VALIDATION OF THE ROOT ZONE WATER QUALITY MODEL (RZWQM): A REVIEW

Authors: Malone, Robert - Rob; Ma, Liwang; Ahuja, Lajpat; Rojas, Kenneth

Submitted to: ASAE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: 7/18/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: Non-point source (NPS) contaminant transport models have been developed to assess pesticide transport over a large range of topographies, soil types, climatic conditions, and management practices primarily or at least partly because performing site specific field studies is often prohibitively expensive. Today many different models exist and evaluation of these models is necessary to provide information for users to select the most suitable model(s). The purpose of this paper is to summarize and review previous water quality validations of the Root Zone Water Quality Model (RZWQM). The RZWQM adequately simulated nitrate in the soil profile and herbicide transport in percolation and runoff in most instances. But some model assessments were unsuccessful in simulating nitrate and pesticide concentration by depth in the soil and nitrate in subsurface water and in runoff. This research will primarily benefit users of water quality models sby helping them determine if RZWQM has been successfully tested under thei proposed uses. This research also summarizes most RZWQM water quality validations and thus will help the developers determine common weaknesses found in the model and make improvements accordingly.

Technical Abstract: Non-point source (NPS) contaminant transport models have been developed to assess pesticide transport over a large range of topographies, soil types, climatic conditions, and management practices primarily or at least partly because performing site specific field studies is often prohibitively expensive. Today many different models exist and evaluation of these models is necessary to provide information for users to select the most suitable model(s). The purpose of this paper is to summarize and review previous RZWQM water quality evaluations. Other aspects of the model have been evaluated (plant growth, water content and movement, ET), but are not included in this review. The RZWQM is a physically-based contaminant transport model that includes sub-models to simulate infiltration and runoff, water distribution, and chemical movement in the soil; macropore flow and chemical movement through macropores; evapotranspiration (ET); heat transport; plant growth; organic matter/N cycling; pesticide processes; and chemical transfer to runoff. The effect of management practices on these processes is a centerpoint of the model. The model is usually calibrated using one or two data sets and model evaluation is performed using another independent dataset. The RZWQM adequately simulated NO**3-N in the soil profile and herbicide transport in percolation and runoff in most instances. But some model assessments were unsuccessful in simulating nitrate and pesticide by depth in the soil and NO**3-N in subsurface water and in runoff for which reasons were not investigated in this paper. To accurately simulate herbicide persistence, the two-site equilibrium-kinetic model was utilized, the two-stage dissipation model was utilized, or the herbicide half-life was calibrated.