Riverine nitrogen export from the continents to the coasts

Abstract

[1] We present an overview of riverine nitrogen flux calculations that were prepared for the International Nitrogen Initiative's current global assessment of nitrogen cycles: past, present, and future . We quantified anthropogenic and natural inputs of reactive nitrogen (N) to terrestrial landscapes and the associated riverine N fluxes. Anthropogenic inputs include fossil-fuel derived atmospheric deposition, fixation in cultivated croplands, fertilizer use, and the net import in human food and animal feedstuffs. Natural inputs include natural biological N fixation in forests and other noncultivated vegetated lands, and fixation by lightning. We use an empirical model relating total N inputs per landscape area to the total flux of N discharged in rivers based on watershed data from contrasting ecosystems spanning multiple spatial scales. With this approach, we simulate riverine N loads to the coastal zone and to inland waters from the continents. Globally, rivers exported about 59 Tg N yr À1 , with 11 Tg N yr À1transported to dry lands and inland receiving waters, and 48 Tg N yr À1 transported to the coastal zone. Rates of riverine N loss vary greatly among the continents, reflecting the regional differences in population and the associated anthropogenic N inputs. We compare our estimates to other approaches that have been reported in the literature. Our work provides an understanding of the sources of N to landscapes and the associated N fluxes in rivers, and highlights how anthropogenic activities impact N cycling around the world.

Assessment of uncertainties in greenhouse gas emission profiles of livestock sectors in Africa, Latin America and Europe

“…Expanding livestock sectors can contribute to greenhouse gas (GHG) emissions, agricultural land expansion and associated deforestation (Steinfeld et al 2006), surface water eutrophication (Seitzinger et al 2005;Boyer et al 2006), decrease in terrestrial biodiversity (Dise et al 2011) and nutrient imbalances (Smaling et al 2008;Menzi et al 2010). The global animal food chain, including land use change, contributes 14.5 % of the global anthropogenic GHG emissions, including carbon dioxide (CO 2 ), methane (CH 4 ) and nitrous oxide (N 2 O), expressed in CO 2 equivalents (CO 2 -eq; Gerber et al 2013).…”

Dissolved nitrogen in rivers: comparing pristine and impacted regions of Brazil

“…So far, we know that in pristine rivers and streams of the tropics, N export is high when compared to those in the temperate zone (Lewis et al, 1999), perhaps as a result of lower N limitation in tropical terrestrial ecosystems. In human altered watersheds of the tropics, higher N export rates have also been reported (Filoso et al, 2003;Boyer et al, 2006;Borbor-Cordova et al, 2006). In particular, the loading of domestic sewage directly into rivers and water bodies without any previous treatment, assumes a very important role in developing countries of the tropics (UNESCO, 2003).…”

“…Accordingly, most modelling efforts to estimate the export of nitrogen from rivers worldwide have used attributes such as population density, land use, urbanisation and sanitation (Howarth et al, 1996;Seitzinger and Kroeze, 1998;Green et al, 2004;Bouwman et al, 2005;Dumont et al, 2005;Boyer et al, 2006).…”

Spatial and temporal dynamics of biogeochemical processes in the Fraser River, Canada : a coupled organic-inorganic perspective

“…Our measurements may exclude significant inputs of N and P from fertilizer and manure runoff and sewage and stormwater overflow, sources which rival or dwarf natural fluxes in many other rivers (Howarth et al, 1996;Boyer et al, 2006;Shen and Liu, 2008;Alvarez-Cobelas et al, 2009)…”

“…Furthermore, appropriate research settings are necessary to answer questions pertaining to natural biogeochemical processes, as many river basins are significantly perturbed by anthropogenic activities affecting fluxes of water (Vörösmarty et al, 2010;Grafton et al, 2012), sediment (Vörösmarty et al, 2003;Syvitski et al, 2005;Walling, 2006), nutrients (Boyer et al, 2006;Laruelle et al, 2009), trace elements (Poulton and Raiswell, 2000;Rauch, 2010), radionuclides (Moran et al, 2002;Sansone et al, 2008), and carbon (Stallard, 1998;Hossler and Bauer, 2013). While no single field site can satisfy all of these goals, the Fraser River basin in British Columbia has many key features (including limited artificial sediment impoundments, diverse terrain, geology, and climate, and low human population density) that make it a valuable window into natural biogeochemical processes within large temperate river systems.…”