Table 2.
Attribution of the changes in the global nitrogen budget from 1860 to 2010 due to changes in land cover and land-use (‘LUCC’), increased atmospheric CO2 abundance (‘CO2’), climatic variability and changes (‘climate’), anthropogenic reactive nitrogen additions (‘deposition’) and industrial fertilizer application (‘fertilizer’). Note that this analysis does not take account of manure additions. Land-use emissions in 2000–2010 are an underestimate, as the dataset for land-use changes stops in 2005 [13]. Values are reported from simulations driven with the NCAR (TM5) nitrogen deposition fields. GPP, Gross primary production; NBP, net biome production = net ecosystem production – anthropogenic C losses.
| 1860s | 2000s | LUCC | CO2 | climate | deposition | fertilizer | |
|---|---|---|---|---|---|---|---|
| fluxes (Tg N yr−1; Pg C yr−1) | |||||||
| natural N input | 112.4 (112.7) | 98.7 (99.0) | −10.0 | 3.1 | 0.1 | −2.5 (−2.3) | −0.1 |
| anthropogenic N input | 28.5 (22.5) | 161.6 (155.2) | 0 | 0 | 0 | 42.1 (44.0) | 85.6 |
| ecosystem N lossesa | 148.2 (144.4) | 237.1 (231.6) | 19.2 | −18.9 | 11.4 | 29.9 (31.2) | 50.0 |
| soil NOx emission | 6.5 (6.3) | 8.5 (8.4) | 0.1 | −0.2 | 0.8 | 0.7 (0.7) | 0.7 |
| soil N2O emission | 6.0 (5.8) | 8.7 (8.6) | 0.3 | −0.6 | 0.8 | 0.8 (0.8) | 1.5 |
| GPP | 99.9 (100.0) | 122.3 (121.6) | −0.4 | 17.1 | 2.9 | 1.66 (1.81) | 0.93 |
| NBP 1990s | 1.3 (1.3) | −0.8 | 2.0 | 0.0 | 0.20 (0.21) | 0.07 | |
| NBP 2000s | 1.9 (1.9) | −0.4 | 2.4 | −0.2 | 0.18 (0.17) | 0.06 | |
| pools (Pg N; Pg C) | |||||||
| vegetation N | 3.4 (3.6) | 3.4 (3.4) | −0.71 | 0.36 | 0.04 | 0.09 (0.10) | 0.03 |
| vegetation C | 615.7 (607.2) | 581.4 (578.1) | −141.3 | 98.6 | 3.8 | 2.7 (2.7) | 0.08 |
| soils N | 103.2 (101.5) | 103.9 (102.2) | −0.50 | 0.83 | −0.39 | 0.61 (0.60) | 0.56 |
| litter and soil C | 1312.3 (1291.3) | 1287.6 (1268.2) | −52.1 | 35.9 | −9.1 | 6.1 (5.8) | 2.4 |
aLeaching + volatilization (NH3 + NOx + N2O + N2).