Biophysical mechanisms of trichloroethane uptake and loss in baldcypress growing in shallow contaminated groundwater

Wetland Vegetation may be useful in the remediation of shallow contaminated aquifers. Mesocosm experiments we re conducted to describe the regulatory mechanisms affecting trichloroethene (TCE) removal rates from groundwater b y flood-adapted wetland trees at a contaminated site. TCE flux through bald cypress [Taxodium distichum (L) Rich] seedlings grown in glass-carboys decr eased from day to night and from August to December. The diel fluctuation c oincided with changes in leaf-level physiology, as the daytime flux was sig nificantly correlated with net photosynthesis but not with respiration at n ight. A decrease in seedling water use from summer to winter explained the large seasonal difference in TCE flux. A simple model that simulates gas-ph ase diffusion through aerenchyma tested the importance of diffusion of TCE vapor from roots to the stem. The modeled diffusive flux was within 64% of the observed Value during the winter but could only explain 8% of the summe r flux. Seedling water use was a good estimator of flux during the summer. Hence, evapotranspiration (ET) in the summer may serve as a good predictor for the potential of TCE removal by baldcypress trees, while diffusive flux may better approximate potential contaminant loss in the winter.