Effects of controlled agricultural practices on water quality in the Minnesota sand-plain aquifer

Abstract

Recent studies of Minnesota's sand plains indicate that ground-water chemistry is related to agricultural practices. Surficial sand-plain aquifers cover 8,000,000 acres of Minnesota and are a major source of water for domestic use, irrigation, and some municipal systems. The sand-plain aquifers consist of sand and gravel deposits that are from 20 to greater than 100 feet thick and are covered by a thin sandy loam that generally is less than 2 feet thick. Sand-plain aquifers are recharged by the downward percolation of precipitation through the soil root zone and the unsaturated zone in the sand to the water table. The water table is the upper surface of the zone of saturation and forms the top of the sand-plain aquifer. Sand-plain aquifers are susceptible to contamination by agricultural chemicals (fertilizers and pesticides), if downward-percolating recharge water contains these chemicals. The concentrations of nitrate, pesticides, and some other chemical constituents fluctuate seasonally and differ with depth below the water table (Anderson, 1989). Despite the availability of water-quality data for about 260 wells that were collected during previous studies in three U.S. Geological Survey (USGS) project areas in Minnesota, it is not known how concentrations of agricultural chemicals in ground water relate to the rate and timing of fertilizer and pesticide application or to the tillage practices used. Field-scale research is needed to determine the effects of different farming practices on the concentrations of nitrate, pesticides, and other agricultural chemicals in ground water in the unsaturated and saturated zones.-

Effects of agricultural and residential land use on ground-water quality, Anoka Sand Plain Aquifer, east-central Minnesota

“…Throughout most of the Anoka Sand Plain aquifer, horizontal movement of water is much more significant than vertical movement. On the basis of ground-water modeling of an adjacent sand-plain area (Anderson and Stoner, 1989), water recharging a sand-plain aquifer under typical hydraulic conditions in relatively flat terrain can be expected to move several hundred feet laterally and only a few feet downward. Therefore, differences in water quality with depth are related to differing conditions in the recharge areas.…”

Presence, distribution, and potential sources of nitrate and selected pesticides in the surficial aquifer along the Straight River in north-central Minnesota, 1992-93

“…The regional ground-water flow paths defined by these gradients were generally in easterly and southeasterly directions, but local ground-water flow paths into ponds and wetlands probably were in many directions. The ground-water flow probably was much greater laterally than vertically because ground water that moves several hundreds of feet laterally typically moves only a few feet vertically in flat-terrain surficial aquifers (Anderson and Stoner, 1989). Ground-water discharge from the surficial aquifer was mainly into the Straight River.…”