Submitted to: Texas Water Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/7/2017
Publication Date: 6/20/2018
Citation: Goebel, T.S., Stout, J.E., Lascano, R.J. 2018. Seasonal changes in water quality of the lower Ogallala Aquifer. Texas Water Journal. 9:69-81.
Interpretive Summary: The main source of water to irrigate crops in the Texas High Plains is the Ogallala Aquifer and it is estimated that since 1985 the water table has declined about a foot per year in this region. As a result of this significant decline a local water conservation district set a goal of preserving 50% of the saturated thickness of the aquifer over the next 50 years. Although this restriction addresses the quantity of water, it does not address the quality of the remaining water. Generally, aquifers are stratified such that the deeper and older water is more saline and thus as the Ogallala Aquifer continues to be mined more of this deeper and more saline water will be used for irrigation. Our objective was to sample irrigation wells across the Texas High Plains and measure the salinity of the water and establish a baseline for groundwater quality. We selected 20 irrigation wells located in Lubbock, Terry, Hockley, Cochran and Lamb counties. These wells were sampled every two weeks starting in the spring of 2014 and the electrical conductivity of the water was measured. Higher conductivity means a higher concentration of dissolved salts. Results showed that salinity increased over the growing season for about half the sampled wells and decreased in the other half. It was found that over the short term, changes in water quality over a growing season do not present a significant challenge to producers in this region. However, some wells are responding to the continued extraction of water from the aquifer and likely the rest of the wells will begin to show similar trends at some point in the future as the aquifer continues to be depleted and more of the deeper more saline water is accessed. Monitoring of these wells will continue as well as new studies will be initiated to study changes in the vertical salinity gradient over time so that we may reach a better understanding of possible future problems with water quality conditions.
Technical Abstract: The Ogallala Aquifer extends beneath eight states in the Great Plains region of North America. It stretches from Texas to South Dakota and is among the largest aquifers in the world. In Texas, extraction of water, primarily for cropland irrigation, far exceeds recharge resulting in a significant decline of the water table. In the Texas High Plains (THP) this decline has prompted one local water conservation district to set a goal of preserving 50% of the saturated thickness of the Ogallala Aquifer over the next 50 years. However, this restriction only addresses the quantity and not the quality of the remaining water. The quality of water extracted from the Ogallala Aquifer has been observed to change over time, especially over the length of a growing season. We measured water quality over a three-year period using an electrical conductivity sensor and measured depth to water at 20 locations across 5 counties in the THP. Results suggest that when wells are actively pumping, water quality can change in complex and unpredictable ways. In some cases, water quality may decline and in other cases water quality may improve. This result has prompted us to further investigate the mechanisms involved in these observed seasonal water quality changes.