An adequate supply of water is important to the success of pretty much every agricultural enterprise, but it is critical for potato and vegetable growers, many of whom regularly need to irrigate their crops.
Tamas Houlihan, executive director of the Wisconsin Potato & Vegetable Growers Association (WPVGA), says having a sufficient supply of water is vital to the 110 farms that are members of his organization, particularly those farming in the Central Sands portions of the state’s Adams, Portage, Waushara and Wood counties.
“We’ve been under a lot of pressure from so-called environmental groups who claim we’re drying up lakes, rivers and streams with our high-capacity wells, but we have not seen the science to support that,” said Houlihan at last month’s WPVGA Grower Conference. “We have looked long and hard at the lakes, rivers and streams in question, and conditions are really driven by climate. When we have a wet year, they flow tremendously. In dry years we do see some declines, but it’s cyclical, and they come back.”
During the recent conference, several sessions focused on several important water issues.
Hydrogeologist David Hart with the Wisconsin Geological and Natural History Survey revealed the connections between geology and groundwater in the Central Sands.
“The Wisconsin glacier produced a mile-high pile of ice that moved forward and then retreated as the ice melted,” said Hart. “As the glacier advanced, part of it was channeled down Green Bay and Lake Michigan, while Lake Superior pushed it off to the west. But at the front of the glacier you have a lot of meltwater, and as it melts it also deposits sand and gravel.”
He noted that as the glacier moved it picked up rocks, clay and other materials and ground them into smaller pieces.
“When the glacier stops, it leaves a ridge called a moraine,” Hart said. “Another glacial feature in the Central Sands is that they have tunnel channels through the moraine, and the base of the glacier may be its warmest part because we have geothermal energy from the earth warming it up.”
Glaciers also had an underground network of channels known as glacial rivers.
“These channels can be very large and can carry a lot of sediment as water drains out of the base of the glacier,” Hart said. “In the Central Sands we have a flat lake basin with out-wash plains near the moraine.”
The region also features sandstone knobs in the basin. “Each of the knobs represents a place where the glacier drained, where water gathered and moved out of the glacier,” Hart said. “Over time, we had the deeper sands and gravel deposited maybe 100 or so feet deep, and the coarser material was separated from the finer material.”
Hart noted that there are separate layers of fine and course material, which could have been formed seasonally with the change in temperature.
“Soil samples from Adams County reveal a thick and deeper silty clay that thins as we move farther north,” he said.
Ground-penetrating radar has helped geologists look deeper below the surface and see tunnel channels below the water table. “We have recharge occurring throughout the area, with discharge to the Wisconsin River,” Hart said. “The upland areas are most sensitive in changes to the flow system, and they don’t have a large recharge area and zone of contribution, which is one of the things that makes them so sensitive.”
Ray Rasmussen, water specialist with the Wisconsin Department of Natural Resources (DNR), detailed some of the substances causing problems with groundwater in Wisconsin. He said Coliform and E. coli bacteria are the most common pathogens found in the state’s wells.
“Looking at the thousands of samples we get from wells each year, we see 23 percent have Coliform and 2 percent have E.coli at various levels,” said Rasmussen. “That doesn’t necessarily mean these are unsafe wells, but merely an indicator that more testing needs to be done.”
Studies related to the sources of the contaminants revealed a nearly even split between agriculture and residential septic systems.
“At DNR, we’re looking to address both sources,” Rasmussen said. “We want to find out exactly what’s going on before we propose a solution.”
According to Rasmussen, other common contaminants include arsenic, chloride—which often results from road salt application—radium, manganese and molybdenum.
“We’re also finding pharmaceuticals that are coming from septic systems, so there are sources of contamination other than nitrates and pesticides,” he said.
Nitrates and pesticides remain a source of groundwater contamination, especially in cases where excessive amounts of fertilizer are applied.
“When more nitrogen is applied than plants can utilize, the excess can leach into the soil and, ultimately, into the groundwater,” Rasmussen said.
When it comes drinking water standards, the Wisconsin DNR recommends a nitrate contaminant limit of 2 milligrams per liter, even though the enforcement standard is 10 milligrams per liter.
“There are health risks, especially to children (including birth defects), when you get above the enforcement standard,” Rasmussen said.
He reported that, statewide, about 10 percent of the wells exceeded the enforcement standard, with large number in Dane and Kewaunee counties.
When considering solutions to groundwater contamination, Rasmussen said there’s no single best solution.
“We’re just starting to talk about how we’re going to address whatever problems we identify with nitrates because we don’t have all the necessary data,” he said. “We need to develop more data so we can pinpoint where our main issues really are.”
Source: Wisconsin State Farmer