Effects of irrigated agroecosystems: 2. Quality of soil water and groundwater in the southern High Plains, Texas

Authors

B. R. Scanlon, University of Texas at Austin
J. B. Gates, University of Nebraska - Lincoln
R. C. Reedy, University of Texas at AustinFollow
W. A. Jackson, Texas Tech University
J. P. Bordovsky, Texas A&M University

Date of this Version

2010

Citation

Scanlon, B. R., J. B. Gates, R. C. Reedy, W. A. Jackson, and J. P. Bordovsky (2010), Effects of irrigated agroecosystems: 2. Quality of soil water and groundwater in the southern High Plains, Texas, Water Resour. Res., 46, W09538, doi:10.1029/2009WR008428.

Comments

Copyright 2010 by the American Geophysical Union. Used by permission.

Abstract

Trade‐offs between water‐resource depletion and salinization need to be understood when promoting water‐conservative irrigation practices. This companion paper assesses impacts of groundwater‐fed irrigation on soil water and groundwater quality using data from the southern High Plains (SHP). Unsaturated zone soil samples from 13 boreholes beneath irrigated agroecosystems were analyzed for water‐extractable anions. Salt accumulation in soils varies with irrigation water quality, which ranges from low salinity in the north (median Cl: 21 mg/L) to higher salinity in the south (median Cl: 180 mg/L). Large Cl bulges under irrigated agroecosystems in the south are similar to those under natural ecosystems, but they accumulated over decades rather than millennia typical of natural ecosystems. Profile peak Cl concentrations (1200–6400 mg/L) correspond to irrigation efficiencies of 92–98% with respect to drainage and are attributed to deficit irrigation with minimal flushing. Perchlorate (ClO₄) also accumulates under irrigated agroecosystems, primarily from irrigation water, and behaves similarly to Cl. Most NO₃‐N accumulation is below the root zone. Groundwater total dissolved solids (TDS) have increased by ≤960 mg/L and NO₃‐Nby ≤9.4 mg/L since the early 1960s. Mobilization of salts that have accumulated under irrigated agroecosystems is projected to degrade groundwater much more in the future because of the essentially closed‐basin status of the aquifer, with discharge occurring primarily through irrigation pumpage. TDS are projected to increase by an additional 2200 mg/L (median), ClO₄ by 21 μg/L, and NO₃‐N by 52 mg/L. Water and salt balances should be considered in irrigation management in order to minimize salinization issues.