Application of Mathematical Modeling to Determine The Size of On-Site Grass Filters for Reducing Farm Pesticide Pollution

This paper presents a mathematical approach for estimating the size of a grass filter area for removing pesticide residues from agricultural drainage waters. The method utilizes a water table management model, DRAINMOD, for simulating drainage waters from agricultural land and then a solute transport model, PRZM2, for simulating pesticideconcentrations in drain effluent discharging from grass filters. DRAINMOD was used to estimate daily drain outflows that occurred in a 100 ha subsurface drained field in the Ottawa- St. Lawrence lowlands by running the model for a one-in-twenty year annual rainfall period. Atrazine (AZ), metolachlor (MT) and metribuzin (MZ) are the most common herbicides that are found in drainage waters. The simulated drain outflows were assumed to contain 50 μg/l of AZ, MT and MZ residues, and simulations were carried out with PRZM2 to determine the required size of grass filter area to make drainage waters safer for aquatic life and a marine habitat. It was found that no more than 6% of the farm area could be used to reduce the concentrations in drainage waters from 50 μg/l to less than 1 μg/l for the three herbicides