Vertical wind shear and concentration gradients of viable, airborne bacteria were used to calculate the upward flux of viable cells above bare soil and canopies of several crops. Concentrations at soil or canopy height varied from 46 colonyforming units per m3 over young corn and wet soil to 663 colony-forming units per

The Episodic Response Project (ERP) was an interdisciplinary study designed to address uncertainties about the occurrence, nature, and biological effects of episodic acidification of streams in the northeastern United States. The ERP research consisted of intensive studies of the chemistry and biological effects of episodes in 13 streams draining forested watersheds in the three study regions: the Northern Appalachian region of Pennsylvania and the Catskill and Adirondack Mountains of New York. Wet deposition was measured in each of the three study regions. Using automated instruments and samplers, discharge and chemistry of each stream was monitored intensively from fall 1988 through spring 1990. Biological studies focused on brook trout and native forage fish. Experimental approaches included in situ bioassays, radio transmitter studies of fish movement, and fish population studies. This paper provides an overview of the ERP, describes the methodology used in hydrologic and water chemistry components of the study, and summarizes the characteristics of the study sites, including the climatic and deposition conditions during the ERP and the general chemical characteristics of the study streams.

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Not every cell of a given bacterial isolate that has ice-nucleating properties can serve as an ice nucleus at any given time and temperature. The ratio between the number of ice nuclei and number of bacterial cells in a culture (i.e. nucleation frequency) was found to vary with incubation temperature, growth medium composition, culture age, and genotype. Optimal conditions for ice nucleus production in vitro included incubation of the bacterial cells at 20 to 24°C on nutrient agar containing glycerol. The relationship between nucleation frequency and frost injury was examined by subjectiag corn seedlngs to -4°C immediately after they were sprayed with bacterial suspensions with different nucleation frequencies and by following both ice nucleus concentration and bacterial population size on leaves of corn seedllngs as a function of time after bacterial application. (1, 4). The other E. herbicola isolates (Nos. 1, 2, 10, 24A, and 30B) were isolated from dilution plates of leaf washings of field-grown corn plants. P. syringae isolate Y-26 and P. syringae pv. coronafaciens isolate No. 5 were from the culture collection of A. Kelman, University of Wisconsin-Madison.Bacterial cultures were grown on NA (3.3 g Bacto peptone, 2.7 g Difco nutrient broth, 2.0 g yeast extract, and 15.0 g Bacto agar/ L distilled H20); NA containing 2.5% glycerol (v/v) or 2.5% glucose (w/v); King's medium B (2); nutrient broth containing 2.5% glycerol, minimal broth (1.0 g glucose, 7.0 g K2HPO4, 0.5 g sodium citrate, 0.1 g MgSO4.7H20, and 1.0 g (NH4)2SO4 in 1 L distilled H20) and minimal agar (minimal broth + 15.0 g Bacto agar/L), at the temperatures and for the times specified for each experiment.4 Liquid cultures were agitated with a reciprocal shaker during incubation.Ice Nucleation Activity of Bacterial Suspensions. Bacterial suspensions for ice nucleus concentration determinations were prepared from colonies on agar medium. Cells were removed with a loop and suspended in either distilled H20 or 0.1 M phosphate buffer (pH 7.0). Broth cultures were diluted directly with distilled H20. All dilutions of cultures were 100-fold or greater in the suspensions in which ice nucleus concentrations were measured. Viable cell densities were determined by dilution plating. Ice nucleation spectra were determined as described elsewhere (4,8