Carbon Sequestration and Hydrologic Export

In the past several years we have systematically investigated changes in the size of potential sinks for the 'excess' carbon assimilated by the C 3 plant community at elevated CO2 . We found an increase in the root biomass pool and winter respiration, but there is still a large imbalance that cannot be explained (Table Below).

Estimates of sinks for the excess C assimilated at elevated CO2
from 1988 to 1999.

Excess C Budget Term

Kg C


4.6 1

Sinks Measured






Winter Respiration 2


Methane Emissions


Hydrologic Export


Soil Organic Matter 3


Vertical Accretion 4


Total Sinks


Remaining Missing Sink


1 Years with significantly different CO 2 assimilation.

2 Summer respiration accounted for in source term.

3 Does not account for changes in surface elevation.

4 New soil organic matter causes soil surface to rise.

One possibility that can now be dismissed is export of dissolved carbon from the chambers, as explained in the next section. In the description of proposed research, we provide a rationale for perhaps the last possible sink to be investigated, an increase in the soil organic matter content that manifests as a rise in the soil surface elevation. Although we measured soil carbon content at the site, we did not account for the possibility that the soil surface has risen due to higher shoot and root productivity.

Research Questions