Simulation of Pesticide Transport Using the Riparian Ecosystem Management Model.

The Riparian Ecosystem Management Model (REMM) is used to estimate the effects of buffer size, vegetation, and soil properties on the movement of water, sediment, carbon, nitrogen, phosphorus, and pesticides.  Interactions among hydrology, sediment transport, and pesticide properties control pesticide dynamics in buffers.  Pesticides enter and move through the buffer system based on their soil organic matter sorption coefficient, octanol/water partitioning coefficient and soil half-life.  The partitioning can be affected by the ionization of the pesticide based on soil pH.  Pesticides bound in leaf litter or taken up by vegetation are simulated as sinks and are no longer processed in the buffer.  Pesticides in solution or adsorbed to soil and sediment are subject to transport and/or degradation. REMM simulates processes that are important to buffer function such as infiltration/co-deposition, litter (residue) interception of water and chemicals, and interactions of surface runoff, groundwater, and exfiltration.  Model results were compared to a field study of atrazine movement conducted on a Coastal Plain buffer near Tifton, Ga. Using literature values for all atrazine parameters and measured or literature values for buffer parameters, REMM simulated observed atrazine concentrations and loads within one standard deviation of the observed mean. REMM also showed similar temporal and spatial patterns as observed in the field study. As with any model, calibration of REMM involves comparing to measured values and changing model parameters to achieve better agreement between modeled and observed. Changing REMM parameters to increase the amount of infiltration by surface runoff improved the match between the simulated and observed. This is consistent with the structure of REMM where daily and event simulations of hydrologic processes control all chemical and sediment transport.