How carbon and nitrogen move through land and water
A plain-language guide to the flows of carbon and nitrogen between the air, plants, soils, rivers and the sea — with every number linked to its published source.
What is a land flux?
A flux is a flow of material from one place to another over time — for example, carbon moving from the air into leaves, from soils into streams, or from rivers into the sea. A stock is the amount held in one place at a given moment, such as the carbon stored in a peat bog. This site is a small, plain-language guide to the carbon and nitrogen fluxes of land, and of the water that drains from it.
Why do they matter?
- The land absorbs part of our CO₂. Each year, land ecosystems take up a large share of the carbon dioxide released by human activity. The Global Carbon Budget 2024 estimates this “land sink” at 3.2 ± 0.9 GtC per year for 2014–2023, about 30% of total CO₂ emissions. Source: Friedlingstein et al. (2025), Global Carbon Budget 2024, doi:10.5194/essd-17-965-2025 · peer-reviewed community synthesis (not independent of IPCC AR6)
- Land and water are linked. Some carbon fixed on land leaks into streams, rivers and lakes, where part is breathed back to the air, part is buried in sediments and part reaches the ocean. Leaving these water pathways out of the accounts can make land storage look larger than it really is. Source: Regnier et al. (2022), doi:10.1038/s41586-021-04339-9 · independent peer-reviewed paper
- Small organisms can add up. Mosses, lichens and soil crusts (“cryptogamic covers”) may account for “nearly half of the biological nitrogen fixation on land”, according to one global estimate. Source: Elbert et al. (2012), doi:10.1038/ngeo1486 · independent peer-reviewed paper
How big are these flows? A log-scale view
Land fluxes differ by more than a thousand-fold, so a normal (linear) chart would squash the small ones into invisibility. On a log scale, each step to the right is ten times larger than the last. Where sources disagree, both ends are shown and both are cited.
| Flux | Value as printed (and source) | Log scale (Pg C/yr) |
|---|---|---|
| Global net primary production (land + ocean) | 104.9 Pg C/yr, with “roughly equal contributions from land and oceans” Source: Field et al. (1998), doi:10.1126/science.281.5374.237 · independent peer-reviewed paper | |
| Carbon net uptake by cryptogamic covers (mosses, lichens, algae, cyanobacteria, fungi on soil, rock and plants) | best estimate 3.84 Pg/yr (90% CI 2.06–7.35); “around 7%” of terrestrial-vegetation NPP Source: Elbert et al. (2012), doi:10.1038/ngeo1486 · independent peer-reviewed paper | |
| Land sink (terrestrial CO₂ sink, SLAND), 2014–2023 mean | 3.2 ± 0.9 GtC/yr (±1σ) Source: Friedlingstein et al. (2025), Global Carbon Budget 2024, doi:10.5194/essd-17-965-2025 · peer-reviewed community synthesis (not independent of IPCC AR6) | |
| Terrestrial sink, 2010–2019 mean | 3.4 ± 0.9 PgC/yr Source: Canadell et al. (2021), doi:10.1017/9781009157896.007 · IPCC assessment (AR6 WGI, Chapter 5) | |
| Carbon transferred from soils to inland waters | AR6: “2.4–5.1 PgC yr−1”; Tian et al.: 2,281 Tg C/yr loadings in the 2010s (= 2.281 Pg C/yr); Drake et al.: “upward of 5.1 Pg of C annually” Source: Canadell et al. (2021), doi:10.1017/9781009157896.007 · IPCC assessment (AR6 WGI, Chapter 5) Source: Tian et al. (2023), doi:10.1029/2023GB007776 · independent peer-reviewed paper Source: Drake et al. (2018), doi:10.1002/lol2.10055 · independent peer-reviewed paper | |
| CO₂ evasion (outgassing) from inland waters | 2.1 Pg C/yr (streams and rivers 1.8; lakes and reservoirs 0.32) Source: Raymond et al. (2013), doi:10.1038/nature12760 · independent peer-reviewed paper | |
| Land-use change emissions (net land-use change / LULUCF) | AR6: 1.6 ± 0.7 PgC/yr (2010–2019); GCB 2024: 1.1 ± 0.7 GtC/yr (2014–2023) Source: Canadell et al. (2021), doi:10.1017/9781009157896.007 · IPCC assessment (AR6 WGI, Chapter 5) Source: Friedlingstein et al. (2025), Global Carbon Budget 2024, doi:10.5194/essd-17-965-2025 · peer-reviewed community synthesis (not independent of IPCC AR6) | |
| Riverine / net carbon export from land to the open ocean | Resplandy et al.: revised “from 0.45 to 0.78 PgC yr−1”; AR6: net export “0.80 PgC yr−1” (medium confidence) Source: Resplandy et al. (2018), doi:10.1038/s41561-018-0151-3 · independent peer-reviewed paper Source: Canadell et al. (2021), doi:10.1017/9781009157896.007 · IPCC assessment (AR6 WGI, Chapter 5) | |
| Pre-industrial land-to-ocean loop (taken up on land, carried to the ocean, outgassed) | 0.65 ± 0.30 Pg C/yr (±2σ) Source: Regnier et al. (2022), doi:10.1038/s41586-021-04339-9 · independent peer-reviewed paper | |
| CO₂ from drained organic soils used for agriculture | “about 780 million tonnes” CO₂/yr ≈ 0.21 Pg C/yr1 Source: Tubiello et al. (2016), doi:10.3390/su8040371 · independent peer-reviewed paper | |
| Organic carbon burial in lakes and reservoirs | 0.15 Pg C/yr (range 0.06–0.25), ~40% of it in reservoirs Source: Mendonça et al. (2017), doi:10.1038/s41467-017-01789-6 · independent peer-reviewed paper |
Units. 1 Pg (petagram) = 1 Gt (gigatonne) = 1015 g = 1,000 Tg. “PgC” and “GtC” are the same unit of carbon. Fluxes (per year) and stocks (amounts) are kept in separate tables and never placed on the same axis.
1 Our conversion, not a figure printed by the source: mass of CO₂ ÷ 3.664 = mass of carbon (44.01/12.011). 780 Mt CO₂ ÷ 3.664 ≈ 213 Mt C ≈ 0.21 Pg C. The source reports total emissions from these soils of “nearly one billion tonnes CO2eq annually”; CO₂-equivalents include other gases and cannot be converted to carbon this way. Back
These are global estimates with real uncertainty; different studies use different methods, periods and definitions, so the rows are not a balanced budget and should not be added together. Read each source for its exact scope.