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GLOBAL BIOGEOCHEMICAL CYCLES,
VOL. 17, NO. 2,
1037,
doi:10.1029/2002GB001984,
2003
Water and carbon cycles in the Mississippi River basin: Potential implications for the Northern Hemisphere residual terrestrial
sink
Dongho Lee
Ottawa-Carleton Geoscience Center,
University of Ottawa,
Ottawa,
Canada
Ján Veizer
Ottawa-Carleton Geoscience Center,
University of Ottawa,
Ottawa,
Canada
Abstract
The hydrologic cycle plays an important role in carbon cycling, due to the coupling of vapor release and CO2 uptake during photosynthesis. This coupling, expressed as Water Use Efficiency (WUE) or Transpiration Ratio, can provide
an inexpensive alternative for estimating the Net Primary Productivity (NPP) of terrestrial ecosystems. The D/H and 18O/16O trends of river water in the Mississippi basin are mostly indistinguishable from those of precipitation. This, combined
with isotopic mass balance relationships, suggests that direct evaporation of surface water is small and evapotranspiration
(ET) flux from the basin therefore consists mostly of interception and transpiration, with interception approximated from
field studies. The calculated water flux associated with transpiration is 1500.8 km3 (77.3% of the evapotranspiration flux). Utilizing the average WUE of 864 mol H2O for each mole of CO2, the NPP of the Mississippi River basin amounts to 1.16 Pg C/yr, similar to the model estimates of the heterotrophic soil
respiration flux of 1.12 Pg C/yr. This does not favor the postulated existence of a major sink for atmospheric CO2 in the temperate Northern Hemispheric ecosystems of the conterminous United States, but due to uncertainties in the input
parameters we cannot discount the possibility that these ecosystems act as a modest sink.
Published 23
April
2003.
Index Terms: 1030 Geochemistry: Geochemical cycles (0330); 1040 Geochemistry: Isotopic composition/chemistry; 1615 Global Change: Biogeochemical processes (4805); 1655 Global Change: Water cycles (1836).
Read Full Article (file size: 807297 bytes) Cited by
Citation: Lee, D., and J. Veizer
(2003),
Water and carbon cycles in the Mississippi River basin: Potential implications for the Northern Hemisphere residual terrestrial
sink,
Global Biogeochem. Cycles,
17(2),
1037,
doi:10.1029/2002GB001984.
Copyright 2003 by the American Geophysical Union.
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