R6 AM Plant Uptake of Organic Pollutants - Processes and Modeling
Thursday, 17 November 2005: 8:00 AM - 11:40 AM in 324-326

(MCK-1117-845931) Plant uptake of organic pollutants: Model performance evaluation.

McKone, T.^{1, 2}, Maddalena, R.², ¹ University of California, Berkeley, CA, United States² Lawrence Berkeley National Laboratory, Berkeley, CA, United States

ABSTRACT- In spite of continuing field and laboratory studies, the role of terrestrial vegetation in transferring chemicals from soil and air into specific plant tissues (stems, leaves, roots, etc.) is still not well understood. This has led to a reliance on models to explain and predict the fate of chemicals in air/plant/soil systems. But models of plant uptake have a number of uncertainties that have not been fully characterized. Here we illustrate performance evaluation of plant uptake models by considering three key sources of uncertainty (1) uncertainties in the conceptual/theoretical formulation of the model, (2) uncertainties in formulating the mathematical algorithm and (3) parameter uncertainty and variability. For the conceptual vegetation mass-balance model, we evaluate the theoretical basis for the model and consider the appropriate level of modeling complexity. We next consider alternate modeling strategies and the associated changes in the reliability, fidelity, and transparency of the model. Here we confront such issues as the how many compartments to include, how to establish mass transfer rates among compartments and whether to build process-based or empirical partition and mass-transfer coefficients. Finally there is the issue of parameter uncertainty and variability. For this we evaluate both the magnitude and primary sources of parameter variability/uncertainty in plant uptake parameters and compare these uncertainties to conceptual uncertainty and model formulation uncertainty. For plant uptake models that must address competing soil-root-leaf and soil-air-leaf pathways, we find that conceptual uncertainties remain a dominant source of overall uncertainty. We also find that variability in plant-species and soil characteristics are large contributors relative to parameter uncertainty when predicting the fate of chemicals in terrestrial vegetation.

Key words: plant uptake, organic chemicals, uncertainty, fate models