The Nanjing Declaration on Management of Reactive Nitrogen

Abstract

igh levels of reactive nitrogencompounds— nitrates, ammonia,and nitrogen oxides,for example— havebecome a threat to the environment onmany scales. Indications are that theproblem will become worse,especially inrapidly developing parts of the world.In-ternational agreements are urgentlyneeded to combat the problem. TheThird International Nitrogen Confer-ence, which will take place this comingOctober in Nanjing, China, offers anideal opportunity to reach agreementon an initial declaration concerning themanagement of reactive nitrogen. Re-searchers and officials should make themost of this important occasion.Although nitrogen makes up about78 percent of the atmosphere, this poolis almost all in gaseous form,which feworganisms can use.Nitrogen gas is con-verted into usable, reactive forms,how-ever,through both natural and industrialprocesses.Globally, about 75 percent ofthe 165 teragrams of reactive nitrogenproduced each year is related in someway to agriculture, and the remaining25 percent results from the combustionof fossil fuels and from industrial uses ofnitrogen (Galloway et al. 2003). Reac-tive nitrogen cascades through differentenvironmental compartments, chang-ing forms as it does so and causing di-verse effects.On the positive side, the greater pro-ductivity of agriculture over the pastcentury— driven almost entirely by fer-tilizers that contain nitrogen— has madeit possible to feed growing numbers ofhumans. Indeed, 40 percent of theworld’ s population would not be alivebut for this massive alteration of the nat-ural nitrogen cycle (Smil 2001).Globally,food production uses 110 teragrams ofreactive nitrogen every year, most ofwhich is generated when componentsof natural gas are made to react with at-mospheric nitrogen. The manufactureof fertilizer accounts for 5 percent ofglobal natural gas consumption.On the downside,when released intothe atmosphere,reactive forms of nitro-gen create smog and aerosols and contribute to global warming andstratospheric ozone depletion. Whenthey fall back to the earth’ s surface,theycontribute to acid rain, which corrodesbuildings,harms plants and forests,andacidifies lakes and streams.The excess ni-trogen causes eutrophication in aquaticecosystems,leading to the domination ofthe plant community by one or a fewspecies— harmful algal blooms are acommon consequence— and thus to a reduction of biodiversity.In forests,thecombination of acidification and eu-trophication is particularly damaging.Acidification decreases the availabilityof base cations by leaching them from thesoil, thus depriving trees of nutrients.Increased nitrogen loads exacerbate theimbalance.Excess reactive nitrogen flowsinto groundwater reservoirs,rivers,andthen the coastal oceans,where it depletesoxygen and so threatens marine life.The growing requirements for foodand energy— especially where there istoo little reactive nitrogen,as in Africa—will further fuel the cascade of environ-mental impacts attributable to reactivenitrogen. Anthropogenic nitrogen ex-ceeds natural levels by a factor of two,butultimately the source of the nitrogen isunimportant. What is important is theadoption of an integrated approach tocombating nitrogen pollution.

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