Anthropogenic Transient

To what degree have these fluxes been influenced or impacted by human activities— that is, how much of this carbon is an anthropogenic transient? The consensus is that human-induced erosion has dramatically accelerated the movement of sediments (and

POC). While some of this material "hangs up" on land (sedimentation, reservoirs), some of it likely escapes to the sea (some of the regions with highest sediment yields have very few dams). There is evidence that anthropogenic processes have an affect on DIC. Raymond and Cole (2003) report an increase in the alkalinity of the Mississippi, which implies an increase in the consumption of atmospheric CO2 through weathering. Jones et al. (2003), however, report a systematic decrease in pCO2 in rivers across the United States, which they attribute to large-scale declines in terrestrial CO2 production and import into aquatic ecosystems and not to terrestrial weathering or in-stream processes.

In the case of DOC, there is simply not enough information available to draw conclusions. Clair et al. (1999) suggested that DOC export from basins in Canada might increase by 14 percent with a doubling in atmospheric CO2. An additional factor rarely addressed in rivers is direct loading from urban and industrial sources (Ver et al 1999; Abril et al. 2002). In evaluating the consequences of continental sedimentation and the potentially higher fluxes of POC, a net transient exported from land of roughly 1 PgC y-1 is possible, with perhaps half of that going to the sea and the other half divided equally between outgassing and sedimentation.

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