Some Hydraulic and Wicking Properties of St. Cloud Zeolite and Zeolite-Soil Mixtures

Abstract

In many riparian regions of New Mexico, indigenous vegetation has been replaced by invasive plant species such as saltcedar (Tamarix spp.) and Russian olive (Elaeagnus angustifolia). The management of these species has been costly, and re-establishment of indigenous vegetation to improve biodiversity has not been successful, especially due to the lack of precipitation water available for new plant growth. New Mexico has a dry, hot climate with a mean annual precipitation of 230 mm in the riparian regions. This study was conducted to determine the possible use of clinoptilolite zeolite (CZ) as a wicking material to raise a sufficient amount of water within the vadose zone from the underlying water table for plant growth. Twelve different core samples were repacked with five different sized CZs, three different soils, three CZ-soil mixtures, and one clay-sand mixture. They were used to determine saturated hydraulic conductivities (Ks) and soil water characteristic curves (SWCC). The RETC program was used to fit the empirical Brooks and Corey (BC) and van Genuchten (VG) models to the measured SWCC. The Ks ranged from 4.27 10-5 to 4.42 10-1 cm/s for CZ, 8.32 10-5 to 2.40 10-3 cm/s for field soils, and 1.26 10-4 to 4.43 10-4 cm/s for soil mixtures. The available water content (AWC), assessed as the difference between the volumetric soil moisture contents at -0.3 and -15 bars, was greatest for fine CZ (25.4%) and lowest for medium CZ (2.5%). The Ks of clay (8.32 10-5 cm/s) was consistently lower than for a mixture of clay and fine-medium CZ (1.26 10-4 cm/s). The Ks of sandy loam and alluvial sand decreased from 8.56 10-4 cm/s to 3.56 10-4 cm/s and from 2.40 10-3 cm/s to 4.43 10-4 cm/s, respectively, when mixed with fine-medium CZ. The AWC was reduced from 19% to about 10% when fine-medium CZ was mixed with clay. Predicted capillary rise in fine CZ using the Lu and Likos (2004) model with a values obtained from BC retention function was 299.5 cm whereas the measured capillary rise in the repacked laboratory column with CZ was 317 cm for 360 days. However, predicted and measured capillary rise reached 150 cm within 22 days. Mixing of fine-medium CZ with sand produced a 33% increase in the predicted capillary rise within 1.5 days. Mixing of clay with sand increased the predicted capillary rise by 336% by the end of 16 days. Since Ks and AWC of the CZ-sand mix and clay-sand mix did not differ significantly, both CZ and clay could be used as wicking materials. It would be easier to use CZ because it is available commercially and sand-zeolite mixture would be more practical. The results demonstrate the potential of CZ to be used as a material for improving the hydraulic and wicking properties of sand in riparian regions.