Valley ag chemicals and water quality
- Created on Thursday, 25 October 2012 00:06
- Written by Ron Riggenbach
It’s hard to imagine with the dry year the San Luis Valley has had, but the combination of shallow groundwater and sandy soils in the San Luis Valley have led to a known issue of nitrates in the unconfined aquifer in areas north of the Rio Grande River.
In 1997 as part of a water quality demonstration project a monitoring network was established to test and monitor the levels of nitrates in the unconfined aquifer. This study was put together using driller’s logs from actual high capacity irrigation wells to form a randomized set of test sites where the wells were drawing water from approximately the same levels in the unconfined aquifer.
To accomplish this, private landowners were asked for permission to take regular water samples from their wells the same week of the month through the irrigation season. The vast majority of landowners was more than willing to cooperate with the project and readily gave permission. Staff from the San Luis
Valley Water Quality Demonstration Project and the Rio Grande Water Conservation District, who also partnered on the study, collected the samples and they were analyzed by the Unites States Geological Survey another partner in the study. Since the network consisted of actual irrigation wells the samples were only taken during the irrigation season and not in the winter months.
The United States Geological Survey took the data from each year’s monitoring effort and were able to extrapolate it into maps showing nitrate concentration and changes from year to year. This data was provided to Valley residents each year of the study by means of presentations at the San Luis Valley Potato/Grain conference hosted by Colorado State University.
Over the years no major issues have been attributed to the high levels of nitrates in the water, however high nitrates are known to cause methemoglobinemia in infants. This condition is more commonly referred to as Blue Baby Syndrome where the nitrates interfere with the blood’s ability to carry oxygen.
High nitrates can also potentially cause issues in crop production by having more nitrogen available at certain crop growth stages than what would be ideal. Several studies have been conducted and some are ongoing that show having high nitrogen available at the end of the growing season can delay skin set in potato tubers and cause issues for potatoes while in storage. Large amounts of available nitrogen can also cause lodging in cereal grains which lead to issues at harvest.
The monitoring network was discontinued at the end of the Water Quality Demonstration Project in 1999; however it would be interesting to see what effects the drop in unconfined aquifer storage is having on the nitrate concentrations. With less water to dilute the nitrates, the concentration in some areas may be getting higher than before.
It is impossible to know the exact cause of the nitrates in the groundwater, but it is most likely to have been caused by agricultural fertilizers in the past when these products were cheap and readily available at a time when the ground water table in the area was most likely at its highest.
Over the years fertilizer has steadily risen in cost, the groundwater table has declined and the irrigation systems have become more efficient. By managing all of their resources to the highest level possible, modern farmers in the Valley have actually become the remedy to the issue of nitrate in the ground water. By using the nitrate water to irrigate their crop along with accounting for the available nitrate along with their fertilizer use, they are removing nitrates from the system and turning them into crop yields.