Recent research is now able to help policymakers identify the dominant factors in each problem area of the nitrogen cascade. Where there is excess nitrogen, the challenges are to use fertilizer more efficiently in agriculture, treat animal and human waste in a manner that will either reuse or eliminate reactive nitrogen, and reduce the amount of nitrogen emitted from fossil-fuel burning. Each of these steps would help to reduce both global and regional impacts. In areas of nitrogen deficiency, the challenge is to boost reactive nitrogen in an affordable and sustainable manner.

Precision agriculture is part of the solution as it matches the amount of nitrogen supplied with how much plants need both in amount and timing, reducing excessive and poorly-timed fertilizer application. Using biological sources of nitrogen inputs, such as nitrogen-fixing trees and cover crops (Sanchez 2002, Conway and Toenniessen 2003), together with, or as an alternative to, fertilizer made in industrial processes, can be part of a sustainable solution in regions where reactive nitrogen is still a limiting factor for food production, whether due to short supply, poor distribution or high cost. Developing countries have an opportunity to avoid the nitrogen overload problems currently plaguing industrialized nations by choosing improved, alternative and appropriate technologies and land use practices for supplying needed nitrogen. The challenge is, of course, not to have a negative impact on food production.

Box 5: Technology at work – sustainable sanitation

Sustainable sanitation can provide the solution for non-serviced or under-serviced communities to meet their hygiene needs while receiving the benefits of recycling organic carbon, nitrogen and phosphorus. By closing nutrient loops, nitrogen and phosphorus fertilizers are recycled back to grow plants, rather than being flushed to rivers and seas where they cause contamination. One approach is to separate the collection of urine and faecal matter. Urine is generally sterile but contributes much of the nitrogen and phosphorus in wastewater. Once diluted, it can be used as a fertilizer. Collected separately, the faecal matter can be composted in a composting toilet of which several designs are available. An alternative approach to achieve sustainable sanitation for household waste is for the graywater (from bathroom and laundry) to be treated through a wetland and the blackwater (faeces and urine) treated to produce biogas (containing methane [CH4]), a source of energy. After treatment the residue, which contains organic carbon, nitrogen and phosphorus, can be applied to crops, producing food rather than moving on through the environment.

Source: UNEP 2002

While recognizing that trade flows are based on a wide range of factors and considerations, from the nitrogen perspective, relocating linked activities could have positive spin-offs. For example, producing animals in the same regions as the food that feeds them (eg soybeans), would avoid shipping large amounts of nutrients into regions such as the European Union, where there is already an excess of nitrogen. Locating food processing and value-added industries in developing regions will not only help alleviate poverty but also maintain nutrients near their agricultural sources for more effective recycling.
Other interventions at strategic points in the nitrogen cascade can reduce the damaging impacts of nitrogen compounds transferred to other parts of the system. Existing technologies can remove virtually all the nitrogen compounds from exhaust gases from burning fossil-fuel. There are costs associated with this, but they are comparatively less than the costs of continued widespread pollution (Moomaw 2002). Alternative energy sources, which are not based on combustion or nitrogen-containing compounds, can also be part of the solution, while appropriate sanitation technologies can help reduce the influx of nitrogen in water systems (Box 5).

A number of countries and regional intergovernmental organizations have taken action on the problem of oxygen deprivation linked to excess nitrogen accumulation in aquatic and marine ecosystems. Goals have been set through regional compacts to reduce reactive nitrogen input to coastal and marine ecosystems such as the Baltic Sea, Chesapeake Bay, and Seto Inland Sea, Japan (Boesch 2002). Steps have been taken to reduce agricultural nitrogen run-off, atmospheric deposition of nitrogen, and emissions of nutrients through sewage and industrial waste. Much of the progress in reducing reactive nitrogen sources is the result of technologically-advanced waste treatment facilities, particularly in Europe and North America, rather than of reductions from diffuse non-point sources such as agriculture, which are more difficult to control.

The northwestern coastal area of the Black Sea is an example of a dramatic improvement of an oxygen-starved zone. Following the collapse of the centrally planned economies in Eastern and Central Europe, use of manufactured fertilizers declined quickly because they were no longer affordable. Within seven years, the amounts of nitrogen and phosphorus entering the Black Sea from the Danube and other rivers had dropped to half of previous levels; the ‘dead zone’ largely disappeared and fisheries have rebounded. Now the management goal is to maintain this situation as the economy of the region redevelops (Mee 2001)

Another example of reduction in nitrogen pollution, this time through policy intervention, comes from the Rhine River. With an internationally agreed policy target to reduce the nitrate load in the Rhine by 50 per cent, improvements in sewage effluents and industrial discharges by countries within the Rhine basin contributed to an estimated 37 per cent reduction in total nitrogen discharge to the North Sea between 1985–2000. Further reductions will largely depend on efforts to reduce diffuse pollution from agriculture (International Commission for Protection of Rhine 2001). The dominance of point sources in the heavily populated and industrialized Rhine region made quick reductions more easily attainable than is likely to be the case in river basins dominated by diffuse agricultural sources of nitrogen.