Column experiments modeling location

The interface of the leachate and clay liner material was modelled using a simple tank system. A perspex box (350 x 350 x 50 mm) was filled with a layer (depth 20 mm) of pre-saturated clay. The clay was collected at the same time and from the same location as the samples used in the column experiments and was pre-saturated with tap water, to minimize wetting and capillary effects. The tank was filled with leachate to a depth of 40 mm and the head space flushed with nitrogen. An oversized lid and water filled trench... 

Commercial gel-filled pH probes were inserted into the soil column at 3 cm intervals, located between the anode and cathode (Figure 1). These were inserted through butyl rubber septa placed into holes drilled into the sides of the column. The pH probes were calibrated using standard buffer solutions before insertion into the soil column. Readings were taken daily for the duration of the experiment, by placing a reference electrode into a well at the top of the column, and connecting the reference and in-situ pH probes to an Orion Model EA 940 Expandable Ion Analyzer. All pH measurements were temperature compensated to 25 °C. 

Figure 4. A comparison of the downward and upward migrations of Daphnia catawba in the presence and absence of UVR. There were three UV-transparent columns and three UV-opaque columns. Each column was suspended 10 cm below the surface of Lake Giles, a high-UV lake located in northeastern PA, USA. The downward experiment was conducted on 14 July 2000 and the upward on 2 August 2000. Mean solar irradiance was measured with a LICOR model LI-200SA pyranometer near solar noon (1300 h) when the experiments were conducted. Mean solar irradiance equaled 659 Wm on 14 July 2000 and 694 W on 2 August 2000.

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