Modeling the fate and transport of atrazine in the Upper Chesapeake Bay

Kristin Goetchius and Haydee Salmun

The fate and transport of atrazine, including effects of photodegradation and a potentail reaction with polysulfides, in the Upper Chesapeake Bay is investigated. A hydrodynamic model that includes all relevant physical and chemical processes is used to show that atrazine is transported vertically down the water column to the sediment water interface where it may react with naturally occurring polysulfides. Limited field data supports these results. Based on reaction rates reported in the literature, model results show that neither photolysis nor the reaction with polysulfides decrease the concentration of atrazine in the Upper Bay in any significant amount. Our modeling study shows that the minimum reaction rate required to decrease the concentration of atrazine in the bottom layer is 1012 M -1 s-1. The wide range of reaction rates used to obtain these preliminary results suggest that a potentail reaction between an herbicide or pesticide and polysulfides is not a significant removal mechanism for agrochemicals in the Upper Chesapeake Bay.

Keywords: Chesapeake Bay, hydrodynamic model, atrazine, photolysis, polysulfides

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