Development of a Macro-pore Flow and Transport component for DRAINMOD, a Step Towards Modeling Phosphorus Fate and Transport in Drained Agricultural Land

Abstract. Artificially drained cropland has recently been identified as a possible source of elevated phosphourus (P) levels in Lake Erie. There is a growing need for developing new models or enhancing existing models to adequately represent different hydrological and biogeochemical processes affecting P fate and transport in artificially drained fields. Since P is highly immobile in soil, most P modeling studies have focused on surface runoff losses ignoring subsurface movement of P. Subsurface drainage, however, can be a critical pathway for P loss, particularly in the presence of macropore flow. Existing models lack or oversimplify integration of hydrological and biogeochemical processes regulating P dynamics in drained agro-ecosystems. A Phosphorus component to DRAINMOD suite of models, namely DRAINMOD-P, is currently being developed. Key hydrological and biochemical processes affecting P dynamics will be represented in the DRAINMOD-P model using a simple P cycle similar to the EPIC model. DRAINMOD hydrological component will be enhanced by adding routines for simulating macropore flow, a key pathway for subsurface transport of P, using procedures similar to MACRO model. The model will simulate water flow and solute transport in both soluble and particulate forms through macropores. The model will also be enhanced to simulate soil erosion and associated surface particulate P transport. The developed model will be tested using field measurements from artificially drained agricultural fields in North Carolina and Ohio. This abstract provides a detailed description of the modeling approach adopted in DRAINMOD to simulate the flow and transport in soil macro-pores