Design and Performance of an Exposure System for Measuring the Response of Crops to Acid Rain and Gaseous Pollutants in the Field

Abstract

During 1982-1984, experiments regarding the nature of crop responses to combinations of acid rain and gaseous pollutant treatments were conducted. Open-top field chambers were used in conjunction with an automatic rain exclusion-simulant distribution system to expose crops to controlled levels of gaseous pollutants and rain acidity in a field setting. Rain exclusion was achieved by automatically moving covers over the experimental plots at the onset of a rain event. The simulant distribution system was automatically activated after 0.25 mm of rain was collected in a recording rain gauge located adjacent to the experimental plots. Rain simulants were dispensed through nozzles until the amount deposited within the plot equaled that deposited by the natural rain outside the plot. The system was capable of dispensing rain simulants with three levels of acidity to ambient air plots and to charcoalfiltered and nonfiltered-air chambered plots. The ability to automatically dispense rain simulants during, and in equal amount to, natural rain events is a feature unique to this system. Advantages of this method of rain simulation for assessment research are that rain simulation occurs with the same seasonal frequency as natural rain events, in the same duration, and at times when other environmental factors reflect the presence of rain. By avoiding scheduled waterings, the experimental crops experience normal dry periods that could influence their response to rain acidity and gaseous pollutants. The real-time application of rain simulants is an alternative to previous acid-rain-effects methodologies, one that allows retention of normal rain event parameters such as duration, frequency, and micrometeorological factors; the potential for experimental artifacts relating to those parameters is reduced.