System-Wide Water Resources Program Nutrient Sub-Model (SWWRP-NSM) Version 1.1

This report discusses major developments that have occurred since the release of NSM Version 1.0. These improvements were in the areas of: 1) partitioning of nutrients (dissolved and adsorbed) within surface runoff, 2) mass transfer of nutrients between the soils and overlying water column, 3) erosion and sedimentation of particulate nutrients, and 4) soil plant dynamics. Nutrients at or near the soil surface can be transformed to overland flow in solution Thrm by the mixing of rainwater with soil solution. A rate-limited mass transfer at the soil overland flow interface controls the dissolved nutrient transfer from soil solution to overland flow, once formed. The mass transfer coefficient will be affected by many factors including characteristics of the raindrops, overland flow, and nutrient characteristics. The predictions of these variables, together with nutrient transport in the surface runoff, need to be validated with the measured data at the field scale. Regarding soil plant dynamics capabilities within NSM, the EPIC formulations appear to provide realistic responses for simple annual based systems. It is necessarily simple for use with the available datasets and should be improved by addition of plant growth processes with nutrient cycling. Further development of this module for a more detailed treatment of plant water uptake and associated nutrient interactions is needed. Attention to refinement of links between soil plant dynamics and hydrological processes is also required. As research continues, improved understanding of nutrient process descriptions and new capabilities will be developed and as such will be integrated into the NSM. Future releases of NSM will include: 1) improved nutrient kinetics for channels, 2) improved soil plant dynamics (EDYS sub-module), 3) inclusion of carbon cycle modules for soils and overland flow, and 4) improved nitrogen and phosphorus kinetics for soils and overland flow.

The original document contains color images. Prepared in collaboration with SpecPro, Inc., Vicksburg, MS.