NITRATE AND PESTICIDE DISTRIBUTION IN THE WEST FORK DES MOINES RIVER ALLUVIAL AQUIFER

C. A. Thompson


Iowa Department of Natural Resources, Geological Survey Bureau,
Technical Information Series 18, 1990, 39 p.

ABSTRACT


Groundwater and river water in the alluvial aquifer system of the West Fork Des Moines River were monitored to investigate the distribution of nitrate and pesticides. The distribution of nitrate in groundwater varied between locations, vertically within the aquifer, and with time. Nitrate concentrations increase in response to precipitation and snowmelt events and decrease as infiltration decreases. Nitrate concentrations decrease with depth. This decrease may be related to the flow regime of the aquifer. Gradients in the aquifer are dominantly horizontal resulting in lateral flow paths. In addition, deeper parts of the aquifer may be recharged from groundwater low in nitrate, such as occurs in the glacial materials. Denitrification might also be occurring in areas with persistently high water tables.

Pesticides were detected in both groundwater and river water with a maximum of four compounds detected. Concentrations were similar, except for alachlor (Lasso), which was found at higher concentrations in groundwater.