Date: Fri, 21 Sep 2001 14:26:13 -0400 From: "Eric T. Sundquist" Organization: U.S. Geological Survey To: "nacp@io.harvard.edu" , "nacp@python.as.harvard.edu" Cc: Richard Birdsey , Dave Schimel , Scott Doney , mark.harmon@orst.edu, bmckee@mailhost.tcs.tulane.edu Subject: lateral carbon transport Below are some suggested words on lateral carbon fluxes. I decided against including a discussion of NBP vs. NEP in this context. There is too much semantic confusion in the literature use of these terms. For example, the definition of NBP used in the IPCC TAR is not the same as that suggested by the IPCC report on Land Use, Land-use Change, and Forestry. (The latter defines NBP as just NEP minus removals by disturbance, whereas the former includes the other non-heterotrophic, non-fire removals that must be included to complete the mass balance.) Eric ====================== Lateral transport (Sundquist, 9/21/01): In linking atmospheric data to spatially explicit estimates of terrestrial carbon exchange, it is important to remember that net ecosystem exchange at one location may contribute to carbon storage or removal at another location. Carbon is transported by rivers, streams, groundwater, and human conveyance. A complete understanding of the terrestrial carbon mass balance must account for the lateral transport of carbon across and below the land surface. For example, soil carbon inventories often show a historical depletion of carbon in agricultural soils, yet some of the removed carbon may have been eroded and buried elsewhere rather than returned to the atmosphere. Even under conditions of steady-state or increasing soil carbon, estimates of local net ecosystem exchange must be high enough to support export due to erosion and leaching as well as any changes in local soil carbon. Likewise, the transport and fate of dissolved carbon in streams and groundwater must be accounted. River transport of particulate and dissolved carbon represents a crucial link between the terrestrial and coastal ocean components of the NACP. Wood and agricultural products must also be followed from their forests and fields of origin to their fate in markets throughout the U.S. and abroad. Preliminary estimates suggest that these effects may be significant at the global and continental scale (Stallard, 1998; Pacala et al., 2001; Smith et al., 2001), but we are not yet able to specify their distribution at the spatial and temporal scales needed for the NACP. Further work is needed using available data in order to develop strategies for monitoring and modeling the effects of lateral carbon transport on NACP estimates of net carbon exchange. -- Eric T. Sundquist U. S. Geological Survey 384 Woods Hole Road Quissett Campus Woods Hole, Massachusetts 02543 USA Phone 508-457-2397 Fax 508-457-2310