Design and performance of an acidic precipitation delivery system for field investigations with plants

An acidic precipitation delivery system is described that was designed and constructed for use in a field investigation of the response of red spruce saplings (Picea rubens Sarg.) to the interactive stresses of ozone and acid rain. The system utilizes hydraulic, solid-cone spray nozzles to produce simulated rainfall with droplet size distributions approximating natural rain events, which are of low intensity, i.e., about 1-1.5 cm hr(-1), and are relatively uniform in distribution of volume over a 2.4 m diameter plot. Three different pH treatments (3.1, 4.1, 5.1) were dispensed randomly to each of three treatment subplots located in twelve open-top field chambers and three ambient control chambers. Storage capacity of the system permitted a 2.3 hr rain event. Construction materials used were chosen for resistance to the corrosive nature of the rain simulant, stability to ambient UV radiation, and resistance to penetration by sunlight. Simulated events were not synchronized to ambient events, but were scheduled to prevent moisture deficits.