for example by wastewater treatment. 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 developed countries. Separate collection systems for urine can reduce nutrient pollution to 15TgN/yr and 1.2TgP/yr (van Puijenbroek, Beusen and Bouwman 2019). When all effluent from sewage systems receive tertiary treatment, global nutrient discharge is projected to decrease to 1990 levels (Ligtvoet et al. 2018). For phosphorus, a further decrease could be realized when all laundry and dishwasher detergents are phosphorus-free. This is now mandatory in the European Union, United States of America, Japan and some other countries.


Increasing crop yields and fertilizer-use efficiencies will have a direct effect on the nutrient loading of streams and rivers. However, starting from a situation of low crop yields and minimal nutrient inputs, nutrient loading of watersheds may well increase in scenarios with a shift towards food production systems now prevalent in industrialized countries. Since watersheds retain nitrogen and phosphorus, there may be legacies of past management. As a consequence, nitrogen concentrations in many rivers respond only slowly to increased nitrogen-use efficiency in food production. For example, due to these legacies, European water quality is threatened by rapidly increasing nitrogen-phosphorus ratios (e.g. Romero et al. 2013). Developing countries can avoid such problems by managing both nitrogen and phosphorus, accounting for residual soil phosphorus, while avoiding legacies associated with the past and continuing mismanagement of high-income countries.


Significant synergies and trade-offs between measures and targets


A number of synergies and trade-offs can be identified between specific measures and the various targets within this cluster. A few important ones are as follows.


v Increased access to and use of improved and safely managed WASH facilities has direct health benefits and can also improve overall quality of life. Women in developing countries often travel long distances to access water and sanitation facilities, even more so than men because of domestic-related tasks that more often fall to women, and because of menstrual hygiene (Pommells et al. 2018). Not only does this leave women more susceptible to health risks from more frequent contact with unsafe facilities, but there is a growing body of literature on the prevalence, and lack of documentation, of assault and rape on these trips (Sorenson, Morssink and Campos 2011; Watt and Chamberlain 2011; Sahoo et al. 2015; Sommer et al. 2015; Freshwater Action Network South Asia and Water Supply and Sanitation Collaborative Council 2016; Pommells et al. 2018).


v Increased levels of access to at least basic safe drinking water and adequate sanitation can drive increased domestic water demand, further contributing to water stress (Hanasaki et al. 2013a; Hanasaki et al. 2013b; Wada et al. 2016).


v Water scarcity negatively affects agriculture and biodiversity and also energy supply. In fact, water stress is one of the five global risks of highest concern according to the World Economic Forum (Wada, Gleeson and Esnault 2014).


v Agriculture is the dominant source of nutrients in global watersheds leading to eutrophication, resulting in hypoxia symptoms in many inland and coastal areas. There is a tendency towards increasing nitrogen-phosphorus ratios and declining silica; this distortion of nutrient ratios leads to the proliferation of harmful algal blooms, both in global watersheds and coastal parts of oceans.


v Improved sanitation facilities without, or with only primary, wastewater treatment are major polluters of freshwater, due to nitrogen and phosphorus discharge (van Puijenbroek et al. 2015),


v While the only option for some water-scarce communities, desalination is very energy-intensive, potentially counteracting interventions to reduce industrial water demand (Pinto and Marques 2017).


22.3.4 Oceans


The selected targets for the oceans cluster are limiting ocean acidification, reducing nutrient pollution and sustainably managing ocean resources (see Chapter 20). For all three targets, trends are projected to go in the wrong direction (see Chapter 21). There is strong evidence that the current trend towards declining fish populations and reduced species richness impair the ecological functioning of oceans, including their role in providing food (Worm et al. 2006). Nutrients from fertilizers used to increase agricultural yields have also found their way into nearly every water body across the globe where they stimulate aquatic plant production. As a consequence, hypoxia, a growing global problem, occurs where organic matter decay consumes oxygen faster than its diffusion from the oxygen-rich surface. Furthermore, the global problem of harmful algae is now on a pathway of more and more frequent blooms, in more places and with increasing severity, with more toxins (Glibert 2017).


Pathways in this cluster are largely linked to developments in other clusters. With respect to ocean acidification, the scenario literature is linked to climate change (i.e. the reduction of CO2


emissions; Section 22.3.2), marine nutrient pollution


with agricultural production measures (Section 22.3.1) and freshwater pollution (Section 22.3.3). Here, we discuss different measures linked to the individual targets, addressing ocean acidification measures and sustainable ocean management. No scenario studies were found that address the reduction of marine nutrient pollution to stop related hypoxia and harmful algal blooms.


Ocean acidification measures Ocean acidification is a result of the increased absorption of CO2


in the oceans, which in turn is a result of an increasing global atmospheric CO2


concentration. Billé et al. (2013)


identify three means of preventing ocean acidification: i.


reducing CO2 or removing CO2


concentrations, either by lowering emissions from the atmosphere, for example through


carbon-capture-and-storage under the seabed (see Section 22.3.2);


ii. limiting ocean warming; and iii. reducing nutrient run-off into the ocean.


Furthermore, they identify means of reversing acidification after it has occurred, including additives (e.g. alkalinization) and ecological restoration.


Pathways toward Sustainable Development 529 22


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