Increased nitrogen export from eastern North America to the Atlantic Ocean due to climatic and anthropogenic changes during 1901–2008

Abstract

Nitrogen export demonstrated substantial spatial variability across the study area. Increased NH 4 + export mainly occurred around major cities in the MAB. NO 3 À export increased in most parts of the MAB but decreased in parts of the GOM. Enhanced DON export was mainly distributed in the GOM and the SAB. PON export increased in coastal areas of the SAB and northern parts of the GOM but decreased in the Piedmont areas and the eastern parts of the MAB. Climate was the primary reason for interannual variability in nitrogen export; fertilizer use and nitrogen deposition tended to enhance the export of all nitrogen species; livestock farming and sewage discharge were also responsible for the increases in NH 4 + and NO 3 À fluxes; and land cover change (especially reforestation of former agricultural land) reduced the export of the four nitrogen species.

Preindustrial nitrous oxide emissions from the land biosphere estimated by using a global biogeochemistry model

“…The previous results of GHG emissions from DLEM simulations have been validated against field observations and measurements at various sites (Lu and Tian, 2013;Ren et al, 2011;Tian et al, 2010Tian et al, , 2011. The estimates of water, carbon, and nutrient fluxes and storage were also compared with the estimates from different approaches on regional, continental, and global scales (Pan et al, 2014;Yang et al, 2015). Different soil organic pools and calculations of decomposition rates have been described in .…”

“…Different soil organic pools and calculations of decomposition rates have been described in . The decomposition and nitrogen mineralization processes in the DLEM have been described in previous publications (Lu and Tian, 2013;Yang et al, 2015).…”

“…Unlike in Chatskikh et al (2005), who set k nit to 0.10 d −1 , k nit varies with different plant functional types (PFTs) in the DLEM with a range of 0.04 to 0.15 d −1 . The detailed calculations of F (T soil ) and F (ψ) have been described in and Yang et al (2015).…”

“…Based on sensitivity analyses of key parameters that affect terrestrial N 2 O fluxes, the most sensitive parameters were identified to conduct uncertainty simulations with the DLEM. These parameters include potential denitrification and nitrification rates, BNF rates, and the adsorption coefficient for soil NH + 4 and NO − 3 (Gerber et al, 2010;Yang et al, 2015). The ranges of five parameters were obtained from previous studies.…”

Global manure nitrogen production and application in cropland during 1860–2014: a 5 arcmin gridded global dataset for Earth system modeling

“…The rest of the surplus nitrogen can leach through the soil profile and contaminate groundwater in the form of nitrate (Ju et al, 2006). Excess nitrogen together with phosphorous can stimulate the eutrophication of inland water (Conley et al, 2009), be transported far away from original sources, exacerbate degrading coastal water quality, and even lead to hypoxia (Burkart and James, 1999;Yang et al, 2015).…”