Published online 16 December 2005
Published in Vadose Zone J 5:77-79 (2005)
DOI: 10.2136/vzj2005.0049
© 2005 Soil Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
NOTES
Suction Lysimeter Modifications to Improve Sampling Efficiency and Prevent Wildlife Damage
Charles G. Crabtree* and
Tina M. Seaman
Edith Angel Environmental Research Center, The Institute of Environmental and Human Health/Texas Tech Univ., 44351 State Hwy. 14, Chariton, IA 50049
* Corresponding author (chuck.crabtree{at}tiehh.ttu.edu)
Received 24 March 2005.
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ABSTRACT
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Duing the course of research using suction lysimeters, it became apparent that simple modifications to the lysimeters could save both time and money. The procedure for extracting samples was inefficient and there was potential for cross-contamination of samples. In addition, wildlife was damaging the lysimeters, causing project delays and costly repairs. Relatively simple and inexpensive modifications to the lysimeters were made to remedy both of these problems without having to purchase new lysimeters. The suction lysimeters were retrofitted with permanent sample extraction tubes and quick-connects to increase the efficiency of sample extraction and to reduce the likelihood of cross-contamination of samples. A protective PVC casing was installed around the lysimeters to prevent wildlife tampering. These casings also served to prevent lysimeter damage from a grass fire at the study site. These modifications increased sampling efficiency by 50% and eliminated damage to lysimeters caused by wildlife and fire.
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INTRODUCTION
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SUCTION LYSIMETERS have been used for many years to collect water samples from the vadose zone. Among other applications, they have been used extensively in agriculture and forestry to monitor the vertical movement of pesticides (Adams and Thurman, 1991; Elliott et al., 1998; Gish et al., 1995; Jayachandran et al., 1994; Tindall and Vencill, 1995; Weaver et al., 1990) and nutrients (Paramasivam et al., 2001; Rasse et al., 1999; He et al., 1999; Neilsen et al., 1997; Holloway et al., 1996; Khakural and Alva, 1996; Hogbom et al., 2001) through the soil in addition to other agricultural applications (Li et al., 1998; Agus et al., 1998). Over the years lysimeters have been redesigned to meet the needs of individual applications, and different designs have been developed and modified (Wu et al., 1995; Ahmed et al., 2001; Corwin, 2000). However, there is little information in the literature on how to modify currently installed lysimeters to improve efficiency and protect the equipment from damage due to wildlife and/or fire. It is important to note that the suction lysimeter modifications discussed here are not new. Suction lysimeters can be purchased with the design described below. However, our purpose is to share with the scientific community an inexpensive method to modify existing suction lysimeters to be more efficient samplers, thereby eliminating replacement costs.
Suction lysimeters were installed on a riparian buffer research site in southern Iowa and were used to extract subsurface, 0.3 to 0.9 m (1–3 ft.), water samples that were analyzed for pesticide residues and nitrates. The original lysimeters were designed to have both a vacuum applied and samples extracted through a single neoprene tube in the lysimeter stopper. Once the vacuum was applied and sufficient water had been drawn into the lysimeters, it was extracted by inserting a clear plastic extraction tube through the neoprene tube to the bottom of the lysimeter. The other end of the extraction tube was then inserted into a rubber stopper on a vacuum flask. A vacuum was applied to the vacuum flask into which the sample was extracted. Continually inserting the clear extraction tube through the neoprene tube proved to be time-consuming, and the use of the same tube to extract samples from multiple lysimeters increased the potential for cross-contamination of samples. It was also discovered that raccoons (Procyon lotor) and/or coyotes (Canis latrans) were damaging the neoprene tubes and lysimeter stoppers, often taking the entire stopper off, leaving the inside of the lysimeters exposed to the elements. We present a design modification for the suction lysimeters, which enhances the efficiency of water sample collection, and present a design for a cost-effective PVC lysimeter casing that eliminates wildlife damage and ultimately protected the lysimeters from fire damage.
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MATERIALS AND METHODS
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The suction lysimeters were purchased from Soilmoisture Equipment Corp. (Santa Barbara, CA). The lysimeters were constructed of 4.8-cm (1.9-in.) outside diameter PVC tube, a porous ceramic cup with a 200-kPa (2-bar) air-entry value, and a Santoprene stopper (Fig. 1
). A single neoprene tube was attached to a 0.6-cm (1/4 in.) diameter tube that was inserted into the top of each stopper. The neoprene tubing was to provide access for drawing a vacuum and extracting water samples. Once the vacuums were drawn, the neoprene tubes were bent over and sealed with a plastic ring (Fig. 1 and 2)
. The lysimeters were modified by boring a second hole approximately 0.6 cm (1/4 in.) from the existing tube hole with a no. 2 cork bore. An extraction tube (Fig. 1) made of clear nylon tubing, 0.5 cm (3/16 in.), was inserted through the new hole in each stopper so that it extended to the bottom of the lysimeters. Approximately 30 to 35 cm (12 to 14 in.) was left extending out beyond the stopper. Instead of using the original neoprene tube for sample extraction, the sample pump was attached to the neoprene tube and the pump was reversed, forcing air into the lysimeter and pushing the water sample out through the extraction tube and into a sample jar. In addition, quick-connects were added to the neoprene tubes to speed up the attachment of the sampling pumps to the lysimeters. A rubber vacuum hose cap and plastic plugs were used to plug the neoprene tube and extraction tube to hold vacuums during sampling (Fig. 1).
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Fig. 1. Comparison of the original lysimeters design (left) with the modified lysimeters design (middle) and the components of the PVC casing (right).
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Fig. 2. Original lysimeters design installed in the field. A rubber collar has been added to prevent water from running down the side of the lysimeters.
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To protect the lysimeters from wildlife tampering it was decided to enclose the top of the lysimeters, yet still allow field technicians to gain access to the sampling tubes. PVC pipe, 10 cm in diameter (4 in.), was cut into 35-cm (14-in.) sections. A 10-cm (4-in.) PVC hub adaptor, manufactured with internal threads, was glued directly onto the pipe section using plumbers' contact and adhesive glue. Finally, a PVC sewer cap was then screwed onto the hub adaptor creating a sealed environment for the lysimeters. A list of materials, vendors, and approximate costs are included in Table 1.
The PVC casing was installed in conjunction with the installation of the lysimeters. The PVC pipe was measured 22.5 cm (9 in.) up from the bottom and marked with a permanent marker. This was to ensure that the casing was not buried deeper than the cup of the lysimeter. A hole was dug and a slurry of silica flour was added. The lysimeters were set in place and back-filled with soil. The casing was then pushed into the ground around the lysimeter up to the line on the casing. More soil was added on the outside and inside of the casing, as needed. Once installed, the extraction tube was coiled into the casing and the sewer lid was screwed on. Finally, drainage holes were drilled into the casing at ground level to allow for water drainage (Fig. 3 ).
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DISCUSSION
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The lysimeter modifications described in this paper reduced our sample collection times in the field by as much as 50%, which has more than paid for the cost of the modifications. Before the modifications, considerable time was spent rinsing the extraction tube and collection flask between lysimeters to prevent sample cross-contamination. This time spent in the field has been completely eliminated since each lysimeter now has its own extraction tube, and the potential for cross-contamination has been virtually eliminated. The replacement of the original ring clamp with quick-connects and rubber vacuum hose caps has saved wear and tear on the neoprene tube, eliminating the need for yearly replacement.
The PVC casing has completely eliminated wildlife tampering and damage to the lysimeters. Although it does take more time to install the lysimeters, the cost savings have been significant. In previous years, we have had to buy replacement stoppers and occasionally replacement lysimeters because of extensive damage due to wildlife. We have regularly had to remove lysimeters for cleaning and reinstall them due to missing stoppers that resulted in contamination of the interior of the lysimeter tube itself. All of these maintenance activities have been completely eliminated, resulting in savings of time and hundreds of dollars per year.
Finally, following the installation of the PVC casings, a brush fire swept through our study site. The fire generated enough heat to melt some of the PVC casings, but none of the suction lysimeters inside the casing were damaged. This one incident alone saved thousands of dollars worth of lysimeters, not to mention the time and the cost of reinstallation.
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REFERENCES
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ABSTRACT
INTRODUCTION
