Adapting carbon dynamic models to characterize biogeochemical processes across terrestrial-aquatic interfaces

Jianqiu Zheng, Vanessa Bailey and Timothy Scheibe, Pacific Northwest National Laboratory, Richland, WA, Melanie A. Mayes, Oak Ridge National Laboratory, Oak Ridge, TN

Background/Question/Methods
Soil represents the largest terrestrial carbon reservoir, yet uncertainty persists regarding the fate of stored organic matter (OM) under the impact of climate change and the increasing occurrence of disturbances. The aquatic interfaces exposing terrestrial soils to oxic-anoxic regime shifts represent “hotspots” of biogeochemical reactions that are extremely sensitive to perturbations and difficult to predict. Interactions among water movement, physical heterogeneity and microbial activity and diversity regulate the molecular transformations and fluxes of carbon, nutrients, and redox sensitive compounds, however we still lack an integrated modeling framework that incorporates the full spectrum of such complex interactions and evaluates how these interactions will play out under various environment conditions.

Results/Conclusions
Here we present an aqueous phase explicit MEND model (AquaMEND) that integrates dynamic coupling of aqueous phase equilibrium and speciation with organo-mineral interactions and microbial dynamics. This new model is able to capture many well-known empirical relationships among redox oscillation, DOM chemistry, mineral association and microbial metabolic pathway shifts that are frequently observed across dynamic aquatic interfaces, such as the rhizosphere, hyporheic zone and systems experiencing oscillating redox conditions. The parallel structure of aqueous and non-aqueous phases allows assessment of key processes and their responses to environmental disturbances both individually and collectively. We expect this new model framework will serve as an integrated tool for identifying quantitatively important mechanisms that determine the fate of OM under short- and long- term environmental perturbations.