Abstract:
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 pesticide
concentrations 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.
