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. Sundquist 1 Katherine Visser Ackerman 2 Norman B. Bliss 3 Robert F. Stallard 4 1 USGS, Woods Hole; 2 USGS, Woods Hole; 3 SAIC, USGS/EROS, Sioux Falls; 4 USGS, Boulder; Special thanks to Skee Houghton and Joe Hackler, Woods Hole Research Center Harvey Terpstra, NRCS Supported by the USGS Mississippi Basin Carbon Project

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

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

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

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

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

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

Eroding soils Effects of erosion on soil carbon mass balance Production / Respiration Net burial Net erosion To coastal oceans Eroding soils Colluvium Alluvium Wetlands Lakes Reservoirs Net CO 2 release or uptake ??? Accreting soils

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

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

Erosion enhances CO 2 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 CO 2 assumed to be zero. This approach followed procedures developed by Stallard (1998), who used a global sediment budget to calculate global burial of PgC/yr, and suggested a comparable global carbon sink assuming replacement of buried carbon in eroding soils.

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

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

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

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

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

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

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

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

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

Terrestrial Carbon Erosion/Deposition/Soil Model (TCEDS)

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 1980’s annual carbon fluxes due to land use change With (red) and without (black, from Houghton et al., 1999) erosion

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 Tg C/yr –Decrease in cumulative historical soil disturbance source by 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