Eric T. Sundquist 1 Katherine Visser Ackerman 2 Norman B. Bliss 3 Robert F. Stallard 4

1. INTEGRATION OF EXISTING DATA TO ESTIMATE THE INFLUENCE OF SOIL AND WATER MANAGEMENT ON CARBON EROSION AND BURIAL IN THE CONTERMINOUS UNITED STATES Eric T. Sundquist1 Katherine Visser Ackerman2 Norman B. Bliss3 Robert F. Stallard4 1USGS, Woods Hole; esundqui@usgs.gov2USGS, Woods Hole; kackerman@usgs.gov3SAIC, USGS/EROS, Sioux Falls; bliss@usgs.gov4USGS, Boulder;stallard@usgs.gov Special thanks to Skee Houghton and Joe Hackler, Woods Hole Research Center Harvey Terpstra, NRCS Supported by the USGS Mississippi Basin Carbon Project

2. Soil carbon response to changing land use:Conventional modeling approach CO2 release CO2 uptake CO2 uptake Secondary Forest Primary Forest Cultivated No-till CO2 release or uptake is calculated using model soil carbon response curves (Houghton et al., 1983; Houghton and Hackler 2000; West et al., 2004)

3. Soil carbon mass balance without erosion Change in soil carbon = Production – Respiration

4. Effects of erosion on soil carbon mass balance Change in soil carbon = Production – Respiration + Profile exposure - Erosion Eroding soils

5. Effects of erosion on soil carbon mass balance Change in soil carbon = Production – Respiration + Profile exposure - Erosion Eroding soils Schimel et al., 1985

6. Effects of erosion on soil carbon mass balance Sediment transport Eroding soils Accreting soils Colluvium Alluvium Wetlands Lakes Reservoirs To coastal oceans

7. Effects of erosion on soil carbon mass balance Production / Respiration Sediment transport Eroding soils Eroding soils Accreting soils Colluvium Alluvium Wetlands Lakes Reservoirs To coastal oceans

8. Effects of erosion on soil carbon mass balance Net CO2 release or uptake ??? Production / Respiration Sediment transport Eroding soils Eroding soils Accreting soils Colluvium Alluvium Wetlands Lakes Reservoirs To coastal oceans Net erosion Net burial

9. The “missing sediment” problem • Erosion flux exceeds sediment delivery flux measured in streams and rivers. • Much eroded sediment is redeposited in upland areas. • Sediment transport occurs by repeated episodes of erosion and redeposition. • Modes of erosion and redeposition evolve in response to changing land management. • There is debate about the magnitude and nature of current U.S. erosion fluxes. Trimble, 1999

10. Erosion enhances CO2 emissions(Lal et al., 1998) (2) Carbon as CO2 = 20% of eroded carbon flux (1) Erosion flux = 10x river flux Figures shown are for the conterminous U.S. This methodology implies global erosion-induced emissions of 1.14 PgC/yr as CO2. (Lal, 1995)

11. Erosion enhances CO2 uptake(Smith et al., 2001) • Sediment erosion and deposition fluxes estimated explicitly from national inventories. • Carbon fluxes calculated from sediment budget combined with estimates of soil and sediment carbon content. • Erosion-induced emission of CO2 assumed to be zero. • This approach followed procedures developed by Stallard (1998), who used a global sediment budget to calculate global burial of 0.6-1.5 PgC/yr, and suggested a comparable global carbon sink assuming replacement of buried carbon in eroding soils.

12. Smith et al., 2001 Lal 1995; Lal et al., 1998 Effects of erosion on soil carbon mass balance Production / Respiration Sediment transport Eroding soils Eroding soils Accreting soils Colluvium Alluvium Wetlands Lakes Reservoirs To coastal oceans Houghton et al., 1999

13. Effects of erosion on soil carbon mass balance Production / Respiration Sediment transport Eroding soils Eroding soils Accreting soils Colluvium Alluvium Wetlands Lakes Reservoirs To coastal oceans This study

14. Erosion and deposition inventories Erosion: National Resources Inventory Deposition: National Inventory of Dams

15. Erosion rates on croplands, pasture lands, and CRP lands Source: National Resources Inventory

16. Carbon erosion on croplands, pasture lands, and CRP lands Source: National Resources Inventory

17. NRI carbon erosion normalized to total drainage area Source: National Resources Inventory

18. Carbon deposition normalized to total drainage area Source: National Inventory of Dams

19. Continuous corn, autumn conventional 0.1998 0.1873 0.1632 0.1549 Continuous corn, No-till Pasture Erosion rates are decreasing due to changing land management Example C factors (Ohio): Elliot and Ward (1995)

20. Effects of water erosion on the U.S. carbon budget

21. Terrestrial Carbon Erosion/Deposition/Soil Model(TCEDS)

23. Terrestrial Carbon Erosion/Deposition/Soil Model(TCEDS)

26. 1980’s annual carbon fluxes due to land use change With (red) and without (black, from Houghton et al., 1999) erosion • Based on figure from Houghton et al., 1999 (shown in black) • Fluxes, cumulative reservoirs, and reservoir changes are shown for effects of land use only • Units: PgC and PgC/yr • Erosion accounts for all of annual cultivated soil carbon depletion • Overall effect is a ~50% increase in net uptake

27. Conclusions • Enhancement of erosion and sediment deposition causes some soil carbon to be buried rather than returned to the atmosphere. • When this enhanced burial is accompanied by some degree of replacement by formation of new soil carbon, the net effect is unequivocally a carbon sink (or smaller carbon source) relative to calculations that do not take this effect into account. • Reasonable quantitative estimates for the conterminous U.S.: • Increase in net annual uptake for 1980’s by 10-20 Tg C/yr • Decrease in cumulative historical soil disturbance sourceby 1-2 Pg C (20-30%) • The decreased historical source has implications for calibration of predictive models. The effects of erosion and sediment deposition on the carbon budget are decreasing with improved land management. • Principal uncertainties: • Soil and sediment carbon dynamics in alluvium/colluvium • Eroding and accreting soil carbon dynamics • Time dependence and spatial distribution of enhanced erosion and deposition rates